A 6-month-old boy has recurrent bacterial infections but no viral infections. Immunoglobulins are absent in serum, but T-cell counts are normal. Lymph nodes show absent germinal centers. Peripheral blood B cells are absent. The MOST likely diagnosis is:

• A DiGeorge syndrome
• B X-linked agammaglobulinemia (Bruton's) ✓
• C Severe combined immunodeficiency (SCID)
• D Common variable immunodeficiency

Explanation

X-linked agammaglobulinemia (Bruton's) results from BTK (Bruton tyrosine kinase) mutation, blocking B-cell maturation at the pre-B cell stage. All immunoglobulin classes are absent, B cells are absent in blood, and germinal centers are absent in lymph nodes, but T-cell numbers and function are normal. Infections begin after maternal antibody wanes (~6 months), primarily with encapsulated bacteria. DiGeorge syndrome involves T-cell deficiency due to thymic aplasia.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.