Genetic Counseling

Ashley Carlson1st Year Genetic Counseling

Sarah Lawrence College Bronxville, NY

What is a Genetic Counselor? A health professional with experience

in medical genetics and counseling. Provides information and support to

families who:– have members with genetic

disorders or birth defects – may be at risk for genetic disorders

or birth defects Practices non-directive counseling

How Can I Become a Genetic Counselor?

Obtain a specialized graduate degree in Genetic Counseling

Most enter the field from a variety of disciplines including biology, genetics, nursing, psychology, public health and social work. (NSGC 1983)

Having experience in counseling is very important

How Did I Become a GC? High school – Took Chemistry, Biology I and

II, and Physical Science Undergrad – Biology, Genetics,

Developmental Bio, Chemistry, Statistics, Evolutionary Bio, Genetic Technology, etc.

Experience in a counseling-based agency – Worked in a Battered Women’s Shelter

Volunteered for two prenatal Genetic Counselors in Wilmington, NC for one year

What Made Me Decide to Become a Genetic Counselor?

Senior Exit Project– The idea came from my brother

Interviewed two genetic counselors Personal History

– Arnold-Chiari

Malformation I

Chromosomes They are the packages that contain

our genetic material – our genes All of our cells have 46 chromosomes Half (23) are inherited from each

parent Chromosomes exist in pairs (23 pairs)

Normal Appearing Female46,XX

Normal Male 46,XY

Cell Division/ReproductionMitosis Cell division All 46

chromosomes copy themselves

Both new cells have the same set of 46 chromosomes

Meiosis How egg and sperm

are formed One cell with 46

chromosomes divides twice resulting in 4 cells that each have only 23 chromosomes

Nondisjunction

Failure of paired chromosomes to separate during meiosis in Anaphase I

Leads to egg or sperm with extra or missing chromosomes

When abnormal egg/sperm is used for fertilization, the result is an aneuploid embryo

Down syndrome

Most common live born chromosome disorder

Extra 21 chromosome Prevalence: 1:800 births

– 350,000 people in USA Mental retardation

– Characteristic facial features

– Heart defects – Vision/hearing problems – Increased risk of Leukemia

and Alzheimer's

Trisomy 18 - Edwards Syndrome

Edwards Syndrome 1:8000 live births Mental deficiency Small jaw Short sternum Heart defects Malformed ears Rocker-bottom feet Characteristic

clenched fist 90% die before 1 yr

Turner Syndrome

Turner Syndrome

1:8000 live births Webbed neck Puffiness of hands

and feet No sexual maturation Broad chest and

widely spaced nipples Learning difficulties

What Are Genes? Genes are the units of heredity we

receive from our parents They are packaged at specific

locations (loci) on our chromosomes Like chromosomes, they occur in

pairs, one from each parent They are sequences of DNA

Reasons for Genetic Disease A change in a gene from its natural state Changes can be inherited or acquired Genes themselves do not cause disease Mutation = gene malfunction = malformed

or absent gene product = disease “She has the breast cancer gene…”

means she has a mutated version of that gene

ALL of us have some version of the Breast Cancer Gene or BRCA

Recessive Inheritance

Autosomal Recessive Conditions

Cystic FibrosisXeroderma PigmentosaTay-SachsSickle Cell Anemia

AlbinismEyes, hair and

skinLack of

pigment25% risk to

children of carriers

Dominant Inheritance

Autosomal Dominant Conditions Achondroplasia – dwarfism Familial Breast Cancer – BRCA1 and 2 Huntington Disease

Crouzon’s Syndrome

Premature fusion of the skull bones

Wide, shallow eyes

Hearing loss

X-Linked Inheritance

X-Linked Traits

Color blindness Hemophilia Fragile X

x-linked dominant: “Incontinentia pigmenti” -various severity from skin abnormality to CNS problems

Fragile X Syndrome Most common cause of

inherited mental impairment

Caused by expanding area of DNA on chromosome X (CGG Repeat)

Prevalence: – 1 in 4000 males – 1 in 6000 females – All races and ethnic groups

What Happens During a Genetic Counseling Session? Family history is taken Discuss medical/genetic

problems in general Provide risk assessment Discuss testing options,

in terms of risks, benefits and limitations

Consent patient for testing

Pedigree Construction Geneticists’ fundamental tool Allows for easy construction of a multi-

generational family history Simple method for detailed

documentation of inheritance of a particular trait in a family

Can often assess the inheritance of a trait based on pattern of affected individuals

Pedigree Fundamentals

Autosomal Recessive(it can be hidden and reappear)

What inheritance pattern?

Autosomal Dominant

What inheritance pattern?

X-Linked Dominant(if father carries, every girl has it)

What inheritance pattern?

Y-linked(all sons of affected fathers are affected, ex; TDF-testes determining factor)

Any ideas on this one?

Mitochondrial Inheritance(all children get mitochondria of mother)

Prenatal Genetics Women who are at

increased risk to have a child with a genetic disorder/ birth defect– Advanced maternal age– Family history of medical

problem/genetic disease– Exposure to drugs,

alcohol, medication– Prenatal sonogram

abnormalities

Maternal Age Effect

As the age of the mother increases, there is an increased risk for a chromosome abnormality in their child.

Different Prenatal Testing

MSAFP – (test mother’s blood)

Amniocentesis CVS Nuchal Fold-

– sonogram measures amount of fluid in fetus’ dorsal neck

Maternal Serum Screen

AFP HCG uE3 Inhibin A

Down

Syndrome

Trisomy

18

N/A

Neural Tube Defect N/A N/A N/A

Neural Tube Defects

Diagnostic Testing CVS – Chorionic

Villi Sampling Amniocentesis

Case 1

Mother is 28 years old Maternal Serum Screen indicates 1/30

for Down Syndrome

TeratogensThalidomideMedications for maternal illness

Osteogenesis Imperfecta

Marfan Syndrome

Ehlers-Danlos Syndrome

Neurofibromatosis

Prader-Willi Syndrome

Treacher Collins Syndrome

Case 2: Huntington Disease

Woman is 31 years old Has a sister and father with HD Wants to be pregnant without knowing

her HD status Goes through 2 rounds of

Preimplantation Genetic Diagnosis (PGD) unsuccessful

At 34 she becomes pregnant naturally

Case 3: Cancer Genetics

Breast cancer in a family with Ashkenazi Jewish heritage

Unaffected father worried about two daughters: 28 and 23 yrs

Information Websites National Society for Genetic Counselors

http://www.nsgc.org The American Board of Genetic

Counseling (ABGC)

http://www.abgc.net Canadian Association of Genetic

Counsellors

http://www.cagc-accg.ca

Caroline LieberDirector of The Joan H. Marks Graduate Program

in Human Genetics

Sarah Lawrence College

1 Mead Way

Bronxville, NY 10708

Tel: 914.395.2371

http://www.slc.edu/grad_humangenetics.php

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