A child with recurrent sino-pulmonary infections from age 6 months, normal lymphocyte count, normal IgM, but very low IgG, IgA, and IgE. B cells are present in normal numbers. Flow cytometry of B cells shows poor surface IgM expression but no CD40L defect. The MOST likely diagnosis is:

• A Common variable immunodeficiency (CVID) ✓
• B X-linked agammaglobulinaemia (Bruton's disease)
• C Hyper-IgM syndrome (CD40L deficiency)
• D Selective IgA deficiency

Explanation

CVID is characterised by low IgG, IgA, and IgE with normal or low IgM, normal B-cell numbers, and poor antibody responses to vaccines — onset typically in the second to third decade but can occur in childhood. Bruton's agammaglobulinaemia presents similarly but B cells are absent (Btk mutation). Hyper-IgM syndrome shows elevated IgM with low IgG/IgA due to CD40L defect preventing class switching. Selective IgA deficiency shows isolated low IgA with normal other immunoglobulins. The combination of low IgG/IgA/IgE with present B cells fits CVID best.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.