The most frequent causes of inherited thrombophilia in the general population are the prothrombin G20210A polymorphismfactor and V Leiden, a genetic polymorphism that makes activated factor V relatively resistant to degradation by activated protein C. Less relevant is the C677T polymorphism of methylenetetrahydrofolate reductase (MTHFR) gene that favors hyperhomocysteinemia. The gene discussed is MTHFR; the disease is hyperhomocysteinemia.