ACVR1WT inhibits BMP2 or BMP4 signalling. FOP mutation ACVR1R206H loses the inhibitory function on BMP2 or BMP4 signalling. ACVR1 ligands BMP6 or BMP7 lead to hyperactivation of ACVR1R206H. Activin A induced BMP signalling of ACVR1R206H is ligand binding domain dependent.