Beta-hexosaminidase (HEX) cleaves the terminal N-acetyl galactosamine (GalNAc) from glucosaminoglycans (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.