Inherited thrombophilia related to clotting inhibitors deficiency (i.e. protein C, Protein S and Antithrombin III deficiencies) [11,12] has been rarely reported such as clotting XII deficiency [13], while data on the role of factor V Leiden are still matter of discussion [14-18] and few data are available on the role of prothrombin A20210G gene polymorphism in RVO pathogenesis [17,19]. The gene discussed is SERPINC1; the disease is hyperinsulinemic hypoglycemia, familial, 4.