ACVR1 and fibrodysplasia ossificans progressiva: Currently, a retinoic acid receptor γ agonist (palovarotene capsules, Sohonos) was approved for treating FOP in Canada and USA but not in Europe, while an anti-Activin A antibody (REGN 2477), an immunosuppressant (rapamycin), and ACVR1 kinase inhibitors (IPN60130, Saractinib, INCB000928) are in clinical trials [3].