Parkinson's disease: Is there a strong environmental contribution?

Parkinson's disease (PD) is the most common cause of the parkinsonian syndromes and the most frequent neurodegenerative disease after Alzheimer's disease. Only a minority of PD cases is due to a single factor, in particular a genetic mutation. In the large majority of cases, it is considered that PD is a complex or multifactorial disease that results from the effect of multiple risk or protective factors, either genetic or environmental, and, possibly, from their interaction. Epidemiological studies, through a variety of approaches, have brought important evidence in favour of the contribution of environmental factors to the etiology of PD. In this review, we will present current evidence by focusing on specific illustrative examples.