ACVR1 and plasma cell myeloma: We hypothesised that BMP inhibition might recapitulate the anabolic effects of anti-sclerostin antibodies in myeloma bone disease in vivo, since: (a) osteocyte-secreted sclerostin is a major mediator of the osteogenesis block in myeloma;45 (b) anti-sclerostin antibodies ‘activate’ quiescent BLCs to become thicker, active and produce bone matrix in vivo5 and (c) both Acvr1 and Bmpr1a knockout in vivo decreased Sost and Dkk1 transcription32,39.