Functional Behavioural Assessment in People With Intellectual Disabilities [Mental Retardation and Developmental Disorders]Authors and Disclosures

Posted: 09/22/2006; Updated: 10/04/2006; Curr Opin Psychiatry CME. 2006;19(5):475-480. © 2006 Lippincott Williams & Wilkins

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Abstract and Introduction Evolution Towards Considering the Function of Problem Behaviour Conclusion

References

Abstract and Introduction

Abstract

Purpose of Review: The presence of problem behaviours often impede an individual's quality of life and ability to be fully included in the environments of his or her choice. Functional behavioural assessment has been gaining widespread use in all settings in which people with intellectual disabilities might present problem behaviours. Understanding the function of these problem behaviours is a critical component to developing an effective intervention plan. This paper presents a review of the current knowledge and findings regarding functional behavioural assessments.Recent Findings: The recent studies on functional behavioural assessment have supported the well established fact that success in reducing behaviour problems is closely linked to understanding the function of the problem behaviour. Implementing functional behavioural assessment in school settings has been met with some challenges. Although a complex process, recent research has shown promise in training nonprofessionals in learning to carry out a functional behavioural assessment and implementing the information gained from the functional behavioural assessment into an effective behavioural intervention.Summary: The necessity of conducting a functional behavioural assessment is uncontested. Developing a behavioural intervention on the information obtained from a thorough functional

behavioural assessment is part of best practice in the field of intellectual disabilities. We have the tools to conduct, and train others to conduct, a comprehensive functional behavioural assessment.

Introduction

Behaviour problems are more prevalent in persons with intellectual disabilities than in the general population. As many as one-third of all individuals with an intellectual disability has a mental health or behaviour problem requiring specialized support services

Behaviour problems are the primary reasons that individuals with intellectual disabilities are maintained in institutional facilities or lose community placements.[2] Researchers have also documented the increased stress and burden on families caring for a child or adult with intellectual disability and co-occurring mental health or behaviour problems.[3-5] These individuals often present with complex clinical pictures that necessitate a comprehensive interdisciplinary clinical assessment to identify the causes of the co-occurring psychopathology.

Functional Behavioral Assessment and Mental Retardation: Evolution Towards Considering the Function of Problem BehaviourAuthors and Disclosures

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Abstract and Introduction Evolution Towards Considering the Function of Problem Behaviour Conclusion

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Evolution Towards Considering the Function of Problem Behaviour

Initially, behaviour change principles were limited to reinforcing desired behaviours and punishing undesired behaviours. This approach came to be known as behaviour modification and

was used extensively with individuals with intellectual disabilities in the 1960s and 1970s. As correctly pointed out by Hastings and Noone,[6*] behaviour modification was a rudimentary behaviour management approach that was more preoccupied with punishing problem behaviour and reinforcing appropriate behaviour than understanding and addressing the function served by the problem behaviour. A more empirical approach, known as applied behaviour analysis (ABA), evolved out of behaviour modification and introduced the concept of analysing the function of behaviour.[7] The ABA approach was much more sophisticated and successful than simple behaviour modification because it developed its interventions empirically and tailored them to the identified function of the target behaviour for that person.

A later breakaway group of ABA clinicians was formed in the mid-1980s and represented individuals concerned with the overreliance on aversive strategies. [8] The group labelled their approach positive behaviour support (PBS). Much like ABA, PBS rests its interventions solidly on the assessment of the function of the problem behaviour and also proposes intervening more heavily on the target behaviour's antecedents versus its consequences. Some of the PBS proponents advocate never using aversive methods, whereas other PBS supporters prefer to restrict the use of aversive methods to strategies that do not inflict pain to the individual. [9]

Realizing that people do not engage in problem behaviour because they have intellectual disabilities is crucial. People with intellectual disabilities engage in problem behaviours because these behaviours serve a function, a purpose. Often, complex behaviour problems have multiple functions and may serve different functions across individuals and settings. Understanding the function of behaviour is critical in the process of intervening in reducing the frequency, severity and/or intensity of behaviour problems (sometimes called challenging behaviours) while improving the individual's quality of life.

Functional Analysis and Functional Behavioural Assessment

Functional analysis was the first method developed to understand behaviour through systematic observation and analysis of the relationship between the behaviour and its antecedents and consequences. Functional analysis was first developed in the laboratory using an analogue assessment procedure.[10] The analogue assessment empirically tests the functional relationship between the target behaviour and its related antecedents or consequences. Depending on the nature of the problem behaviour and the inherent dangers involved in performing an analogue assessment, the risks associated with this approach to functional assessment may outweigh its benefits.

Iwata and Worsdell [11*] recently presented an excellent review of functional behavioural assessment (FBA) methodology. These authors summarized the outcome of a well conducted FBA as including three elements for identifying the function of problem behaviour: (a) identify the antecedents that might be triggering/causing the behaviour, (b) identify the consequences that might be maintaining/reinforcing the behaviour, and (c) generate ideas about functional alternatives to the target behaviour that can serve the same function but are more socially acceptable.

It has become a well accepted ethical standard, as highlighted by Hastings and Noone,[6*] that a behavioural intervention or support plan must be derived from an individualized FBA of the problem behaviour. An individualized behaviour support plan that is not derived from a systematic FBA is a throwback to the days of behaviour modification of the mid-1960s and should be promptly discarded.

Interdisciplinary and Multimethod Assessment Process

The relationship between problem behaviours and psychiatric disorders in people with intellectual disabilities is complex.[12] Individuals with intellectual disabilities experience signs and symptoms that are clearly attributable to a specific psychiatric disorder defined by the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) or International Classification of Diseases, Tenth Revision (ICD-10). Some clinicians have also proposed using certain behaviours as equivalents or substitutes to DSM symptoms when attempting to establish certain mental health diagnoses in individuals with intellectual disabilities,[13] whereas others feel that the evidence is lacking to support the use of behavioural equivalents.[14,15] Mental health and behaviour problems may also be related to the onset of a medical condition (e.g. ear infection, ulcer, diabetes, seizure disorder, and thyroid disorder) or factors related to the environment. Behavioural problems also exist that a functional assessment can clearly document as caused or maintained by learning history or contingencies in the individual's environment. In most cases, co-occurring mental health problems in individuals with intellectual disabilities are caused or maintained by a combination of factors. These multiple factors might relate to biology, physical environment, social environment, life experiences, psychology or any combination thereof. As such, using an interdisciplinary or multimethod assessment approach to effectively assess and diagnose or rule out health and mental health problems in individuals with intellectual disabilities is recommended. [16]

Several comprehensive evaluation methods to assess psychiatric disorders and behaviour problems in individuals with intellectual disabilities have been proposed in the literature: multimodal evaluation approach [17], comprehensive ecobehavioural assessment model,[18] and expert consensus.[19] Model evaluations incorporate a multimethod approach including the following:

1. personal/social history (e.g. recording of recent stressors);2. physical examination and medical history;3. evaluation of current medication and possible side effects or interaction effects;4. psychiatric evaluation;5. FBA.

Once medical, dental, psychiatric and pharmacological influences have been assessed and either treated or ruled out, proceeding with an FBA to identify the factors triggering or maintaining the behaviour is advised.

Functional Behavioural Assessment

FBA is a process that contains the following crucial components in identifying the function of behaviour.[20*]

1. clear operational definition of the problem behaviour(s);2. identification of the times, places and circumstances in which the problem behaviour(s)

occurs and does not occur;3. identification of the factors that precede the occurrence of the problem behaviour (i.e.

antecedents);4. identification of the factors that follow the occurrence of the problem behaviour (i.e.

consequences);5. experimental functional analysis of antecedents and consequences to observe their causal

relationship with the target behaviour;6. development of hypotheses regarding the function or relationship between the problem

behaviour and the individual's environment, which then lead to proposed intervention strategies;

7. ongoing data collection to monitor/revise hypothesized functional relationship and/or implemented intervention strategies.

Operational definition of target behaviour

The first step in conducting an FBA is operationally defining the target behaviour. Although this seems like a simple task, often this step is not done well or not done at all. In an exhaustive review of the State's implementation of FBA requirements in the public schools under the U.S. Individuals with Disabilities Education Act, Weber and colleagues [21*] found that 88% of states provide a clear guideline that personnel must provide a definition of the target behaviour. Generally, this definition should be operational to the extent that it will lead to observers being able to reliably document its occurrence or absence. Recent research on the effectiveness of the implementation of FBAs in American schools paints a worrisome picture. Although states may require in their regulations that an FBA contain a definition of the target behaviour, it seems that school personnel often fail the first step of conducting an FBA, providing an adequate operational definition of the target problem behaviour. Van Acker et al. [22**] reported on an extensive review of best practice across Wisconsin. They reported that despite receiving systematic training in the elements in conducting an FBA, many school teams continued to present major deficiencies in conducting FBAs. Of the FBAs reviewed by the authors, 70% contained operational definitions of the target behaviour that contained vague/subjective (e.g. rude) terms or broad categories (e.g. disruptive). Almost one out of five FBAs reviewed did not even contain an operational definition of the target behaviour.[22**]

Conducting an effective FBA starts with a clear set of definitions of all target behaviours under study. Staff needs to be trained in how to define a target behaviour. A good operational definition of problem behaviour is one (a) that can be seen, (b) the frequency of which can be counted and (c) on which different observers agree completely regarding its occurrence and absence.

Assessing the Antecedents and Consequences

Components #2, #3, and #4 are gathered from a combination of sources that most likely include the use of direct observation [e.g. Antecedent-Behaviour-Consequence (ABC) Monitoring Sheets or Scatter plot]; indirect observation measures such as rating scales [e.g. Motivation Assessment System, Questions About Behavioural Function (QABF)], and interviews of individuals, family members, teachers, direct-support staff, among others (e.g. use of the interview format proposed by O'Neill et al.

In the past year, much research has focused on comparing the contribution of indirect methods and direct methods of obtaining information regarding the function of problem behaviour against the 'gold standard' of the experimental functional analysis. The experimental functional analysis is a complex procedure requiring extensive training to effectively implement but is the only method that allows for cause-effect conclusions.[11*]

Direct Measures. Direct measures involve direct observation and recording of the target behaviour and its antecedents and consequences as they occur in real time in the environment. Examples of direct measures are (a) computer-assisted observation systems that permit coding of observed behaviour and (b) ABC observation recording sheets. Both these measures typically record information such as time of occurrence of problem behaviour, antecedent, consequence, who was present, setting information, and so forth.

Indirect Measures. Two of the better known rating scales that provide indirect measures of the function of problem behaviour include (a) Motivation Assessment Scale [23] and (b) QABF.[24] Both rating scales are completed by the informant who has observed the individual display the problem behaviour. A series of items (e.g. person engages in behaviour in order to avoid a demand) are rated on a likelihood scale (e.g. Never ... Often). These rating scales are scored indicating the likelihood that the behaviour serves a function such as the following: get social attention, escape a demand, obtain a tangible, and so forth. The main advantage of these indirect methods over the direct methods of gathering functional information is their economy in time of administration. These scales can be typically completed in less than 15 min.

