HEXA and Tay-Sachs disease: Mutations in the genes encoding the α- (HEXA) and β-subunits (HEXB), or GM2A (GM2A) lead to Tay-Sachs Disease (TSD; OMIM #272800), Sandhoff Disease (SD; OMIM #268800) and AB-Variant GM2 gangliosidosis (ABGM2; OMIM #272750), respectively.