Tay-Sachs and Sandhoff diseases
Tay-Sachs and Sandhoff diseases are genetic diseases as they are caused by mutations in certain genes. They are known as autosomal recessive conditions. This means that both copies of the gene need to be mutated in order to cause disease. Most commonly, the individual with the disease has inherited one mutated gene from each of their parents. Rarely, the individual with the disease has inherited one mutated gene from one of their parents, and the other gene has mutated spontaneously (by chance) in the individual.
With autosomal recessive conditions, parents who have one mutated copy of the gene are known as carriers. As they have one functioning copy of the gene, carriers do not develop the disease. As a consequence, parents of children with Tay-Sachs or Sandhoff disease rarely know they are carriers of the disease until after it is diagnosed in their child.