Hurler Syndrome (MPS I)

Inherited storage disease

There is a group of genetic disorders called mucopolysaccharidoses (MPS) in which critical body enzymes (chemicals) are missing or not enough. In MPS I, alpha-L-iduronidase is deficient. This enzyme breaks down long chains of sugar molecules so the body can dispose them. Without the enzyme, the big molecules build up and progressively damage parts of the body.

MPS I is inherited in an autosomal recessive pattern, meaning that a child must inherit two copies of the gene for MPS I, one from each parent, in order to develop the disease. It is not known exactly how often MPS I occurs worldwide.

Ranges of MPS

MPS I is considered to exist on a spectrum from severe to mild (attenuated).

• Severe form, also known as Hurler syndrome or MPS I H: Children affected with the severe form may have mental retardation, short stature, stiff joints, speech and hearing impairment, heart disease, pain and a shortened life span.
• Attenuated form, also known as Scheie syndrome or MPS I S: Children born with this form have normal intelligence and may live to adulthood.

Some children may have normal intelligence and mild to severe physical symptoms; this condition may be called Hurler-Scheie syndrome or MPS I H-S.

These symptoms are very similar to those of Hunter syndrome, but Hurler syndrome symptoms become worse much faster than Hunter syndrome type A.

How does Hurler syndrome affect a child?

A baby will show few signs at birth that he has the disorder, but within a few months symptoms begin. Bone deformities may be detected. The heart and respiratory system are affected, as are other internal organs including the brain. The child grows but remains behind in both physical and mental development for his age. He may have trouble crawling and walking, and problems with his joints develop, causing parts of the body like his hands to be unable to straighten out. Children with Hurler syndrome usually succumb to problems such as heart failure or pneumonia.

Diagnosis

Diagnosis of Hurler syndrome is based on the child's physical symptoms. Generally, the symptoms of severe MPS I will be present during the first year of life, while the symptoms of attenuated MPS I appear in childhood.

Treatment

There is as yet no cure for MPS I, so treatment has focused on relieving symptoms. Aldurazyme (laronidase) replaces the deficient enzyme in MPS I. Aldurazyme is given by intravenous infusion once per week for life to people with MPS I. Aldurazyme helps relieve symptoms but is not a cure.

Another treatment available for MPS I is bone marrow transplant, which puts normal cells in the body that will manufacture the missing enzyme. However, many children with Hurler syndrome have heart disease and are not able to go through the chemotherapy required for the transplant.

Many specialists are involved in the care of an individual with MPS I. A genetic counselor can talk with the family and relatives about the risks of passing on the syndrome.

_Source:

"MPS I (Hurler, Hurler-Scheie, Scheie syndrome)." MPS & Related Diseases. National MPS Society. 27 Mar 2009.