Findings in this model, supported by studies in the previously reported transgenic Ifitm5c.-14C>T mice (19), as well as in zebrafish and in vitro cell culture models, point to downstream activation of extracellular signal–regulated kinase/mitogen-activated protein kinase (ERK/MAPK) signaling and increased SOX9 protein, leading to the abnormal osteo-chondroprogenitor differentiation in OI type V pathogenesis. This evidence concerns the gene MAPK1 and osteogenesis imperfecta type 5.