Selective immunoglobulin A deficiency

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Overview
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.

Epidemiology
Prevalence varies by population, but is on the order of 1 in 500 to 1 in 800 people, making it relatively common for a genetic disease.

Pathophysiology
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.

Symptoms and diagnosis
People with selective IgA deficiency are asymptomatic, or have increased frequency of infections such as sinusitis. These infections are generally mild and would not usually lead to an in-depth workup except when unusually frequent. 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.

Treatment
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 (except for bone marrow transplant, which is far too drastic to be used). In the absence of normal IgA, the body can develop an immune response against IgA itself (anti-IgA antibodies), which can lead to severe reactions including anaphylaxis to blood transfusions or intravenous immunoglobulin. Therefore, people known to have this condition must notify their healthcare providers. Since this is a genetic condition, careful discussion should be undertaken prior to having children.

Prognosis
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.