hereditary metabolic disorder that causes progressive mental and neurologic deterioration and results in death in early childhood. The disease is inherited as an autosomal recessive trait and occurs most commonly among people of eastern European (Ashkenazic (Ashkenazi)) Jewish (Jew) origin.

In infants born with the disease, abnormally low activity of the enzyme hexosaminidase A allows an unusual sphingolipid, ganglioside G_M2, to accumulate in the brain, where it soon exerts devastating effects on neurological function. In some affected children, the enzyme is present but the sphingolipid accumulates nonetheless. Tay-Sachs infants appear normal at birth but become listless and inattentive during the first few months of life. As the disease progresses, the child loses motor abilities already gained, such as crawling and sitting, develops uncontrollable seizures, and is unable to lift its head or swallow. A cherry-red spot develops on the retina, and blindness and a general paralysis usually precede death. There is no treatment for the disease.

About 1 in 2,500 Ashkenazic Jewish infants is afflicted with Tay-Sachs disease, as compared to 1 in 360,000 non-Jewish babies. The disease can be detected by prenatal tests. About 1 in 25 Ashkenazic Jews is a carrier of the Tay-Sachs gene. Adult genetic carriers can be identified by measuring the level of hexosaminidase A in their blood or other fluids.