Tay-Sachs disease - Causes of Tay-Sachs disease
- Introduction
- Symptoms of Tay-Sachs disease
- Causes of Tay-Sachs disease
- Testing for Tay-Sachs disease
- Treating Tay-Sachs disease
- Prevention
Tay-Sachs disease is caused by a genetic mutation in the HEXA gene.
This mutation affects the production of an enzyme called Hexosaminidase-A (Hex-A). Enzymes are proteins that the body uses for chemical reactions.
The Hex-A enzyme plays a vital role in helping to remove a fatty substance called ganglioside from nerve cells. Without the Hex-A enzyme, ganglioside will build up inside these cells and they gradually stop functioning.
In most cases of Tay-Sachs disease, this enzyme is completely absent. However, in the rarer forms of the condition that develop later in life, the enzyme is present but its function is severely limited. This means it takes longer for ganglioside to damage the nerve cells.
The build-up of ganglioside in the nerve cells can have a catastrophic effect on many bodily functions, including vision and hearing, speech, physical movement and mental functions.
How the mutation is inherited
All the genes in your body come in pairs. You receive one half of the pair from your mother and the other half from your father.
Mutations in the HEXA gene that causes Tay-Sachs disease do so in an autosomal recessive manner. This means that a child with the condition received two copies of the mutated gene: one from their mother and one from their father.
If you only receive one copy of the mutated gene from one of your parents, you will not develop Tay-Sachs disease. However, you will be a carrier of the mutated gene.
If you are a carrier of a HEXA mutation and you have a baby with a partner who is also a carrier of a HEXA mutation, there is:
- a 25% chance that the baby will receive a pair of normal genes and will not develop the condition
- a 25% chance that the baby will receive a pair of mutated genes and will develop Tay-Sachs disease
- a 50% chance that the baby will receive one normal gene and one mutated gene, and will become a carrier of a HEXA mutation but will not develop the condition
It's estimated that around 1 in 250 people are carriers of the HEXA mutation.
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