No family link seen between Parkinson's, melanoma

NEW YORK (Reuters Health) - Research has suggested that families affected by melanoma skin cancer may also have a higher-than-average rate of Parkinson's disease -- but a large new study found no evidence of such a link.

This doesn't mean no genetic link exists, the authors of the new study say. But it does suggest that such a link might not have very important effects.

Melanoma is the least common, but most serious, form of skin cancer. The disease sometimes runs in families, and people with two or more close relatives who have had melanoma are considered to be at higher-than-average risk.

Recent research has hinted of a possible genetic link between melanoma and Parkinson's disease, a neurological disorder in which cells in the brain that regulate movement start to die off or become disabled. As a result, patients have symptoms like tremors, rigidity in the joints, slowed movement and balance problems.

Last year, a study of more than 150,000 U.S. adults found that first-degree relatives of melanoma patients (that is, their parents, children, and siblings) were twice as likely to be diagnosed with Parkinson's as people with no family history of melanoma. And in a separate study, the same research team found that a particular form of a gene called MC1R -- a form already tied to red hair and an increased melanoma risk -- was also linked with a higher-than-average risk of Parkinson's.

Those findings were in line with some earlier large studies from the U.S., the U.K. and Denmark showing that people with Parkinson's disease had an elevated rate of melanoma.

However, while those studies all suggest that melanoma and Parkinson's could share a common genetic underpinning, it does not prove that is the case.

And this latest study, published in the journal Epidemiology, casts doubt on such a genetic link.

Using data from Denmark's system of population registers, researchers identified 4,626 people born in the country after 1954 who were diagnosed with early-onset melanoma (at the age of 50 or younger). They then looked at cases of melanoma and Parkinson's among 15,877 parents and siblings of those patients.

Between 1977 and 2008, the study found, 54 relatives were hospitalized for Parkinson's disease -- just slightly higher than the rate of 48 hospitalizations that would be expected in the general population. In addition, none of the melanoma patients' siblings had a hospitalization for Parkinson's, even though 1.3 cases would be expected.

In contrast, the melanoma patients' family members did show a higher-than-normal risk of developing melanoma. Between 1955 and 2007, 135 of the parents and siblings were diagnosed with melanoma (at any age) compared with an expected incidence of 59 cases.

The researchers found no overlap between the 54 families in which a relative was diagnosed with Parkinson's and the 135 in which a relative was diagnosed with melanoma.

Altogether, the findings suggest that "people with a family history of malignant melanoma are predisposed to malignant melanoma, but not to Parkinson disease," lead researcher Dr. Jorgen H. Olsen, of the Danish Cancer Society in Copenhagen, told Reuters Health in an email.

"This seems to support the view that the link between malignant melanoma and Parkinson disease, seen in the same individuals, is likely not a genetic link," said Olsen.

Still, the study, like the previous ones on the theorized melanoma-Parkinson's link, has its limitations. For one, the researchers were limited to only the information provided in the national databases they analyzed.

One consequence was that they had to study only relatives of people with early-onset, and not later-onset, melanoma. Denmark's Central Population Register was begun in 1968, and that allowed Olsen's team to link only relatively younger melanoma patients with their first-degree relatives.

Olsen noted that if there were a genetic link only for melanomas diagnosed after age 50 and Parkinson's disease, then the current study would be unable to detect a connection.

He said that given the remaining questions, there should be further studies on the potential melanoma-Parkinson's link before any conclusions are drawn.