... family of cytoplasmicenzymes that are important for several aspects of leu-kocyte biology. Both loss- and gain -of- function muta-tions in humans have been instrumental in ourunderstanding of their ... second largest family of cyto-plasmic tyrosine kinases. In 1993, loss- of- function mutations in the BTKgene were reported as the cause of X-linked agammaglobulinemia. Of allthe existing 90 ... compilation ª 2011 FEBSMINIREVIEWTEC family kinases in health and disease – loss- of- function of BTK and ITK and the gain -of- function fusions ITK–SYKand BTK–SYKAlamdar Hussain1,2,*, Liang Yu1,3,*,...