Immunoglobulins are essential for defense against invading bacterial pathogens, as is clearly illustrated by the high infectious burden in patients with agammaglobulinemia such as X-linked agammaglobulinemia (XLA) [1], which is caused by mutations in Bruton’s Tyrosine Kinase (Btk) resulting in the failure of B-lymphocyte maturation [2]. The gene discussed is BTK; the disease is Bruton-type agammaglobulinemia.