Tay-Sachs disease

Recessive hereditary metabolic disorder, mostly in Ashkenazi Jews, causing progressive mental and neurologic deterioration and death by age five. A lipid, ganglioside GM, accumulates in the brain (because of inadequate activity of the enzyme that breaks it down), with devastating neurological effects. Infants appear normal at birth but soon become listless and inattentive, lose motor abilities, and develop seizures. Blindness and general paralysis usually precede death. Tests can detect the disease in fetuses and the Tay-Sachs gene in carriers. There is no treatment.