Lack of replication of the GRIN2A-by-coffee interaction in Parkinson disease

The etiology of Parkinson disease (PD) involves both genetic susceptibility and environmental exposures. In particular, coffee consumption is inversely associated with PD but the mechanisms underlying this intriguing association are unknown. According to a recent genome-wide gene–environment interaction study, the inverse coffee–PD association was two times stronger among carriers of the T allele of SNP rs4998386 in gene GRIN2A than in homozygotes for the C allele. We attempted to replicate this result in a similarly sized pooled analysis of 2,289 cases and 2,809 controls from four independent studies (Denmark, France, Seattle-United States (US), and Rochester-US) with detailed caffeinated coffee consumption data and rs4998386 genotypes. Using a variety of definitions of coffee drinking and statistical modeling techniques, we failed to replicate this interaction. Notably, whereas in the original study there was an association between rs4998386 and coffee consumption among controls, but not among cases, none of the datasets analyzed here indicated an association between rs4998386 and coffee consumption among controls. Based on large, well-characterized datasets independent from the original study, our results are not in favor of an interaction between caffeinated coffee consumption and rs4998386 for PD risk and suggest that the original finding may have been driven by an association of coffee consumption with rs4998386 in controls. The next years will likely see an increasing number of papers examining gene–environment interactions at the genome-wide level, which poses important methodological challenges. Our findings underline the need for a careful assessment of the findings of such studies