Hunter syndrome, or MPS type II, is a rare X-linked recessive disorder caused by a functional deficiency of the lysosomal enzyme Iduronate-2-sulfatase (encoded by the IDS gene in humans), which is critical for the catabolism of certain glycosaminoglycans (GAGs); the dermatan- and heparan-sulfate-GAG-species [14]. The gene discussed is IDS; the disease is mucopolysaccharidosis type 2.