An apple a day to prevent Parkinson disease

The search for environmental risk factors for Parkinson disease (PD) has yielded few potentially causal associations.¹ The recognition of genetic factors in the etiology of PD,^2,3 in conjunction with PD pathology, has led to the suggestion that PD results from abnormal α-synuclein, its propagation, eventual deposition as Lewy bodies, and subsequent neurodegeneration.^4,5 The potential role of oxidative damage in this process, possibly through mitochondrial insult by environmental toxins,⁶ has provided additional leads for the effects of environmental factors, notably pesticides.⁷ The search for environmental factors is made more difficult as the pathology is likely to have begun many years prior to the diagnosis of PD.¹

The rarity of PD,⁸ about 100 per 100,000 in the oldest age groups, presents a challenge for epidemiologic study. A longitudinal cohort study, starting with unaffected persons, requires large numbers and long follow-up to accrue an adequate number of cases for analysis. Another key requirement is reliable and accurate measurement of the hypothesized exposures, at baseline and throughout the study. Further, because “clinical incidence” may occur many years after pathology …