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Causes of Tay-Sachs

An inherited disease, Tay-Sachs is caused by a defect of the HEXA gene. This gene produces an enzyme that helps break down a fatty substance in nerve cells. Mutations in the HEXA gene disrupt activity of the enzyme, resulting in a toxic accumulation of lipids in the brain and spinal cord. The disease is inherited; it can't be transmitted in any other way.

What Causes Tay-Sachs?

The cause of Tay-Sachs disease is a genetic defect (mutation) that is passed from parent to child. This genetic defect is located in the HEXA gene, which is found on chromosome 15.

Understanding the HEXA Gene

The HEXA gene makes part of an enzyme called beta-hexosaminidase A, which plays a critical role in the nervous system. This enzyme helps break down a fatty substance called GM2 ganglioside in nerve cells.
Mutations in the HEXA gene disrupt the activity of beta-hexosaminidase A, preventing the breakdown of the fatty substances. As a result, this compound can accumulate to toxic levels in the brain and spinal cord. Progressive damage caused by the buildup of GM2 ganglioside leads to the destruction of nerve cells, which causes the signs and symptoms of Tay-Sachs disease.

How Is Tay-Sachs Disease Inherited?

Children inherit a HEXA gene from each parent. If both HEXA genes are faulty, the person will develop Tay-Sachs disease. If either or both HEXA genes are active, the body produces enough of the enzyme to prevent the abnormal buildup of the GM2 ganglioside lipid. Carriers of Tay-Sachs disease (people who have one copy of the inactive gene, along with one copy of the active gene) are healthy. They do not have Tay-Sachs disease, but they may pass on the faulty gene to their children.
Tay-Sachs carriers have a 50 percent chance of passing on the defective gene to their children. A child who inherits one inactive gene is a Tay-Sachs carrier like the parent. If both parents are carriers and their child inherits the defective Tay-Sachs disease gene from each of them, the child will have Tay-Sachs disease. When both parents are carriers of the defective Tay-Sachs gene, each child has a 25 percent chance of having Tay-Sachs disease and a 50 percent chance of being a carrier.
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