Comparing Methods

Hall [25**] used a sample of four adults with significant developmental disabilities and complex behaviour problems (some of the target behaviours included head banging, hair pulling, eating nonedibles, hitting staff, pulling staff's hair, and kicking staff) to systematically compare the information obtained via direct and indirect methods of FBA and functional data verified through an empirical functional analysis (analogue assessment). In his study, Hall compared the function of behaviour information obtained via (a) informants using the QABF checklist,[24] (b) direct observations obtained in each participant's natural setting over a 4-week period using a handheld-computer observational system and (c) systematic experimental analogue functional assessment [10] carried out in a quiet room in the individual's natural environment. During the experimental functional analysis, all participants were systematically assessed for the following functions: staff attention, escape demand, obtain tangible, and alone-internally reinforced.

The hypotheses of the function of problem behaviour obtained for the four participants from the direct methods (direct observation system) and indirect methods (QABF) were compared against

the functions identified in the empirical functional analysis. Interestingly, the direct observation data led the author to conclude that the problem behaviours for the four participants were maintained by staff attention. This was corroborated by the experimental functional analysis in only one case. Thus, the direct method and experimental method concurred in only one out of four participants. The indirect method (QABF) and functional analysis were in agreement regarding the function of the target behaviours in three out of four participants. Hall [25**] concluded that the indirect method using the QABF provided concordant hypotheses regarding the function of the problem behaviours of most individuals and can be used as an adequate source of information when conducting an FBA. The empirical functional analysis remains a key component of any FBA; however, these data provide empirical support for the use of indirect measures of functional assessment as alternatives to the more time-consuming and professional-intensive functional analysis. As there was a much lower agreement between the direct method and the conclusions of the experimental functional analysis, direct observational measures should only be used in conjunction with other methods.

Scott and colleagues [26*] reported that school teams, despite receiving training in FBA, often resorted to interventions that they were familiar with even when they did not fit with the conclusions of their FBA. This finding was corroborated by similar research done by Van Acker et al. [22**]. Furthermore, Scott et al. reported that many of the reviewed intervention plans in the schools that were supposedly derived following an FBA proposed interventions that relied upon a greater propensity towards punitive strategies rather than more reinforcement-based interventions such as teaching alternative behaviours.

Rapport and Staff Attributions

Several authors have studied the relationship between individuals with intellectual disabilities and their staff and how the quality of their rapport impact the staff attributions towards the function of their clients' problem behaviours. Conversely, staff attributions may impact rapport and may act as a setting event that influences the occurrence of challenging behaviour.[27**] McLaughlin and Carr [28**] demonstrated that when an intervention specifically targets the improvement of rapport between the staff and the client, the severity of problem behaviour decreases. This is also a critical line of research as it can lend credence to the use of staff interviews about behavioural function and get staff to complete rating scales assessing different possible functions of existing problem behaviours.

Noone and colleagues [27**] studied staff attributions of clients' aggressive behaviour towards staff. In their study of attributions assigned to the cause of their client's problem behaviours, 23 staff members were able to provide differential information about two different clients both of whom presented aggressive behaviour directed towards staff. Using an adapted version of the Attributional Style Questionnaire, staff reported differing functions, thus indicating that the personnel were able to discern differences in function of similar topographies of problem behaviours in different individuals with intellectual disabilities. These findings are important as a potential line of intervention and in light of the wide spread use of indirect methods (rating scales completed by staff, interviews of personnel about their observations of behavioural functions) in completing comprehensive FBAs.

Training Staff and Parents to Conduct a Functional Behavioural Assessment

Training of staff in conducting FBAs has been shown to be successful. McClean and colleagues [29**] used a method that they coined 'person-focused training', which essentially refers to training direct support in conducting FBA and designing and implementing function-based behavioural intervention plans. The authors trained 138 staff and person-focused training consisted of 9 days across 6 months with practical exercises in between blocks of training. This training consisted of approximately 4 days' worth of training on functional assessment and the remaining 5 days on intervention and case review strategies. McClean et al. reported a substantial reduction in problem behaviour in 77% of the participants at almost 2-year follow-up. Wacker and colleagues [30**] also reported encouraging results in training parents of young children with intellectual disabilities in conducting functional analytic procedures. Wacker et al. demonstrated the feasibility of successfully training parents in understanding and conducting experimental factor analysis and implementing subsequent effective intervention over a 4-year period. The authors reported an average suppression of problem behaviours of 85% following the parents' training in functional assessment and intervention implementation. It should be noted that parents in Wacker et al.'s study had easy access to a behaviour specialist for consultation and support. This might be a salient feature of the success of their program.

These results are encouraging in that they indicate success in training nonprofessionals in achieving success in conducting FBAs and subsequent behavioural interventions.

Functional Behavioral Assessment and Mental Retardation: ConclusionAuthors and Disclosures

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Abstract and Introduction Evolution Towards Considering the Function of Problem Behaviour Conclusion

References

Conclusion

Best practice dictates that any behavioural intervention or support plan for an individual with intellectual disabilities be based upon a systematic and detailed FBA of the problem behaviours. Any individualized intervention aimed at changing problem behaviour that is not preceded by an FBA runs counter to established ethical standards. A planned behavioural intervention should not be driven by intuition but rather by observable and measurable data. Clinical judgement should not be used as a substitute to a rigorous analysis of the relationship between individuals' problem behaviours and their environment. In fact, Schalock and Luckasson [31] pointed out that clinical judgment is not intuition or opinion but a higher order level of judgment that is rooted in training, experience, and expertise and that is also based soundly upon extensive data. Hence, clinical judgment may drive hypotheses about the function of problem behaviour but only after completing a comprehensive FBA and not before. An FBA is a detailed process requiring multiple sources of direct, indirect and at times empirical methods in determining the key elements to be addressed in an intervention plan. FBA, when done properly, can lead to improved functioning and a better quality of life for individuals with intellectual disabilities who also present with complex problem behaviours. Parents and nonprofessionals can be trained to become effective partners in conducting an FBA. Another important area of focus in the past year of research has been with respect to staff attributions and rapport between staff and clients and the impact of the quality of rapport on severity of problem behaviours.

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Table of Contents

Abstract and Introduction Evolution Towards Considering the Function of Problem Behaviour Conclusion

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References

1. Emerson E. Prevalence of psychiatric disorders in children and adolescents with and without intellectual disability. J Intellect Disabil Res 2003; 47:51-58.

2. Lakin KC, Hill BK, Hauber FA, et al. New admissions and readmissions to a national sample of public residential facilities. Am J Ment Defic 1983; 88:13-20.

3. Hastings RP, Beck A. Practitioner review: stress intervention for parents of children with intellectual disabilities. J Child Psychol Psychiatry 2004; 45:1338-1349.

4. Lecavalier L, Leone S, Wiltz J. The impact of behaviour problems on caregiver stress in young people with autism spectrum disorders. J Intellect Disabil Res 2006; 50:172-183.

5. McIntyre LL, Blacher J, Baker BL. Behaviour/mental health problems in young adults with intellectual disabilities: the impact on families. J Intellect Disabil Res 2002; 45:239-249.

6. * Hastings RP, Noone SJ. Self-injurious behaviour and functional analysis: Ethics and evidence. Educ Train Dev Disabil 2005; 40:335-342. The authors present a good review of the ethical guidelines as well as the literature documenting the clinical merits of conducting a FBA prior to developing a behavioural intervention plan.

7. Baer DM, Wolf MM, Risley TR. Some current dimensions of applied behavior analysis. J Appl Behav Anal 1968; 1:91-97.

8. Bambara LM, Dunlap G, Schwartz I. Positive behavior support: critical articles on improving practice for individuals with severe disabilities. Austin, TX: PRO-ED Inc.; 2002.

9. Horner RH, Dunlap G, Koegel RL, et al. Towards a technology of 'nonaversive' behavioral support. J Assoc Persons Severe Hand 1990; 15:125-132.

10. Iwata BA, Dorsey MF, Slifer KJ, et al. Toward a functional analysis of self-injury. J Appl Behav Anal 1994; 27:197-209.

11. * Iwata BA, Worsdell AS. Implications for functional analysis methodology for the design of intervention programs. Exceptionality 2005; 13:25-34.

12. Rojahn J, Matson JL, Naglieri JA, Mayville E. Relationships between psychiatric conditions and behavior problems among adults with mental retardation. Am J Ment Retard 2004; 109:21-33.

13. Hemmings CP, Gravestock S, Pickard M, Bouras N. Psychiatric symptoms and problem behaviours in people with intellectual disabilities. J Intellect Disabil 2006; 50:269-276.

14. Ross E, Oliver C. The assessment of mood in adults who have severe or profound mental retardation. Clin Psychol Rev 2003; 23:225-245.

15. Tsiantis J, Diareme S, Dimitrakaki C, et al. Care staff awareness training on mental health needs of adults with learning disabilities: results from a Greek sample. J Learn Disabil 2004; 8:221-234.

16. Ferron FR, Kern CA, Hanson RH, Wiesler NA. Psychiatric diagnosis in mental retardation. In: Wieseler NA, Hanson RH, editors. Challenging behavior of person with mental health disorders and severe developmental disabilities. Washington, DC: American Association on Mental Retardation; 1999. pp. 3-12.

17. Gardner WI. Aggression and other disruptive behavioural challenges: biomedical and psychosocial assessment and treatment. Kingston, NY: NADD Press; 2002.

18. Feldman MA, Griffiths D. Comprehensive assessment of severe behavior problems. In: Singh NN, editor. Prevention and treatment of severe behavior problems: models and methods in developmental disabilities. Pacific Grove, CA: Brooks/Cole Publishing Company; 1997. pp. 23-48.

19. Rush AJ, Frances A. Expert consensus guideline series: treatment of psychiatric and behavioural problems in mental retardation. Am J Ment Retard 2000; 105:159-228.

20. O'Neill RE, Horner RH, Albin RW, et al. Functional analysis of problem behavior: a practical assessment guide. 2nd ed. Pacific Grove, CA: Brooks/Cole; 1997.

21. * Weber KP, Killu K, Derby KM, Barretto A. The status of functional behavioral assessment (FBA): adherence to standard practice in FBA methodology. Psychol Schools 2005; 42:737-744. On the basis of their survey of the practice of conducting FBAs in school in the 50 states, the authors concluded that many school districts are not keeping up with standards of practice in the area of FBA.

22. ** Van Acker R, Boreson L, Gable RA, Potterton T. Are we on the right course? Lessons learned about current FBA/BIP practices in schools. J Behav Educ 2005; 14:35-56. Provides a listing of

frequently observed problems and errors found in individualized behaviour plans and FBAs done in schools. The authors also provide useful resources to avoid these errors.

23. Durand MV, Crimmins DB. Identifying the variables maintaining self-injurious behaviors. J Autism Dev Disord 1988; 18:99-117.

24. Matson JL, Vollmer TR. User's guide: questions about behavioral function (QABF). Baton Rouge, LA: Scientific Publishers Inc; 1995/2000.

