The most common cause of common variable immunodeficiency in adults is a heterogenous immunodeficiency disorder characterized by an increase in recurrent infections, autoimmune phenomena, and neoplastic disease. Most patients present with low IgG levels, but over time, all antibody classes including IgA and IgM may be affected. Most patients have a normal circulating B-cell count but defective synthesis or release of immunoglobulins. Many also exhibit progressive deterioration of cell-mediated (T-cell) immunity. Although unproven, a genetic influence occurs in siblings. Family members are at higher risk of hypogammaglobulinemia, selective IgA deficiency, and autoimmune disease.

Complications include a spruelike syndrome with diarrhea, malabsorption, steatorrhea, and a protein-losing enteropathy. Giardia lamblia GI infection and upper and lower respiratory tract infections as well as recurrent sinusitis also occur. Autoimmune diseases have occurred, and there’s an increased risk of B-cell neoplasms, including lymphomas, gastric carcinomas, and skin cancers, as well.