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Causes of Tay-Sachs disease

The condition is due to the absence of an essential enzyme that breaks down a substance called ganglioside, present mainly in the nervous system. It is the accumulation of this material that is so damaging.

A recessive genetic disorder is one in which both father and mother must carry the gene before the child can develop the disease. Chromosomes come in pairs, each member of a pair having an almost identical set of genes.

Parents carrying the mutated gene can only have it on one of the gene pairs, the other gene being normal. When sperms and eggs are formed, only one of each chromosome pair enters the sperm or egg.

So it is pure chance whether the sperm and the egg carry the mutated gene or the normal one. For the disease to occur, a sperm carrying the mutation (50:50 chance) must fertilise an egg carrying the mutation (50:50 chance).

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