Mucopolysaccharidosis type I (MPS I) is caused by deficient activity of alpha-L-iduronidase (IDUA; EC 3.2.1.76); it is divided into three subtypes based on the severity of symptoms: Hurler syndrome (severe, OMIM 607016), Hurler–Scheie syndrome (intermediate, OMIM 607015) and Scheie syndrome (attenuated, OMIM 607016). Here, IDUA is linked to Hurler syndrome.