WEDNESDAY, Feb. 2 (HealthDay News) -- Five new genetic variants believed to play a role in Parkinson's disease have been identified by researchers.

It was long believed that Parkinson's disease was caused by environmental factors. But since 2007, scientists have pinpointed six genetic variants that may affect a person's risk of developing the condition. This new study brings that to a total of 11 genetic variants.

Andrew Singleton, of the National Institute on Aging at the U.S. National Institutes of Health in Bethesda, Md., and an international team of scientists conducted a meta-analysis of five genome-wide association studies that were conducted in Europe and the United States and covered about 7.7 million possible genetic variants.

The analysis showed that 20 percent of people with the highest number of the 11 identified gene variants were 2.5 times more likely to develop Parkinson's disease than the 20 percent of people with the least number of genetic risk factors.

The new findings are a starting point for further research into how Parkinson's disease develops, said the researchers.

"The identification of additional common and rare risk variants for Parkinson's disease will probably revise our estimate of the genetic component of [the] disease upward," they concluded in their report.

The study was released online Feb. 2 in advance of publication in an upcoming print issue of The Lancet.

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