25. ** Hall SS. Comparing descriptive experimental and informant-based assessments of problem behaviors. Res Dev Disabil 2005; 26:514-526.

26. * Scott TM, Liaupson C, Nelson CM, McIntyre J. Team-based functional behavior assessment as a proactive public school process: a descriptive analysis of current barriers. J Behav Educ 2005; 14:57-71. This study reviewed the work of a number of school-based FBA teams and concluded that the school personnel in their sample lacked the knowledge base and skills to conduct comprehensive FBAs and develop effective behaviour intervention plans.

27. ** Noone SJ, Jones RSP, Hastings RP. Care staff attributions about challenging behaviors in adults with intellectual disabilities. Res Dev Disabil 2006; 27:109-120.

28. ** McLaughlin DM, Carr EG. Quality of rapport as a setting event for problem behavior. J Positive Behav Intervent 2005; 7:68-91. The authors demonstrated that an intervention aimed solely at improving the quality of rapport between a client and the staff resulted in a decrease in the client's problem behaviour.

29. ** McClean B, Dench C, Grey I, et al. Person focused training: a model for delivering positive behaviour supports to people with challenging behaviours. J Intellect Disabil Res 2005; 49:340-352.

30. ** Wacker D, Berg WK, Harding JW, et al. Treatment effectiveness, stimulus generalization, and acceptability to parents of functional communication training. Educ Psychol 2005; 25:233-256. These authors reported on the successful training of parents to conduct FBAs and implement effective behavioural intervention plans in their homes with their children.

31. Schalock RL, Luckasson R. Clinical judgment. Washington, DC: American Association on Mental Retardation; 2005.

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Authors and Disclosures

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Author(s)

Marc J Tassé, PhD

Marc J. Tassé, PhD, Associate Professor of Psychiatry, University of North Carolina at Chapel Hill

Disclosure: Disclosure: Marc J. Tassé, PhD, has disclosed no relevant financial relationships.

CME Author(s)

Désirée Lie, MD, MSEd

Clinical Professor, Family Medicine, University of California, Orange; Director, Division of Faculty Development, UCI Medical Center, Orange, California

Disclosure: Désirée Lie, MD, MSED, has disclosed no relevant financial relationships.

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CME Released: 10/04/2006; Valid for credit through 10/04/2007

This activity has expired.

The accredited provider can no longer issue certificates for this activity. Medscape cannot attest to the timeliness of expired CME activities.

Target Audience

This review is targeted toward primary care clinicians, psychiatrists, psychologists, developmental specialists, and other specialists who care for individuals with intellectual disabilities.

Goal

The goal of this review is to update clinicians on successful approaches to changing and improving problem behaviors in individuals with intellectual disabilities and the principles underpinning these approaches.

Learning Objectives

Upon completion of this activity, participants will be able to:

1. Describe the prevalence of mental and behavioral problems in persons with intellectual disabilities

2. Define the differences between the behavior modification and the positive behavior support (PBS) approach to problem behaviors

3. Describe the process involved in functional behavioral assessment (FBA)

4. List components of the multimethod approach to assessing behavioral problems5. Identify factors that improve suppression of problem behaviors in those with intellectual

disabilities

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Contents of Functional Behavioural Assessment in People With Intellectual Disabilities [Mental Retardation and Developmental Disorders]

1. Functional Behavioural Assessment in People With Intellectual Disabilities [Mental Retardation and Developmental Disorders]

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Reprint Address

Correspondence to: Marc J. Tassé PhD, Associate Professor of Psychiatry,University of North Carolina at Chapel Hill, CB #7255, Chapel Hill,NC 27599-7255, USA. Tel: +1 919 966 4647. Fax: +1 919 966 2230. E-mail: marc.tasse@cdl.unc.edu

Abbreviation Notes

ABA = applied behaviour analysis; FBA = functional behavioural assessment; PBS = positive behaviour support; QABF = Questions About Behavioural Function

Curr Opin Psychiatry CME. 2006;19(5):475-480. © 2006 Lippincott Williams & Wilkins

Contents of This Activity

Contents of Functional Behavioural Assessment in People With Intellectual Disabilities [Mental Retardation and Developmental Disorders]

1. Functional Behavioural Assessment in People With Intellectual Disabilities [Mental Retardation and Developmental Disorders]

CME Information

Mental RetardationAuthor: Ari S Zeldin, MD, FAAP, Senior Clinical Fellow/Clinical Instructor in Autism and Neuro-Developmental Disorders, Division of Pediatric Neurology, Department of Neurosciences, University of California, San Diego, School of MedicineCoauthor(s): Alicia T F Bazzano, MD, MPH, Consulting Faculty, Division of Pediatric Emergency Medicine, Harbor/UCLA Medical Center; Attending Staff, Department of Emergency Medicine, Children's Hospital Los Angeles; Chief Physician, Westside Regional CenterContributor Information and Disclosures

Updated: Nov 10, 2010

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Overview Differential Diagnoses & Workup Treatment & Medication Follow-up

References Keywords

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Introduction

Background

Mental retardation (MR) or intellectual disability (ID) is a descriptive term for subaverage intelligence and impaired adaptive functioning arising in the developmental period (<18 y). MR/ID and other neurodevelopmental disabilities are seen often in a general pediatric practice.

Terminology for MR/ID has been particularly challenging as the term mentally retarded carries significant social and emotional stigma. The American Association for Intellectual and Developmental Disability (AAIDD) has been particularly influential in terminology changes such that most professionals working in the field now refer to mental retardation as intellectual disability. The DSM-V is expected to adopt this new terminology.1

Developmental delay is often used inappropriately as synonymous with MR/ID. Developmental delay is an overly inclusive term and should generally be used for infants and young children (< 5 y) in which the diagnosis is unclear, such as those too young for formal testing.1

Approximately 10% of children have some learning impairment, while as many as 3% manifest some degree of MR/ID. The population prevalence of these combined disorders of learning rivals that of the common childhood disorder asthma.

MR/ID originates during the developmental period (ie, conception through age 18 years) and results in significantly subaverage general intellectual function with concurrent deficits in functional life skills. The diagnosis of MR/ID requires an intelligence deficit of at least 2 standard deviations (SDs) below the mean IQ. This generally translates into an intelligence quotient (IQ) score of 70-75, given a population mean of 100. Equivalent deficits in at least 2 areas of functional life skills or adaptive skills also must be present to meet the diagnostic criteria for MR/ID. Adaptive skills encompass functional life skills within the domains of communication, self-care, home living, social and interpersonal skills, use of community resources, self-direction, functional academic skills, work, leisure, health, and safety.

MR/ID is currently categorized broadly as follows.2

Table 1. Intellectual disability categorization

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Table

Category

IQscore*

(SD below mean)

Proportion of MR/ID

Educational level/adaptive skills

Intensity of supports required

Prevalence in total population

Mild 50-55 to 70(2-3)

85% Up to about 6th grade; vocational

Intermittent, especially under stress

0.9-2.7%

Moderate 35-40 to 50-55(3-4)

10% up to about 2nd grade; unskilled or semi-skilled, supervised

Limited;usually supervised

0.3-0.4%

Severe 20-25 to 35-40(4-5)

4% May learn words; elementary self-care skills

Extensive; closely supervised group or family home

Profound <20-25 (>5)

1% Little to no self-care skills Constant aid and supervision

*IQ scores are considered +/-5 points due to measurement error.

Category

IQscore*

(SD below mean)

Proportion of MR/ID

Educational level/adaptive skills

Intensity of supports required

Prevalence in total population

Mild 50-55 to 70(2-3)

85% Up to about 6th grade; vocational

Intermittent, especially under stress

0.9-2.7%

Moderate 35-40 to 50-55(3-4)

10% up to about 2nd grade; unskilled or semi-skilled, supervised

Limited;usually supervised

0.3-0.4%

Severe 20-25 to 35-40(4-5)

4% May learn words; elementary self-care skills

Extensive; closely supervised group or family home

Profound <20-25 (>5)

1% Little to no self-care skills Constant aid and supervision

*IQ scores are considered +/-5 points due to measurement error.

The DSM-V is widely expected to change the definition of MR/ID, relying less on specific IQ levels.3 IQ scores can vary based on age, instrument, and practitioner. Furthermore, testing prior to school age does not correlate well with future performance. IQ scores can be measured using assessment instruments, such as the Stanford-Binet, Wechsler Adult Intelligence Scale (WAIS), or Wechsler Intelligence Scale for Children (WISC-IV). Nonverbal children can be tested with the Leiter International Performance Scale (Leiter-R).

The second component of diagnosis, adaptive skills, is usually measured with a self-reported or parent/caregiver-reported inventory, such as the Vineland Adaptive Behavior Scales, Second Edition (VABS-II). The DSM-V diagnosis is expected to require adaptive measurements of less than 2 SDs as compared to the population mean, with standard scores of 70 or less, in at least 2 of the following domains:3

Conceptual skills (communication, language, time, money, academic) Social skills (interpersonal skills, social responsibility, recreation, friendships) Practical skills (daily living skills, work, travel)

MR/ID also can be categorized as syndromic, if associated with dysmorphic features, or nonsyndromic, if not associated with dysmorphisms or malformations. The understanding of specific MR/ID syndromes is expanding with recent molecular genetic advances. More than 800 recognized syndromes listed in the Online Mendelian Inheritance in Man (OMIM) database are associated with MR/ID, reflecting clinical diagnostic advances in the field. The most common associated chromosomal abnormality is trisomy 21, or Down syndrome. The most common X-linked abnormality associated with MR/ID is fragile X syndrome. However, for most cases of MR/ID, no specific genetic abnormalities are found.

Some forms of MR/ID are due to nongenetic factors and may be identifiable by their associated dysmorphisms and clinical presentation. Examples include prenatal exposure to teratogens (eg, anticonvulsants, warfarin, alcohol) or prenatal thyroid dysfunction. Prenatal and postnatal exposure to lead and the associated decrement in IQ may increase an individual's chance of functioning in the MR/ID range.

Pathophysiology

MR/ID is the end result of many disorders of CNS function. Most individuals with significant intellectual impairment have no discernible structural abnormalities of the brain. CNS malformations, a visual correlate of the disorders, are diagnosed in 10-15% of cases; dysfunction

is localized primarily to the cortical structures, including the hippocampus and the medial temporal cortex. The most common malformations consist of neural tube defects, hydranencephaly, and microcephaly. Less commonly, CNS malformations include disorders of migration (the lissencephalies) and agenesis of the corpus callosum.

Multiple congenital anomaly syndromes with malformations confined to nonneurologic organ systems may be present in 5% of all patients with MR/ID. Between 3% and 7% of cases may be associated with a wide array of inborn errors of metabolism complicated by multiorgan system disease. Alcohol exposure in utero may account for as many as 8% of those with mild MR/ID.

Most individuals with mild MR/ID and other learning disorders do not have other neurologic complications, CNS malformations, or dysmorphisms. They are more likely, however, to be born into families of low socioeconomic status, low IQ, and little education. The etiologic contribution of poverty to their poor cognitive function remains unclear. Clearly, however, poor cognitive functioning and MR are correlated positively with a life of poverty.

