Among hereditary thrombophilias, factor V Leiden (prevalence ~3%-8%) and prothrombin G20210A mutation (~1%-3%) are the most common, whereas PAI-1 4G/4G polymorphism and MTHFR mutations are considered less frequent and are typically tested when common thrombophilic disorders are excluded [15,33-35]. The gene discussed is MTHFR; the disease is Rare hereditary thrombophilia.