ACVR1 and fibrodysplasia ossificans progressiva: A peculiar condition that could be paradigmatic to recognize the role of Act-A signaling in promoting ectopic calcification is FOP, a rare genetic disorder due to the mutation of the activin receptor 1/activin receptor-like kinase 2 (ACVR1/ALK2, c.617 G>A, R206H) gene encoding for BMP type-1 receptor (BMPR1) [113].