|Selective immunoglobulin A deficiency|
|Classification and external resources|
The dimeric IgA molecule. 1 H-chain, 2 L-chain, 3 J-chain, 4 secretory component
Selective immunoglobulin A (IgA) deficiency is a relatively mild genetic immunodeficiency. People with this deficiency lack immunoglobulin A (IgA), a type of antibody that protects against infections of the mucous membranes lining the mouth, airways, and digestive tract. It is defined as an undetectable serum IgA level in the presence of normal serum levels of IgG and IgM. It is the most common of the primary antibody deficiencies.
Prevalence varies by population, but is on the order of up to 1 in 333 people,  making it relatively common for a genetic disease.
It is more common in males than in females.
There is an inherited inability to produce immunoglobulin A (IgA), a part of the body's defenses against infection at the body's surfaces (mainly the surfaces of the respiratory and digestive systems). As a result, bacteria at these locations are somewhat more able to cause disease.
People with selective IgA deficiency are usually asymptomatic, but can have increased frequency of infections, particularly in the respiratory, digestive and genitourinary systems, for example, sinusitis and urinary tract infections. These infections are generally mild and would not usually lead to an in-depth workup except when unusually frequent. They may present with severe reactions including anaphylaxis to blood transfusions or intravenous immunoglobulin due to the presence of IgA in these blood products. When suspected, the diagnosis can be confirmed by laboratory measurement of IgA level in the blood. Patients have an increased susceptibility to pneumonia and recurrent episodes of other respiratory infections and a higher risk of developing autoimmune diseases in middle age.
The treatment consists of identification of comorbid conditions, preventive measures to reduce the risk of infection, and prompt and effective treatment of infections. Infections in an IgA-deficient person are treated as usual (i.e., with antibiotics). There is no treatment for the underlying disorder.
Prognosis is excellent, although there is an association with autoimmune disease. Of note, selective IgA deficiency can complicate the diagnosis of one such condition, celiac disease, as the deficiency masks the high levels of certain IgA antibodies usually seen in celiac disease.