Remarkably, Src knockout mice donot exhibit any obvious functional or phenotypic abnormalities except osteopetrosis[3], which is a skeletal abnormalitycaused by a defect in osteoclasts [4].Osteoclasts are multinucleated cells derived from the hematopoietic precursors ofthe monocyte/macrophage lineage with high Src expression [5]. The gene discussed is SRC; the disease is osteopetrosis.