We induced these iPSCs to mesenchymal stromal cells (iMSCs) and discovered that Activin-A, which induces TGFβ signaling in normal cells, induces BMP signaling via FOP-ACVR1A to promote the chondrogenic differentiation of iMSCs derived from FOP patients (FOP-iMSCs) and to initiate HO by FOP-iMSCs in vivo [10]. Here, TGFB1 is linked to fibrodysplasia ossificans progressiva.