Researchers say a genetics test for Parkinson's disease could be available before the end of the year for people suspected of having an inherited form of the neurological disorder. This follows the discovery that a gene might cause the disease in certain groups, including North African Arabs and Ashkenazi Jews. Experts also say the finding could lead to discovery of better therapy for the disorder.

Many researchers believe Parkinson's disease is caused by a combination of genetic and environmental factors. But the latest scientist evidence, reported in the New England Journal of Medicine, suggests that, at least in some groups, there appears to be a very strong genetic component.

Researchers at the Albert Einstein College of Medicine in New York tested the DNA of Ashkenazi Jews suffering from Parkinson's disease and the DNA of healthy Jews.

They found a mutation in a key Parkinson's protein in about 18 percent of Parkinson's sufferers, compared to one percent of the general population.

The Ashkenazis trace their ancestry to eastern Europe and comprise the largest group of Jews worldwide.

Researchers in Paris, meanwhile, found the same genetic abnormality in about 40 percent of North African and Arab Parkinson's patients.

Albert Einstein molecular geneticist Laurie Ozulius led the U.S. study. She says the findings are an important step toward developing treatment for Parkinson's.

"We could study potential responses to drugs: who responds and who doesn't. Those kinds of things," she said. "So, this is kind of important because the frequency of this mutation is relatively high, we should be able to get a decent size group of patients to look at these kind of clinical features."

The study's senior author, Susan Bressman, who is the head of Albert Einstein's Department of Neurology, says a test that could help to confirm a diagnosis of the disease will likely be available before the end of the year.

Professor Bressman says she plans to offer the test to her patients, who may be conflicted about whether to take it.

"Knowing may just generate a lot of anxiety," she said. "And for some people, that's true. And they don't want to know. And for other people, they want to know. And they feel they have a right to know. And that's really the dilemma."

About 30 percent of people who carry the Parkinson's mutation develop the disease, according to Dr. Bressman, who says it may one day make sense to screen relatives of Parkinson's patients, if and when treatment for the disease is developed.