Tay-Sachs

Dr. Tay and Dr. Sachs were the first to describe the disease in the mid-1880's. Tay-Sachs is presents frequently in Jews of Eastern-European decent. In the United States, one in every 27 Jews is thought to be a carrier. Similar carrier frequencies are found in Cajun and French-Canadians in Louisiana. In the general population, about one in every 250 people is a carrier of Tay-Sachs. It is inherited through an autosomal recessive pattern.

Tay-Sachs is caused by a mutation in the HEX A gene on chromosome 15. HEX A normally codes for the alpha subunit of the hexosaminidase A protein, which is necessary for breaking down GM2 gangliosides in nerve cells. GM2 is an acidic, fatty material. The accumulation of GM2 is toxic and eventually leads to cell death. The buildup is especially common in the nerve tissues of the brain.

There are three types of Tay-Sachs Disease: infantile or early onset, juvenile (which is extremely rare), and adult or late onset (also rare). Babies with early onset Tay-Sachs begin to show symptoms at the age of six months. From then on, due to the gradual buildup of the fatty GM2 material disturbing nerve cells, the infants lose or do not gain motor and mental skills. The babies become blind, deaf, and unable to swallow, and some muscles begin to atrophy. Other neurological symptoms include dementia, seizures, and increased startle reflexes to noise. This is followed by paralysis and death before the age of five. Juvenile Tay-Sachs appears around the age of five, and progresses slower than infantile, though the symptoms are similar. Patients die between five and fifteen years. In adults, Tay-Sachs manifests itself in the person's twenties or thirties through symptoms including muscle weakness and cramps, unsteady gait, progressive neurological deterioration, changes in behavior, and slurred speech. Progress of this form can only be slowed, not reversed. Late onset Tay-Sachs usually does not kill. Victims of all ages have characteristic "cherry red" spots in the retinas of their eyes.

Unfortunately, at this time there is no cure for Tay-Sachs Disease, although a few short-term treatments are used. Some anitconvulsant medicines can control seizures, at least for a little while, and other "supportive treatments" are healthy diets and proper hydration. Techniques to keep the airway open are used, and children may eventually need a feeding tube. None of these treatments prevent the buildup of GM2, and so none could be considered cures. Several other methods of treatment have been investigated for Tay-Sachs disease, but none have passed the experimental stage.

Parents at risk of being carriers of the disease and passing it on to their children are able to be screened to find out if they carry the mutated gene. Embryos can be diagnosed before birth. A relatively simple blood test that measures the activity of beta-hexosaminidase A is used to detect patients and carriers of the disease. The disease only is passed on to children if both parents carry the mutated gene. Then, there is a 25% chance in each pregnancy that the child will be affected. The children of unaffected carrier parents have a 50% chance of also being carriers. There is some evidence that the presence of the gene in a heterozygous parent promote intelligence, but this is not known for sure.

http://en.wikipedia.org/wiki/Tay-Sachs_disease http://www.ygyh.org/tay/whatisit.htm http://www.ninds.nih.gov/disorders/taysachs/taysachs.htm