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Primary immunologic deficiency diseases are estimated to affect 1 in 4000 individuals; many are genetically determined and present in childhood. Nonetheless, several important immunodeficiency disorders present in adulthood, most notably the antibody deficiency syndromes: selective IgA deficiency, common variable immunodeficiency, and specific (functional) antibody deficiency (Table 20–14). Antibody deficiency predisposes patients to recurrent infections, particularly of the respiratory tract, including refractory chronic rhinosinusitis, bronchitis, pneumonia, and bronchiectasis. Patients are most susceptible to infections with encapsulated bacteria (eg, Haemophilus influenzae type b, Streptococcus pneumoniae, Neisseria meningitides). However, any part of the innate or adaptive immune system can be defective and results in infections with different spectra of organisms.
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1. SELECTIVE IgA DEFICIENCY
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Selective IgA deficiency is the most common primary immunodeficiency disorder and is characterized by undetectable serum IgA levels (lower than 7 mg/dL) with normal levels of IgG and IgM; its prevalence is about 1 in 500 individuals (Table 20–14). Most affected individuals are asymptomatic. A minority of patients have recurrent infections such as sinusitis, otitis, and bronchitis. Selective IgA deficiency can be associated with atopic diseases and autoimmune disorders, including Graves disease, SLE, juvenile rheumatoid arthritis, type 1 diabetes mellitus, and celiac disease.
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Some individuals with undetectable levels of serum IgA may have high titers of anti-IgA antibodies and are at risk for anaphylactic reactions to ...