What does skin cancer have to do with Parkinson's disease, the degenerative brain condition that causes tremors, slowed gait and problems with balance and coordination? According to a new study, more than you might think.

People with a family history of melanoma, the deadliest form of skin cancer, have twice the risk of developing Parkinson's disease as people who didn’t have a parent or sibling with the cancer, according to research released today ahead of April's annual American Academy of Neurology meeting in Seattle. The study followed nearly 132,000 men and women for 14 to 20 years; at the end of that period, 543 people had developed Parkinson's. The likelihood of getting Parkinson's was almost double — 90 percent greater, to be exact — in those with a close relative who had received a melanoma diagnosis than among those without that family history. (For comparison, the baseline risk of Parkinson’s is about 1 percent for those over 60, according to the Michael J. Fox Foundation.)

The link held even after the scientists from Harvard School of Public Health adjusted for other risk factors such as age, smoking status and caffeine intake. (While coffee and especially cigarettes cause a laundry list of health problems, for unknown reasons they seem to protect against Parkinson's.)

The relationship between melanoma and Parkinson's isn’t known, says co-author Xiang Gao, an instructor and epidemiologist at the school. It’s probably not because getting melanoma increases the risk of Parkinson’s, but that the two conditions may share common genes. Red hair color has previously been identified as a risk factor for melanoma, and a study Gao published last month in the Annals of Neurology found that the lighter a person's hair, the higher their risk for Parkinson's. That suggests that genes that code for the metabolism of pigment may be implicated in Parkinson's, too, Gao says.

Image © iStockphoto/Benjamin Albiach Galán