Tay-Sachs Disease (TSD; GM2-Gangliosidosis, type I; B-Variant GM2-Gangliosidosis; Hexosaminidase A Deficiency; HEXA Deficiency; Tay-Sachs Disease Variant B1), is an autosomal recessive lysosomal storage disease. TSD is caused by a mutation in the alpha subunit of the hexosaminidase A gene (HEXA), which codes for the enzyme hexosaminidase A. HEXA degrades GM2 gangliosides and other molecules with terminal N-acetyl hexosamines in the brain and other tissues. A defect in this enzyme causes accumulation of oligosaccharides in urine. The most lethal variant of this disease is the classical infantile Tay-Sachs disease, in which children exhibit developmental retardation, dementia and blindness, finally ending in death by the second or third years. Tay-Sachs disease also has debilitating juvenile and adult forms. The majority of cases of TSD are found among (but not limited to) the Ashkenazi Jews and French Canadians in Eastern Quebec. Symptoms include ataxia, visual impairment and loss, cherry-red spot on retinal macula, dystosis multiplex, mental retardation, myoclonus, encephalopathy and psychosis.
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