A genetically transmitted disease of the central nervous system.

Tay-Sachs disease is a fatal childhood degenerative disease of the central nervous system that is genetically transmitted and found primarily among Jews of Eastern European ancestry (Ashkenazim). Tay-Sachs is caused by the absence of a particular enzyme, hexosaminidase (hex-A). Without hex-A, fatty substances (lipids) build up in the brain and interfere with the functioning of the central nervous system. The disease is named for two doctors who were pioneers in identifying and describing it. In 1881, Warren Tay, a British ophthalmologist, first noted the red spot on the retina that is a distinctive mark of the disorder. In the United States, neurologist Bernard Sachs identified the cause of the illness and discovered its prevalence among Ashkenazic Jews in 1887.

Although the disease is already present in utero, the symptoms do not usually become apparent until the child is about...