Alpha-L-iduronate deficiency

Definition

Hurler syndrome is a rare, inherited disease of metabolism in which a person cannot break down long chains of sugar molecules called glycosaminoglycans (formerly called mucopolysaccharides).

Hurler syndrome belongs to a group of diseases called mucopolysaccharidoses, or MPS.

See also:

• MPS II, Hunter syndrome
• MPS IV (Morquio syndrome)
• MPS III (Sanfilippo syndrome)
• MPS I S (Scheie syndrome)

Alternative Names

Alpha-L-iduronate deficiency; Mucopolysaccharidosis type I; MPS I H

Causes

Persons with Hurler syndrome do not make a substance called lysosomal alpha-L-iduronidase. This substance, called an enzyme, helps break down long chains of sugar molecules called glycosaminoglycans (formerly called mucopolysaccharides). These molecules are found throughout the body, often in mucus and in fluid around the joints.

Without the enzyme, glycosaminoglycans build up and damage organs, including the heart. Symptoms can range from mild to severe.

Hurler syndrome is inherited, which means that your parents must pass the disease on to you. Both parents need to pass down the faulty gene in order for you to develop Hurler syndrome.

Hurler syndrome is a type of mucopolysaccharidosis called MPS I. Hurler syndrome is the most severe type. It is categorized as MPS I H.

The other subtypes of MPS I are:

• MPS I H-S (Hurler-Scheie syndrome)
• MPS I S (Scheie syndrome)

Symptoms

Symptoms of Hurler syndrome most often appear between ages 3 and 8. Infants with severe Hurler syndrome appear normal at birth. Facial symptoms may become more noticeable during the first 2 years of life.

Symptoms include:

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

Exams and Tests

Urine tests are usually done first. These tests may show extra mucopolysaccharides, but they can't determine the specific form of MPS. More specific tests are done to diagnose the disease, including genetic testing for the alpha-L-iduronidase (IDUA) gene.

Other tests may include a spinal x-ray and EKG.

Treatment

Enzyme replacement therapy helps the body make alpha-L-iduronidase.

A bone marrow transplant can improve some of the symptoms of the disease. To prevent mental retardation, a bone marrow transplant probably should be done at a very young age.

Other treatments depend on the organs that are affected.

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

Outlook (Prognosis)

Hurler syndrome is a disease with a poor outlook. Children with this disease develop nervous system problems, and can die young.

When to Contact a Medical Professional

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 show symptoms of Hurler syndrome.

Prevention

Experts recommend genetic counseling and testing for couples with a family history of Hurler syndrome who are considering having children.

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. 03-5115. February 13, 2007.