The exact cause of selective IgA deficiency remains unknown. In some patients, there appears to be a history of familial occurrence. This suggests the disorder may be inherited as either an autosomal dominant or recessive trait.
In order to inherit the disorder as an autosomal recessive disorder, one mutated gene from each parent must be inherited. Individuals who only have one mutated gene and do not express symptoms are called carriers. Carriers have a 50% chance of passing the abnormal gene to each of their children. If both parents are carriers, there is a 25% chance that each of their children will inherit the disorder and a 50% chance that each of their children will be a carrier.
In order to inherit the disorder as an autosomal dominant disorder, the child only needs to inherit one mutated gene. Individuals who have the disorder have a 50% chance of passing the disorder on to each of their children.
Selective IgA deficiency also occurs frequently in immediate relatives of patients who have a condition called common variable immunodeficiency (CVID).
Selective IgA deficiency has also been associated with ataxia-telangiectasia (degenerative disease that causes a loss of muscle control and reddening of the skin), frequent respiratory (lung) infections, and immunodeficiencies.
Most patients who have selective immunoglobulin A (IgA) deficiency experience no symptoms. Because the IgA antibodies protect body surfaces that are frequently exposed to foreign substances from outside of the body (like the nose, throat, lungs, and intestines), these patients may suffer from recurrent infections of these surfaces. Ear infections, sinus infections, and pneumonia are the most common infections that occur in symptomatic patients. However, most infections are generally mild.
Allergies, which range from mild to severe, are also common among patients. Allergic asthma and food allergies are especially common. Allergic asthma causes difficulty breathing, wheezing, and coughing, and may be less responsive to drug treatment than is typically expected in healthy patients. Food allergies may cause symptoms like abdominal cramps and diarrhea.
General: A diagnosis of selective immunoglobulin A (IgA) deficiency can be made after low or absent levels of IgA are observed in a patient. Healthy adults typically have IgA levels of 100-400 milligrams/deciliter in the blood. The IgA will either be absent or below 7 milligrams/deciliter in patients who have selective IgA deficiency. Immunoglobulin G (IgG) and immunoglobulin M (IgM) will be present in normal levels.
Serum immunoelectrophoresis: A serum immunoelectrophoresis may be performed to determine whether a patient has selective IgA deficiency. During the procedure, a sample of the patient's blood is analyzed for the presence of immunoglobulins. The antibodies are separated from the blood sample during a process called electrophoresis. Based on the antigen-antibody interaction, it can be determined whether or not the patient has IgA antibodies.
Nephelometry: Nephelometry is another test that is often used to determine whether a patient has selective IgA deficiency. During the procedure, a sample of blood is taken from the patient. Anti-immunoglobulins are added to the blood sample. A medical instrument then measures the movement of particles in a substance that is caused by the interaction between immunoglobulins and anti-immunoglobulins. The test quickly and accurately measures the amount of IgM, IgG, and IgA in the patient's blood.
Infections and allergic asthma, which are often associated with selective IgA deficiency, may be less responsive to antibiotics than is typically expected in healthy patients. Ear infections may cause complications such as hearing loss (short-term or long-term) or ruptured ear drum. Sinusitis may cause complications such as acute asthma, meningitis or vision loss. Pneumonia may cause complications like fluid in the lungs or abscesses (pus-filled cavities) in the lungs.
If IgA is completely absent, the patient may develop an autoimmune disorder. If this occurs, the patient's immune system creates antibodies to IgA. Once these antibodies are made, severe allergic reactions, including anaphylaxis (life-threatening allergic reaction) may occur if the patient receives a blood transfusion or blood products containing IgA (like intravenous immune globulin). This is because the immune cells mistake the IgA as an antigen (foreign substance), and they will attack the immunoglobulin.