Mucopolysaccharidosis Type I

Gene : IDUA

What is Mucopolysaccharidosis type I?

Mucopolysaccharidosis type I (MPS1), also known as Hurler syndrome, is a rare inherited disorder caused by deficiency of the alpha-L-iduronidase (IDUA) enzyme. IDUA is necessary for the breakdown of large sugar molecules. Accumulation of these sugar molecules prevents cells, tissues, and organs from functioning correctly. There are two forms of Hurler syndrome: severe MPS1 and attenuated MPS1. Children affected by severe MPS1 appear normal at birth but begin to show signs and symptoms within the first year of life. They may have a large head, buildup of fluid in the brain, heart disease, enlarged liver and spleen, and large tongue. Children may also develop distinctive facial features. All children develop progressive skeletal dysplasia, as well as progressive intellectual disability. Some children will have hearing and vision loss. Death usually occurs in the first decade of life. Individuals affected by the attenuated MPS1 usually have milder progression of the disease with the possibility of longer life expectancy. Currently there is no cure for Hurler syndrome, although bone marrow transplant and enzyme replacement therapy can help improve some but not all symptoms if treatment begins early enough in life. Hurler syndrome is caused by pathogenic variants in the IDUA gene.

How is Mucopolysaccharidosis type I inherited?

Hurler syndrome is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for Hurler syndrome. However, the risk to have a child affected with Hurler syndrome is increased. Testing of reproductive partners is recommended for carriers of Hurler syndrome.

How common is Mucopolysaccharidosis type I?

Hurler syndrome is a rare condition that affects all ethnicities. Severe MPS I is estimated to occur in 1 in 100,000 newborns and in 1 in 500,000 newborns for attenuated MPS1.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems








Carrier Rates
Detection Rate
Carrier Frequency
General Population > 99% 1 in 158
Northern European Caucasian > 99% 1 in 145

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