In contrast to the above studies, Kahn et al., in a multicenter, prospective study of 145 patients with an unprovoked episode of proximal DVT, found that the presence of factor V Leiden or the prothrombin G20210A mutation was an independent predictor of both a lower risk (OR 0.33, 95% CI 0.15–0.73, P = 0.006) and reduced severity (1.6 point decrease (95% CI 0.06–3.2, P = 0.045) in Villalta score if thrombophilia was present) of PTS [31]. The gene discussed is F2; the disease is Rare hereditary thrombophilia.