NAGLU and mucopolysaccharidosis type 3B: Mucopolysaccharidosis type IIIB or Sanfilippo syndrome type IIIB (OMIM #252920) is a lysosomal storage disease caused by the presence of biallelic pathogenic variants in the NAGLU gene (17q21.2), resulting in a deficient enzymatic activity of alpha-N-acetylglucosaminidase (NAGLU, E.C. 3.2.1.50).