Learning Objective
Describe key primary B-cell immunodeficiencies, their genetic or functional defects, clinical presentation, and characteristic laboratory findings.
B-Cell Immunodeficiencies
| Disease | Defect | Presentation | Key Findings |
|---|---|---|---|
| X-linked (Bruton) agammaglobulinemia | Mutation in the BTK tyrosine kinase gene → failure of B-cell maturation; X-linked recessive → affects boys | Recurrent bacterial and enteroviral infections after 6 months (loss of maternal IgG protection) | Very low B cells in blood; low levels of all immunoglobulins; absent/scant lymph nodes and tonsils (no germinal centers). Avoid live vaccines. |
| Selective IgA deficiency | Most common primary immunodeficiency; may be genetic, medication-induced, or post-infection | The majority are asymptomatic; they may develop recurrent sinopulmonary and GI infections, autoimmune disease, atopy, and anaphylaxis after IgA-containing blood products | Low IgA with normal IgG and IgM; ↑ risk of Giardia infection; false-negative celiac serology |
| Common variable immunodeficiency (CVID) | Defective B-cell differentiation; causes often unknown | Usually diagnosed after puberty; recurrent sinopulmonary infections; ↑ risk of autoimmune diseases, bronchiectasis, and lymphoma | ↓ immunoglobulins; ↓ plasma cells |
High-yield distinctions
✔ Bruton: BTK mutation, boys, absent lymphoid tissue
✔ Selective IgA deficiency: blood transfusion reactions
✔ CVID: autoimmune disease + lymphoma risk, later onset
