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Abstract
The causes of Parkinson's disease (PD), the second most common neurodegenerative disorder,
are still largely unknown. Current thinking is that major gene mutations cause only
a small proportion of all cases and that in most cases, non-genetic factors play a
part, probably in interaction with susceptibility genes. Numerous epidemiological
studies have been done to identify such non-genetic risk factors, but most were small
and methodologically limited. Larger, well-designed prospective cohort studies have
only recently reached a stage at which they have enough incident patients and person-years
of follow-up to investigate possible risk factors and their interactions. In this
article, we review what is known about the prevalence, incidence, risk factors, and
prognosis of PD from epidemiological studies.