Hurler syndrome

Definition

Hurler syndrome is an inherited disease that belongs to a group of diseases called mucopolysaccharidoses, or MPS.

Causes, incidence, and risk factors

Hurler syndrome (MPS1) is an inherited and progressive disorder that results from the body's inability to make lysosomal alpha-L-iduronate, an enzyme that helps breakdown mucopolysaccharides. Mucopolysaccharides are made of a Jello-like material and are found throughout the body, often in mucus secretions and in fluids surrounding the joints.

The enzyme deficiency found in Hurler syndrome causes mucopolysaccharides to build up in the body.  The result is a multisystem disorder with symptoms that range from mild to severe. The disease damages many organs, including the heart.

In the past, MPS1 was called Hurler syndrome, Hurler-Scheie syndrome, or Scheie syndrome. Because there is no clear distinction between the groups, a classification based on disease severity has been suggested:

• Hurler as severe MPS1
• Hurler-Scheie as intermediate MPS1
• Scheie as mild MPS1

Hurler syndrome is inherited as an autosommal recessive trait. Approximately 1 in 115,000 individuals are affected.

Symptoms

The symptoms of intermediate MPS1 usually develop between 3 and 8 years of age. Survival into adult life is common.

Infants with severe MPS1 appear normal at birth. Coarsening of facial features is noted during the first two years of life. Symptoms are progressive and include:

• Halted growth
• Progressive  mental retardation
• Thick, coarse facial features with low nasal bridge
• Cloudy corneas
• Deafness
• Joint disease, including stiffness
• Heart value problems
• Abnormal bones of spine and claw hand

Signs and tests

Tests that may be performed include:  

• Urine testing for mucoploysacchariduria (heparan and dermatan sulphate). Urine studies are usually conducted first. They may show excess MPS when present, but can not determine the exact form of MPS. A definite diagnosis relies on specific enzyme testing. 
• Alpha-L-Iduronidase testing in blood, skin or plasma
• Molecular genetic testing for the Alpha-L-Iduronidatase (IDUA) gene
• Spine x-ray
• EKG 

Treatment

Enzyme replacement therapy is now possible for patients with a defect in the enzyme a-L-iduronidase.

Bone marrow transplantation can improve some of the symptoms of the disease. To prevent mental retardation, a bone marrow transplant probably should be performed at a very young age. Other treatments depend on the affected organ system.

Support Groups

For more information and support, contact one of the following organizations:

• The National MPS Society: www.mpssociety.org
• Canadian Society for MPS and Related Diseases: www.mpssociety.ca
• Society for MPS Diseases: www.mpssociety.co.uk

Expectations (prognosis)

Hurler syndrome is a disease with a poor prognosis. Children with this disease have progressive neurological impairment. Early death can occur.

Calling your health care provider

Call your health care provider if you have a family history of Hurler syndrome and are considering having children, or if your child begins to develop a group of the characteristic signs and symptoms of Hurler syndrome.

Prevention

Prospective parents with a family history of Hurler syndrome should have genetic counseling and testing, along with a complete family history profile.

References

Staba SL, Escolar ML, Poe M, et al. Cord-blood transplants from unrelated donors in patients with Hurler's syndrome. N Engl J Med. 2004 May 6;350(19):1960-9.

National Institute of Neurological Disorders and Stroke. Mucolipidoses Fact Sheet. Office of Communications and Public Liaison. Bethesda, MD; Publication No. 05-4899. February 9, 2005.

Illustrations

Low nasal bridge

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