X-linked agammaglobulinemia (XLA) ( MIM: 300755) is an inherited immunodeficiency caused by mutation in the Bruton's tyrosine kinase (Btk) gene (chromosome locus  Xq21.33-q22). It leads to failure in development of mature B lymphocytes and a reduced Ig production. Patients typically present in early childhood with recurrent infections. XLA is treated by infusion of human antibody.