Mucopolysaccharidosis type I (MPS I) includes Hurler syndrome, Hurler–Scheie syndrome, and Scheie syndromes that are caused by homozygous or compound heterozygous mutations in alpha-l-iduronidase (IDUA) gene that result in developmental abnormalities and intellectual disability. The gene discussed is IDUA; the disease is Hurler-Scheie syndrome.