Selective immunoglobulin A (IgA) deficiency is a primary immune deficiency that occurs when individuals are unable to produce antibodies called immunoglobulin A.
Immunoglobulins (Ig), also called antibodies, play an essential role in the body's immune system. They detect and bind to foreign substances (like bacteria, viruses, fungi, or allergens) that enter the body. This signals other immune cells to destroy the foreign substance. The antibodies are present in the bloodstream or bound to the cell membranes of B-cells or plasma cells.
The IgA antibodies protect body surfaces (like the nose, airway passages, digestive tract, ears, eyes, saliva, tears, and vagina) that are frequently exposed to foreign organisms and substances from outside of the body.
The B-cells of selective IgA patients are unable to switch from making immunoglobulin M (IgM) to IgA. Healthy individuals express IgM on their B-cells. Once the B-cells come into contact with a foreign substance in the body, they become plasma cells and produce other antibodies, including IgA.
The amount of IgA produced is either significantly reduced or absent. Healthy adults have IgA levels that range from 100-400 milligrams/deciliter in the blood, while IgA deficient patients have IgA levels of 7 milligrams/deciliter or less.
The disorder is considered selective because all other antibodies (IgD, IgE, IgG, and IgM) are present at normal or increased levels. Other cells of the immune system, including the T-cells and phagocytic cells, are also produced at normal or increased levels. The T-cells and phagocytic cells are responsible for engulfing (destroying) the foreign substances that are bound to the antibodies.
Selective IgA deficiency appears to be an inherited disease that is passed down from parents to children. However, the exact genes involved remain unknown.
Most patients who have IgA deficiency experience no symptoms. Others may experience mild and recurrent infections of the mucosal surfaces, such as the nose, throat, lungs, and intestines. Ear infections, sinus infections, and pneumonia are most commonly associated with selective IgA deficiency. The frequency of these infections varies among patients.
Selective IgA deficiency is the most common primary immunodeficiency. Primary immunodeficiencies are disorders that occur because part of the body's immune system does not function properly. Unlike secondary immunodeficiencies, which are caused by factors (like viruses or chemotherapy) outside of the immune system, primary immunodeficiencies are caused by intrinsic or genetic defects of the immune system. In general, researchers estimate that selective IgA Deficiency occurs in about one out of 400-2,000 individuals worldwide. However, the incidence varies among people of different races and ethnicities. It occurs most frequently among people of European ancestry. Researchers estimate that one out of 500-700 people from this group develop the disorder.
There is currently no cure for selective IgA deficiency, although many patients do not require any medical treatment. Some patients need to take antibiotics to treat infections commonly associated with the disorder. For unknown reasons, some patients gradually develop normal levels of IgA without treatment.
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