Tay-Sachs disease
Tay-Sachs disease is an inherited birth defect which first becomes noticeableat about four to six months of age when an otherwise healthy baby graduallyceases to smile, crawl, turn over, or reach out, and ultimately becomes blindand paralyzed. Death occurs at about the age of five years. Tay-Sachs disease is among a number of genetic disorders that result from the body's inability to produce lipid-degrading enzymes. Lacking these enzymes, lipids accumulate in the cells, resulting in kidney failure, enlargement of the liver and spleen, mental retardation, blindness, skeletal deformities, and, eventually, the shut-down of the entire nervous system.
Tay-Sachs disease was the first of its type to be studied, and was first recognized by the British ophthalmologist, Warren Tay (1843-1927) in 1881. Tay noticed a cherry-red spot on the retina of a one-year-old child who exhibited many of the signs of the disorder. The child gradually deteriorated and died.
A similar report was published by Bernard Sachs (1858-1944), an American neurologist, who was the first person to describe the cellular changes that accompany the disease and to comment on its prevalence among Eastern European Jews. Today we know that Tay-Sachs disease is an autosomally recessive genetic disorder that occurs because of the body's failure to produce the enzyme (protein) hexosaminidase A (hex A). Approximately one in every 27 American Jews carries the Tay-Sachs gene. Also, non-Jewish descendants of French-Canadians from the East St. Lawrence River Valley in Quebec and Cajuns from Louisiana experience approximately 100 times the rate of the disorder than the general population. In this hereditary disorder, the carrier of the Tay- Sachs gene does not develop the illness, nor do their children who do, however, standa 50 percent chance of inheriting the gene. When both parents carry the gene,each of their children has a one in four possibility of having the disease.Programs for DNA-based genetic testing were developed in the early 1980s, measurement of hex A enzyme in the blood will also identify a carrier, and prenatal testing called amniocentesis and chronic villus sampling (CVS) will diagnose Tay-Sachs before birth. There is no treatment to prevent the disease from progressing, nor is there a cure.
Carriers of Canavan disease, a similar yet less readily identifiable diseaseto Tay- Sachs, affects one in 37 Eastern European Jews. This disease can nowalso be identified through genetic testing. The defective gene can be passedfrom generation to generation before a baby is born with the disease. Therefore, even families with no known history of the disease can carry the gene.
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