A baby with Tay-Sachs disease appears healthy at birth, and seems to be developing normally for a few months. Symptoms generally appear by six months of age. While symptoms vary from one child to the next, there is always a slowing down of development. Gradually, Tay-Sachs children lose motor skills and mental functions. Over time, the child becomes blind, deaf, mentally retarded, paralyzed and non responsive to the environment. Tay-Sachs children usually die by age five.
Children with Tay-Sachs disease lack a vital enzyme, hexosaminidase A (Hex-A). Hex-A is needed for the body to break down a fatty waste substance found in brain cells. Without Hex-A, this substance accumulates abnormally and causes progressive damage until the nervous system can no longer sustain life.
A person with only one Tay-Sachs gene is perfectly healthy, but is a Tay-Sachs carrier. When both parents are carriers, there is a 1 in 4 (25%) chance, with every pregnancy, of having a child with Tay-Sachs disease.
When both parents are carriers, there is a 2 in 4 (50%) chance, with every pregnancy, of having a child who is a carrier.
When only one parent is a carrier, there is no chance the child will have Tay-Sachs disease. There is a 2 in 4 (50%) chance, with every pregnancy, of having a child who is a Tay-Sachs carrier.
Among Jews of Sephardic origin and in the general, non-Jewish population, the carrier rate is about one in 250. There are certain exceptions. French-Canadian and the Cajun community of Louisiana have the same carrier rate as Ashkenazi Jews, one in 27. Also, individuals with ancestry from Ireland are at increased risk for the Tay-Sachs gene. Current research indicates that among Irish Americans, the carrier rate is about one in 50.
All couples planning to have children should carefully consider their ancestry to evaluate the risk of each partner. Any person who can trace his or her lineage to a high-risk population should be tested. In addition, close relatives of carriers (children, sisters, brothers, cousins, aunts, uncles) must be tested since they may also be carriers.
The Tay-Sachs blood test, referred to as carrier screening, identifies Tay-Sachs carriers and non-carriers. It is urgent to understand that the Tay-Sachs gene gets passed from one generation to the next. Without carrier screening, it can remain hidden in a family for decades, surfacing unexpectedly and tragically with the birth of an affected child. the fact that there is no family history of Tay-Sachs disease does not lower an individual's risk of being a carrier. It my simply be a lucky accident that, thus far, no child inherited a pair of Tay-Sachs genes.
Prenatal diagnosis early in pregnancy will reveal if the fetus has Tay-Sachs or Canavan disease. At-risk couples can choose from two procedures: amniocentesis, done around the 16th week of pregnancy, and chorionic villus sampling (CVS), performed between the 10th and 13th weeks. In either case, if the fetus is affected with Tay-Sachs or Canavan, couples may elect to have a therapeutic abortion.
In addition to adoption, there are several medical procedures available to couples for whom abortion is not an option. Your genetic counselor can explain these alternatives so that you are prepared to meet with a medical specialist, should you choose this route.