ACVR1 and fibrodysplasia ossificans progressiva: Finally, to visualize how amiR-RH6.ACVR1opt treatment prevents the pathogenesis of spontaneous HO in FOP mice, Acvr1(R206H)Fl;PDGFRα-cre mice were further crossed with PDGFRα-GFP reporter mice and P1 Acvr1(R206H)Fl;PDGFRα-cre;PDGFRα-GFP (PDGFRα-GFP;Acvr1R206H) mice were i.v. injected with rAAV9 carrying mCherry control or amiR-RH6.ACVR1opt.