NAGLU and mucopolysaccharidosis type 3B: MPS III includes four distinct diseases (A, B, C, D) due to the deficiency of enzymes involved in heparan sulfate (HS) degradation; in particular, MPS IIIB (Sanfilippo type B syndrome) is due to the deficiency of the lysosomal enzyme α-N-acetylglucosaminidase (NAGLU).