Systemic lupus erythematosus (SLE) was observed in a 7-year-old boy with IgG2 and IgG4 subclass deficiencies who had been treated with immunoglobulin (100-200 mg/kg/4 weeks) since 2 years of age. The mother and the half-brother displayed the same deficiency. Serum IgG mainly consisted of IgG1 (98.9%) during the acute phase of SLE due to transient IgG3 deficiency. While he had no common manifestations of SLE such as arthritis or nephropathy, he developed cardiac tamponade due to massive pericardial effusion.
Conclusion: The clinical features of SLE in the present case such as the development of cardiac tamponade and the absence of renal involvement may result from the markedly imbalanced IgG subclass distribution among auto-antibodies.