Ketonemia was absent and a glucagon test was compatible with hyperinsulinism: at a blood glucose of 27 mg/dl (reference value 76–110), plasma insulin was 10 microU/ml (3–25), peptide C 2.71 ng/ml (1.10–4.40), cortisol 9.39 μg/dl (6.20–19.40), and growth hormone 13 ng/ml (0.06–5). The gene discussed is GCG; the disease is hyperinsulinism.