Mucopolysaccharidosis (MPS) IIIA, also known as Sanfilippo syndrome type A, is a neurodegenerative lysosomal storage disorder caused by a deficiency in the enzyme N-sulfoglucosamine sulfohydrolase (SGSH, EC:3.10.1.1), which is involved in the degradation of heparan sulfate. This evidence concerns the gene SGSH and mucopolysaccharidosis type 3A.