ACVR1 and fibrodysplasia ossificans progressiva: However, although FOP and a group of DIPGs share the same ACVR1/ALK2 gene mutations, germline and somatic respectively, no cases of DIPG have been described in FOP patients to date, probably because ALK2 mutations likely do not initiate tumorigenesis themselves, but rather lead to DIPG when coexisting with other mutations.