ACVR1 and fibrodysplasia ossificans progressiva: Much recent interest has focused on the BMP receptor kinase ALK2, encoded by the gene ACVR1, due to the discovery that gain of function mutations in the receptor’s intracellular domain associate with the rare congenital syndrome fibrodysplasia ossificans progressiva (FOP), as well as the pediatric brain tumor diffuse intrinsic pontine glioma (DIPG) [6,7].