Families with Parkinson disease and cancer.

W E ARE REACHING THE CONVERgence of 2 important lines of research on the etiology of Parkin-son disease (PD). The first line involves the accumulation of evidence on the familial aggregation of multiple neurode-generative diseases, including PD. The second line involves the accumulation of evidence on the association of PD with a decreased risk of some types of cancer and an increased risk of some other types of cancer, primarily melanoma. Along the first line of research, first-degree relatives of patients with younger-onset PD were found to have an increased risk not only of PD or parkinsonism but also of essential tremor, cognitive impairment or dementia, anxiety disorders, and depressive disorders, compared with relatives of controls. 1-3 A reciprocal familial aggre-gation of other neurodegenerative disorders, including PD, was also found among relatives of patients with amyo-trophic lateral sclerosis or with dementia. 4,5 These studies suggest that some genetic or environmental factors may cluster in some families and may cause several distinct neurologic or psychiatric diseases. Along the second line of research, several studies have shown an association of PD with a decreased risk of some types of cancers and an increased risk of some other types of cancers. Although the literature concerning PD and most cancers remains controversial, 6,7 a consistent association between PD and increased risk of melanoma has been reported. In a recent review of the literature, 6 the association was found to be significant when a diagnosis of PD preceded a diagnosis of melanoma but not when a diagnosis of melanoma preceded a diagnosis of PD, and the association was stronger for men than for women. Another study 8 showed that a positive family history of melanoma among first-degree relatives was a risk factor for PD after adjustment for known environmental risk factors. However, that study 8 did not find a significant association of family history of other types of cancers (such as colorectal, lung, prostate, or breast cancer) with the risk of PD. In this issue of Archives of Neurology, Kareus and colleagues 9 report new findings from the Utah statewide linkage database suggesting that PD is associated with mela-noma at the individual level and also across first-, second-, and third-degree relatives. Thus, relatives of patients with PD had an increased risk of melanoma. In separate analyses , relatives of patients with melanoma also had an increased risk of PD, suggesting common underlying causes of both …