Gao X et al. (2007) Erectile function and risk of Parkinson's disease. Am J Epidemiol 166: 1446–1450

Erectile dysfunction (ED) is common in men with Parkinson's disease, perhaps because both disorders are associated with dopamine and testosterone status. Gao and colleagues' analysis of retrospective data from the Health Professionals Study has now shown that ED might precede the onset of Parkinson's motor symptoms by many years, and might help to identify men with an increased risk of developing Parkinson's disease.

In total, 32,616 Health Professionals Study participants without Parkinson's disease at baseline in 1986 responded to a questionnaire, mailed in 2000, that assessed their erectile function between 1984 and 2000. Compared with men who reported very good erectile function before 1986, men who reported first onset of ED before 1986 were four times more likely to develop Parkinson's disease by 2002 (P <0.0001). After adjustment for potentially confounding variables, the prevalence of ED in the 200 men who had developed Parkinson's disease by 2000 was much higher than in men who had not (68% versus 32%). This association was evident in all age-groups, but was strongest in men with the youngest age at onset of ED.

Gao and colleagues note that ED and constipation (another common complaint in men who eventually develop Parkinson's disease) are both manifestations of parasympathetic cholinergic failure. They conclude that symptoms of autonomic dysfunction might be evident years before Parkinson's disease is clinically recognizable.