mucopolysaccharidosis type I

What is Mucopolysaccharidosis Type I?

Mucopolysaccharidosis type I (MPS I) is an inherited condition in which the body lacks an enzyme called alpha-L-iduronidase. Without this enzyme, the body cannot properly break down long chains of sugar molecules called glycosaminoglycans. As a result, these molecules accumulate in the body, causing numerous health problems. MPS I is caused by harmful genetic changes (variants) in the IDUA gene. MPS I has two forms: a severe form and a milder (attenuated) form. However, there is a significant overlap between the forms of the condition.

Severe Mucopolysaccharidosis Type I

This form of the condition is also known as Hurler syndrome. Children with the condition appear normal at birth but may develop symptoms before age one. Infants may develop bulging of organs or tissue (hernia) at the belly button or inner groin, distinct facial features, abnormalities of the heart, and bone malformations. Ear, nose, and throat infections are common. Delays in development are usually present in the first year of life and progress as the child ages. Growth slows by age three, and hearing loss is common. Enlargement of the liver and spleen may be present, and heart and lung disease frequently develop. A dangerous build-up of fluid around the brain (hydrocephalus) can also occur.

Attenuated Mucopolysaccharidosis Type I

This form of the condition is also known as Hurler-Scheie syndrome or Scheie syndrome. Children usually develop symptoms between the ages of 3 and 10 years. There is a wide range of disease severity in children with attenuated MPS I, ranging from individuals living normal lifespans to individuals having complications leading to death by the age of 20 to 30 years. Individuals with a more typical lifespan may still have significant issues from progressive joint disease (arthropathy) as well as heart and lung disease. Learning disabilities can be present, and hearing loss and cardiac valvular disease are common.

How common is Mucopolysaccharidosis Type I?

The prevalence of MPS I is 1 in 100,000 individuals for the severe form and 1 in 500,000 for the attenuated form. MPS I has been found in people of all ethnicities.

How is Mucopolysaccharidosis Type I treated?

There is no cure for MPS I. However, there are treatments available. Treatment is usually based on the form of MPS I (severe or attenuated) that an individual has. Hematopoietic stem cell transplantation (HSCT) is the primary form of treatment for severe MPS I and is recommended before the age of two. Enzyme replacement therapy (ERT) is another available treatment. ERT has been shown to improve many physical symptoms but cannot treat neurological symptoms. Other treatments are based on an individual's symptoms and include physical and occupational therapy, treatment of infections, and surgical procedures to correct heart problems. Early treatment leads to better outcomes and less severe disease.

What is the prognosis for a person with Mucopolysaccharidosis Type I?

Without treatment, the prognosis for individuals with severe MPS I is generally poor. They typically need special education and assistance to perform daily functions and are often wheelchair-bound. Death usually occurs within the first ten years of life. Early treatment can improve symptoms and extend lifespan. Heart and breathing problems are often the cause of death among children with severe MPS I. Individuals with attenuated MPS I have a variable severity of disease and lifespan.