Based on the diagnosis of homocystinuria type III caused by MTHFR deficiency, betaine therapy was continued at the dosage of 300 mg/kg/day, which raised plasma Met levels to 14–40 μmol/L, and reduced plasma tHcy concentrations to 50–110 μmol/L. This evidence concerns the gene MTHFR and hyperinsulinemic hypoglycemia, familial, 4.