This and other manuscripts have found how aberrant Activin signalling in FOP patients (Figure 3) is recapitulated not only in FAPs, but also in other cell types such as dermal fibroblasts, urine epithelial cells, blood-derived monocytic and endothelial cells, and periodontal ligament fibroblasts [112,116,134,135,136,137,138]. Here, INHBE is linked to fibrodysplasia ossificans progressiva.