The recent CHANCE-2 clinical trial found that genotype-guided treatment (e.g., identification of CYP2C19 loss of function allele) with ticagrelor and aspirin for minor small vessel strokes or high-risk transient ischemic attack resulted in a higher relative risk reduction of stroke re-occurrence at 90 days compared to using short term clopidogrel and aspirin (106). Here, CYP2C19 is linked to transient ischemic attack.