Genetic Screening Leona Al-Sayah National Institutes of
Health
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Background Information Genetic screening is a process to
analyze DNA, and serves as an important tool of modern preventive
medicine. The purpose is to identify persons whose genotype places
them or their offspring at risk. Such screening has the potential
to lessen the devastating impact of genetic disease. The human race
carries 3,000 - 4,000 diseases in its genes. The faulty gene that
causes any of these diseases will be a one in 100,000 and 200,000
healthy gene in each cell. In order to locate this faulty gene,
scientists search for variations in larger pieces of DNA called
markers. They are found nearby the DNA and become the basis of
genetic screening. With such markers it becomes theoretically
possible to screen individuals of every age, from infants to
adults, even babies before birth.
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History Although much has been discovered in recent decades to
improve genetic testing, the history of genetics is ratheran old
science and has been studied for many years. Between 1879 and 1882
Walter Fleming discovered chromosomes or DNA which is the subject
of study in genetics and so began the history of real genetic
testing. In 1902 inherited diseases were first linked to
chromosomes and following this a number of other genetic disorders
were found and described by various geneticists. In 1975, a method
to isolate and analyze DNA fragments was discovered which is now
known as the "Southern blot analysis" and it is urrently used in
genetic testing. In 1983 the PCR method of DNA analysis was
discovered and is now a popular method of DNA analysis in genetic
testing. Today genetic testing is becoming more and more popular
and the history of genetic testing has laid the foundation for
modern analysis into diseases as well as paternity and ancestry DNA
testing.
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Uses To determine sex To check for abnormal chromosome number
To check for early onset conditions (sickle cell, cystic fibrosis)
To check for late onset conditions (Huntingtons disease, Polycystic
kidney disease) To find susceptibility to diseases
(hypercholesterol, alcoholism) To determine carriers of recessive
genes (sickle cell, cystic fibrosis)
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Screening There are two classes of genetic screening:
Presymptomatic screening - this is used to test individuals whose
health is in danger Carrier screening - carried out in healthy
individuals where genes are harmful to the health of their future
offspring. Other types of genetic screening usually include
parental screening, newborn screening, forensic screening and
susceptibility screening.
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Once a person decides to proceed with genetic testing, a
medical geneticist, primary care doctor, specialist, or nurse
practitioner can order the test. Genetic testing is often done as
part of a genetic consultation. Genetic testing uses a sample of
DNA-containing material like blood, saliva and amniotic fluid to
search for variations in chromosomes genes and proteins. There are
many different procedures used in genetic testing and many
different reasons for their use. The screening of a particular
disorder is carried out on one of the following samples: blood,
bone marrow, amniotic fluid, hair, semen, skin. A procedure called
a buccal smear uses a small brush or cotton swab to collect a
sample of cells from the inside surface of the cheek. The sample is
sent to a laboratory where technicians look for specific changes in
chromosomes, DNA, or proteins, depending on the suspected disorder.
The laboratory reports the test results in writing to a persons
doctor or genetic counselor. Procedure
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DNA Amplification Genetic testing can be done on very small
samples. However, when more DNA is required for testing than is
available, it can be amplified through processes like polymerase
chain reaction, which copies a DNA molecule by stimulating the
DNA-reproduction process. Karyotyping Conditions such as Down's and
Turner's syndromes, which are caused by the inheritance of an extra
or too few chromosomes can be revealed through karyotyping, which
creates an image of the chromosomes found in an individual's
somatic cells. This is one of the simplest forms of genetic testing
as no molecular study is necessary. Molecular Study Genetically
linked conditions have a standard form for healthy, sick or at-risk
individuals. Genetic testing can isolate deletions or mutations of
a gene or protein and either confirm a diagnosis or alert to the
risk of developing a condition such as Huntington's chorea years or
even decades before symptoms develop.
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Newborn Screening Newborn screening is concerned with the
analysis of blood or tissue samples taken in early infancy in order
to detect genetic diseases for which early intervention can avert
serious health problems or death. This started in 1960 with the
ability to test newborns for a rare metabolic disease,
phenylketonuria (PKU). Two other examples of newborn screening are
the testing of African - American infants for sickle cell anemia
and Ashkenazic Jews for Tay- Sachs disease. Newborn screening tests
are done on a small blood sample, which is taken by pricking the
babys heel. Unlike other types of genetic testing, a parent will
usually only receive the result if it is positive. If the test
result is positive, additional testing is needed to determine
whether the baby has a genetic disorder.
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Positive Viewpoint Genetic testing has potential benefits
whether the results are positive or negative for a gene mutation.
Test results can provide a sense of relief from uncertainty and
help people make informed decisions about managing their health
care. A negative result can eliminate the need for unnecessary
checkups and screening tests in some cases. A positive result can
direct a person toward available prevention, monitoring, and
treatment options. Some test results can also help people make
decisions about having children. Newborn screening can identify
genetic disorders early in life so treatment can be started as
early as possible.
