mucopolysaccharidosis type 3D (MONDO_0009658, a Monarch Disease Ontology entry) is a rare autosomal recessive lysosomal storage disease caused by deficiency of the enzyme N-acetylglucosamine-6-sulfatase. It is characterized by behavioral changes, sleep disturbances and mental developmental delays. Also known as: GNS deficiency, MPS III D, MPS3D, MPSIIID, Sanfilippo D, Sanfilippo syndrome D, Sanfilippo syndrome type D, glucosamine N-acetyl-6-sulfatase deficiency.