Mucopolysaccharidosis type II (MPS II, OMIM #309900), or Hunter syndrome, is a pediatric X‐linked lysosomal storage disorder caused by mutations in the IDS gene, leading to deficiencies in iduronate‐2‐sulfatase enzyme (EC 3.1.6.13). The gene discussed is IDS; the disease is mucopolysaccharidosis type 2.