IDS and mucopolysaccharidosis type 2: Mucopolysaccharidosis (MPS) II (Hunter syndrome; OMIM 309900) is a progressive, X-linked LSD caused by variants in the iduronate-2-sulfatase (I2S) gene (IDS), which results in deficiency of the I2S enzyme required for the lysosomal degradation of glycosaminoglycans (GAGs), such as heparan sulfate (HS) and dermatan sulfate (DS) [2].