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Tay-Sachs disease is a very rare genetic disorder that destroys neurons in the nervous system (brain and spinal cord) causing severe mental and developmental retardation. The metabolic disorder caused by Tay-Sachs disease derives from the presence of too much of a fatty substance called ganglioside, which builds up in the nerve cells of the brain. This build up eventually destroys those cells, causing mental and physical problems.
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Tay-Sachs is most common in Eastern European Ashkenazi Jews. According to the Center for Jewish Genetic Diseases, Tay-Sachs disease is the most well known Jewish genetic disease, potentially affecting one in every 2,500 Ashkenazi Jewish newborns. In the United States, its occurrence is very low. The disease appears in some Amish communities in Pennsylvania, and amongst the Cajun population of Louisiana and in French-Canadian communities of Quebec.
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Genetics of Tay-Sachs Disease
Tay-Sachs disease is caused by a defect in a gene known as HEXA. The HEXA gene (isolated on chromosome 15) provides the code for making part of an enzyme called beta-hexosaminidase A. The enzyme is located in lysosomes, cellular structures that degrade toxic substances. Beta-hexosaminidase A breaks down a fat called GM2 ganglioside. But in people with Tay-Sachs disease the enzyme deficiency brought on by the genetic mutation leads to an accumulation of the GM2-ganglioside.
Tay-Sachs disease is an autosomal recessive genetic disorder. This means that each parent of an affected child is a carrier of one copy of the mutated gene, although they do not exhibit any signs or symptoms. If both parents are carriers of the mutated gene there is 25% chance in each pregnancy that the child will have Tay-Sachs disease.
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Signs and Symptoms of Tay-Sachs Disease
Symptoms may appear in childhood; this is the most common form. Development starts normally, but an early sign of the disease, at about three to six months, is the appearance of a cherry-red spot in the child´s retina. Characteristic symptoms of Tay-Sachs disease include muscle weakness, loss of muscle coordination (ataxia) and other problems with movement, speech problems, and mental illness. There is currently no cure for Tay Sachs disease. According to the Medline Plus web site, even with the best of care, children with Tay-Sachs disease usually die by the age of four.
Tay sachs can also appear later on in childhood or adulthood, though this is much rarer. Symptoms here are usually much milder.
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Center for Jewish Genetic Diseases. Diseases: Tay-Sachs Disease (http://www.mssm.edu/jewish_genetics/diseases/tay-sachs.shtml)
Tay-Sachs Disease Medline Plus. (http://www.nlm.nih.gov/medlineplus/taysachsdisease.html)
Tay-Sachs disease. Genetics Home Reference (http://ghr.nlm.nih.gov/condition=taysachsdisease)