IgG subclass deficiency is one of the more minor forms of immunodeficiency disease, and most patients with this condition who are optimally managed can expect a normal life span. The typical presentation is as illustrated in the question stem. The deficiency may involve either or both IgG2 and IgG3 with or without IgG4 deficiency. (IgG1 is the major form, and its deficiency leads to a deficiency of total IgG, and so, by definition, it is not considered a "subclass" deficiency.) A potentially clinically impoant point is that some patients with IgG2 deficiency also have IgA deficiency and may develop anaphylaxis if given IgA-containing blood products. C3 deficiency tends to produce pyogenic infections. C4 deficiency tends to produce an SLE-like syndrome. IgE deficiency can be seen in some incomplete antibody deficiency syndromes, but is usually not clinically significant. Ref: Hellmann D.B., Imboden J.B. (2013). Chapter 20. Rheumatologic & Immunologic Disorders. In M.A. Papadakis, S.J. McPhee, M.W. Rabow, T.G. Berger (Eds), CURRENT Medical Diagnosis & Treatment 2014