A key question was if, and to what degree, GRIN2A_rs4998386 genotype modifies the effect of coffee on PD risk (Table 3): Within heavy drinkers, PD risk was 58% lower (OR = 0.42, P = 2×10−6) for rs4998386_TC, and 81% lower (OR = 0.19, P = 0.05) for rs4998386_TT genotype than rs4998386_CC; whereas in light drinkers genotype had no effect on risk. Here, GRIN2A is linked to Parkinson disease.