Common variable immunodeficiency is best described as which of the following?

• A. Hyper-IgM syndrome
• B. Severe combined immunodeficiency
• C. IgA deficiency
• D. Common variable immunodeficiency

Answer: (D)

Common variable immunodeficiency represents a defect in B cell maturation and antibody production, leading to low levels of immunoglobulins—especially IgG—with poor antibody responses to vaccines. This results in recurrent bacterial infections, particularly of the sinopulmonary tract, often beginning in adolescence or adulthood. The hallmark is hypogammaglobulinemia with impaired specific antibody production, while T-cell function is typically preserved.

This differs from hyper-IgM syndrome, where class-switching from IgM to other isotypes is defective, leading to normal or high IgM with low IgG/IgA/IgM; from severe combined immunodeficiency, which involves profound defects in both T and B cell immunity presenting early in infancy; and from IgA deficiency, which is mainly a selective loss of IgA with generally normal IgG and fewer systemic antibody-production issues.