Inheriting Tay-Sachs: An Overview
Tay-Sachs disease is a condition that is passed from parent to child through a defect (mutation) of the HEXA gene located on chromosome number 15.
Tay-Sachs is an autosomal recessive condition, which means that both parents must have this defective gene in order for a child to inherit Tay-Sachs.
Chances of Inheriting Tay-Sachs
Each parent has two copies of every chromosome, but gives only one copy to each child. For Tay-Sachs to occur, both parents must be carriers and pass along the defective gene. People who are carriers of Tay-Sachs have one normal HEXA gene and one defective HEXA gene. They do not have any
symptoms of Tay-Sachs, however, because the body produces enough of the enzyme to prevent the abnormal buildup of the GM2 ganglioside lipid.
Tay-Sachs carriers have a 50 percent chance of passing on the defective gene to their children. A child who inherits one defective gene is a Tay-Sachs carrier like the parent. If both parents are carriers and their child inherits the defective 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.
Tay-Sachs disease can be identified by a simple blood test that measures beta-hexosaminidase A activity. Both parents must carry the mutated gene in order to have an affected child. In these instances, there is a 25 percent chance with each pregnancy that the child will be affected with Tay-Sachs disease. Prenatal diagnosis is available, if desired.
