The exact cause of IgA deficiency is unknown. However, several theories exist. (See What causes IgA deficiency?)

Mild to severe chronic pulmonary disease (such as asthma) and chronic diarrheal diseases commonly result from IgA deficiency. A patient who develops significant levels of antibodies to IgA may have a severe anaphylactic reaction if he receives a transfusion of normal blood or blood products. Other complications include cancer, pneumonia, uncontrolled allergies, and complications from related disorders.

Some IgA-deficient patients have no signs or symptoms. Among those who do develop symptoms, the most common complaint is chronic sinopulmonary infection. The patient may also complain of symptoms of other disorders. These include respiratory allergy, often triggered by infection; GI tract diseases, such as spruelike disease, ulcerative colitis, and regional enteritis; autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, chronic hepatitis, and immunohemolytic anemia; and malignant tumors, such as squamous cell carcinoma of the lungs, reticulum cell sarcoma, and thymoma.

Hematologic analyses of the IgA-deficient patient show serum IgA levels below 5 mg/dl. Although the patient usually has no IgA in his secretions, such levels are occasionally normal. The patient has normal immunoglobulin E levels; his IgM levels may be normal or elevated in serum and secretions. Normally absent low molecular weight IgM may be present. Hematocrit may be decreased because of anemia. Coombs’ test results may be positive, and pulmonary test results may be abnormal.