Beta-hexosaminidase (HEX) cleaves the terminal N-acetyl galactosamine (GalNAc) from glycosaminoglycans (GAGs) and any other molecules containing a terminal GalNAc. There are two forms of HEX; HEXA and B. The A form is a trimer of the subunits alpha, beta A and beta B. The B form is a tetramer of 2 beta A and 2 beta B subunits (O'Dowd et al. 1988). Defects in the two subunits cause lysosomal storage diseases marked by the accumulation of GM2 gangliosides in neuronal cells.Defects in the beta subunits are the cause of GM2-gangliosidosis type 2 (GM2G2; MIM:268800), also known as Sandhoff disease (Sandhoff et al. 1968, Banerjee et al. 1991). Sandhoff disease is an autosomal recessive lysosomal storage disease clinically indistinguishable from GM2-gangliosidosis type 1, presenting early blindness with cherry-red spots on the macula, progressive motor and mental deterioration and macrocephaly. Death usually occurs by the age of 3 years.