IgAdeficient

Selective IgA deficiency (sIgAD) is the most common primary immunodeficiency, defined by very low or absent serum IgA with normal levels of IgG and IgM and intact overall immune function. Many people with sIgAD are asymptomatic and discovered incidentally during testing for other conditions.

Population prevalence ranges widely, estimated from about 1 in 200 to 1 in 700 in different groups. Symptoms, when present, include recurrent respiratory tract infections, sinusitis, bronchitis, chronic diarrhea, malabsorption, and allergies or autoimmune diseases. Some individuals have anaphylactic reactions to blood products containing IgA due to anti-IgA antibodies.

Most cases arise sporadically; familial tendencies exist. The exact mechanism is not fully understood; impaired production of mucosal IgA and dysregulation of B-cell maturation are thought to contribute. sIgAD is associated with higher frequency of celiac disease, autoimmune thyroid disease, rheumatoid arthritis, systemic lupus erythematosus, atopy, and asthma.

Diagnosis requires laboratory evidence of persistently low serum IgA with normal IgG and IgM on at least two occasions and after ruling out secondary causes such as protein loss, nephrotic syndrome, or acute infections. Measuring anti-IgA antibodies may be relevant for transfusion planning.

Management is supportive: vaccination against common pathogens (notably pneumococcus and influenza) and treatment of infections according to standard guidelines. There is no curative therapy for sIgAD. Individuals with anti-IgA antibodies should avoid IgA-containing products; IVIG may pose risk and is used with caution if needed. Prognosis is generally good; most individuals lead normal lives, though they may have recurrent infections or autoimmune conditions.