Is there seasonal variation in risk of Parkinson's disease?

Recent studies suggest that, for many adult-onset neurological diseases, persons born at a certain time of year are at higher risk of the disease. Small-scale studies have suggested that persons born in the spring may be at higher risk of developing Parkinson's disease (PD) late in life. There have also been suggestions that there are clusters of PD birth dates in the years of major influenza pandemics. To determine whether there is any seasonal variation in the birth dates of PD patients, we examined birth dates of 8,168 PD patients collected from subspecialty movement disorder clinics across Canada. Patterns of seasonality of birth were examined and compared with the general Canadian population. In addition, we compared counts of patients born in the years of major influenza pandemics with the number born in the surrounding years. We found no evidence of systematic seasonal variation in PD incidence by birth date, or of clustering of birth dates during influenza pandemic years in PD patients.