Genetic Causes of Mental Retardation - Tay-Sachs Disease

Tay-Sachs disease is named after Warren Tay, an ophthalmologist who documented a case in which an infant patient had an odd red spot on the retina, and Bernard Sachs, a neurologist who described cellular abnormalities and familial links associated with a novel disorder that is today known as Tay-Sachs disease.

Tay-Sachs disease is an inherited disorder most commonly found among people of eastern European Jewish (Ashkenazim) decent. The disorder is fatal in children and life expectancy does not surpass five years of age. The disorder's cause is genetic, involving the absence of hexosaminidase A (Hex A), an enzyme responsible for metabolizing GM2 ganglioside (a fatty acid/lipid) that otherwise can build up in cells with toxic effects. When this lipid accumulates, the individual suffers damage to cells mostly affecting the brain and the nervous system. Genetic testing prior to pregnancy can help potential parents to determine if they carry the gene problem that leads to the disorder.

Although damage to brain cells and the nervous system begins during fetal development, the condition is not apparent at birth. Babies appear normal for the first several months of life. Symptoms differ and can appear as a slowing of normal development and a loss of peripheral vision. Affected children do not react appropriately to sensory stimulation. For example, they may overreact to sounds. Seizures and deteriorating mental functioning are apparent starting in the first two years of life.

As the disorder progresses, affected babies progressively lose previously mastered skills like crawling, turning over, and reaching. After a time, blindness ensues and the child becomes unable to move and is unresponsive to his environment. Ultimately, the infant becomes unable to breathe or swallow. Presently there is no cure for Tay-Sachs disease and there is no successful treatment for symptoms. Research into possible therapies is exploring the use of replacement therapies to provide the missing Hex-A gene or the missing enzyme. One of the biggest obstacles researchers face is finding a way to get the brain to accept the enzyme.