Researchers have identified a single genetic mutation that accounts for more than 20 percent of all cases of Parkinson's disease among Arabs, North Africans, and Jews -- a big surprise for a major disease in which genetics was thought to play a relatively minor role.
Although the mutation is rare in people with ethnic roots outside the Middle East, its discovery raises the prospect that undiscovered mutations may be major causes of Parkinson's in other groups.
''Genetics are going to be a lot more important in Parkinson's than people have appreciated," said study leader Susan Bressman, a neurologist at Albert Einstein College of Medicine of Yeshiva University and Beth Israel Medical Center in New York.
The finding -- described in a pair of reports in last week's New England Journal of Medicine -- could help reveal at last the mysterious underpinnings of Parkinson's, which causes tremors, rigidity, and mental decline and is growing more common as the population ages.
But it also raises the delicate question of whether some people should be offered tests to see if they harbor the predisposing glitch -- a tough call, as there is no known way to prevent the disease.
In this era of Arab-Israeli tensions, the discovery of shared genetic flaws might even serve as a small olive branch, scientists said.
''Yasser Arafat once said we are all cousins. Well, it's the truth," said Neil Risch, director of the University of California at San Francisco's Center for Human Genetics.
Parkinson's affects at least 500,000 Americans and has no cure.