TNFRSF11A is a member of the TNF-receptor superfamily. In mouse, it is also known as CD265. TNFRSF11A contains 4 TNFR-Cys repeats and is widely expressed with high levels in skeletal muscle, thymus, liver, colon, small intestine and adrenal gland. It is an essential mediator for osteoclast and lymph node development. TNFRSF11A and its ligand are important regulators of the interaction between T cells and dendritic cells. It can interact with various TRAF family proteins, through which this receptor induces the activation of NF-kappa B and MAPK8/JNK. Defects in TNFRSF11A can cause familial expansile osteolysis (FEO). FEO is a rare autosomal dominant bone disorder characterized by focal areas of increased bone remodeling. Defects in TNFRSF11A also can cause Paget disease of bone type 2 (PDB2). PDB2 is a bone-remodeling disorder with clinical similarities to FEO. Defects in TNFRSF11A are the cause of osteopetrosis autosomal recessive type 7 which characterized by abnormally dense bone, due to defective resorption of immature bone.