Sanfilippo syndrome is classified into four different subtypes based on the deficient enzyme: MPSIIIA (OMIM#252900) is caused by N-sulfoglucosamine sulfohydrolase (EC 3.10.1.1) deficiency (Kresse and Neufeld, 1972); MPSIIIB (OMIM#252920) by α-N-acetylglucosaminidase (EC 3.2.1.50) deficiency (von Figura and Kresse, 1972); MPSIIIC (OMIM#252930) by heparan-α-glucosaminide N-acetyltransferase (HGSNAT, EC 2.3.1.78) deficiency (Klein et al., 1978); and MPSIIID (OMIM#252940) is the result of N-acetyl-glucosamine-6-sulfatase (EC 3.1.6.14) deficiency (Kresse et al., 1980). This evidence concerns the gene NAGLU and mucopolysaccharidosis type 3.