XLA is caused by pathogenic variants in the BTK gene, which is a cytosolic tyrosine kinase protein composed of five domains i.e. pleckstrin homology (PH), Tec homology (TH), Src homology domain (SH2), SH3, and kinase (Catalytic) domains [40]. The gene discussed is TH; the disease is Bruton-type agammaglobulinemia.