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X-linked agammaglobulinaemia — MRCPCH TAS MCQ

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ModerateImmunologyX-linked agammaglobulinaemiaMRCPCH TAS

An 11-month-old boy develops recurrent otitis media and pneumonia after being well for the first few months of life. Immunoglobulins are very low and mature B cells are absent. What is the most likely mechanism?

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Correct answer: D — BTK mutation impairing B-cell maturation

X-linked agammaglobulinaemia is due to BTK mutations causing failure of B-cell maturation and very low immunoglobulins after maternal IgG declines. Thymic aplasia is seen in DiGeorge syndrome and primarily affects T cells. The pearl is that recurrent encapsulated bacterial infections are typical of antibody deficiency.

Reference: Nelson Textbook of Pediatrics; RCPCH Theory examination syllabi; Lissauer's Illustrated Textbook of Paediatrics