Selective immunoglobulin A deficiency (sIgAD) is the most common of the primary antibody deficiencies, affecting up to 1 in 600 people. It is not usually associated with bacterial infections but may be associated with autoimmune or allergic diseases. The genetic causes of sIgAD are unclear. People affected have very low or absent levels of one type of antibody, called immunoglobulin A (IgA), but produce protective antibodies of the other types of immunoglobulin (IgG and IgM). This could be why many people with sIgAD may appear healthy.
IgA works to protect body surfaces, such as the respiratory tract and gut that come into contact with outside organisms, so if someone has infections, these are the most common sites of infection. Such individuals may have a partial IgG deficiency despite apparently normal IgG levels in the blood, and so should be investigated in an immunology clinic.
People with IgA deficiency may have allergies (e.g. allergic asthma) or an increased tendency to develop autoimmune conditions, where the immune system attacks itself, and this may result in conditions such as coeliac disease, which affects about 10 per cent of IgA-deficient patients. No specific treatment is required for sIgAD. Infections should be treated promptly with antibiotics.