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Primary immunologic deficiency diseases are estimated to affect 1 in 4000 individuals; most are genetically determined and present in early childhood. Nonetheless, several important immunodeficiency disorders present in adulthood, most notably the antibody deficiency syndromes: selective IgA deficiency, common variable immunodeficiency (CVID), and specific (functional) antibody deficiency (Table 20–14). Antibody deficiency predisposes patients to recurrent serious bacterial 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, which results in infections with different spectra of organisms depending on the severity of the immune defect.
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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 (Table 20–14); its prevalence is about 1 in 500 individuals, with a higher prevalence in White persons. Most affected individuals are asymptomatic. A minority of patients have recurrent bacterial infections such as sinusitis, otitis, bronchitis, and GI infections. Selective IgA deficiency can be associated with an increased incidence of atopic and autoimmune disorders, including Graves disease, SLE, juvenile rheumatoid arthritis, type 1 diabetes mellitus, and celiac disease.
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