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Hurler syndrome

Hurler syndrome, also known as mucopolysaccharidosis type I (MPS I) or "Hurler's disease", is a genetic disorder that results in the deficiency of alpha-L iduronidate, which is an enzyme that breaks down mucopolysaccharides. Without this enzyme, the buildup of heparan sulfate and dermatan sulfate occurs in the body (the heart, liver, brain etc.). Symptoms appear during childhood and early death can occur due to organ damage. more...

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MPS I is divided into three subtypes based on severity of symptoms. All three types result from an absence of, or insufficient levels of, the enzyme alpha-L-iduronidase. Children born to an MPS I parent carry the defective gene. MPS I H or Hurler syndrome is the most severe of the MPS I subtypes. The other two types are MPS I S or Scheie syndrome and MPS I H-S or Hurler-Scheie syndrome

Features

The condition is marked by progressive deterioration, hepatosplenomegaly, dwarfism, gargoyle-like facies. There is a progressive mental retardation, with death occuring by the age of 10 years.

Developmental delay is evident by the end of the first year, and patients usually stop developing between ages 2 and 4. This is followed by progressive mental decline and loss of physical skills. Language may be limited due to hearing loss and an enlarged tongue. In time, the clear layers of the cornea become clouded and retinas may begin to degenerate. Carpal tunnel syndrome (or similar compression of nerves elsewhere in the body) and restricted joint movement are common.

Affected children may be quite large at birth and appear normal but may have inguinal (in the groin) or umbilical (where the umbilical cord passes through the abdomen) hernias. Growth in height may be faster than normal but begins to slow before the end of the first year and often ends around age 3. Many children develop a short body trunk and a maximum stature of less than 4 feet. Distinct facial features (including flat face, depressed nasal bridge, and bulging forehead) become more evident in the second year. By age 2, the ribs have widened and are oar-shaped. The liver, spleen and heart are often enlarged. Children may experience noisy breathing and recurring upper respiratory tract and ear infections. Feeding may be difficult for some children, and many experience periodic bowel problems. Children with Hurler syndrome often die before age 10 from obstructive airway disease, respiratory infections, or cardiac complications.

There is some clinical similarity with Hunter syndrome.

Diagnosis

Diagnosis often can be made through clinical examination and urine tests (excess mucopolysaccharides are excreted in the urine). Enzyme assays (testing a variety of cells or body fluids in culture for enzyme deficiency) are also used to provide definitive diagnosis of one of the mucopolysaccharidoses. Prenatal diagnosis using amniocentesis and chorionic villus sampling can verify if a fetus either carries a copy of the defective gene or is affected with the disorder. Genetic counseling can help parents who have a family history of the mucopolysaccharidoses determine if they are carrying the mutated gene that causes the disorders.

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Infusions help babies with Hurler's syndrome
From Science News, 5/8/04 by N. Seppa

Hurler's syndrome is a rare hereditary condition caused by the lack of an enzyme needed to regulate basic cell functions. Treatments to replace the enzyme help children with the condition but don't salvage cells in all parts of the body. Bone marrow transplantation, which supplies a child with new cells that can make the enzyme, has been the only way to cure Hurler's syndrome. But unless a child has a closely matching marrow donor, such transplants often introduce severe complications.

In recent years, doctors have started giving Hurler's babies infusions of donated umbilical cord blood as a way to provide enzyme-making cells. In the first study to analyze this practice over several years, scientists report success--a high survival rate, manageable side effects, and a general reversal of Hurler's syndrome in most babies getting the treatment. The findings appear in the May 6 New England Journal of Medicine.

If both parents carry a mutation in the gene that underlies Hurler's syndrome, a child has a 1-in-4 chance of getting two defective gene copies. The result is a lack of the enzyme alpha-L-iduronidase. Without it, sugar molecules accumulate in cells, causing irreversible tissue damage. Hurler's syndrome is marked by mental retardation, stunted growth, and heart problems. Untreated children usually die by age 10.

Infusions of manufactured alpha-L-iduronidase can ameliorate some symptoms but probably don't penetrate the blood-brain barrier and therefore don't prevent brain damage, says study coauthor Joanne Kurtzberg, a pediatric oncologist at Duke University Medical Center in Durham, N.C.

Bone marrow and cord blood both contain various stem cells that develop into producers of alpha-L-iduronidase. After a bone marrow or cord-blood transplant, these cells, which include nascent white blood cells and brain cells called oligodendrocytes, appear to mature in the recipients, Kurtzberg says.

Researchers at Duke gave cord-blood infusions to 20 babies or toddlers diagnosed with Hurler's syndrome during a 7-year period. The donors weren't relatives of the babies. The babies had first received chemotherapy to wipe out their own defective bone marrow.

Of the six immune system proteins that doctors use as guideposts to match donors with recipients, only one Hurler's baby had a six-out-of-six match with the cord-Mood donor. Eleven babies had a five-out-of-six match, and eight babies had matches in only three or four of the proteins.

Nevertheless, 17 of the 20 babies survived their transplants and are still alive, Kurtzberg says. The oldest is now 7 years old. All the babies experienced some graft-versus-host disease, in which immune cells in the cord blood attack the recipient. But this complication was largely limited to temporary skin rashes.

Notably, the surviving cord-blood recipients are showing stabilized or improved brain development. All those who are old enough are attending school in the grade appropriate for their age, Kurtzberg says.

More than 200 Hurler's babies have successfully received bone marrow transplants since 1980. However, finding a closely matched marrow donor remains difficult, says Joseph Muenzer, a pediatrician and geneticist at the University of North Carolina at Chapel Hill.

"With cord blood, [doctors] can use a partial match," he notes. "That's probably the big plus." Still, it's too early to say whether cord blood will be a more valuable treatment than bone marrow transplants for Hurler's patients, Muenzer concludes.

COPYRIGHT 2004 Science Service, Inc.
COPYRIGHT 2004 Gale Group

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