Osteoclasts also express Bruton's Tyrosine Kinase (Btk) and Tec, which have a physiological role in B cells (43), and mice double knock out for both these kinases manifest osteoclast-poor osteopetrosis, likely due to a suppression of the RANKL induced phosphorylation of PLCγ (44). This evidence concerns the gene BTK and osteopetrosis.