Tay-Sachs Disease

Essay by kaaanchA, February 2011

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Tay-Sachs Disease

Tay-Sachs disease was named after two physicians, British ophthalmologist Warren Tay and American neurologist Bernard Sachs. Both described the disease independently in 1881 and 1887, respectively. TaySachs disease is an inborn error associated with the abnormal breakdown of a particular sugar-containing lipid called GM2 ganglioside. The important hallmarks of Tay-Sachs disease are a massive storage of GM2 ganglioside in the brain and also in the macular region of the eye, on which an ophthalmologist can detect the characteristic "cherry red spot." Clinical onset of this disease is usually at 5 to 6 months of age, and the symptoms include retardation in development, loss of motor function and intellectual capacity, and blindness. The disease progresses rapidly and is usually fatal by the age of 3 to 4 years old. However, some with milder cases have lived into teens and adulthood. The disease incidence in Ashkenazi Jewish population is about 1 in 4,000 births, while the incidence in non-Jews is one hundred times lower.

The disease is inherited from parents in an autosomal recessive manner. This means that each parent, though not affected by the disease, carries a defective gene in an autosome (the chromosomes other than the sex chromosome), and the affected child has inherited a pair of chromosomes both containing the defective gene.

The normal breakdown of GM2 ganglioside requires a specific enzyme, β-hexosaminidase A (Hex A), and a helper protein called GM2 activator. Thus, Tay-Sachs disease can be caused by the deficiency or defect of either Hex A or GM2 activator. Human tissues contain two forms of β-hexosaminidases, Hex A and Hex B. Hex A contains two different protein chains, alpha- and beta-chains, and Hex B contains two betachains. Therefore, Tay-Sachs disease can result from the mutations in any one of the three genes, which are responsible...