ACVR1 and fibrodysplasia ossificans progressiva: The most prevalent mutant variant, Alk2 p.R206H, leads to the loss of autoinhibition of BMP signaling and confers constitutive activation in response to activins, a response not observed in wild-type receptors.185 Postnatal expression of the human mutant Alk2 (Alk2-R206H) in mice recapitulates an FOP-like phenotype, further confirming the central role of dysregulated Alk2 signaling in FOP pathogenesis.186 RK783 is a novel small-molecule inhibitor designed to selectively target the activity of BMP type-I receptors.