Hurler's Syndrome

Affecting one in 100,000 people, Hurler's syndrome is a rare genetic disorder where the enzyme (alpha-L-iduronidase), which normally breaks down the mucopolysaccharides dermatan and heparin sulphate, is missing. These mucopolysaccharides build up in all tissues in the body causing progressive deterioration and eventual death. The disease was first described in 1919 in Germany by Dr. Gertrud Hurler. Hurler's syndrome babies often develop normally during the first year, but as the storage material (mucopolysaccharides) start to build up, the symptoms begin to appear. Early symptoms include frequent colds and ear infections. Hurler's children will, without therapy, experience profound mental retardation, coarse facial features and excessive hair growth, vision problems (due to clouded cornea), and severe heart problems (as the coronary arteries narrow and the heart valves thicken). Other symptoms may include carpal tunnel syndrome, curvature of the spine, frequent runny nose, hernias, and hearing loss. Most patients die of heart failure between the ages of 5 and 10. Because Hurler's syndrome is genetic, it is difficult to cure. Current approaches to Hurler's syndrome include genetic counseling for parents who are carriers of the disease, and improvements in early detection of the disease in unborn children (Hurler's can be detected with amniocentesis early in the second trimester). For Hurler's syndrome patients, a variety of treatments have been tried. The goal of treatment is to get the missing enzyme into the body. While the enzyme is now FDA-approved and available, studies have shown this doesn’t move into the brain well enough to prevent the neurologic aspects of the disease. To introduce alpha-L-iduronidase into the body, both gene therapy and blood, marrow or cord blood transplants are being explored. In gene therapy, researchers use a virus to place the gene that produces alpha-L-iduronindase into the patient’s cells. Transplants are performed to provide cells producing enzyme through the growth of normal, healthy blood cells. These blood cells appear to provide enzyme to other cells of the brain, preserving neurologic function. However, the enzyme does not appear to penetrate into the brain. Following successful transplant, patients do not suffer cardiac deterioration, and the accumulated mucopolysaccharides in the liver, lungs, and marrow slowly disappear. Vision and hearing generally improve post transplant, as well. Though the mental retardation does not progress, the patient’s IQ will typically stabilize. Thus the most successful transplants are those that are performed as soon as possible after diagnosis. Transplants performed after age 2 have disappointment results, because a BMT cannot repair the considerable amount of damage already done. Because older patients and those with prior lung problems do particularly poorly with transplant, the use of enzyme therapy prior to transplantation may be advantageous. The University of Minnesota has pioneered a study to test the use of enzyme prior to transplant, which is currently enrolling patients.