Tay-Sachs Disease

Abstract

Tay-Sachs disease is a fatal inherited disease of the central nervous system. The most common form of the disease affects babies. Affected babies appear healthy at birth and seem to develop normally for the first few months of life. After this time, development slows and symptoms begin. Sadly, there is no effective treatment for these babies. Babies with Tay-Sachs lack an enzyme (protein) called hexosaminidase A (hex A) necessary for breaking down certain fatty substances in brain and nerve cells. These substances build up and gradually destroy brain and nerve cells, until the entire central nervous system stops working. Symptoms of classical Tay-Sachs disease first appear at 4 to 6 months of age when an apparently healthy baby gradually stops smiling, crawling or turning over, loses its ability to grasp or reach out and, eventually, becomes blind, paralyzed and unaware of its surroundings. Death occurs by age 5.

Who Is at Risk of Tay-Sachs Disease?

Tay-Sachs disease occurs most frequently in descendants of Central and Eastern European (Ashkenazi) Jews. About one out of every 30 American Jews carries the Tay-Sachs gene. Some non-Jewish individuals of French-Canadian ancestry (from the East St. Lawrence River Valley of Quebec), and members of the Cajun population in Louisiana, are at similarly increased risk. These groups have about 100 times the rate of occurrence of other ethnic groups. The juvenile form of Tay-Sachs, however, may not be increased in these groups.

How Is the Disease Transmitted?

Only through heredity. A Tay-Sachs carrier has one normal gene for hex A and one Tay-Sachs gene. The carrier does not have the illness and leads a normal, healthy and full life. However, when two carriers become parents: There is a one-in-four chance that any child they have will inherit a Tay-Sachs gene from each parent and have the disease. There is a one-in-four chance that the child will inherit the normal gene from each parent and be completely free of the disease and the Tay-Sachs gene. There is a two-in-four chance that the child will inherit one of each kind of gene and be a carrier like the parents and free of disease. 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 being a carrier.

Are There Other Forms of Tay-Sachs Disease Besides the Classical Type That Affects Babies?

The classic infantile type of Tay-Sachs is the most common. However, there are other rare deficiencies of the hex A enzyme that sometimes are included under the name of Tay-Sachs disease. These often are referred to as juvenile, chronic and adult-onset forms of hex A deficiency. Affected individuals have low levels of the hex A enzyme that is missing entirely in the classical, infantile form. This may help explain why symptoms begin later in life and, generally, are milder than in the classical, infantile Tay-Sachs disease. Children with juvenile hex A deficiency develop symptoms between the ages of 2 and 5 that resemble those of the classical, infantile form. Although the course of the disease is slower, death generally occurs by age 15. Symptoms of chronic hex A deficiency also may begin by age 5, but are far milder than those that characterize the infantile and juvenile forms. Mental abilities, vision and hearing remain intact; but there may be slurred speech, muscle weakness, muscle cramps, tremors, unsteady gait and, sometimes, mental illness. Individuals with adult-onset hex A deficiency experience many of the same symptoms as individuals with the chronic form, but the symptoms begin later in life.

Is There Any Treatment for Tay-Sachs?

Tragically, there is no cure, and no treatment that will prevent the disease from running its course. Affected children can only be made as comfortable as possible.

Can Tay-Sachs Disease Be Diagnosed Before Birth?

Yes. Prenatal tests called amniocentesis and chorionic villus sampling (CVS) can diagnose Tay-Sachs before birth. In amniocentesis, which usually is done between the 15th and 18th week of pregnancy, a needle is inserted into the mother’s abdomen to take a sample of fluid that surrounds the fetus. The fluid contains fetal cells that can be examined for the presence of hex A.