We found that nearly half of the patients with FMF had low serum IgG levels; however, the patients with low serum IgG levels did not have frequent URTI. Inocencio et al. reported a case of a patient with FMF with frequent URTI having normal levels of IgG, IgA, and IgM; however, in further Ig subgroup analysis, IgG3 deficiency was detected in this patient, and frequent URTI decreased after starting intravenous immunoglobulin treatment [21]. The gene discussed is IGHG3; the disease is hyperinsulinemic hypoglycemia, familial, 4.