Selective IgA deficiency
What is IgA?
IgA is immunoglobulin type A, a protein produced in the bone marrow by plasma cells. IgA is found in mucous membrane secretions, including vaginal secretions, semen, tears, saliva, colostrum and secretions from the respiratory and gastrointestinal tract.
What is selective IgA deficiency?
Patients with selective IgA deficiency have normal levels of all immunoglobulins except for IgA. Other component of the immune system such as phagocytes, complement proteins and T cells are normal.
Selective IgA deficiency is one of the most common primary immunodeficiency diseases. It occurs in the Caucasian population in 1 in every 500–700 births. It is much less common in other races.
What causes selective IgA deficiency?
The exact cause of selective IgA deficiency is unknown. Genetic inheritance is responsible for around a quarter of all cases. Drug-induced IgA deficiency may also occur.
What are the signs and symptoms of selective IgA deficiency?
Patients with selective IgA deficiency may be asymptomatic, mildly ill, or seriously ill (25–50%). Their presentations fall into three broad categories:
- Frequent infections. These can include sinusitis, bronchitis, pneumonia, otitis media, and bronchiectasis secondary to multiple respiratory infections, oral infections and conjunctivitis. They may also present with gastrointestinal conditions such as ulcerative colitis, Crohn disease and chronic diarrhoea.
- Autoimmune disease. Autoimmune diseases occur in around 25–33% of patients with selective IgA deficiency. The most frequent are systemic lupus erythematosus, rheumatoid arthritis and thrombocytopaenic purpura.
- Allergies and asthma. 10–15% of patients with selective IgA deficiency will also present with a broad range of allergies and/or otherwise unexplained asthma.
How is selective IgA deficiency diagnosed?
Diagnosis of selective IgA deficiency is based on:
- Patient symptoms, including history of recurrent infections, chronic diarrhoea and autoimmune diseases
- Quantitative immunoglobulin studies, which generally reveal low IgA and normal levels of other immunoglobulins (though some patients may also have low IgG levels)
- Additional testing, which may include a complete blood count, thyroid, lung and kidney function tests, urinalysis, tests to determine the presence of autoantibodies and nutrient absorption tests
What is the treatment for selective IgA deficiency?
There is no cure for selective IgA deficiency and it is currently impossible to treat it with immunoglobulin replacement therapy. Treatment is aimed at specific signs and symptoms such as:
- Infections. Antibiotics—sometimes prophylactic—are used for infection control.
- Low concurrent IgG levels. These can be corrected with immunoglobulin replacement therapy.
- Autoimmune disorders. These may be treated with systemic corticosteroids and other drugs to reduce inflammation or biologics (monoclonal antibodies). Hormone replacement therapy may also be used in case of endocrine system involvement.