In osteoblasts, mutations in COPII coat subunits (e.g. Sec23A and Sec24d) that regulate budding of collagen-containing vesicles from the ER are associated with skeletal defects in patients with cranio-lenticulo-sutural dysplasia3 and osteogenesis imperfecta (OI)4–6, respectively. Here, SEC23A is linked to osteogenesis imperfecta.