"Parkinson's disease (PD) is the most common cause of parkinsonism and neurodegenerative disorder after Alzheimer's disease. It is caused by the progressive loss of dopaminergic neurons of the substantia nigra pars compacta which is accompanied by the presence of Lewy bodies. Its diagnosis is clinical and there is a risk of misdiagnosis with other causes of parkinsonism. PD is exceptional before age 50, and its frequency increases with age, with an incidence of about 1 to 5 per 1000 person-years after age 60. PD has consistently been shown to be about 1.5 times more common in men than in women. PD is considered as a multifactorial disease resulting in the majority of cases of multiple factors. Monogenic PD occurs in a minority of patients, but several small-effects susceptibility genes are implicated in sporadic forms. Heritability is however small, and it is generally considered that environmental factors are involved in PD aetiology."

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