(2) Since Acvr1(R206H)Fl;PDGFRα-cre and tamoxifen-induced Acvr1(R206H)Fl;Cre-ERT2 mice express ACVR1R206H receptor only in a subset of HO-causing cells, these mouse models may not recapitulate the full spectrum of FOP phenotypes seen in patients with FOP. The gene discussed is ACVR1; the disease is fibrodysplasia ossificans progressiva.