February 16 (HealthDay News) -- People with a family history of melanoma are twice as likely to develop Parkinson's disease, a new study finds.

While the reasons for this association are not clear, other studies have shown that people with Parkinson's diseases are at greater risk for developing melanoma.

"For people with a family member with melanoma, they may be at risk for Parkinson's disease," said lead researcher Dr. Xiang Gao, an instructor in medicine at Harvard University School of Public Health. "This study suggests that some genetic components for melanoma are associated with Parkinson's disease."

Earlier studies had found that Parkinson's patients taking levodopa, a common treatment for the condition, were more susceptible to melanoma, Gao said. "They thought that levodopa increased the risk of melanoma," he explained.

But later reports found that people with melanoma were at high risk of developing Parkinson's disease, Gao said. "This suggests that it may not be the drugs, it could be something else, which is why I did this study," he said.

The finding was released Monday and was also expected be presented at the American Academy of Neurology's annual meeting, April 25 to May 2, in Seattle.

For the study, Gao's team collected data on almost 157,000 men and women who did not have Parkinson's disease. These individuals participated in the Health Professional Follow-up Study and the Nurses Health Study.

During 14 years of follow-up, 616 people developed Parkinson's disease. Among those people who also reported a family history of melanoma, the risk for developing Parkinson's disease was doubled, the researchers found.

After adjusting for other factors such as colorectal, lung, prostate or breast cancer as well as age, smoking or caffeine consumption, only the association between melanoma and Parkinson's disease was significant, the researchers reported.

Dr. Roberto Zanetti, director of the Piedmont Cancer Registry in Torino, Italy, and an expert in the connection between Parkinson's and melanoma, doesn't think this study adds much to what has already been reported.

"It seems to add a piece of evidence to the question of the association between Parkinson's disease and melanoma," Zanetti said. "The abstract does not add much about the mechanisms. And, in terms of interpretation, it does not seems to add much to what we have discussed in The Lancet two years ago," he said.

SOURCES: Xiang Gao, M.D., Ph.D., instructor, medicine, Harvard University School of Public Health, Boston; Roberto Zanetti, M.D., Ph.D., director, Piedmont Cancer Registry, Torino, Italy; April 25-May 2, 2009, presentation, American Academy of Neurology annual meeting, Seattle