COL1A1 and osteogenesis imperfecta: Osteogenesis imperfecta (OI) is a serious inherited “brittle bone” disease most commonly resulting from mutations that compromise the function of type I collagen, either by reducing expression of COL1A1 or COL1A2, or causing mutant protein misfolding and degradation.1COL1A1 and COL1A2 encode the two collagen α‐chain subunits, α1(I) and α2(I), which heterotrimerize into the functional [α1(I)]2α2(I) collagen molecules.