MPS I (Hurler Syndrome)

What is MPS I (Hurler syndrome)?

Mucopolysarcharidosis type I (MPS I) is a rare, inherited disorder. MPS I is also known as Hurler syndrome. Children with Hurler syndrome have an abnormal accumulation of complex sugars in their cells, which affects many of the systems in their bodies. Hurler syndrome is currently divided into “severe” and “attenuated” (less severe) subtypes. Hurler syndrome is one of about 50 diseases classified as lysosomal storage disorders (LSD). In these disorders, genetic variations disrupt the normal activity of lysosomes in human cells. 

What are lysosomes and what do they do?

Lysosomes contain specific proteins (enzymes) that are responsible for breaking down and recycling molecules such as fats and sugars. Individuals with a lysosomal storage disorder lack one of these necessary enzymes, or do not contain one of these enzymes in sufficient quantities to break down molecules for cells to function properly.

What causes Hurler syndrome?

Hurler syndrome is caused by a variation in the IDUA gene, which contains the instructions for the production of a specific enzyme known as alpha-L-iduronidase. This specialized protein is normally found in the lysosomes of cells, where it helps to break down complex sugars called glycosaminoglycans (GAGs). Genetic variations in the IDUA gene result in a deficiency or a complete absence of alpha-L-iduronidase, which in turn results in an abnormal accumulation of GAGs in the body’s cells.

This condition is genetic and is inherited in an autosomal recessive pattern, which means that an affected child has received one defective copy of the IDUA from each parent.

What are the symptoms of Hurler syndrome?

Newborns with the less severe subtype of MPS I may not show signs or symptoms of the disorder at birth. Those with severe MPS I may have clinical symptoms when they are born.

Symptoms fall on a spectrum. Some children have only a few, mild symptoms. Other children experience significant complications of the disease.

Symptoms may include:

  • clouding of the front part of the eye (corneal clouding)
  • frequent upper respiratory infections
  • enlarged tonsils and/or adenoids
  • distinct facial features (coarse facial features)
  • hernias

Other symptoms children might experience over time include:

  • thickening and dysfunction of the heart valves
  • abnormal curvature of the spine (scoliosis, kyphosis)
  • enlargement of the liver and spleen (hepatosplenomegaly)
  • accumulation of fluid around the brain (hydrocephalus)
  • compression of the spinal cord
  • progressive neurological decline

How is Hurler syndrome treated?

Current approaches to Hurler syndrome are tailored to specific patients and may include enzyme replacement therapy, bone marrow transplant, hematopoietic stem cell transplant and targeted symptom management. Treatment plans require interdisciplinary collaboration and depend greatly on your child’s age and specific disease presentation. 

How we care for Hurler syndrome

The team of providers in the Boston Children’s Lysosomal Storage Disorder (BoLD) Program is committed to the care of complex patients. As part of Boston Children’s Hospital, we are prepared to meet the challenge of providing multifaceted care by partnering with you and your child to deliver direct care in our BoLD clinic. We work with the broad array of world-class specialists at Boston Children’s to optimize the care we provide your child with Hurler syndrome.