A rare autosomal recessive lysosomal storage disease caused by deficiency of the enzyme N-acetyl-alpha-D-glucosaminidase. It is characterized by behavioral changes, sleep disturbances, and mental developmental delays. The disease is mucopolysaccharidosis type 3B (Monarch Disease Ontology id MONDO_0009656). Also known as: MPS III B, MPS3B, MPSIIIB, N-acetyl-alpha-glucosaminidase deficiency, Sanfilippo B, Sanfilippo syndrome B, Sanfilippo syndrome type B, mucopolysaccharidosis type IIIB.