In patients with FOP, a gain-of-function mutation in the ACVR1 gene, encoding the activin A receptor type 1, a bone morphogenetic protein (BMP) type 1 receptor, drives the heterotopic ossification process by aberrantly initiating both ligand-dependent and -independent activation of the BMP signalling cascade (Hino et al., 2015; Kaplan et al., 2012; Pang et al., 2016), a response coincident with local tissue damage and inflammation (Matsuo et al., 2019). Here, ACVR1 is linked to fibrodysplasia ossificans progressiva.