Children born to an MPS I parent carry a defective IDUA gene, which has been mapped to the 4p16.3 site on chromosome 4. The gene is named IDUA because of its iduronidase enzyme protein product. As of 2001, 52 different mutations in the IDUA gene have been shown to cause Hurler syndrome.

Hurler syndrome is an autosomal recessive disorder, affected persons have two bad copies of the IDUA gene. If someone is born with one normal and one defective copy of the gene he is called a carrier and will produce less alpha-L-iduronidase than an individual with two normal copies of the gene. The reduced production of the enzyme, however, is sufficient for normal function and the person should not show any symptoms of the disease.