In SD patients, excessive accumulation of undegraded substrates including GM2 ganglioside (GM2) with a terminal N-acetylgalactosamine residue and oligosaccharides with a terminal β-linked N-acetylglucosamine residue (GlcNAc-oligosaccharides) is observed, particularly in neurons, due to the deficiencies of HexA and HexB, which leads to neurological symptoms in the central nervous system (CNS), such as the startle response, mental retardation, spasms and quadriplegia. Here, HEXA is linked to Salla disease.