The genetic subgroup analysis of the CHANCE study revealed that patients carrying CYP2C19 LoF alleles did not show a significant reduction in stroke recurrence when treated with clopidogrel plus aspirin compared with aspirin alone.93 There was an interaction between the treatment group and genetic variation. 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 This evidence concerns the gene CYP2C19 and transient ischemic attack.