The most striking and severe clinical manifestation of hyperfunctioning BMP signaling is Fibrodysplasia Ossificans Progressiva (FOP), caused by mutation in the ACVR1/Alk-2 gene that encodes the ACVR1/ALK-2 type I receptor [5], [6]. The gene discussed is ACVR1; the disease is fibrodysplasia ossificans progressiva.