GRIN2A and Parkinson disease: They investigated gene-environment interaction in PD, namely, caffeinated-coffee intake and GRIN2A, the gene encodes for a subunit of the NMDA-glutamate-receptor, and it was found that carriers of GRIN2A_rs4998386-T allele had a lower risk of PD than carriers of rs4998386-CC genotype among heavy coffee drinkers.