COL1A1 and osteogenesis imperfecta: Finally, in the field of hereditary bone diseases, approximately 90% of osteogenesis imperfecta (OI) cases are caused by mutations in the type I collagen α-chain genes (collagen type I alpha 1 chain/collagen type I alpha 2 chain [COL1A1/COL1A2]), leading to either quantitative defects (reduced synthesis) or qualitative defects (structural abnormalities) of type I collagen [280,281].