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Joubert syndrome

Joubert syndrome is a rare genetic disorder that affects the area of the brain that controls balance and coordination. The disorder is characterized by absence or underdevelopment of a part of the brain called the cerebellar vermis and a malformed brain stem. The most common features include ataxia (lack of muscle control), an abnormal breathing pattern called hypernea, sleep apnea, abnormal eye and tongue movements, and hypotonia. Other malformations such as extra fingers and toes, cleft lip or palate, tongue abnormalities, and seizures may also occur. There may be mild or moderate retardation. more...

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Treatment for Joubert syndrome is symptomatic and supportive. Infant stimulation and physical, occupational, and speech therapy may benefit some patients. Infants with abnormal breathing patterns should be monitored.

The prognosis for individuals with Joubert syndrome varies. Some patients have a mild form with minimal motor disability and good mental development, while others may have severe motor disability and moderate mental retardation.

Two genes that are mutated in individuals with Joubert syndrome have been identified. Mutation in gene of unknown function called AHI1 is associated with the majority of Jourbert syndrome cases. In cases where an individual has Joubert syndrome with progressive kidney disease to a gene called NPHP1 is mutated in addition to AHI1.


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Motor ways: gene mutation impairs muscle coordination
From Science News, 9/18/04 by Diana Parsell

Individuals with a rare inherited disorder called Joubert syndrome are clumsy when they walk or use their hands, and they have irregular breathing and eye movements. Patients with severe symptoms tend to die young.

Scientists have now identified a gene that underlies Joubert syndrome. Christopher A. Walsh of Harvard University and his colleagues found that when the Abelson helper integration site gene (AHI1) on chromosome 6 is abnormal, it disrupts prenatal development of a brain region that controls coordinated movement of hands, feet, and other parts of the body. The finding appears in the September Nature Genetics.

First described 35 years ago, Joubert syndrome affects about 1 in 30,000 people. In 1997, medical experts discovered that patients with the disorder have tooth-shaped lesions in the cerebellum and brain stem. Now, the roots of the disorder are coming to light.

Walsh's team focused on six children with Joubert syndrome from five families in Saudi Arabia and Turkey. By analyzing DNA from these children and from symptom free family members and nonrelatives, the researchers tracked down atypical AHI1 genes in the affected children.

Other scientists had identified AHI1 earlier, but its function wasn't known. Walsh and his colleagues report that the protein encoded by AHI1 is critical to the biochemical process whereby certain nerve cells in the brain grow, branch out across the brain stem, and connect with neurons on the other side of the spinal cord.

When wired to the right partners, these neurons ensure proper muscle control and coordination, Walsh explains. If AHI1 is faulty, however, the neurons fail to cross the brain and instead connect with neurons on the same side. As a result, the feet or hands of Joubert syndrome patients tend to move in the same direction.

When Walsh's team compared the AHI1 of various mammals, it found substantial differences that pinpointed a portion of the gene as being "particularly dynamic evolutionarily." Walsh says the discovery of AHI1's function could increase scientists' understanding of how specific brain structures accommodate human motor skills. "We now know that this gene, which hadn't been suspected of having any role in the brain at all, is essential for so many wiring decisions that affect movement," he says.

Other genes may contribute to the disorder by disrupting brain development in different ways, Walsh notes. Indeed, several research teams are homing in on additional candidate genes, located on chromosomes 9 and 11.

Moreover, because symptoms vary widely, investigators suspect that additional genes play secondary roles in the disorder. Joubert syndrome sometimes includes mental retardation, autistic behavior, or kidney and liver problems. Melissa Parisi of the University of Washington in Seattle and her colleagues recently reported that a previously known gene deletion on chromosome 2 causes kidney failure in a subgroup of Joubert syndrome patients.

Parisi calls the finding by Walsh's group an "important discovery" and says that researchers hope many other findings about Joubert syndrome will soon be coming down the pipeline. Such findings, she notes, may lead to prenatal tests to reveal the disorder soon after conception and to better diagnosis and treatment.

COPYRIGHT 2004 Science Service, Inc.
COPYRIGHT 2004 Gale Group

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