Analysis of Ig subclass deficiency: First reported case of IgG2, IgG4, and IgA deficiency caused by deletion of Cα1, ψCγ, Cγ2, Cγ4, and Cε in a Mongoloid patient

Abstract Background: The cause of Ig class or subclass deficiencies has been unclear except for IgH gene deletions and a homozygous 1-base insertion (1793insG) in Cγ2 exon 4 of IgG2 deficiency. In addition, there are no reports that IgH gene deletions are found in patients who are Mongoloid (a category that includes most of the people of Asia, such as the Japanese, Chinese, Indonesians and Malaysians). Objective: To investigate the cause of Ig subclass deficiency, we extensively investigated 4 Japanese patients with low serum IgG2 levels. Patient 1 was a 23-month-old girl whose serum IgG2, IgG4, and IgA levels were under the detection limits; she also had idiopathic thrombocytopenic purpura. Patient 2 was a 5-year-old boy whose serum IgG2 level was under the detection limit. Patient 3 was a 14-month-old boy whose serum IgG2 and IgG4 levels were under the detection limits. Patient 4 was 3-year-old girl whose IgG2 level was low and whose IgA level was under the detection limit. Methods: DNA was extracted from neutrophils, and Southern blot analysis was performed. Results: Southern blot analysis revealed that patient 1 had lost the Cα1, ψCγ, Cγ2 , Cγ4, and Ce genes and was a homozygous carrier of the deletion described above. Her mother was of the heterozygous genotype. DNA from patients 2, 3, and 4 revealed no deletions in comparison with control DNA. Conclusion: This is a report of the first case of a Mongoloid in whom IgG2, IgG4, and IgA deficiency was caused by deletion of Cα1, ψCγ, Cγ2 , Cγ4, and Ce. Our finding contributes to investigations of Ig subclass deficiency. (J Allergy Clin Immunol 2001;108:602-6.)