NAGLU and mucopolysaccharidosis type 3B: Mucopolysaccharidosis type IIIB (MPS IIIB), an inherited lysosomal disorder, is a sub-type of MPS III caused by deficiency of α-N-acetylglucosaminidase (EC 3.2.1.50 [NAGLU]), a lysosomal acid hydrolase that normally degrades heparan sulfate.1