Atypical missense mutations (L196P, R202I, Q207E, R258G/S, G328R/W/E, G356D and R375P) in the GS or protein kinase (PK) domains of ACVR1 have also been identified in some FOP patients (Petrie et al., 2009; Katagiri et al., 2018a,b; Furuya et al., 2008; Huning and Gillessen-Kaesbach, 2014; Kaplan et al., 2009). Here, ACVR1 is linked to fibrodysplasia ossificans progressiva.