Thirty-three patients were screened for thrombophilia; 21 of these with positive findings hereunder 14 with a severe thrombophilia (six with protein S deficiency, two with protein C deficiency, three with homozygous factor V Leiden polymorphism, two with antithrombin deficiency, and one with a combination of prothrombin and heterozygous factor V Leiden polymorphisms). The gene discussed is PROS1; the disease is hyperinsulinemic hypoglycemia, familial, 4.