Frequency

United States

The frequency of MR/ID of all degrees ranges from 1.6-3% of the population. The statistical definition of subaverage intelligence (2 SDs below the mean) would indicate a predicted prevalence of 2.5%.

International

A study with excellent ascertainment conducted in Aberdeen, Scotland, yielded a prevalence of 1 in 300 for severe MR and 1 in 77 for mild MR. Among those with severe MR were more boys than girls (male-to-female ratio 1.2:1), and among those with IQ >70, in the mild range of deficiency, boys exceeded girls by a ratio of 2.2:1.4

Although prevalence rates vary from country to country, the variance in prevalence may be attributed to ascertainment bias, the standardization methods employed from study to study, and a generalized upward drift in IQ scores over time. Even so, the greatest variance in statistics of prevalence is most likely to fall within the category of mild MR, a group for which the ascertainment bias is large.

Mortality/Morbidity

MR/ID itself is not necessarily associated with an increased premature death rate. However, individuals with severe to profound MR/ID experience a decreased life expectancy related to the underlying etiology or additional complicating neurologic disorders, such as epilepsy. Neurologic dysfunction resulting in immobility, significant oral motor incoordination, dysphagia, and aspiration confers a greater risk of premature death than MR/ID itself. When significant neurologic dysfunction is associated with other organ system anomalies, an individual's life expectancy is shortened further.

Respiratory disease is the most prevalent cause of death among individuals with profound MR/ID. In particular, respiratory infections were the leading cause of death among a Finnish cohort of children with MR/ID.5 For those affected by mild MR/ID, life expectancy does not differ from that of the general population.

Comorbid psychiatric conditions are diagnosed more frequently in those with intellectual disabilities than in the general population. Even so, psychiatric disorders probably are underappreciated in this population.

o Attention deficit/hyperactivity disorder (ADHD) is diagnosed in 8-15% of children and 17-52% of adults with MR.

o Self-injurious behaviors require treatment in 3-15%, particularly in the severe range of MR/ID.

o Major depression, bipolar disorders, anxiety disorders, and other mood disorders are the most common psychiatric diagnoses in adults with MR/ID. Obsessive-compulsive disorder, conduct disorder, tic disorders, and other stereotypic behaviors are also diagnosed more commonly in those with MR/ID. Schizophrenia may have a prevalence of 3% in individuals with MR/ID, compared to 0.8% in the general population.

In the 1970 Isle of Wight study, as many as 30% of children with MR/ID exhibited an emotional or behavioral disorder, compared to 6% of children in the general population. MR compounded by epilepsy conferred a 56% risk of comorbid psychiatric disease in this study.6

Occult visual and auditory deficits occur in 50% of those with MR/ID, particularly when refractive errors are considered.

The rates of transmittable diseases, including sexually transmitted diseases (STDs), hepatitis B, and Helicobacter pylori infection, are increased significantly among individuals with MR/ID.

One in 5 individuals with MR/ID also has cerebral palsy (CP). As many as 20% of individuals with MR/ID have seizures. GI complications with MR/ID include feeding dysfunction, excess drooling, reflux esophagitis,

and constipation. GU complications with MR/ID include urinary incontinence and poor menstrual hygiene. A profound social morbidity affects individuals with MR/ID and their families. This morbidity can

be measured in lost wages, dependence on social services, impaired long-term relationships, and emotional suffering.

Race

Consistent racial differences in prevalence of MR/ID and associated mortality rates are not known to exist.

Sex

The gender ratios for mortality and morbidity do not differ from the gender ratio noted in the severe/profound ranges of intellectual disability (ie, male-to-female ratio, 1.2:1).

Age

MR/ID refers to intellectual impairment that develops prior to the age of 18 years.

Certain syndromes associated with MR/ID, such as Down syndrome, are associated with shorter

life expectancy than the general population. In a comparison of those with MR/ID with and without Down syndrome from the California Department of Developmental Services cohort, excess mortality in the Down syndrome group tended to decrease with advancing age up to 35-39 years but increased thereafter. The increase in death rate from age 40 years was steeper in patients with Down syndrome than in those without Down syndrome.7

Clinical

History

Presenting signs/symptoms

The presenting symptoms and signs of MR/ID typically include cognitive skills delays, language delay, and delays in adaptive skills. Developmental delays vary depending on the level of MR/ID and the etiology. For example, in mild nonsyndromic MR/ID, delays may not be notable until the preschool years, whereas with severe or profound MR associated with syndromes or extreme prematurity, for example, significant delays in milestones may be noted from birth.

Language delay: One of the first signs of MR/ID may be language delays, including expressive language (speech) and receptive language (understanding). Red flags include no mama/dada/babbling by 12 months, no 2-word phrases by age 2, and parents reporting they are concerned that the child may be deaf.

Fine motor/adaptive delayo Significant delays in activities such as self-feeding, toileting, and dressing are typically

reported in children with MR/ID.o Prolonged, messy finger feeding and drooling are signs of oral-motor incoordination.

Cognitive delay: Children with MR/ID have difficulties with memory, problem-solving and logical reasoning. This may be expressed early on with preacademic difficulties or difficulty following directions (particularly multipart directions).

Social delays: Children with MR may display lack of interest in age-appropriate toys and delays in imaginative play and reciprocal play with age-matched peers. Rather than their chronological age, play reflects their developmental levels.

Gross motoro Delays in gross motor development infrequently accompany the cognitive, language,

and fine motor/adaptive delays associated with MR/ID unless the underlying condition results in both MR/ID and cerebral palsy.

o Subtle delays in gross motor acquisition, or clumsiness, may be identified in the developmental assessment.

Behavioral disturbanceso Even before an age at which psychopathology can be identified, infants and toddlers

who go on to have MR/ID may be more likely to have difficult temperaments, hyperactivity, disordered sleep, and colic.

o Associated behaviors may include aggression, self-injury, defiance, inattention, hyperactivity, sleep disturbances, and stereotypic behaviors.

Neurologic and physical abnormalities

o Prevalence of MR is increased among children with seizure disorders, microcephaly, macrocephaly, history of intrauterine or postnatal growth retardation, prematurity, and congenital anomalies.

o In the process of addressing somatic problems, assessment of a child's cognitive abilities is often overlooked.

Family history

Guidelines from the American Academy of Pediatrics recommend that the evaluation of a child with MR/ID includes an extensive family history, with particular attention to family members with mental retardation, developmental delays, consanguinity, psychiatric diagnoses, congenital malformations, miscarriages, stillbirths, and early childhood deaths. The clinician should construct a pedigree of 3 generations or more.8

Physical

Developmental assessmento The American Academy of Pediatrics recommends developmental screening for all

children at regular intervals. Methods include several parental surveys, such as the Parents' Evaluation of Developmental Status (PEDS), Ages and Stages Questionnaires (ASQ) and Child Development Inventories (CDI). Other instruments require direct observation, such as the Bayley Infant Neurodevelopmental Screener, Battelle Developmental Inventory, Early Language Milestone Scale, and Brigance Screens.

o Key behavioral observations should focus on the child's communicative intent, social skills, eye contact, compliance, attention span, impulsivity, and style of play.

o For the diagnoses of developmental delay and MR/ID, an expanded neurodevelopmental and psychological examination is required. Various tests can be administered to assess language comprehension, language expression, nonverbal cognitive abilities, fine motor and adaptive abilities, attention span, memory, gross motor skills, and adaptive behaviors. The most common psychological tests for children include the Bayley Scales of Infant Development-III, the Stanford-Binet Intelligence Scale, the Wechsler Intelligence Scale for Children-IV, the Wechsler Preschool and Primary Scale of Intelligence-Revised, and the Vineland Adaptive Behavior Scales-II.

Physical examinationo Head circumference: Measurement of all growth parameters must include head

circumference. Microcephaly correlates highly with cognitive deficits. Macrocephaly may indicate hydrocephalus and is associated with some inborn errors of metabolism and may also be seen early on in some children later diagnosed with autism.9,10

o Height: Short stature may suggest a genetic disorder, fetal alcohol syndrome, or hypothyroidism. Tall stature may suggest fragile X syndrome (FraX), Soto syndrome, or other overgrowth syndrome associated with MR/ID.

o Neurologic: This examination should include assessments of head growth (for micro/macrocephaly), muscle tone (for hypotonia or spasticity), strength and coordination, deep tendon reflexes, persistent primitive reflexes, ataxia, and other abnormal movements such as dystonia or athetosis.

o Sensory: Vision and hearing should always be tested in suspected cases of MR/ID. Children with disabilities and MR/ID are more likely than other children to have visual

impairment (refractive errors, strabismus, amblyopia, cataracts, abnormal retinal pigmentation, and cortical blindness) and hearing deficits, particularly among those with severe impairments.

o Skin: Cutaneous findings of etiologic interest include hyperpigmented and hypopigmented macules, such as café-au-lait macules (associated with neurofibromatosis type 1), and ash-leaf spots (associated with tuberous sclerosis), fibromas, and irregular pigmentation patterns.

o Extremities: Examine for dysmorphic features and organ system dysfunction indicative of syndromes. Although MR/ID with multiple congenital anomalies and major malformations accounts for only 5-10% of all cases, most of these affected individuals have 3-4 minor anomalies, especially involving the face and digits.

Causes

Prenatal conditions (genetic)o Trisomy 21 or Down syndrome

This disorder accounts for 25-50% of persons with severe MR; Down syndrome occurs in approximately 1 per 800 live births.

In infancy, this disorder is recognized by specific facial features, including flat facial profile, brachycephaly, up-slanted and narrow palpebral fissures, and anomalous auricles.

Hypotonia, joint hyperextensibility, neonatal jaundice, simian crease, shortened digits, and excess skin on the back of the neck contribute to the clinical features.

Congenital heart disease is present in approximately 40%. GI malformations are present in 5%. Congenital cataracts are found in 3%, and as many as 35% require treatment for strabismus or refractive error. Infantile spasms may develop in 5%.

The IQ score ranges from 25-50. Generally, verbal-linguistic skills lag behind visual-spatial skills and social performance is usually above the mental age.

In trisomy 21, gene expression of chromosome 21 is increased in a dosage-dependent fashion that varies by tissue type. While some trisomic 21 genes are not expressed at elevated levels, many are. Of those significantly increased, several encode proteins critical for mitochondrial function and for neurogenesis.

o Other chromosomal abnormalities (eg, deletions, duplications, translocations) may be present in as many as 25% of individuals with severe MR.

The most commonly occurring abnormalities of this class, detectable at the 500 band level of chromosomal analysis, are 5p- (ie, Cri du chat syndrome) and 4p- (ie, Wolf-Hirschhorn syndrome).

Cryptic subtelomeric deletions are diagnosed with increasing frequency as fluorescently tagged molecular DNA probes allow detection of deletions below the microscopic resolution of a standard karyotype.

Cryptic subtelometric rearrangements now account for 5-6% of cases of idiopathic mental retardation.

