ACVR1 and diffuse intrinsic pontine glioma: 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].