NAGLU and mucopolysaccharidosis type 3B: Sanfilippo syndrome type B (Sanfilippo type B, mucopolysaccharidosis IIIB, or MPS IIIB) is a rare inherited lysosomal storage disorder caused by mutations in the gene encoding α-N-acetylglucosaminidase (NAGLU, EC 3.2.1.50), an enzyme required for the degradation of the glycosaminoglycan heparan sulfate (HS).1