Chromosomal analysis is undergoing further refinement with the application of gene array hybridization techniques that may detect abnormalities in up to 20% of cases of idiopathic mental retardation.

o Fragile X syndrome

The population prevalence of this disorder is approximately 1 in 3500 males, giving a prevalence within the MR population of about 1 in 76. For males with severe MR, the prevalence rises to about 1 in 13. Other studies have found in populations of those with mental retardation positive fragile X studies in 5.9% of males and 0.3% of females.11 About 1 in 2000 females carries the fragile X (FraX) gene. Current studies suggest that FraX is the most prevalent form of inherited MR.

Males with the full FMR1 trinucleotide repeat expansion (ie, the full mutation) usually function in the moderate to severe range of MR.12 Other features include testicular enlargement in the postpubertal period and minor facial anomalies (eg, large forehead, elongated face, protuberant auricles, prominent chin).

Females with the full FMR1 trinucleotide repeat expansion may have no symptoms, although some have mild learning disabilities or even mild to moderate MR.

Mitral valve prolapse and seizures may occur. Up to 20% of FraX males meet criteria for autism; autisticlike behaviors can be

present in affected females as well. Direct DNA analysis of the FMR-1 gene is the method of choice for diagnosing

both affected individuals with the full trinucleotide repeat expansion (>200 repeats) and unaffected carriers with the premutation (60-200 repeats).

Contiguous gene deletion syndromeso Although less common, some of these syndromes can be readily identified clinically. The

following syndromes often can be confirmed by utilizing a fluorescence in situ hybridization (FISH) probe to the deleted region in question.

o Prader-Willi syndrome The Prader-Willi syndrome (PWS) involves deletion at 15q11-q13 (deletion of

the paternally derived region). Classic clinical features include neonatal and infantile hypotonia, feeding

problems or failure to thrive in infancy, excessive weight gain with hyperphagia beginning between ages 12 months and 6 years, food compulsions, hypogonadism, global developmental delay, almond-shaped eyes, thin upper lip, and down-turned corners of the mouth.

The candidate gene within the Prader-Willi gene region is SNRPN, which encodes a ribonucleoprotein involved in mRNA splicing. How SNRPN contributes to the hypothalamic dysfunction that defines many clinical features of PWS is unclear.

It is the first known human disorder of genomic imprinting, leading to revolutionary changes in the field of molecular genetics and the understanding of uniparental disomy.

Negative FISH results in PWS may be due to maternal uniparental disomy (UPD) of chromosome 15 (2 number 15 chromosomes from the mother) and can be confirmed with molecular studies.

o Angelman syndrome The Angelman syndrome (AS) also involves deletion at 15q11-q13 (deletion of

the maternal copy of the gene region). MR, absent speech, microcephaly, seizures, puppetlike ataxic movements,

inappropriate laughter, and facial dysmorphisms characterize AS.

The candidate genes within the AS critical region include UBE3A, whose protein product is important in the posttranslational modification of proteins by ubiquitination, and GABRA3, a subunit of the GABAa receptor.

Negative FISH results in AS may be due to paternal UPD of chromosome 15 (2 number 15 chromosomes from the father) and can be confirmed with molecular studies.

Point mutations occasionally are found in AS with negative results on FISH and UPD studies.

o Smith-Magenis syndrome Smith-Magenis syndrome (SMS) involves deletion at 17p11.2. MR, short stature, brachydactyly, minor skeletal and facial anomalies, sleep

disturbance, self-injurious behaviors, and other organ system malformations characterize this contiguous gene deletion syndrome.13

Although as many as 100 genes may be deleted in SMS, the physical characteristics are subtle.

o CATCH 22 syndrome The CATCH 22 syndrome, which comprises DiGeorge Syndrome (DGS) and

velocardiofacial syndrome (VCF), involves deletion at 22q11. Infants with classic DGS are identified readily by aplasia or hypoplasia of the

thymus, T cell lymphopenia, conotruncal cardiac defects, oral-motor dysfunction, and facial dysmorphisms (eg, low-set malformed ears, small jaw, palatal defects, hypertelorism, antimongoloid palpebral slant).

Minor variants may meet clinical criteria for the VCF syndrome. With a prevalence of 1 in 4,000 people, it is the most common known microdeletion disorder.

The majority of individuals with CATCH 22 have learning disabilities or mild MR and comorbid psychiatric disorders including schizophrenia and mood disorders with psychosis.

o Williams syndrome The Williams syndrome involves deletion at 7q11.14

Characteristic facial features are described as "elfin." In the majority, valvular stenosis, poor growth, hypotonia, late-onset contractures, dental anomalies, infantile colic, oral-motor discoordination, and hyperacusis (ie, hypersensitivity to sound) are reported. Infantile hypercalcemia may be transient and is often subclinical.

Mild to moderate MR, relative preservation of language, and associated weakness in visual-spatial development are typical.

Elastin is the candidate gene presumed responsible for some of Williams syndrome features, including supravalvular aortic stenosis.

o Wolf-Hirschhorn syndrome The Wolf-Hirschhorn syndrome, also known as 4p- syndrome, involves deletion

at 4p16.3. Severe growth retardation, microcephaly, "Greek helmet" facies and orofacial

clefts, and other midline fusion defects characterize this syndrome. The region of deletion is gene dense, and an undefined number of genes may

contribute to this phenotype.o Langer-Giedion syndrome

This syndrome, also known as trichorhinophalangeal syndrome type II, involves deletion at 8q24.1.

Learning disabilities and the presence of MR vary. Facial dysmorphisms include microcephaly, large ears, bulbous nose, broad

nasal bridge, elongated philtrum, and sparse scalp hair. Multiple nevi and skeletal anomalies may be present.

o Miller-Dieker syndrome The Miller-Dieker syndrome (MDS) involves deletion at 17p13.3. Infants present with severe neurologic impairment, seizures, and hypotonia

secondary to lissencephaly. The smooth cerebral cortex with absent or decreased gyral formation results from abnormal neuronal migration.

The identified gene LIS1 may function as a G protein subunit in cellular signal transduction that is important in telencephalon development.

o Many contiguous gene deletion syndromes for which a FISH probe is not available have been recognized in association with MR. A comprehensive survey is beyond the scope of this article.

Single gene mutation syndromeso Tuberous sclerosis

Hypopigmented cutaneous macules (ie, ash-leaf spots), calcified intracranial cortical tubers with or without heterotopias, seizures, retinal hamartomas, and renal angiomyolipomas characterize this hamartomatous condition.

MR may or may not be seen in affected individuals; the presence of seizures is the factor most associated with poor cognitive outcome. Autism is a rather common finding in children with tuberous sclerosis associated with MR.

This is an autosomal-dominant inherited condition with about half of affected individuals resulting from a new mutation. Two genes have been identified, one at 9q34 (TSC1) and the other at 16p13 (TSC2). A variety of deletions, rearrangements, and point mutations have been implicated in tuberous sclerosis.

o Rubinstein-Taybi syndrome Broad terminal phalanges, beaked nose, down-slanting palpebral fissures,

epicanthal folds, and microcephaly characterize this syndrome. Behavioral aspects include variable degrees of impulsivity, distractibility,

instability of mood, and stereotypies.15

This is an autosomal-dominant inherited condition, with the majority of cases representing new deletions or point mutations of the CREB-binding protein gene (16p13.3).

o Coffin-Lowry syndrome This syndrome is characterized by hypertelorism, down-slanting palpebral

fissures, frontal prominence, thickened lips and nasal septum, as well as dental and skeletal anomalies.

It is an X-linked condition, with females having mild manifestations. The syndrome results from mutations in the RSK2 gene, which encodes a CREB kinase (Xp22.2-p22.1).16

o Rett syndrome Developmental stagnation then regression, progressive microcephaly, seizures,

ataxia, and autisticlike behaviors are seen in affected females.

This X-linked dominant condition with presumed lethality for affected males is caused by mutations in MeCP2, a transcriptional repressor (Xq28).17

o Smith-Lemli-Opitz syndrome Malformations consistent with holoprosencephaly sequence, syndactyly of toes

2 and 3, micrognathia, cleft palate, and moderate to severe MR are seen. This autosomal-recessive inherited condition results from increases in 7-

dehydrocholesterol (7-DHC) due to mutations in the 7-DHC reductase gene (11q12-q13).

Treatment with an oral cholesterol "cocktail" has shown some promise in this syndrome.

o Costello syndrome Characteristic clinical features include polyhydramnios, failure to thrive, cardiac

anomalies, and tumor predisposition. Mean IQ is in the mild MR range, but the spectrum extends from severe MR to

average intelligence. Affected males are lower functioning than females and have significantly more behavioral problems.18

Mutation in HRAS is identified, resulting in a gain of function of the encoded protein and increased activation of the cellular signaling pathway Ras-MAPK.19

o Many other single-gene disorders are associated with MR with additional phenotypic and behavioral features including such problems as microcephaly, seizures, or short stature, with or without dysmorphic facies.

Recent advances in genetic linkage analysis techniques in families with multiple affected members have revealed more than 50 candidate genes along the X chromosome. In some kindreds with a pattern of X-linked nonsyndromic mild MR (XLMR), linkage analysis has identified candidate genes that code for interleukin receptors, G protein signaling factors, transcription factors, and transcriptional repressors.

Environmental causeso Fetal alcohol syndrome and fetal alcohol effect

Alcohol results in a wide range of teratogenic effects.20 The most severely affected individuals meet criteria for fetal alcohol syndrome (FAS) by demonstrating short palpebral fissures, dental crowding, camptodactyly flattened philtrum, thin vermillion border, flattening of the maxillary area, microphthalmia, prenatal and postnatal growth deficiency, microcephaly, and developmental delay.

Fetal alcohol effect (FAE) can be diagnosed only in the context of (1) maternal history of alcohol use and (2) a child with developmental and behavioral abnormalities that also manifests growth deficiency or the characteristic facial dysmorphisms.

The prevalence of FAS may be as high as 1.9 in 1000 live births and is the leading cause of MR in the western world. The impact of the milder FAE remains unknown. The teratogenic effects of alcohol may be responsible for as many as 8% of cases of mild MR. Alcohol's deleterious effects on cortical plasticity contribute to cognitive impairment.

o Congenital hypothyroidism Congenital hypothyroidism (known as cretinism in the past) is a neurologic

syndrome that results from severe thyroid hormone deficiency during the fetal period. In the infant, the syndrome comprises deaf mutism, moderate to severe MR, spasticity, and strabismus.

Normal fetal brain development requires sufficient production of both maternal and fetal thyroid hormones. Normal glandular production of T4 and T3 requires sufficient dietary intake of iodine.

Iodine deficiency may affect an estimated 800 million people worldwide. It can result in endemic goiter, fetal wastage, milder degrees of developmental delay, and endemic congenital hypothyroidism.

