ACVR1 (ALK-2, Activin A receptor, type I) is transmembrane receptor of the transforming growth factor-beta (TGF-beta) superfamily that is involved in growth and differentiation. It is important for neurogenesis as well as the development and repair of the skeletal system via its involvement in the BMP (bone morphogenic) pathway. Mutations in this gene are associated with fibrodysplasia ossificans progressive as well as diffuse intrinsic pontine glioma (DIPG). In immunohistochemistry, ACVR1 has cytoplasmic positivity throughout the body. References: Pediatr Endocrinol Rev. 2013 Jun;10 Suppl 2:437-48, PMID: 23858627; Nat Genet. 2006 May;38(5):525-7, PMID: 16642017; Nat Genet. 2014 May;46(5):457-461, PMID: 24705252; Journal of Neuroscience. 2013. 33 (16): 6766-6775, DOI: 10.1523/JNEUROSCI.0128-13.2013;