GRIN2A was the most significant result in GWAS in heavy coffee-drinkers.

See also Figure 2. Standard GWAS (PD-SNP association, no interaction) was conducted among heavy and light coffee drinkers separately. GRIN2A was most notable only among heavy coffee drinkers. Odds ratio (OR) of 0.41–0.46 suggests that among heavy coffee drinkers, who are known to be at reduced risk for PD, GRIN2A genotypes further modifies risk by over two-fold. As expected due to interaction, GRIN2A did not have a significant effect in light coffee drinkers. This is in contrast to known PD genes which exhibited their effects on PD risk regardless of coffee consumption.