Mucopolysaccharidosis type III (MPS III) or Sanfilippo syndrome includes five subtypes, each of which results from a specific impaired lysosomal enzyme, including sulfamidase (MPS IIIA); α-N-acetylglucosaminidase (NAGLU, MPS IIIB); heparan acetyl CoA α-glucosaminide N-acetyltransferase (MPS IIIC); N-acetylglucosamine 6-sulfatase (MPS IIID) and N-glucosamine 3-O-sulfatase (MPS IIIE) [1]. The gene discussed is NAGLU; the disease is mucopolysaccharidosis type 3.