Perinatal/postnatal conditions: These conditions are responsible for fewer than 10% of all MR cases.

o Congenital cytomegalovirus (CMV)o Congenital rubella - No longer an important etiology in countries with high vaccination

rateso Intraventricular hemorrhage related to extreme prematurity - An important cause only

in societies with advanced neonatal care and survival of the prematureo Hypoxic-ischemic encephalopathy - Always results in combined CP/MRo Traumatic brain injury - Shaken baby syndrome, closed head injury sustained in motor

vehicle accidentso Meningitis - Decreasing in importance as the incidence of Haemophilus influenzae type B

decreases in vaccinated populationso Trichomoniasis during pregnancy21

o Neurodegenerative disorders

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eMedicine Specialties > Neurology > Pediatric Neurology

Mental RetardationAuthor: Ari S Zeldin, MD, FAAP, Senior Clinical Fellow/Clinical Instructor in Autism and Neuro-Developmental Disorders, Division of Pediatric Neurology, Department of Neurosciences, University of California, San Diego, School of MedicineCoauthor(s): Alicia T F Bazzano, MD, MPH, Consulting Faculty, Division of Pediatric Emergency Medicine, Harbor/UCLA Medical Center; Attending Staff, Department of Emergency Medicine, Children's Hospital Los Angeles; Chief Physician, Westside Regional CenterContributor Information and Disclosures

Updated: Nov 10, 2010

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Introduction

Background

Mental retardation (MR) or intellectual disability (ID) is a descriptive term for subaverage intelligence and impaired adaptive functioning arising in the developmental period (<18 y). MR/ID and other neurodevelopmental disabilities are seen often in a general pediatric practice.

Terminology for MR/ID has been particularly challenging as the term mentally retarded carries significant social and emotional stigma. The American Association for Intellectual and Developmental Disability (AAIDD) has been particularly influential in terminology changes such that most professionals working in the field now refer to mental retardation as intellectual disability. The DSM-V is expected to adopt this new terminology.1

Developmental delay is often used inappropriately as synonymous with MR/ID. Developmental delay is an overly inclusive term and should generally be used for infants and young children (< 5 y) in which the diagnosis is unclear, such as those too young for formal testing.1

Approximately 10% of children have some learning impairment, while as many as 3% manifest some degree of MR/ID. The population prevalence of these combined disorders of learning rivals that of the common childhood disorder asthma.

MR/ID originates during the developmental period (ie, conception through age 18 years) and results in significantly subaverage general intellectual function with concurrent deficits in functional life skills. The diagnosis of MR/ID requires an intelligence deficit of at least 2 standard deviations (SDs) below the mean IQ. This generally translates into an intelligence quotient (IQ) score of 70-75, given a population mean of 100. Equivalent deficits in at least 2

areas of functional life skills or adaptive skills also must be present to meet the diagnostic criteria for MR/ID. Adaptive skills encompass functional life skills within the domains of communication, self-care, home living, social and interpersonal skills, use of community resources, self-direction, functional academic skills, work, leisure, health, and safety.

MR/ID is currently categorized broadly as follows.2

Table 1. Intellectual disability categorization

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Table

Category

IQscore*

(SD below mean)

Proportion of MR/ID

Educational level/adaptive skills

Intensity of supports required

Prevalence in total population

Mild 50-55 to 70(2-3)

85% Up to about 6th grade; vocational

Intermittent, especially under stress

0.9-2.7%

Moderate 35-40 to 50-55(3-4)

10% up to about 2nd grade; unskilled or semi-skilled, supervised

Limited;usually supervised

0.3-0.4%

Severe 20-25 to 35-40(4-5)

4% May learn words; elementary self-care skills

Extensive; closely supervised group or family home

Profound <20-25 (>5)

1% Little to no self-care skills Constant aid and supervision

*IQ scores are considered +/-5 points due to measurement error.

Category

IQscore*

(SD below mean)

Proportion of MR/ID

Educational level/adaptive skills

Intensity of supports required

Prevalence in total population

Mild 50-55 to 70(2-3)

85% Up to about 6th grade; vocational

Intermittent, especially under stress

0.9-2.7%

Moderate 35-40 to 50-55(3-4)

10% up to about 2nd grade; unskilled or semi-skilled, supervised

Limited;usually supervised

0.3-0.4%

Severe 20-25 to 35-40(4-5)

4% May learn words; elementary self-care skills

Extensive; closely supervised group or family home

Profound <20-25 (>5)

1% Little to no self-care skills Constant aid and supervision

*IQ scores are considered +/-5 points due to measurement error.

The DSM-V is widely expected to change the definition of MR/ID, relying less on specific IQ levels.3 IQ scores can vary based on age, instrument, and practitioner. Furthermore, testing prior to school age does not correlate well with future performance. IQ scores can be measured using assessment instruments, such as the Stanford-Binet, Wechsler Adult Intelligence Scale (WAIS), or Wechsler Intelligence Scale for Children (WISC-IV). Nonverbal children can be tested with the Leiter International Performance Scale (Leiter-R).

The second component of diagnosis, adaptive skills, is usually measured with a self-reported or parent/caregiver-reported inventory, such as the Vineland Adaptive Behavior Scales, Second Edition (VABS-II). The DSM-V diagnosis is expected to require adaptive measurements of less than 2 SDs as compared to the population mean, with standard scores of 70 or less, in at least 2 of the following domains:3

Conceptual skills (communication, language, time, money, academic) Social skills (interpersonal skills, social responsibility, recreation, friendships) Practical skills (daily living skills, work, travel)

MR/ID also can be categorized as syndromic, if associated with dysmorphic features, or nonsyndromic, if not associated with dysmorphisms or malformations. The understanding of specific MR/ID syndromes is expanding with recent molecular genetic advances. More than 800 recognized syndromes listed in the Online Mendelian Inheritance in Man (OMIM) database are associated with MR/ID, reflecting clinical diagnostic advances in the field. The most common associated chromosomal abnormality is trisomy 21, or Down syndrome. The most common X-linked abnormality associated with MR/ID is fragile X syndrome. However, for most cases of MR/ID, no specific genetic abnormalities are found.

Some forms of MR/ID are due to nongenetic factors and may be identifiable by their associated dysmorphisms and clinical presentation. Examples include prenatal exposure to teratogens (eg, anticonvulsants, warfarin, alcohol) or prenatal thyroid dysfunction. Prenatal and postnatal

exposure to lead and the associated decrement in IQ may increase an individual's chance of functioning in the MR/ID range.

Pathophysiology

MR/ID is the end result of many disorders of CNS function. Most individuals with significant intellectual impairment have no discernible structural abnormalities of the brain. CNS malformations, a visual correlate of the disorders, are diagnosed in 10-15% of cases; dysfunction is localized primarily to the cortical structures, including the hippocampus and the medial temporal cortex. The most common malformations consist of neural tube defects, hydranencephaly, and microcephaly. Less commonly, CNS malformations include disorders of migration (the lissencephalies) and agenesis of the corpus callosum.

Multiple congenital anomaly syndromes with malformations confined to nonneurologic organ systems may be present in 5% of all patients with MR/ID. Between 3% and 7% of cases may be associated with a wide array of inborn errors of metabolism complicated by multiorgan system disease. Alcohol exposure in utero may account for as many as 8% of those with mild MR/ID.

Most individuals with mild MR/ID and other learning disorders do not have other neurologic complications, CNS malformations, or dysmorphisms. They are more likely, however, to be born into families of low socioeconomic status, low IQ, and little education. The etiologic contribution of poverty to their poor cognitive function remains unclear. Clearly, however, poor cognitive functioning and MR are correlated positively with a life of poverty.

Frequency

United States

The frequency of MR/ID of all degrees ranges from 1.6-3% of the population. The statistical definition of subaverage intelligence (2 SDs below the mean) would indicate a predicted prevalence of 2.5%.

International

A study with excellent ascertainment conducted in Aberdeen, Scotland, yielded a prevalence of 1 in 300 for severe MR and 1 in 77 for mild MR. Among those with severe MR were more boys than girls (male-to-female ratio 1.2:1), and among those with IQ >70, in the mild range of deficiency, boys exceeded girls by a ratio of 2.2:1.4

Although prevalence rates vary from country to country, the variance in prevalence may be attributed to ascertainment bias, the standardization methods employed from study to study, and a generalized upward drift in IQ scores over time. Even so, the greatest variance in statistics of prevalence is most likely to fall within the category of mild MR, a group for which the ascertainment bias is large.

Mortality/Morbidity

MR/ID itself is not necessarily associated with an increased premature death rate. However, individuals with severe to profound MR/ID experience a decreased life expectancy related to the underlying etiology or additional complicating neurologic disorders, such as epilepsy. Neurologic dysfunction resulting in immobility, significant oral motor incoordination, dysphagia, and aspiration confers a greater risk of premature death than MR/ID itself. When significant neurologic dysfunction is associated with other organ system anomalies, an individual's life expectancy is shortened further.

Respiratory disease is the most prevalent cause of death among individuals with profound MR/ID. In particular, respiratory infections were the leading cause of death among a Finnish cohort of children with MR/ID.5 For those affected by mild MR/ID, life expectancy does not differ from that of the general population.

Comorbid psychiatric conditions are diagnosed more frequently in those with intellectual disabilities than in the general population. Even so, psychiatric disorders probably are underappreciated in this population.

o Attention deficit/hyperactivity disorder (ADHD) is diagnosed in 8-15% of children and 17-52% of adults with MR.

o Self-injurious behaviors require treatment in 3-15%, particularly in the severe range of MR/ID.

o Major depression, bipolar disorders, anxiety disorders, and other mood disorders are the most common psychiatric diagnoses in adults with MR/ID. Obsessive-compulsive disorder, conduct disorder, tic disorders, and other stereotypic behaviors are also diagnosed more commonly in those with MR/ID. Schizophrenia may have a prevalence of 3% in individuals with MR/ID, compared to 0.8% in the general population.

In the 1970 Isle of Wight study, as many as 30% of children with MR/ID exhibited an emotional or behavioral disorder, compared to 6% of children in the general population. MR compounded by epilepsy conferred a 56% risk of comorbid psychiatric disease in this study.6

Occult visual and auditory deficits occur in 50% of those with MR/ID, particularly when refractive errors are considered.

The rates of transmittable diseases, including sexually transmitted diseases (STDs), hepatitis B, and Helicobacter pylori infection, are increased significantly among individuals with MR/ID.

One in 5 individuals with MR/ID also has cerebral palsy (CP). As many as 20% of individuals with MR/ID have seizures. GI complications with MR/ID include feeding dysfunction, excess drooling, reflux esophagitis,

and constipation. GU complications with MR/ID include urinary incontinence and poor menstrual hygiene. A profound social morbidity affects individuals with MR/ID and their families. This morbidity can

be measured in lost wages, dependence on social services, impaired long-term relationships, and emotional suffering.

Race

Consistent racial differences in prevalence of MR/ID and associated mortality rates are not known to exist.

Sex

The gender ratios for mortality and morbidity do not differ from the gender ratio noted in the severe/profound ranges of intellectual disability (ie, male-to-female ratio, 1.2:1).

Age

MR/ID refers to intellectual impairment that develops prior to the age of 18 years.

