Molecular Basis of IgG2 Deficiency Molecular Basis of Selective IgG2 Deficiency The Mutated Membrane-bound Form of ␥ 2 Heavy Chain Caused Complete IgG2 Deficiency in Two Japanese Siblings

Abstract Patients with IgG2 deficiency have recurrent sinopulmonary infections caused by Pneumococcus and Hemophilus . Hereditary and selective IgG2 deficiency was suspected in two Japanese siblings whose serum IgG2 levels were under detection limits, while other serum levels of immunoglobulin subclasses were within normal ranges. Expression level of spontaneous germline C ␥ 2 transcript was normal, but that of the spontaneous mature C ␥ 2 transcript was greatly decreased in the patients' PBMCs, suggesting the presence of a defect at or after the class switch to C ␥ 2. We sequenced the C ␥ 2 gene region, and in both patients a homozygous one-base insertio