ESID working criteria for clinical diagnosis of IEIs are even more stringent, requiring, along with IgM deficiency (<2 standard deviations [SD] below age-matched mean), preserved IgG and IgA, the presence of infections, normal concentrations of IgG subclasses and vaccination responses, and exclusion of T-cell defects [4]. The gene discussed is CD40LG; the disease is hyperinsulinemic hypoglycemia, familial, 4.