IDS and lysosomal storage disease: Mucopolysaccharidosis type II (MPS II; Hunter syndrome; OMIM +309900) is an X-linked recessive, multisystemic lysosomal storage disorder caused by deficient activity of iduronate-2-sulfatase (IDS), which catalyzes a sequential step in the catabolism of glycosaminoglycans (GAGs), heparan sulfate and dermatan sulfate.