We report the case of a 10-year-old boy, with a history of recurrent sinopulmonary infections, presenting with pneumococcal meningitis. Immune workup found low immunoglobulin G (IgG), IgA, and IgE and elevated IgM. Specific antibodies to pneumococcus, tetanus, and mumps were low. Genetic testing identified CD40L and uracil-DNA glycosylase as normal. Sequence analysis for mutations in activation-induced cytidine deaminase (AID) gene on chromosome 12p13 revealed a single missense mutation in exon 3 caused by a point mutation. AID is an enzyme that is specifically present in activated B cells and necessary for isotype switching. This case highlights the significance of AID deficiency in hyper-IgM immunodeficiency.
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