SMAD4 and brachydactyly: So far, two skeletal disorders are known to be explicitly related to BMP-signaling: Myhre syndrome caused by SMAD4 pathogenic variants (MIM: # 139210)7 and BMPR1B-related brachydactyly (MIM: # 609441, # 616849, # 112600)8, but both show no hyperostosis.