COL1A1 and osteogenesis imperfecta: The majority of individuals with OI (80–85% in Western countries; about 60% in countries with a high incidence of consanguinity) are caused by structural or quantitative defects in collagen type I genes, COL1A1 and COL1A2, encoding the α1(I) and α2(I) chains of type I collagen, respectively.