Genetic variability could be a cause of susceptibility to recurrent stroke in patients with AF: 2 genes (CYP2C9 and VKORC1) may play a role in individual patient response to and efficacy of VKA,30, 31, 32, 33 but no such variability of response is known for DOACs. The gene discussed is CYP2C9; the disease is atrial fibrillation.