Certain syndromes associated with MR/ID, such as Down syndrome, are associated with shorter life expectancy than the general population. In a comparison of those with MR/ID with and without Down syndrome from the California Department of Developmental Services cohort, excess mortality in the Down syndrome group tended to decrease with advancing age up to 35-39 years but increased thereafter. The increase in death rate from age 40 years was steeper in patients with Down syndrome than in those without Down syndrome.7

Clinical

History

Presenting signs/symptoms

The presenting symptoms and signs of MR/ID typically include cognitive skills delays, language delay, and delays in adaptive skills. Developmental delays vary depending on the level of MR/ID and the etiology. For example, in mild nonsyndromic MR/ID, delays may not be notable until the preschool years, whereas with severe or profound MR associated with syndromes or extreme prematurity, for example, significant delays in milestones may be noted from birth.

Language delay: One of the first signs of MR/ID may be language delays, including expressive language (speech) and receptive language (understanding). Red flags include no mama/dada/babbling by 12 months, no 2-word phrases by age 2, and parents reporting they are concerned that the child may be deaf.

Fine motor/adaptive delayo Significant delays in activities such as self-feeding, toileting, and dressing are typically

reported in children with MR/ID.o Prolonged, messy finger feeding and drooling are signs of oral-motor incoordination.

Cognitive delay: Children with MR/ID have difficulties with memory, problem-solving and logical reasoning. This may be expressed early on with preacademic difficulties or difficulty following directions (particularly multipart directions).

Social delays: Children with MR may display lack of interest in age-appropriate toys and delays in imaginative play and reciprocal play with age-matched peers. Rather than their chronological age, play reflects their developmental levels.

Gross motoro Delays in gross motor development infrequently accompany the cognitive, language,

and fine motor/adaptive delays associated with MR/ID unless the underlying condition results in both MR/ID and cerebral palsy.

o Subtle delays in gross motor acquisition, or clumsiness, may be identified in the developmental assessment.

Behavioral disturbanceso Even before an age at which psychopathology can be identified, infants and toddlers

who go on to have MR/ID may be more likely to have difficult temperaments, hyperactivity, disordered sleep, and colic.

o Associated behaviors may include aggression, self-injury, defiance, inattention, hyperactivity, sleep disturbances, and stereotypic behaviors.

Neurologic and physical abnormalitieso Prevalence of MR is increased among children with seizure disorders, microcephaly,

macrocephaly, history of intrauterine or postnatal growth retardation, prematurity, and congenital anomalies.

o In the process of addressing somatic problems, assessment of a child's cognitive abilities is often overlooked.

Family history

Guidelines from the American Academy of Pediatrics recommend that the evaluation of a child with MR/ID includes an extensive family history, with particular attention to family members with mental retardation, developmental delays, consanguinity, psychiatric diagnoses, congenital malformations, miscarriages, stillbirths, and early childhood deaths. The clinician should construct a pedigree of 3 generations or more.8

Physical

Developmental assessmento The American Academy of Pediatrics recommends developmental screening for all

children at regular intervals. Methods include several parental surveys, such as the Parents' Evaluation of Developmental Status (PEDS), Ages and Stages Questionnaires (ASQ) and Child Development Inventories (CDI). Other instruments require direct observation, such as the Bayley Infant Neurodevelopmental Screener, Battelle Developmental Inventory, Early Language Milestone Scale, and Brigance Screens.

o Key behavioral observations should focus on the child's communicative intent, social skills, eye contact, compliance, attention span, impulsivity, and style of play.

o For the diagnoses of developmental delay and MR/ID, an expanded neurodevelopmental and psychological examination is required. Various tests can be administered to assess language comprehension, language expression, nonverbal cognitive abilities, fine motor and adaptive abilities, attention span, memory, gross motor skills, and adaptive behaviors. The most common psychological tests for children include the Bayley Scales of Infant Development-III, the Stanford-Binet Intelligence Scale, the Wechsler Intelligence Scale for Children-IV, the Wechsler Preschool and Primary Scale of Intelligence-Revised, and the Vineland Adaptive Behavior Scales-II.

Physical examinationo Head circumference: Measurement of all growth parameters must include head

circumference. Microcephaly correlates highly with cognitive deficits. Macrocephaly may indicate hydrocephalus and is associated with some inborn errors of metabolism and may also be seen early on in some children later diagnosed with autism.9,10

o Height: Short stature may suggest a genetic disorder, fetal alcohol syndrome, or hypothyroidism. Tall stature may suggest fragile X syndrome (FraX), Soto syndrome, or other overgrowth syndrome associated with MR/ID.

o Neurologic: This examination should include assessments of head growth (for micro/macrocephaly), muscle tone (for hypotonia or spasticity), strength and coordination, deep tendon reflexes, persistent primitive reflexes, ataxia, and other abnormal movements such as dystonia or athetosis.

o Sensory: Vision and hearing should always be tested in suspected cases of MR/ID. Children with disabilities and MR/ID are more likely than other children to have visual impairment (refractive errors, strabismus, amblyopia, cataracts, abnormal retinal pigmentation, and cortical blindness) and hearing deficits, particularly among those with severe impairments.

o Skin: Cutaneous findings of etiologic interest include hyperpigmented and hypopigmented macules, such as café-au-lait macules (associated with neurofibromatosis type 1), and ash-leaf spots (associated with tuberous sclerosis), fibromas, and irregular pigmentation patterns.

o Extremities: Examine for dysmorphic features and organ system dysfunction indicative of syndromes. Although MR/ID with multiple congenital anomalies and major malformations accounts for only 5-10% of all cases, most of these affected individuals have 3-4 minor anomalies, especially involving the face and digits.

Causes

Prenatal conditions (genetic)o Trisomy 21 or Down syndrome

This disorder accounts for 25-50% of persons with severe MR; Down syndrome occurs in approximately 1 per 800 live births.

In infancy, this disorder is recognized by specific facial features, including flat facial profile, brachycephaly, up-slanted and narrow palpebral fissures, and anomalous auricles.

Hypotonia, joint hyperextensibility, neonatal jaundice, simian crease, shortened digits, and excess skin on the back of the neck contribute to the clinical features.

Congenital heart disease is present in approximately 40%. GI malformations are present in 5%. Congenital cataracts are found in 3%, and as many as 35% require treatment for strabismus or refractive error. Infantile spasms may develop in 5%.

The IQ score ranges from 25-50. Generally, verbal-linguistic skills lag behind visual-spatial skills and social performance is usually above the mental age.

In trisomy 21, gene expression of chromosome 21 is increased in a dosage-dependent fashion that varies by tissue type. While some trisomic 21 genes are not expressed at elevated levels, many are. Of those significantly increased, several encode proteins critical for mitochondrial function and for neurogenesis.

o Other chromosomal abnormalities (eg, deletions, duplications, translocations) may be present in as many as 25% of individuals with severe MR.

The most commonly occurring abnormalities of this class, detectable at the 500 band level of chromosomal analysis, are 5p- (ie, Cri du chat syndrome) and 4p- (ie, Wolf-Hirschhorn syndrome).

Cryptic subtelomeric deletions are diagnosed with increasing frequency as fluorescently tagged molecular DNA probes allow detection of deletions below the microscopic resolution of a standard karyotype.

Cryptic subtelometric rearrangements now account for 5-6% of cases of idiopathic mental retardation.

Chromosomal analysis is undergoing further refinement with the application of gene array hybridization techniques that may detect abnormalities in up to 20% of cases of idiopathic mental retardation.

o Fragile X syndrome The population prevalence of this disorder is approximately 1 in 3500 males,

giving a prevalence within the MR population of about 1 in 76. For males with severe MR, the prevalence rises to about 1 in 13. Other studies have found in populations of those with mental retardation positive fragile X studies in 5.9% of males and 0.3% of females.11 About 1 in 2000 females carries the fragile X (FraX) gene. Current studies suggest that FraX is the most prevalent form of inherited MR.

Males with the full FMR1 trinucleotide repeat expansion (ie, the full mutation) usually function in the moderate to severe range of MR.12 Other features include testicular enlargement in the postpubertal period and minor facial anomalies (eg, large forehead, elongated face, protuberant auricles, prominent chin).

Females with the full FMR1 trinucleotide repeat expansion may have no symptoms, although some have mild learning disabilities or even mild to moderate MR.

Mitral valve prolapse and seizures may occur. Up to 20% of FraX males meet criteria for autism; autisticlike behaviors can be

present in affected females as well. Direct DNA analysis of the FMR-1 gene is the method of choice for diagnosing

both affected individuals with the full trinucleotide repeat expansion (>200 repeats) and unaffected carriers with the premutation (60-200 repeats).

Contiguous gene deletion syndromeso Although less common, some of these syndromes can be readily identified clinically. The

following syndromes often can be confirmed by utilizing a fluorescence in situ hybridization (FISH) probe to the deleted region in question.

o Prader-Willi syndrome The Prader-Willi syndrome (PWS) involves deletion at 15q11-q13 (deletion of

the paternally derived region). Classic clinical features include neonatal and infantile hypotonia, feeding

problems or failure to thrive in infancy, excessive weight gain with hyperphagia beginning between ages 12 months and 6 years, food compulsions, hypogonadism, global developmental delay, almond-shaped eyes, thin upper lip, and down-turned corners of the mouth.

The candidate gene within the Prader-Willi gene region is SNRPN, which encodes a ribonucleoprotein involved in mRNA splicing. How SNRPN contributes to the hypothalamic dysfunction that defines many clinical features of PWS is unclear.

It is the first known human disorder of genomic imprinting, leading to revolutionary changes in the field of molecular genetics and the understanding of uniparental disomy.

Negative FISH results in PWS may be due to maternal uniparental disomy (UPD) of chromosome 15 (2 number 15 chromosomes from the mother) and can be confirmed with molecular studies.

o Angelman syndrome The Angelman syndrome (AS) also involves deletion at 15q11-q13 (deletion of

the maternal copy of the gene region). MR, absent speech, microcephaly, seizures, puppetlike ataxic movements,

inappropriate laughter, and facial dysmorphisms characterize AS. The candidate genes within the AS critical region include UBE3A, whose protein

product is important in the posttranslational modification of proteins by ubiquitination, and GABRA3, a subunit of the GABAa receptor.

Negative FISH results in AS may be due to paternal UPD of chromosome 15 (2 number 15 chromosomes from the father) and can be confirmed with molecular studies.

Point mutations occasionally are found in AS with negative results on FISH and UPD studies.

o Smith-Magenis syndrome Smith-Magenis syndrome (SMS) involves deletion at 17p11.2. MR, short stature, brachydactyly, minor skeletal and facial anomalies, sleep

disturbance, self-injurious behaviors, and other organ system malformations characterize this contiguous gene deletion syndrome.13

Although as many as 100 genes may be deleted in SMS, the physical characteristics are subtle.

o CATCH 22 syndrome The CATCH 22 syndrome, which comprises DiGeorge Syndrome (DGS) and

velocardiofacial syndrome (VCF), involves deletion at 22q11. Infants with classic DGS are identified readily by aplasia or hypoplasia of the

thymus, T cell lymphopenia, conotruncal cardiac defects, oral-motor dysfunction, and facial dysmorphisms (eg, low-set malformed ears, small jaw, palatal defects, hypertelorism, antimongoloid palpebral slant).

