Parkinson's disease, smoking and family history

There is growing evidence that both genetic and environmental factors play a role in the etiology of Parkinson's disease (PD). The hypothesis of an interaction between genetic and environmental risk factors has been little explored, and never using a population-based case-control study design. Our objective was to investigate the possible interaction between smoking and family history in the etiology of PD, as a part of a collaborative population-based case-control study. We included 149 nondemented PD patients ascertained in three European prevalence surveys using a two-phase design. Each patient was matched by age (±2 years), gender, and center to three controls drawn from the same populations (n=375). Presence of PD among first-degree relatives and smoking history were assessed through an interview for 127 cased and 306 controls. In the overall sample we found suggestive evidence that family history and eversmoking interact in determining the risk of PD (P=0.09), with individuals exposed to both risk factors having the highest risk (OR=10.0; 95% CI=2.0–49.6). Analyses were repeated after stratification into two age-groups (cutoff: 75 years). In older patients, the joint exposure to both risk factors was associated with a significant increase in the risk of PD (OR=17.6; 95% CI=1.9–160.5). Among younger subjects, the OR for joint exposure was not significant. In conclusion, our findings suggest that smoking and family history interact synergistically on a multiplicative scale in determining the risk of PD in individuals older than 75 years. Received: 28 January 2000 / Received in revised form: 1 May 2000 / Accepted: 28 May 2000