Tay-Sachs disease is a rare, inherited disease. It is a type of lipid metabolism disorder. It causes too much of a fatty substance to build up in the brain. This buildup destroys nerve cells, causing mental and physical problems. .
Infants with Tay-Sachs disease appear to develop normally for the first few months of life. Then mental and physical abilities decline. The child becomes blind, deaf, and unable to swallow. Muscles begin to waste away and paralysis sets in. Even with the best of care, children with Tay-Sachs disease usually die by age 4.
The cause is a gene mutation which is most common in Eastern European Ashkenazi Jews. To get the disease, both parents must have the gene. If they do, there is a 25% chance of the child having the disease. A blood test and prenatal tests can check for the gene or the disease.
There is no cure. Medicines and good nutrition can help some symptoms. Some children need feeding tubes.
Causes
Each year, about 16 cases of Tay-Sachs are diagnosed in the United States. Although people of Ashkenazi Jewish heritage (of central and eastern European descent) are at the highest risk, people of French-Canadian/Cajun heritage and Irish heritage have also been found to have the Tay-Sachs gene.
Some people carry the genetic mutation that causes Tay-Sachs, but do not develop the full-blown disease.
A child can only have Tay-Sachs disease if both parents are carriers of the gene. When two carriers have a child together, there’s a:
- 50% chance that their child will be a carrier, but not have the disease
- 25% chance that their child will not be a carrier and not have the disease
- 25% chance that their child will have the disease
Diagnosis
A simple blood test can identify Tay-Sachs 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.
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, more than 50 different mutations in this gene have been identified. Nevertheless, some mutations are not yet known. The current tests detect about 95 percent of carriers of Ashkenazi Jewish background and about 60 percent of carriers in the general population.
If both parents are carriers, they may want to consult with a genetic counselor for help in deciding whether to conceive or whether to have a fetus tested for Tay-Sachs. Extensive carrier testing of Ashkenazi Jews has significantly reduced the number of Tay-Sachs children in this population group. Today most cases of Tay-Sachs disease occur in populations thought not to be at high risk.
Prenatal testing for Tay-Sachs can be performed around the 11th week of pregnancy using chorionic villi sampling (CVS). This involves removing a tiny piece of the placenta. Alternatively, the fetus can be tested with amniocentesis around the 16th week of pregnancy. In this procedure, a needle is used to remove and test a sample of the fluid surrounding the baby.
Assisted reproductive therapy is an option for carrier couples who don’t want to risk giving birth to a child with Tay-Sachs. This new technique used in conjunction with in-vitro fertilization enables parents who are Tay-Sachs carriers to give birth to healthy babies. Embryos created in-vitro are tested for Tay-Sachs genetic mutations before being implanted into the mother, allowing only healthy embryos to be selected.
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