Two parents carrying a mutated gene and passing it on to their offspring cause the disease. Even with both parents carrying the disease in their genome, there is only a 25% chance that they will have a child containing the genetic coding for the disease (see figure right). Each form of the disease is caused by the differences in the various mutations of the genome, in particular the codons on the 14 exons in the HEX B gene located within chromosome 5 (see figure bottom), leading to the differences in severities of the symptoms. The difference in the codons has the consequence of inhibiting two enzymes located in the lysosomes of the neurons of the central nervous system. Lysosomes contain various enzymes to break down byproducts and toxins to ensure they do not accumulate enough to interfere with the function of the central nervous system. Using restriction enzymes, it was discovered that a mutation on chromosome 5 particularly within the C1214T allele caused the adult onset form of<unk> . For the patient showing symptoms of the infantile or juvenile form they have a mutation on exon I207V from their father, and a 16 base pair deletion from their mother which can be located on as many as five exons, exons 1–5. Mutations and polymorphism Articles regarding<unk>  frequencies among distinct groups of people contain discrepancies from one another. More than 25 mutations have been reported other than novel mutations. One article says that<unk>  is found commonly in individuals with a non-Jewish descent. Others say that it is more commonly in: * the Creole population of northern Argentina * the indigenous Métis in Saskatchewan * Christian Maronite communities from Cyprus Discovery of several mutations in Ashkenazi Jews may reflect ascertainment bias rather than a high population frequency, because Ashkenazi Jews were the targeted population in a mass screening program for Tay-Sachs disease. Several rare SD mutations were discovered as researchers resolved cases of enzyme deficiency among suspected TSD carriers, but no cases of the disease itself have been reported. However, since it is an autosomal recessive disease, it is likely found in any ethnic group passing from generation to generation through carriers without being expressed in their offspring. Even though the family may not have a history of<unk> , it is possible for two individuals to have a child with the disease. Since<unk>  was only discovered in 1968, there are years the disease has gone undetected because of misdiagnoses.
Sandhoff disease
Tay–Sachs disease
Stratton Parker syndrome
Menkes disease
Gerstmann–Sträussler–Scheinker syndrome
Scheie syndrome
Aceruloplasminemia
Batten disease