Tay-Sachs disease is a rare and extremely severe genetic condition that affects the brain and nerves. A baby with Tay-Sachs disease appears normal at birth, but development starts to slow down at about 6 months of age. Gradually, the child becomes blind, deaf and paralysed. Children with Tay-Sachs disease usually die before the age of five. There is no cure for this devastating disorder, and no effective treatment.