Causes of Tay-Sachs disease

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 the body usesfor 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 builds 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 that develop later in life, the function of the enzyme is severely limited. This means it takes longer for ganglioside to damage the nerve cells.

The build-upof ganglioside in thenerve cellseffects 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 from your mother and the other half from your father.

It takestwocopies of the mutated HEXA genes to cause Tay-Sachs disease, one from the mother and one from thefather.

If you only receive one copy of the mutated gene from one of your parents, you won't develop Tay-Sachs disease. However, you'll be a carrier of the mutated gene.

If you're a carrier ofa HEXA mutation and you have a baby with a partner who is also a carrier of a HEXA mutation, there's:

• a 25%chance the baby will receive a pair of normal genes and won't develop the condition
• a 25%chance the baby will receive a pair of mutated genes and will develop Tay-Sachs disease
• a50% chance the baby will receive one normal gene and one mutated gene, and will become a carrier of a HEXA mutation but won't develop the condition

It's estimated that around 1 in 250 people are carriers of the HEXA mutation.