Novel variant in <i>IGHM</i> gene in a patient with agammaglobulinemia: A case report of a preschool child presenting with recurrent pneumonia

Introduction: Agammaglobulinemia is a primary immunodeficiency characterized by absent B cells and originates from X-linked or autosomal mutations affecting B cell maturation. While the most common agammaglobulinemia is X-linked, one well-documented site of autosomal recessive agammaglobulinemia is within the immunoglobulin μ heavy chain protein, encoded by the IGHM gene. Such variants frequently result in clinical presentations of recurrent bacterial infections early in life. Aim: To describe a case of a five-year-old female with agammaglobulinemia resulting from a novel homozygous IGHM variant, presenting with pneumonia complicated by empyema and H. influenzae bacteremia. Methods: Case data was compiled retrospectively from the patient’s medical chart, including relevant laboratory testing for immunoglobulins, quantitative B cell subsets, and genetic testing using a primary immunodeficiency panel. Results: The proband is a 5-year-old female with a history of recurrent pneumonia, presenting with H. influenzae bacteremia in the context of pneumonia complicated by an empyema. Investigations revealed low immunoglobulin levels, absent vaccine responses, and undetectable B cells on flow cytometry. Genetic testing revealed a novel homozygous variant in the IGHM gene: c.775T&gt;C, p.Trp259Arg. Conclusion: Autosomal recessive agammaglobulinemia is a rare but severe, treatable disorder of the immune system which typically presents in early childhood. Hypomorphic mutations, while less commonly reported in the literature, are an important consideration in atypical presentations of primary immunodeficiencies, such as in the case presented. Statement of Novelty: Herein, we report a case of agammaglobulinemia presenting with a novel homozygous variant in the IGHM gene leading to later onset agammaglobulinemia in a 5-year-old female.