MCTO with or without nephropathy is an autosomal dominant disease due to V-maf musculoaponeurotic fibrosarcoma oncogene ortholog B (MAFB) encoding the basic leucine zipper transcription factor MafB, which regulates the receptor activator of nuclear factor-kB ligand (RANKL); the consequence of genetic defect is an increase of bone reabsorption. The gene discussed is MAFB; the disease is kidney disorder.