Minor variants may meet clinical criteria for the VCF syndrome. With a prevalence of 1 in 4,000 people, it is the most common known microdeletion disorder.

The majority of individuals with CATCH 22 have learning disabilities or mild MR and comorbid psychiatric disorders including schizophrenia and mood disorders with psychosis.

o Williams syndrome The Williams syndrome involves deletion at 7q11.14

Characteristic facial features are described as "elfin." In the majority, valvular stenosis, poor growth, hypotonia, late-onset contractures, dental anomalies, infantile colic, oral-motor discoordination, and hyperacusis (ie, hypersensitivity to sound) are reported. Infantile hypercalcemia may be transient and is often subclinical.

Mild to moderate MR, relative preservation of language, and associated weakness in visual-spatial development are typical.

Elastin is the candidate gene presumed responsible for some of Williams syndrome features, including supravalvular aortic stenosis.

o Wolf-Hirschhorn syndrome

The Wolf-Hirschhorn syndrome, also known as 4p- syndrome, involves deletion at 4p16.3.

Severe growth retardation, microcephaly, "Greek helmet" facies and orofacial clefts, and other midline fusion defects characterize this syndrome.

The region of deletion is gene dense, and an undefined number of genes may contribute to this phenotype.

o Langer-Giedion syndrome This syndrome, also known as trichorhinophalangeal syndrome type II, involves

deletion at 8q24.1. Learning disabilities and the presence of MR vary. Facial dysmorphisms include microcephaly, large ears, bulbous nose, broad

nasal bridge, elongated philtrum, and sparse scalp hair. Multiple nevi and skeletal anomalies may be present.

o Miller-Dieker syndrome The Miller-Dieker syndrome (MDS) involves deletion at 17p13.3. Infants present with severe neurologic impairment, seizures, and hypotonia

secondary to lissencephaly. The smooth cerebral cortex with absent or decreased gyral formation results from abnormal neuronal migration.

The identified gene LIS1 may function as a G protein subunit in cellular signal transduction that is important in telencephalon development.

o Many contiguous gene deletion syndromes for which a FISH probe is not available have been recognized in association with MR. A comprehensive survey is beyond the scope of this article.

Single gene mutation syndromeso Tuberous sclerosis

Hypopigmented cutaneous macules (ie, ash-leaf spots), calcified intracranial cortical tubers with or without heterotopias, seizures, retinal hamartomas, and renal angiomyolipomas characterize this hamartomatous condition.

MR may or may not be seen in affected individuals; the presence of seizures is the factor most associated with poor cognitive outcome. Autism is a rather common finding in children with tuberous sclerosis associated with MR.

This is an autosomal-dominant inherited condition with about half of affected individuals resulting from a new mutation. Two genes have been identified, one at 9q34 (TSC1) and the other at 16p13 (TSC2). A variety of deletions, rearrangements, and point mutations have been implicated in tuberous sclerosis.

o Rubinstein-Taybi syndrome Broad terminal phalanges, beaked nose, down-slanting palpebral fissures,

epicanthal folds, and microcephaly characterize this syndrome. Behavioral aspects include variable degrees of impulsivity, distractibility,

instability of mood, and stereotypies.15

This is an autosomal-dominant inherited condition, with the majority of cases representing new deletions or point mutations of the CREB-binding protein gene (16p13.3).

o Coffin-Lowry syndrome This syndrome is characterized by hypertelorism, down-slanting palpebral

fissures, frontal prominence, thickened lips and nasal septum, as well as dental and skeletal anomalies.

It is an X-linked condition, with females having mild manifestations. The syndrome results from mutations in the RSK2 gene, which encodes a CREB kinase (Xp22.2-p22.1).16

o Rett syndrome Developmental stagnation then regression, progressive microcephaly, seizures,

ataxia, and autisticlike behaviors are seen in affected females. This X-linked dominant condition with presumed lethality for affected males is

caused by mutations in MeCP2, a transcriptional repressor (Xq28).17

o Smith-Lemli-Opitz syndrome Malformations consistent with holoprosencephaly sequence, syndactyly of toes

2 and 3, micrognathia, cleft palate, and moderate to severe MR are seen. This autosomal-recessive inherited condition results from increases in 7-

dehydrocholesterol (7-DHC) due to mutations in the 7-DHC reductase gene (11q12-q13).

Treatment with an oral cholesterol "cocktail" has shown some promise in this syndrome.

o Costello syndrome Characteristic clinical features include polyhydramnios, failure to thrive, cardiac

anomalies, and tumor predisposition. Mean IQ is in the mild MR range, but the spectrum extends from severe MR to

average intelligence. Affected males are lower functioning than females and have significantly more behavioral problems.18

Mutation in HRAS is identified, resulting in a gain of function of the encoded protein and increased activation of the cellular signaling pathway Ras-MAPK.19

o Many other single-gene disorders are associated with MR with additional phenotypic and behavioral features including such problems as microcephaly, seizures, or short stature, with or without dysmorphic facies.

Recent advances in genetic linkage analysis techniques in families with multiple affected members have revealed more than 50 candidate genes along the X chromosome. In some kindreds with a pattern of X-linked nonsyndromic mild MR (XLMR), linkage analysis has identified candidate genes that code for interleukin receptors, G protein signaling factors, transcription factors, and transcriptional repressors.

Environmental causeso Fetal alcohol syndrome and fetal alcohol effect

Alcohol results in a wide range of teratogenic effects.20 The most severely affected individuals meet criteria for fetal alcohol syndrome (FAS) by demonstrating short palpebral fissures, dental crowding, camptodactyly flattened philtrum, thin vermillion border, flattening of the maxillary area, microphthalmia, prenatal and postnatal growth deficiency, microcephaly, and developmental delay.

Fetal alcohol effect (FAE) can be diagnosed only in the context of (1) maternal history of alcohol use and (2) a child with developmental and behavioral abnormalities that also manifests growth deficiency or the characteristic facial dysmorphisms.

The prevalence of FAS may be as high as 1.9 in 1000 live births and is the leading cause of MR in the western world. The impact of the milder FAE remains unknown. The teratogenic effects of alcohol may be responsible for as many as

8% of cases of mild MR. Alcohol's deleterious effects on cortical plasticity contribute to cognitive impairment.

o Congenital hypothyroidism Congenital hypothyroidism (known as cretinism in the past) is a neurologic

syndrome that results from severe thyroid hormone deficiency during the fetal period. In the infant, the syndrome comprises deaf mutism, moderate to severe MR, spasticity, and strabismus.

Normal fetal brain development requires sufficient production of both maternal and fetal thyroid hormones. Normal glandular production of T4 and T3 requires sufficient dietary intake of iodine.

Iodine deficiency may affect an estimated 800 million people worldwide. It can result in endemic goiter, fetal wastage, milder degrees of developmental delay, and endemic congenital hypothyroidism.

Perinatal/postnatal conditions: These conditions are responsible for fewer than 10% of all MR cases.

o Congenital cytomegalovirus (CMV)o Congenital rubella - No longer an important etiology in countries with high vaccination

rateso Intraventricular hemorrhage related to extreme prematurity - An important cause only

in societies with advanced neonatal care and survival of the prematureo Hypoxic-ischemic encephalopathy - Always results in combined CP/MRo Traumatic brain injury - Shaken baby syndrome, closed head injury sustained in motor

vehicle accidentso Meningitis - Decreasing in importance as the incidence of Haemophilus influenzae type B

decreases in vaccinated populationso Trichomoniasis during pregnancy21

o Neurodegenerative disorders

More on Mental RetardationOverview: Mental Retardation

Differential Diagnoses & Workup: Mental Retardation

Treatment & Medication: Mental Retardation

Follow-up: Mental Retardation

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References

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Further Reading[ CLOSE WINDOW ]

Keywords

intellectual disability, developmental delay, developmental disability, autism, autism spectrum disorder, cognitive impairment, intelligence quotient, IQ less than 70, learning disability, Down syndrome, Fragile X syndrome, Prader-Willi syndrome, Angelman syndrome, Smith-Magenis syndrome, CATCH 22 (22q11 deletion) syndrome, DiGeorge syndrome, velocardiofacial syndrome, Williams syndrome, Wolf-Hirschhorn syndrome, Langer-Giedion syndrome, Miller-Dieker syndrome, tuberous sclerosis, Rubinstein-Taybi syndrome, Coffin-Lowry syndrome, Rett

syndrome, Smith-Lemli-Opitz syndrome, fetal alcohol syndrome, fetal alcohol effects, cretinism, congenital hypothyroidism, congenital cytomegalovirus, congenital rubella, intraventricular hemorrhage, hypoxic-ischemic encephalopathy, traumatic brain injury, shaken baby syndrome, meningitis, global developmental delays

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Contributor Information and Disclosures

Author

Ari S Zeldin, MD, FAAP, Senior Clinical Fellow/Clinical Instructor in Autism and Neuro-Developmental Disorders, Division of Pediatric Neurology, Department of Neurosciences, University of California, San Diego, School of MedicineAri S Zeldin, MD, FAAP is a member of the following medical societies: American Academy of Neurology, American Academy of Pediatrics, and Child Neurology Society Disclosure: Nothing to disclose.

Coauthor(s)

Alicia T F Bazzano, MD, MPH, Consulting Faculty, Division of Pediatric Emergency Medicine, Harbor/UCLA Medical Center; Attending Staff, Department of Emergency Medicine, Children's Hospital Los Angeles; Chief Physician, Westside Regional CenterAlicia T F Bazzano, MD, MPH is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American Public Health Association, and American Society for Bioethics and Humanities Disclosure: Nothing to disclose.

Medical Editor

Beth A Pletcher, MD, Associate Professor, Co-Director of The Neurofibromatosis Center of New Jersey, Department of Pediatrics, University of Medicine and Dentistry of New JerseyBeth A Pletcher, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Medical Genetics, American Medical Association, and American Society of Human Genetics Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicineDisclosure: eMedicine Salary Employment

Managing Editor

Kenneth J Mack, MD, PhD, Senior Associate Consultant, Department of Child and Adolescent Neurology, Mayo Clinic

Kenneth J Mack, MD, PhD is a member of the following medical societies: American Academy of Neurology, Child Neurology Society, Phi Beta Kappa, and Society for Neuroscience Disclosure: Nothing to disclose.

Chief Editor

Amy Kao, MD, Attending Neurologist, Children's National Medical Center, Washington DCAmy Kao, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Pediatrics, American Epilepsy Society, and Child Neurology Society Disclosure: Nothing to disclose.

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Differential DiagnosesAutism Learning Disorder, Mathematics

Borderline intellectual functioning Learning Disorder, Reading

Child Abuse & Neglect, Posttraumatic Stress DisorderLearning Disorder, Written Expression

Childhood Disintegration Disorder Pervasive Developmental Disorder

Cognitive Deficits Rett's Syndrome

Depression Severe communication/language disorders

Other Problems to Be Considered

CNS traumaEnvironmental deprivationMajor sensory deficits (eg, deafness, blindness)MalnutritionMitochondrial cytopathiesNeurodegenerative disorders