TCIRG1 and autosomal recessive osteopetrosis: As TCIRG1 encodes the osteoclast-specific 116-kD subunit of the vacuolar proton pump and its defect is responsible for a subset of human autosomal recessive osteopetrosis (Frattini et al., 2000), TCIRG1 could be regarded as the potential targets for KIRC metastasis, especially to skeletal metastasis.