Epidemiology of early-onset Parkinson's disease in Finland

The contribution of genetic causes to Parkinson's disease (PD) is strongest in early-onset cases. We ascertained a nationwide cohort of patients in order to study the genetic epidemiology of early-onset PD (EOPD) in Finland.

By means of a search in a national database we ascertained all patients with EOPD. These patients had become eligible for reimbursement of PD drugs between the years 1995-2006 and were <55 years of age at the time of PD diagnosis. A total of 441 patients consented and provided clinical and genealogical information.

The incidence of EOPD increased 1.7-fold between the years 1995-2006, the mean annual incidence being 3.3/100,000. Fifty-two patients (11.8%) reported an affected first-degree relative. The birthplaces of patients with PD among first-degree relatives were clustered in certain regions in the southwestern and western coastal provinces of Finland and in the eastern province of Savo. Furthermore, the distance between the birthplaces of the patients' parents was smaller for patients, who had first-degree relatives with PD than for patients with no family history of PD.

Our data suggest that the incidence of EOPD is increasing. The birthplaces of patients with PD among first-degree relatives were clustered in certain provinces of Finland suggesting that monogenic forms of PD or genetic susceptibility of PD are present in the population.