Osteogenesis imperfecta (OI), or “brittle bone disease,” is caused by mutations in the collagen type I genes COL1A1 and COL1A2 (or other collagen genes for rarer types of OI), causing production of a defective collagen type I that results in significant alterations in different tissues in the body. Here, COL1A2 is linked to osteogenesis imperfecta.