Mutations in the pro-α1 and -α2 chains, encoded by COL1A1 and COL1A2, can cause defects in type I collagen synthesis or assembly resulting in osteogenesis imperfecta (OI), a genetic disorder characterized by bone fragility and deformity, blue sclera, short stature, dentinogenesis imperfecta, and hearing loss. The gene discussed is COL1A1; the disease is osteogenesis imperfecta.