The CHANCE-2 study found that among patients with minor stroke or high-risk TIA who carry CYP2C19 LoF (*2, *3) alleles, ticagrelor plus aspirin demonstrated superior efficacy in preventing stroke recurrence compared with clopidogrel plus aspirin (HR 0.77, 95% CI 0.64 to 0.94, p=0.008).6 The PRINCE study found that in patients who had a stroke or TIA carrying CYP2C19 LoF alleles, early administration of ticagrelor with aspirin reduced platelet hyper-reactivity and lowered the risk of 90-day stroke recurrence (secondary outcome) compared with clopidogrel with aspirin.94 Here, CYP2C19 is linked to stroke disorder.