F2 and ischemic stroke: In the case-control study done by De Stefano et al. (1998) on 72 patients with a known history of ischemic stroke before the age of 50 years and without any traditional risk factors like hypertension (HTN), diabetes, and hyperlipidemia, it was observed that the mutant prothrombin gene allele frequency (7.6%, 95% confidence interval [CI], 3.3 to 11.9) was significantly higher in cases than in the control group (1.2%; 95% CI, 0.1 to 2.3; P = .0001).