TGFB1 and Miyoshi myopathy: In addition, activin A, initially isolated as a gonadal protein, a member of the transforming growth factor‐β (TGF‐β) superfamily, is found to have a broad spectrum of biological functions including regulating the extracellular matrix formation and mineralization of the bone.(25, 26) MM cells induce the secretion of activin A by BMSCs, which stimulates osteoclast growth and possibly inhibits osteoblast function.(27, 28) Activin A levels are found elevated in MM patients, especially in those with advanced disease and extensive MBD.(29)