Genetic Testing Health Article

Definition

A genetic test examines the genetic information contained inside a person's cells, called DNA, to determine if that person has or will develop a certain disease or could transmit a disease to a child. Genetic tests also determine whether or not couples are at a higher risk than the general population for having a child affected with a genetic disorder.

Purpose

Some families or ethnic groups have a higher incidence of a certain disease than do the population as a whole. For example, individuals of Eastern European, Ashkenazi Jewish descent are at higher risk for carrying genes for rare conditions such as Tay-Sachs disease (a lipid storage disease) that occur much less frequently in populations from other parts of the world. Before having a child, a couple from such a family or ethnic group may want to know if their child would be at risk of having that disease. Genetic testing for this type of purpose is called genetic screening.

During pregnancy, a baby's cells can be studied for certain genetic disorders or chromosomal problems such as Down syndrome. Chromosome testing is most commonly offered when a mother is 35 years or older at the time of delivery. When there is a family medical history of a genetic disease or there are individuals in a family affected with developmental and physical delays, genetic testing may also be offered during pregnancy. Genetic testing during pregnancy is called prenatal diagnosis.

Prior to becoming pregnant, couples who are having difficulty conceiving a child or who have had multiple miscarriages may be tested to see if a genetic cause can be identified.

A genetic disease may be diagnosed at birth by performing a physical evaluation of the baby and observing characteristics of the disorder. Genetic testing can help to confirm the diagnosis made by a physical evaluation. In addition, biochemical tests (e.g., blood phenylalanine measurement) are performed routinely on all newborns to screen for certain genetic diseases that can affect a newborn baby's health shortly after birth.

There are several genetic diseases and conditions in which the symptoms do not occur until adulthood. One such example is Huntington's disease. This is a serious disorder affecting the way in which individuals walk, talk and function on a daily basis. Genetic testing may be able to determine if someone at risk for the disease will in fact develop the disease.

Some genetic abnormalities may make a person more susceptible to certain types of cancer. Testing for these abnormalities can help predict a person's risk. Other types of genetic tests help diagnose, predict, and monitor the course of certain kinds of cancer, particularly leukemia, lymphoma, and breast cancer.

Precautions

Genetic tests are performed on cells derived from blood, bone marrow, amniotic fluid, or tissues. The health care worker collecting the specimen should observe universal precautions for the prevention of transmission of bloodborne pathogens. Because genetic testing is not always accurate and because there are many concerns surrounding insurance and employment discrimination for an individual receiving a genetic test, genetic counseling should always be performed prior to genetic testing. A genetic counselor is an individual with a master's degree in genetic counseling. A medical geneticist is a physician specializing and board certified in genetics.

A genetic counselor reviews a person's family history and medical records and the reason for the test. The counselor explains the likelihood that the test will detect all possible causes of the disease in question (known as the sensitivity of the test), and the likelihood that the disease will develop if the test is positive (known as the positive predictive value of the test).

Learning about the disease in question, the benefits and risks of both a positive and a negative result, and what treatment choices are available if the result is positive, will help prepare a person undergoing testing. During the genetic counseling session, an individual interested in genetic testing will be asked to consider how the test results may affect his or her life, family, and future decisions.

After this discussion, persons should have the opportunity to indicate, in writing, that they gave informed consent to have the test performed, verifying that the counselor provided complete and understandable information.