Hurler Syndrome (Mucopolysaccharidosis Type 1)

What Your Test Results Mean:

Carriers typically show no symptoms of Hurler syndrome; however, carriers are at an increased risk of having a child with Hurler syndrome. Risk for current or future pregnancies is dependent on your partner’s carrier status. Carrier testing of your partner is recommended in addition to consultation with a genetic counselor.

Disease Explained:

Hurler syndrome is an inherited lysosomal storage disorder in which glycosaminoglyans (sugar molecules) accumulate in the body and can damage organs. Individuals with Hurler syndrome do not make enough of the lysosomal enzyme alpha-L-iduronidase. Without enough of this enzyme, the body cannot properly break down glycosaminoglycans. The build up of glycosaminoglycans leads to multisystem organ damage.

Individuals with Hurler syndrome may appear normal at birth but typically develop the symptoms within the first two years of life. Cloudy corneas can develop leading to vision issues and even blindness, heart valve issues and narrowed arteries may occur, lung disease with frequent infections can develop, and decreased brain development can occur. Life expectancy is typically ten years of age but with treatment may be increased.

Available treatment includes enzyme replacement therapy, the incorporation of the missing enzyme into the body through the veins. Incorporation of this enzyme may reduce the excess glycosaminoglycans and lead to functional improvements; however, the enzyme does not cross the blood-brain barrier and the neurological complications of the disorder will not typically improve with enzyme replacement therapy. Bone marrow transplant is possible and can help expand the lifespan of the affected individual.

How the Genetics Works:

Hurler syndrome is an autosomal recessive disorder caused by a pathogenic variants in the IDUA gene. In general individuals have two copies of the IDUA gene. Carriers of Hurler syndrome have a variant in one copy of the IDUA gene while individuals with Hurler syndrome have variants in both copies their genes, one inherited from each parent. Risk for two carriers to have a child with the disorder is 25%.

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