GALT activity was 12.6 U/dl blood, with the NBS cut-off <2 U/dl; total galactose in our patient was 1000 μmol/L, with the upper limit of normal (ULN) for GALT deficiency being 1350 μmol/L and ULN for GALK1 deficiency 2100 μmol/L (if combined with normal GALT activity) (Table 1). The gene discussed is GALT; the disease is hyperinsulinemic hypoglycemia, familial, 4.