GRIN2A and Parkinson disease: To summarize, there are currently nine datasets in the literature that have examined PD risk as a function of GRIN2A and coffee use (classified as ever/never or by dose): four have statistically significant evidence in favor of GRIN2A being a modifier of PD–coffee association (NGRC, PAGE, Sweden, and Denmark) and three show a consistent trend towards interaction (HIHG, PEG, and France).