Age at onset of Parkinson's disease among subjects occupationally exposed to metals and pesticides

Studies suggest that genetic and environmental factors interact to influence the progression of idiopathic Parkinson's disease (PD). Family history of PD is a risk factor for the disease. Genetic factors have been associated with early and late onset forms of PD. Exposure to certain metals (e.g., manganese) and pesticides such as paraquat has been associated with parkinsonism, but no consistent association has been made between exposure to these chemicals and the prevalence or incidence of idiopathic PD. A younger age at onset of PD has recently been reported to be associated with occupational exposures to manganese and hydrocarbon solvents suggesting that exposure to neurotoxic chemicals may hasten the progression of idiopathic PD. To elucidate on the role of occupational exposure to metals and pesticides in the progression of idiopathic PD while minimizing the effect of heritable genetic factors which may also influence age at onset, we evaluated age at onset of PD among 58 subjects with no family history of the disease. Independent Samples t-Test revealed that subjects with occupational exposure to metals and/or pesticides (n = 36) were significantly (p = .013) younger than unexposed controls (n = 22). Subjects were then divided into three groups [high (n = 18), low (n = 18), and unexposed (n = 22)] to ascertain if duration of exposure further influenced age at onset of PD. Data was analyzed using one-way ANOVA with Tukey's Honestly Significant Difference test for post hoc analysis. Subjects in the high exposure group were significantly (p = .0121) younger (mean age: 50.33 years) than unexposed subjects (mean age: 60.45 years). Subjects in the low exposure group were younger than the unexposed subjects (mean age: 56 years) but this difference did not reach statistical significance (p = .207). Although the majority of exposed subjects were male, gender did not significantly (p = .572) influence age at onset. These results suggest chronic exposure to metals and pesticides is associated with a younger age at onset of PD among patients with no family history of the disease and that duration of exposure is an important factor in this effect.