COL1A1 and osteogenesis imperfecta: Osteogenesis imperfecta (OI) is an autosomal dominant connective tissue disorder occurring in approximately one per 20,000 live births.1 This condition is caused primarily by mutations in COL1A1 and COL1A2 genes, which result in defective synthesis of type I collagen, a structural protein contributing to the mechanical integrity of bone, tendons, skin, and blood vessel walls, among other tissues.