Tay-Sachs (TSD) is an incurable degenerative hereditary disease that affects young children. Tay-Sachs can only occur if both parents are carriers of a mutated gene. With this being said a child can however have two parents that are carriers and be unaffected by Tay-Sachs. It is believed that there are between 75 and 100 different mutations that can cause TSD. Tay-Sachs is caused by the lack of, or mutation of the essential enzyme Hexosaminidase-A (Hex-A). Hex-A is used to breakdown a class of lipids (gangliosides) which are essentially waste products found in nerve cells in the brain. The inability to break down these products lead to a build up until they eventually burst, releasing their toxic contents into the cell, which kills it.
Tay-Sachs disease is undetectable at birth and the first symptoms aren’t usually visible until the child is between 5 and 8 months. During this time some mental deterioration is apparent, such as; blindness. More constant deterioration follows as the child gets older. Children with Tay-Sachs rarely live beyond the age of 7.
The severity of the disease is directly related to how much Hex-A is passed onto the child, if any. If the child has no Hex-A then the disease will develop more quickly and the child will most likely die before age 3. If the child still has some Hex-A they will be able to survive a few years longer but they will also eventually die a young child.
Who’s at risk?
Tay-Sachs is a relatively rare hereditary disease in most populations, with only 1 in every 300,000 births in the U.S being affected. However in the Jewish community and more specifically Ashkenazi Jews the likelihood of being infected is 1 in every 2,500 births. Within the Jewish community it’s estimated that 1 in 28 people are carriers of Tay-Sachs disease. This clearly demonstrates that genetic diseases can be much more common depending on your specific population’s history. Overall, worldwide 1 in 250 people are carriers of the disease.
A person is only at risk of contracting Tay-Sachs and becoming ill if both parents are carriers. If this is the case than three outcomes are possible:
- Both parents don’t pass the mutated gene onto their child and the child won’t become a carrier.
- Only one parent will pass the mutated gene to the child, the child will not suffer from TSD but will be a carrier of the Tay-Sachs gene.
- Both parents pass the mutated gene to the child and the child is affected by Tay-Sachs disease.
- That parent passes the gene on to their child and the child becomes a carrier of the disease
- The parent doesn’t pass the gene on and the child is perfectly healthy and normal.
- 1 in 27 Ashkenazi Jews, French Canadians and Louisiana Cajuns
- 1 in 50 Irish Americans
- 1 in 250 from the general population
How Do I know If I Am a Carrier?
Fortunately there are two methods of detecting if a parent is a carrier of the Tay-Sachs disease. These tests also show if the parents have passed the defective genes on too the baby whilst still in the womb. Being tested for the Tay-Sachs gene if increasingly important if both parents know they are from a high risk ethnic group.
The first test is called Amniocentesis. This test can only take place when the mother is 16 to 18 weeks into her pregnancy. A needle is inserted into the mother’s abdomen and fluid surrounding the fetus is retrieved. This fluid can be examined for the gene Hex-A. If Hex-A is undetected than the child will be infected by Tay-Sachs.
The other method of testing is called Chorionic Villus Sampling (CVS). This technique is performed by inserting a tube through the vagina and cervix of the placenta to retrieve cells. These cells are then examined in the same way the Amniocentesis test is by looking for the gene Hex-A. This form of testing is generally preferred because it is a very safe procedure that is performed early in the pregnancy. This procedure can be performed about 10 weeks into the pregnancy.
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