In the substudy of the Clopidogrel in High-Risk Patients with Acute Non-disabling Cerebrovascular Events (CHANCE) trial, the combination of clopidogrel and aspirin did not reduce the risk of a new stroke in the carriers of the CYP2C19 loss-of-function alleles which are especially prevalent in East Asians.[12, 27] Since the antiplatelet effect of ticlopidine is known to be unaffected by the loss of function of CYP2C19,[14] ticlopidine needs to be reevaluated regarding the usefulness for patients with clopidogrel resistance in this era of precision medicine. This evidence concerns the gene CYP2C19 and stroke disorder.