Bruton tyrosine kinase

Bru·ton tyrosine kinase (Btk),

an intracellular enzyme involved in B-cell signaling. Congenital deficiency of Btk occurs in X-linked agammaglobulinemia (XLA). [Ogden C. Bruton]

BTK

A gene on chromosome Xq21.33-q22 that encodes a protein which plays a central role in B-cell development, differentiation and signalling. Binding of antigens to the B-cell antigen receptor (BCR) triggers signalling that leads to B-cell activation. 
Molecular pathology
Defects of BTK cause X-linked agammaglobulinaemia (OMIM:300755), as well as X-linked hypogammaglobulinaemia and isolated growth hormone deficiency (OMIM:307200).