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Progress Markers have already been found for various diseases
such as Huntington's disease, cystic fibrosis, Duchenne's muscular
dystrophy, hemophilia and thalassaemia, and some rare cancers.
Scientists are also searching for the genetic connection with more
common disorders where environment may play a role - Alzheimer's
disease, diabetes, epilepsy, certain cancers and heart disease. The
term testing is usually used when seeking to identify individuals
or those within a family, screening for analyzing samples from a
larger group of people, perhaps within a population. However, both
these terms are often used to describe the same thing as the
process and intent is the same: to discover if someone has disease
or is a healthy carrier.
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Diseases Found by Screening Source: Office of Technology
Assessment
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Negative Viewpoint Genetic discrimination: People with genetic
flaws, not all of which show up as dysfunctions, may be denied life
insurance, health insurance, and access to schooling or to jobs.
Differential treatment: Employers could hire only those people
whose genes indicate they are resistant to the health hazards of
the work place, which is a cheaper alternative to making the work
place safe for all. Eugenics: Social or political pressure may be
applied to people to make childbearing decisions on the basis of
genetic information. Mating between those with valued genes may be
encouraged while mating between two people with dangerous recessive
traits may be prohibited. Women carrying fetuses with genetic
abnormalities may be encouraged to abort. Genetic determinism:
Genetic determinism is the belief that behavioral and personality
characteristics, such as intelligence or criminal behavior, are
mostly a function of genes. Genetic determinism implies a
fatalistic attitude toward health and disease. It can be used to
justify bigotry and to perpetuate racial or ethnic inequalities. A
genetic underclass could be created. Drastic procedures may be
taken that may not have been necessary
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Issues Even those diagnosed with the present tests might be
told they carry a debilitating mutation when they may never get
sick in their lifetime. With each new test that detects a new
mutation there will be a higher risk of misdiagnoses, and since
there are now at least 360 known mutations that result in cystic
fibrosis, population screening would be a costly and time-consuming
process that would not achieve the intended results.
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Genetic Discrimination Genetic discrimination occurs when
people are treated differently by their employer or insurance
company because they have a gene mutation that causes or increases
the risk of an inherited disorder. People who undergo genetic
testing may be at risk for genetic discrimination. The results of a
genetic test are normally included in a persons medical records.
When a person applies for life, disability, or health insurance,
the insurance company may ask to look at these records before
making a decision about coverage. An employer may also have the
right to look at an employees medical records. As a result, genetic
test results could affect a persons insurance coverage or
employment. People making decisions about genetic testing should be
aware that when test results are placed in their medical records,
the results might not be kept private. Fear of discrimination is a
common concern among people considering genetic testing. Several
laws at the federal and state levels help protect people against
genetic discrimination; however, genetic testing is a fast-growing
field and these laws dont cover every situation.
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Cost Genetic tests may be expensive because they are somewhat
rare and labor intensive, undergo multiple levels of review, and
may include any cost for blood draw or specimen collection,
shipping costs, and genetic counseling or physician fees. These
costs may vary depending on the type of test and who orders it.
Costs for Selected Genetic Tests by Disorder and Type of Test LAB
TestSequencingAnalysis Denaturing gradient gel electrophoresis
Allele Specific olligonucleotide Protein truncation test
HNPCC$500-3000$260$250-800-- FAP$800-1000--$350-450$235
BRCA1$1290--$350-450- BRCA2$1290--$190-354- BRCA- Ashkenazi
mutations -----
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Legal Matters With regard to genetic testing and information in
general, legislation in the United States called the Genetic
Information Nondiscrimination Act prohibits group health plans and
health insurers from denying coverage to a healthy individual or
charging that person higher premiums based solely on a genetic
predisposition to developing a disease in the future. The
legislation also bars employers from using individuals genetic
information when making hiring, firing, job placement, or promotion
decisions The legislation, the first of its kind in the U.S. was
passed by the United States Senate on April 24, 2008, on a vote of
95-0, and was signed into law by President George W. Bush on May
21, 2008. It went into effect on November 21, 2009.
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Opinion Genetic testing has many benefits that may save a
person and his or her family from troubles and ease their pains.
Newborn screening may be used to avoid the medical and emotional
hardships that accompany deadly disorders such as Tay-Sachs and
cystic fibrosis that have onsets early in a child's life. The fact
that there is a probability of the disease occurring also raises
problems and concerns, for some people may take extreme measures to
prevent the disease from occurring as they have seen family members
struggle. Such as in the case of a woman who got a mastectomy after
a screening that showed she was susceptible to breast cancer to
avoid getting it like her sister who died from it. It is wonderful
that deadly diseases can be avoided in some cases using this new
technology, but it definitely has the potential to be misused.
Therefore, genetic testing and screening must be used sparingly and
at all costs avoid becoming a commercial service that can be
exploited. Regulations to protect the wellbeing and identity of
those tested must be enforced.