INHBE and fibrodysplasia ossificans progressiva: For example, ACVR1 is now described as a BMP receptor, but early work indicated that it could bind Activin and TGF-β (Massagué, 1996; Miettinen et al., 1994), and very recently it has been shown to signal downstream of Activin in the context of the disease, fibrodysplasia ossificans progressiva (Hatsell et al., 2015; Hino et al., 2015).