Hurler syndrome is one of several storage disorders in which the body lacks a particular enzyme needed to metabolize a substance, such as sugar. The substance builds up in the body and causes harm to organs and tissues. Hurler’s syndrome is also known as mucopolysaccaridosis 1 (MPS-1). This group of MPS disorders has a gene mutation which affects an enzyme known as alpha-L-iduronidase (IDUA). The body uses IDUA to break down complex sugars known as glycosaminoglycans (GAGS). These GAGS are used in building tissues and bones.
Hurler syndrome is a rare autosomal recessive condition which affects 1 in 100,000 people. The IDUA gene mutation is inherited from both parents. If only one genetic mutation is passed down, the child will not have the condition but will be a carrier. Hurler syndrome affects all ethnic groups. There are three types of MPS disorders, which vary in severity. Hurler syndrome is the most severe form. Over time, the GAGS build up in the brain, spleen, liver, bones, and other organs.
In the most severe form of MPS-1 disorders, symptoms begin to appear between 6 months and 2 years of age. Over half of all children with Hurler’s syndrome do not live to age 5, and few survive until age 10. Common symptoms include mental retardation, short stature, bone problems, and joint stiffness. Other symptoms include heart disease, deafness, cloudy corneas, and breathing difficulties.
Tests for the condition include genetic testing to test for the IDUA gene mutation and urine tests for extra GAGS. Blood and tissue tests determine whether or not the body is producing the IDUA enzyme. X-rays can reveal spinal damage, and EKGs or echocardiograms reveal heart abnormalities. Families in which the genetic mutation is present may want to consult with a genetic counselor about family planning.
Treatments for Hurler syndrome include enzyme replacement therapy and a bone marrow or cord blood transplant. The drug Aldurazyme can help treat breathing problems, growth, bone problems, and the heart. It is most effective on the milder forms of the condition that do not have mental retardation, as the drug has not been shown to improve mental function.
Bone marrow or cord blood transplant is the only option that stops the progression of mental damage. Transplants are most effective when performed early, before the condition progresses. Even with successful treatment, most children will need multiple surgeries to address problems with bones and joints. Transplant is risky, and may result in graft-vs-host disease, graft failure, or pulmonary hemorrhage. Even with transplant, mortality rates still remain high.