RARG and fibrodysplasia ossificans progressiva: However, promising therapies, including palovarotene (RARγ agonists; refs. 38–40), activin A antibodies (41, 42), saracatinib (ALK2 inhibitors; ref. 43), and rapamycin (mTOR inhibitor; ref. 44), are currently undergoing phase II or III clinical trials that may yield directed therapies for patients with FOP.