In particular, CLOCK and PER2 were negatively associated with PM2.5 exposure in the 4 days before the stroke event, (P4days = 0.018 for CLOCK and P4days = 0.032 for PER2), while CRY1 and NPAS2 were positively associated with the PM2.5 exposure in the 5 days before the stroke event (P5days = 0.046 for CRY1 and P5days = 0.009 for NPAS2). This evidence concerns the gene CLOCK and Stroke.