These indications are necessary for a definite diagnosis of XLA: the patient must be male and have less than 2% CD19+ B cells with mutations in the BTK gene, absent BTK mRNA on a northern blot analysis of neutrophils or monocytes, absent BTK proteins in monocytes or platelets, as well as maternal cousins, uncles, or nephews who have mutations[8]. Here, BTK is linked to Bruton-type agammaglobulinemia.