Case report of a novel mutation in Bruton’s tyrosine kinase gene with confirmed agammaglobulinemia and absent B lymphocytes

Background: X-linked agammaglobulinemia type 1 (XLA) is one of the most common pediatric inborn errors of immunity affecting the humoral immune system. The condition is caused by a mutation in the Bruton’s tyrosine kinase gene (BTK), located in the long arm of the X-chromosome. BTK is crucial for B lymphocyte differentiation and activation. Therefore, a defect in BTK results in B lymphocyte maturation arrest, absence of plasma cells, and failure of immunoglobulin production. XLA affected individuals present with a history of frequent severe pyogenic infections such as pneumonia, conjunctivitis, otitis media, and bacteremia. Laboratory evaluation classically reveals undetectable immunoglobulins and the absence of B cells. The mainstay treatment is immunoglobulin replacement which can be administered intravenously (IVIG) or subcutaneously (SCIG). Aggressive antimicrobial treatment is also administered to reduce complications such as bronchiectasis or invasive bacterial infections during active infections.

Aim: To report the clinical presentation, immune features, and genetic mutation in a case of a four-year-old boy with a novel mutation in the BTK gene leading to XLA.

Results: The patient’s chart was reviewed. We describe the phenotypical and diagnostic characteristics of an established case in a four-year-old boy who suffered from recurrent infections. Genetic analysis revealed a pathogenic novel mutation in the BTK gene (c.1953C>A; p.Tyr651*), while flow cytometry found 0% CD19+ (B cells), and low serum Ig levels.

Discussion: We report the clinical presentation, immune features, and genetic mutation in a patient with a novel mutation in the BTK gene causing XLA. Genetic analysis along with patient history, physical examination, and laboratory results are necessary to identify and diagnose XLA associated with pathogenic mutations in the BTK gene.

Statement of novelty: We present an established case of a novel mutation in the BTK gene (c.1953C>A; p.Tyr651*), based on genetic analysis, absent CD19+cells (B cells), and low Ig serum levels.