Hereditary defects related to thrombosis, relatively recently discovered, include the G1691A mutation in the factor V gene, the G20210A mutation in the prothrombin gene, the C677T mutation and the A1298C mutation in methylenetetrahydrofolate reductase (MTHFR) gene, antithrombin III, protein C and protein S deficiency. Here, MTHFR is linked to hyperinsulinemic hypoglycemia, familial, 4.