All six children (P1–P6) with CBS deficiency had significantly elevated plasma tHcy (104.7–227.2 μmol/L vs. the normal range of 0–15 μmol/L) and Met levels (176–438 μmol/L vs. the normal range of 8–50 μmol/L). The gene discussed is CBS; the disease is hyperinsulinemic hypoglycemia, familial, 4.