Mucopolysaccharidosis type I, or MPS I, is caused by the deficiency of the lysosomal enzyme α-l-iduronidase (IDUA; E.C. 3.2.1.76) involved in lysosomal catabolism of two specific GAGs: heparan sulfate (HS) and dermatan sulfate (DS). The gene discussed is IDUA; the disease is Scheie syndrome.