WASHINGTON (AP) -- Federal regulators on Friday cleared the first treatment approved in the United States for Huntington's, a rare inherited disease that causes uncontrolled movements, deterioration of mental abilities and, ultimately, death.

The medication, called Xenazine, will not cure the condition_and it has some potentially serious side effects, such as raising the risk of suicidal behavior. However, it does provide relief for a major disabling symptom of Huntington's: the jerky, involuntary movements known by the medical term chorea and force many patients to live as shut-ins.

"A lot of patients won't go out because they are embarrassed by those movements," said Dr. Frederick J. Marshall, a University of Rochester Medical Center neurologist who led the clinical study that provided evidence of the drug's effectiveness. "Suppressing those movements means a lot to people with Huntington's disease."

The disease affects only about 30,000 patients in the United States. Developing and testing medications for such a small population is a difficult process, with uncertain financial rewards. So the Food and Drug Administration granted Xenazine a special "orphan drug" designation that provides additional years of patent protection and allows the manufacturer, Prestwick Pharmaceuticals, to write off some development costs. The medication had already been approved in Canada, Europe and Australia.

"For the first time, there is a treatment that can help patients with this disease gain some quality of life," said Dr. Timothy Cote, head of the FDA's orphan drugs office. Huntington's usually strikes between early adulthood and middle age, and patients can expect to live for 15 to 20 years after they first begin to experience symptoms.

The drug works by reducing the amount of a chemical, dopamine, available at key junction sites in the brain. Dopamine is essential in communicating signals between nerve cells, but in people with Huntington's this system is overactive. By reducing the amount of dopamine available at certain sites in the brain, the drug decreases the involuntary movements associated with Huntington's.

But Xenazine also has some serious side effects, which include depression and suicidal thoughts and actions. The FDA said the drug should not be taken by patients who are suicidal or who have untreated depression. People with Huntington's disease often struggle with depression to begin with, because of the severity of the disease. The agency is requiring a special risk management program to monitor patients for worsening psychiatric symptoms.

Until now, many patients with Huntington's have gone untreated, Marshall said, while others have experimented with anti-psychotic drugs or imported Xenazine from abroad, in technical violation of U.S. law. Approval of the drug means U.S. patients will have access to a medication that should be covered by Medicare and other government and private insurance plans.

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