Hunter syndrome, also called mucopolysaccharidosis II, is an X-linked genetic lysosomal disorder caused by loss-of-function mutations in the IDS gene, encoding iduronate-2-sulfatase (I2S). I2S is a lysosomal enzyme responsible for the cleavage of glycosaminoglycans (GAGs), and its deficiency results in accumulation of GAGs leading to a multisystemic disorder.