Occupational and environmental risk factors for Parkinson's disease

Abstract

The etiology of Parkinson's disease (PD) remains obscure. Current research suggests that a variety of occupational and environmental risk factors may be linked to PD. This paper provides an overview of major occupational and environmental factors that have been associated with the development of PD and tries to assess current thinking about these factors and their possible mechanisms of operation. While clear links to rural living, dietary factors, exposure to metals, head injury, and exposure to infectious diseases during childhood have not been established, there is general agreement that smoking and exposure to pesticides affect the probability of developing PD.

Introduction

Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by neuronal cell loss in the substantia nigra and subsequently reduced secretion of dopamine. As the prevalence and incidence of PD increase with age [1], [2], [3], the number of PD patients will dramatically increase in the coming century as the world population aged [4].

Despite intensive research during the past decades, the cause or causes of PD remain uncertain. Several etiologies such as heredity [5], head injury [6], infection [7], neurotoxin [8], [9], environmental factor [10], and gene expression [11], as well as multifactorial theories of geno-environment interaction [12], [13], [14], [15] have been proposed. Although a positive family history has been implicated as a significant risk factor for PD in several epidemiological studies [16], familial PD is not necessarily indicative of a genetic cause as families with a family history of PD may well share the same environment. While studies of several large kindreds with PD or a parkinsonian syndrome revealed that some genes such as α-synuclein and parkin may play a role in the cause of parkinsonism, such genes are not responsible for sporadic cases of PD [17]. The largest twin study showed that genetic factors appear to be significant only when disease begins at or before 50 years of age [18].

Several studies have reviewed the current understanding about epidemiological and genetic risk factors [17], [19], [20], [21], but to date there have not been many articles presenting a broad based assessment of occupational and environmental risk factors such as xenobiotics, lifestyle (e.g. rural living, farming activities, and well water drinking), exposure to pesticides and metals, dietary factors and antioxidants, trauma and head injury, infectious diseases, and smoking. The purpose of this paper is to review and discuss current research into the possibility of occupational and environmental risk factors contributing to the development of PD.