Understanding Tay-Sachs disease

Children with Tay-Sachs disease have no working version of a gene that makes a particular enzyme called hexoaminidase-A (Hex-A). This enzyme normally breaks down excess fatty substances in the nerve cells. Without it, fats build up and eventually destroy the nerve cells of the affected child. This process starts in the embryo, but is not noticeable until the baby is between 6 and 9 months old. Carriers of Tay-Sachs only have half the normal levels of Hex-A in their bodies, but they are not affected by the condition.

Sheila and Philip Koch had two children who died of Tay-Sachs disease in the 1960s. Dr Koch later developed the enzyme test to detect unaffected carriers of the condition.