SEC24D and osteogenesis imperfecta: 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.