Arthritic cartilage from OA patients showed decreased activities of MRC complex compared with the normal tissue.[26] More specifically, deletion of NDUFS4, an essential complex I subunit, causes systemic inflammation and osteopetrosis by shifting osteoclasts to macrophages,[27] both of which are capable of driving the progression of OA. The gene discussed is NDUFS4; the disease is osteopetrosis.