NAGLU and lysosomal storage disease: Background/Objectives: Sanfilippo Syndrome type B or Mucopolysaccharidosis type IIIB (MPS IIIB, OMIM 252920) is a lysosomal storage disease caused by deficiency of alpha-N-acetylglucosaminidase (NAGLU, E.C. 3.2.1.50) due to pathogenic variants in the NAGLU gene (17q21.2).