Tay-Sachs disease is a rare disorder passed from parents to a child. In the most common form, a baby about 6 months old will begin to show early symptoms. Tay-Sachs disease results when an enzyme that helps break down fatty substances is absent. These fatty substances build up to toxic levels in the child's brain and affect the nerve cells. As the disease progresses, the child's body loses function, leading to blindness, deafness, paralysis and lastly death. Unfortunately, there is no cure for Tay-Sachs disease. Gene therapy or enzyme replacement therapy research may eventually lead to a cure or treatment to slow the progression of Tay-Sachs disease. Tay-Sachs disease occurs most frequently among people whose ancestors come from Eastern and Central European Jewish communities (Ashkenazi Jews), from certain French Canadian communities in Quebec, the Old Order Amish community in Pennsylvania and from the Cajun community of Louisiana. A child who inherits the gene from both parents develops Tay-Sachs disease.
Frequency
Tay-Sachs disease is very rare in the general population. The genetic mutations that cause this disease are more common in people of Ashkenazi (eastern and central European) Jewish heritage than in those with other backgrounds. The mutations responsible for this disease are also more common in certain French-Canadian communities of Quebec, the Old Order Amish community in Pennsylvania, and the Cajun population of Louisiana.
Causes
Tay-Sachs disease results from defects in a gene on chromosome 15 that codes for production of the enzyme Hex-A. We all have two copies of this particular gene. If either or both Hex-A genes are active, the body produces enough of the enzyme to prevent the abnormal build-up of the GM2 ganglioside lipid. Carriers of Tay-Sachs, people who have one copy of the inactive gene along with one copy of the active gene, are healthy. They do not have Tay-Sachs disease but they may pass on the faulty gene to their children.
Carriers have a 50 percent chance of passing on the defective gene to their children. A child who inherits one inactive gene is a Tay-Sachs carrier like the parent. If both parents are carriers and their child inherits the defective Hex-A gene from each of them, the child will have Tay-Sachs disease. When both parents are carriers of the defective Tay-Sachs gene, each child has a 25 percent chance of having Tay-Sachs disease and a 50 percent chance of being a carrier.
Tests for Tay Sachs disease
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 you have a family history of Tay-Sachs disease or if you're a member of a high-risk group and plan to have children, genetic testing and genetic counseling is strongly recommended.
