Tay-Sachs Disease (TSD) is a fatal degenerative disease of the nervous system that is found primarily (but not exclusively) among Ashkenazi Jews - those of East European ancestry.
Tay Sachs disease is named for Warren Tay (1843-1927), a British ophthalmologist who in 1881 first described the cherry-red spot on the retina of the eye (one of the characteristic symptoms of this disorder) and for Bernard Sachs (1858-1944), a New York neurologist, who described the cellular changes of Tay-Sachs and noted an increased prevalence in the Eastern European Jewish population of 1887.
TSD is one of the most tragic inherited conditions. The symptoms first appear at about the age of six months when an apparently healthy, happy baby stops smiling, crawling or tuning over, loses the ability to grasp or reach out, and gradually becomes blind, paralyzed and unaware of the surrounding world.
Death usually occurs by three or four years of age. Babies with TSD are born without a blood chemical that is necessary for breaking down certain fatty deposits in brain and nerve cells. The cells soon become clogged, causing the entire nervous system to stop working.
Tay-Sachs Disease is now known to be caused by the absence of a gene called hex A. The absence of the gene results in absence of the metabolic pathway necessary to prevent the deposition of damaging fatty deposits in nerve cells. Carriers of the gene (see below) make about 50% less of the enzyme required, but that is sufficient to protect them from nerve damage.
TSD affects about one in every 2,500 Ashkenazic Jews(Eastern and Central European origin), and it is estimated that approximately one in every 25 Jews in the United States is a carrier of the TSD gene. Two other populations of French descent also show an increased risk - French Canadians, particularly from Quebec Provence, and those of Cajun ancestry in Louisiana.
TSD is transmitted through heredity. It cannot be caught from another child and cannot develop in later life. The carrier state cannot turn into the illness. The Tay-Sachs carrier has one normal gene and one Tay-Sachs gene. The carrier does not have the illness and can lead a normal, healthy life.
However, when two carriers become parents, there is a 1 in 4 chance that any child will inherit a Tay-Sachs gene from each parent and have the fatal disease. There is a 1 in 4 chance that any child will inherit the normal gene from each parent and be completely free of the disease and the Tay-Sachs gene. However, there is a 2 in 4 chance that the child will inherit one of each kind of gene and become a carrier, the same as the parents.
If only one parent is a carrier, none of their children can have the disease, but each child has a 50/50 chance of inheriting the Tay-Sachs gene and becoming a carrier. All of these odds or chances hold true for each child of the same parents. In some families, the disease will occur more than once. In others, all the children may be normal and their parents never know they are carriers.
Diagnosis Before Birth
Tay-Sachs and many other defects can be diagnosed before birth by amniocentesis and chorionic villus sampling (CVS).
In amniocentesis, a needle is inserted into the mother’s abdomen between weeks 16 and 18 of pregnancy to take a sample of fluid which surrounds the fetus. The fluid contains sloughed-off fetal cells which can be examined for the presence of the gene called hex A which is absent in Tay-Sachs. If the chemical is present, the baby will not have TSD. If it is missing, he or she will be affected.
In CVS, the doctor retrieves a sample of cells through a tube inserted through the vagina and cervix to the placenta. The placenta contains cells of fetal origin. These are examined for the presence of the chemical. CVS is usually done around week 10 of pregnancy. Since this procedure can be done safely earlier in pregnancy, it is preferred.
There is no cure or treatment to date that will prevent the disease from running its fatal course. Affected children can only be made as comfortable as possible.
Screening for Carriers of the Disease
Members of the high risk groups mentioned above may wish to know if they are at risk for transmitting the disease because they are carriers. This is particularly important if two prospective parents are both from a high-risk ethnic origin group. A list of centers throughout the U.S. that can perform the needed blood screening tests is available from the National Tay-Sachs and Allied Diseases Association. If you have questions about your risks for this disorder, ask your primary care physician about a consultation with a medical genetics specialist.
While pregnant, what tests will you be performing? Which is most accurate? What are the risks?
For the child, what testing is needed to diagnose this disease?
What course can we expect of the disease?
Are there any special facilities in the area to take care of the child?
How do you care for the child at home?
Is there psychological counseling available?