FGFR1 and Osteopenia: We created the first animal model of OGD, a disorder characterized by craniosynostosis, distinctive craniofacial features, profound short stature with femoral shortening, and osteopenia (9) caused by GoF variants in the Fibroblast Growth Factor Receptor 1 gene (FGFR1), resulting in constitutive receptor tyrosine kinase activity and aberrant downstream signaling.