The most important of this group are factor V gene Leiden mutation G1691A (FVL), prothrombin G20210 (FII), homozygosity for the thermolabile of methyltetrahydrofolate reductase deficiency C677T (MTHFR), antithrombin deficiency, protein C deficiency, and protein S deficiency [1–7]. The gene discussed is F2; the disease is hyperinsulinemic hypoglycemia, familial, 4.