Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is characterized by low levels of immunoglobulins (hypogammaglobulinemia). Typically presents without an apparent cause, such as a specific genetic mutation or other identifiable disorder. Instead, there are a variety of potential genetic mutations as well as unknown environmental factors.

What is it?

In CVID, B-cell numbers are usually preserved, yet their function is defective, leading to impaired antibody production and class switching. This functional deficiency is often the result of defects in critical signaling molecules such as IL-4, CD40 ligand, or tyrosine kinase pathways—mechanisms that are essential for coordinating T-cell–B-cell interactions necessary for antibody class switching. Consequently, patients exhibit reduced levels of IgG, IgA, and sometimes IgM, which compromises their ability to mount effective humoral immune responses against pathogens, particularly encapsulated bacteria and viruses.

Cause

CVID is not defined by a single genetic cause but rather by a constellation of clinical and immunological features, including recurrent infections, especially of the respiratory tract and gastrointestinal system, and an increased risk of autoimmune disorders, lymphoproliferative diseases, and malignancies such as lymphoma. Diagnosis is typically made by excluding other known immunodeficiencies and identifying persistent hypogammaglobulinemia, often with normal or near-normal B-cell counts on flow cytometry.

Management

Therapeutic management centers on immunoglobulin replacement therapy (IVIG or SCIG) to restore protective antibody levels, alongside antimicrobial prophylaxis and prompt treatment of infections. In some cases, adjunctive therapies targeting underlying immune dysregulation or autoimmune phenomena may be employed.

Compared to Bruton's Agammaglobulinemia

Unlike Bruton’s agammaglobulinemia, which presents with early-onset, near-complete absence of B cells due to a nonsense or frameshift mutation in the BTK gene (X-linked recessive), CVID typically manifests later in life, often after the first year of life, and is associated with missense mutations that impair B-cell signaling pathways rather than complete loss of B-cell development. This later in life onset typically has a somewhat milder course compared to disease that happens earlier, such as Bruton's.

• XLA (Bruton’s): No B cells at all, onset in infancy, X-linked → only boys
• Selective IgA deficiency: Only IgA is low, often asymptomatic, but risk of anaphylaxis to transfused blood with IgA
• CVID: Normal B cell numbers, multiple Ig deficiencies, later onset, autoimmune/lymphoma risk