Unfortunately, homozygous UNG deficiency is an exceptionally rare disease (76), and the national reference centers for immunodeficiency of The Netherlands (Erasmus Medical Center Rotterdam), France (Hôpital Necker-Enfants Malades, Paris), and Germany (University Medical Center Freiburg) do not have additional UNG-deficient patients in their registries and were also unable to provide us material from the three originally described patients (77). The gene discussed is UNG; the disease is hyperinsulinemic hypoglycemia, familial, 4.