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Q: My husband and I are planning on having a baby. He is Jewish and I'm not. Should we both be tested for Tay-Sachs Disease?
A: Testing should start with your partner, since his ethnic background puts him at a higher risk of being a carrier for Tay-Sachs Disease (or TSD).
TSD is considered a lysosomal (a small component of the cell) storage disease in which substances called gangliosides accumulate throughout the body, causing progressive destruction of the central nervous system and death in early childhood.
The disease is caused by an absence of an enzyme called Hexosaminidase A (sorry I'm getting so biochemical here!). The appropriate genes need to be present in order to produce this enzyme, and if there is a mutation in the defining gene or genes, production is either limited or absent.
In order to produce this enzyme, two sets of appropriate “make Hexosaminidase A” genes — one from each parent — need to work appropriately.
A mutation in one set of genes causes a “carrier state”; the individual can still metabolize their glycosides properly and does not develop TSD. However, if we test the activity level of the enzyme, it's somewhat lower than the level of activity in individuals who are not carriers.
If both sets of genes are abnormal (i.e. two individuals are carriers and their abnormal genes are passed along to the fetus), that child will be born with TSD.
Among Jewish individuals of Eastern European descent (Ashkenazi), the carrier rate is approximately one in 30. By comparison, the carrier rate for non-Jews is estimated to be about one in 300.
Individuals of French Canadian and Cajun descent have also been found to have a greater carrier frequency than that found in the general population.
A blood test is needed to establish if you are a carrier. This can be done in one of two ways: either by biochemical analysis, where Hexosaminidase A activity is measured, or by molecular analysis for mutations in the TSD gene.
The biochemical analysis is less expensive and more sensitive, and will detect 98 percent of carriers. However, biochemical carrier screening of serum (the fluid in blood separated by centrifuge from red and white blood cells) can be inaccurate when women are pregnant or taking oral contraceptives. Some of these women will be misclassified as carriers (known as a “false positive”).
So, if you wait until you're pregnant or on birth control pills, a special leukocyte (white blood cell) testing procedure should be performed. Your doctor has to specify this when your blood sample is sent to the lab.
A new committee opinion just issued by the American College of Obstetricians and Gynecologists (ACOG for short) makes the following recommendations:
- Screening for TSD should be offered before pregnancy if both parents-to-be are of Ashkenazi, French Canadian or Cajun descent, or have a family history of TSD.
- When one member of a couple is at high risk due to his or her ethnic background, but the other is not, the high-risk partner should be offered screening. If that individual is found to be a carrier, the other partner should be offered screening. (If the woman is already pregnant, however, screening should be offered to both partners at once to ensure the results are obtained quickly and that all options are available to the couple.)
- Biochemical analysis (not molecular gene testing) should be used for individuals in low-risk populations.
- For TSD biochemical screening in women who are pregnant or using birth control, the leukocyte testing method should be used.
- Ambiguous screening test results and positive test results should be confirmed by doing a DNA analysis for the most common mutations.
- If both partners are carriers, genetic counseling and prenatal diagnosis should be offered.
Dr. Reichman’s Bottom Line: If your partner’s or your ethnic background puts you at risk for TSD, ask your doctor to test you according to the above guidelines before you attempt to get pregnant.
Dr. Judith Reichman, the “Today” show's medical contributor on women's health, has practiced obstetrics and gynecology for more than 20 years. You will find many answers to your questions in her latest book, "Slow Your Clock Down: The Complete Guide to a Healthy, Younger You," which is now available in paperback. It is published by William Morrow, a division of HarperCollins.