The btk gene has recently been identified as the causative gene in X-l
inked agammaglobulinemia (XLA). This has opened up many new possibilit
ies for the treatment. of this B-cell immunodeficiency. Christine Kinn
on and colleagues review the high degree of sequence of homology of bt
k to the non-receptor tyrosine kinases and speculate on putative roles
for this gene in B-cell development.