Taken together, preclinical mechanistic data and human metabolomics support a preventive role for paraxanthine in PD, particularly in genetically predisposed populations; nonetheless, it requires randomized, genotype-stratified clinical trials and focused mechanistic work (e.g., paraxanthine treatment in LRRK2 and GBA1 cellular/animal models) to validate paraxanthine as a therapeutic candidate or biomarker. This evidence concerns the gene LRRK2 and Parkinson disease.