|
About Genetic Services
Uses of Genetic Testing
Clinically applicable genetic tests may be used for:
Research tests generally do not give clinically
applicable results. Research testing is discussed further
in the "Ordering Genetic Testing" section.
Diagnostic Testing
Diagnostic testing is used to confirm or rule out a
known or suspected genetic disorder in a symptomatic
individual.
Points to consider:
- DNA testing may yield diagnostic information at a
lower cost and with less risk than other procedures
(Clinical
Example).
- Diagnostic testing is appropriate in symptomatic
individuals of any age (Clinical
Example).
- Confirming a diagnosis may alter medical management
for the individual (Clinical
Example).
- Diagnostic testing of an individual may have
reproductive or psychosocial implications for other
family members as well (Clinical
Example).
- Establishing a diagnosis may require more than one
type of genetic test (Clinical
Example).
- DNA testing may not always be the best way to
establish a clinical diagnosis (Clinical
Example).
Predictive Testing
Predictive testing is offered to asymptomatic
individuals with a family history of a genetic disorder.
Predictive testing is of two types: presymptomatic
(eventual development of symptoms is certain when the gene
mutation is present, e.g., Huntington disease) and
predispositional (eventual development of symptoms is
likely but not certain when the gene mutation is present,
e.g., breast cancer).
Points to consider:
Carrier Testing
Carrier testing is performed to identify individuals who
have a gene mutation for a disorder inherited in an
autosomal recessive or X-linked recessive manner. Carriers
usually do not themselves have symptoms related to the gene
mutation. Carrier testing is offered to individuals who
have family members with a genetic condition, family
members of an identified carrier, and individuals in ethnic
or racial groups known to have a higher carrier rate for a
particular condition.
Points to consider:
- Identifying carriers allows reproductive choices
(Clinical
Example).
- Genetic counseling and education should accompany
carrier testing because of the potential for personal and
social concerns (Clinical
Example).
- Molecular genetic testing of an affected family
member may be required to determine the disease-causing
mutation(s) present in the family (Clinical
Example).
- In some situations, DNA testing may not be the
primary way of determining carrier status (Clinical
Example).
- Carrier testing can improve risk assessment for
members of racial and ethnic groups more likely to be
carriers for certain genetic conditions (Clinical
Example).
Prenatal Testing
Prenatal testing is performed during a pregnancy to
assess the health status of a fetus. Prenatal diagnostic
tests are offered when there is an increased risk of having
a child with a genetic condition due to maternal age,
family history, ethnicity, or suggestive multiple marker screen
or fetal ultrasound
examination. Routine prenatal diagnostic test
procedures are amniocentesis and chorionic villus
sampling (CVS). More specialized procedures include
placental biopsy, periumbilical blood sampling (PUBS), and
fetoscopy with fetal skin biopsy.
Points to consider:
- A laboratory that performs the disease-specific test
of interest must be identified before any prenatal
diagnostic test procedure is offered (Clinical
Example).
- All prenatal diagnostic test procedures have an
associated risk to the fetus and the pregnancy;
therefore, informed consent is required, most often in
conjunction with genetic counseling.
- In most cases, before prenatal diagnosis using
molecular genetic testing can be offered, specific gene
mutation(s) must be identified in an affected relative or
carrier parent(s) (Clinical
Example).
- Prenatal testing for adult-onset conditions is
controversial. Individuals seeking prenatal diagnosis for
these conditions should be referred to a professional
trained in genetic counseling for a complete discussion
of the issues. See ACMG/ASHG Report: Points to Consider: Ethical Legal and Psychosocial Implications of Genetic Testing in Children and Adolescents (1995).
Preimplantation Testing (Preimplantation Genetic
Diagnosis)
Preimplantation testing is performed on early embryos
resulting from in vitro fertilization in order to decrease
the chance of a particular genetic condition occurring in
the fetus. It is generally offered to couples with a high
chance of having a child with a serious disorder.
Preimplantation testing provides an alternative to prenatal
diagnosis and termination of affected pregnancies.
Points to consider:
- Preimplantation testing is only performed at a few
centers and is only available for a limited number of
disorders.
- Preimplantation testing is not possible in some cases
due to difficulty in obtaining eggs or early embryos and
problems with DNA analysis procedures.
- Due to possible errors in preimplantation diagnosis,
traditional prenatal diagnostic methods are recommended
to monitor these pregnancies.
- The cost of preimplantation testing is very high and
is usually not covered by insurance.
Newborn Screening
Newborn screening identifies individuals who have an
increased chance of having a specific genetic disorder so
that treatment can be started as soon as possible.
Points to consider:
- Newborn
screening programs are usually legally mandated and
vary from state to state.
- Newborn screening is performed routinely at birth,
unless specifically refused by the parents in
writing.
- Screening tests are not designed to be diagnostic,
but to identify individuals who may be candidates for
further diagnostic tests (Clinical
Example).
- Many parents do not realize that newborn screening
has been done (or which tests were included), even if
they signed a consent form when their child was
born.
- Education is necessary with positive screening
results in order to avoid misunderstandings, anxiety and
discrimination (Clinical
Example).
|