Tay Sachs Carrier Testing - A Closer Look

Is there a test to identify carriers?

Tay-Sachs most often appears in families with no prior history of the disease. The TSD gene can be carried without being expressed through many generations. Before 1970, the only way to learn if one was a Tay-Sachs carrier was to be the parent of a baby with TSD. Now, safe and reliable carrier testing is available to identify Tay-Sachs carriers. Most important, testing can identify carrier couples who are at risk for bearing a child with TSD - before a tragedy occurs. With this vital information, couples can explore the various options that will enable them to protect their families from this devastating disease.

A simple blood test can distinguish Tay-Sachs carriers from non-carriers. Blood samples can be analyzed by either enzyme assay or DNA studies. The enzyme assay is a biochemical test that measures the level of Hex-A in a person’s blood. Carriers have less Hex-A in their body fluid and cells than non-carriers. (Babies with Tay-Sachs disease have a total absence of Hex-A in their cells.) The biochemical test is able to detect all Tay-Sachs carriers of all ethnic backgrounds.

Accurate biochemical testing requires laboratories to be proficient in specialized laboratory procedures and experienced in the interpretation of test results. To ensure accuracy, persons seeking such carrier testing for TSD should verify that the analysis is being performed at a laboratory that participates in the International Tay-Sachs Laboratory Quality Control Program supported by NTSAD. A complete list of laboratories affiliated with the Quality Control Program is available through NTSAD at Testing Centers near you.

DNA-based carrier testing looks for specific mutations, or changes, in the gene that codes for Hex-A. Since 1985, when the Hex-A gene was isolated, 75 to over 100 mutations in this gene have been identified. Some are more prevalent than others; a few are associated with a later-onset form of the disease, rather than with the infantile form described here.

The limitation of DNA-based carrier testing is that not all known mutations in the Hex-A gene are detected by the test, and others have yet to be identified. The tests currently available detect about 95% of carriers of Ashkenazi Jewish background and about 60% of non-Jewish individuals. Therefore, some people who are carriers will not be identified by DNA analysis alone.

DNA testing can provide very important information when used in conjunction with biochemical testing, especially in cases where both members of a couple are determined to be carriers. Knowing information about the mutations carried by each parent, and whether they are classical or late-onset Tay-Sachs mutations, is important if a couple chooses to undergo prenatal diagnosis.

Tay-Sachs carrier testing is vital for individuals in high-risk populations who are planning to have children. Even if your childbearing years are over, your carrier status can be an extremely important piece of information. If you are a carrier, your close relatives (children, brothers, sisters, cousins, aunts, uncles) should be alerted so that they can be tested as well. Tay-Sachs carrier testing is also vital for the close relatives of families with an affected child, regardless of ethnic background, since all parents of children with Tay-Sachs are, by definition, carriers.

For persons of Ashkenazi Jewish decent

All around the world distinct ethnic groups have been identified as having increased risk for particular genetic disorders. In the Ashkenazi Jewish (Eastern European) population, several such inherited disorders are known. It is considered standard of care for doctors to offer carrier testing for Tay-Sachs, Canavan, Familial Dysautonomia and cystic fibrosis to individuals of Ashkenazi Jewish decent and their non-Jewish partners.

In addition to the genetic diseases listed above, there are a number of other disorders that occur more often in those of Ashkenazi Jewish heritage for which carrier testing is also available. It is often referred to as the ‘Jewish Panel;’ always confirm with your doctor or genetic counselor which diseases are included in the ‘Jewish Panel.’ Interested couples can have a blood test to learn about their specific chances of having a child affected by one of these diseases. Please note not all the common Ashkenazi Jewish diseases fall under the NTSAD umbrella. Please contact the provided resource for additional information on that particular disease.