IDS and mucopolysaccharidosis type 2: Hunter syndrome, also known as Mucopolysaccharidosis type II (MPS II, OMIM 309900)1, is an X-linked lysosomal storage disease caused by genetic deficiency of the enzyme iduronate-2-sulfatase (IDS, EC 3.1.6.13), required for the step-wise degradation and recycling of complex glycosaminoglycans (GAGs).