COL1A1 and osteogenesis imperfecta: Numerous OI types are classified by associated clinical and genetic characteristics, the majority (85%–90%) of which are caused by variants in the type I collagen genes COL1A1 and COL1A2.2 Pathogenic variants can result in type I collagen haploinsufficiency, often associated with a lower disease burden, or structurally abnormal type I collagen, which presents with higher disease burden.1