... loss-of-functionof BTK and ITK and the gain-of-function fusions ITK–SYK and BTK–SYKAlamdar Hussain1,2,*, Liang Yu1,3,*, Rani Faryal1,2, Dara K. Mohammad1, Abdalla J. Mohamed1,4 and C. I. Edvard ... metazoans [1] and com-prise five members in mammals: Bruton’s tyrosinekinase (BTK), inducible T-cell kinase (ITK), TEC,BMX [also known as epithelial and endothelial tyro-sine kinase (ETK)] and TXK ... screen [8].Mutations affecting BTK causeX-linked agammaglobulinemia (XLA) and provide insight into basic signalingmechanismsIn 1992, two TFKs were already known, namely TEC and ITK (reviewed...