COL2A1 and osteogenesis imperfecta: Mutations in the multiple collagen encoding genes, like COL1A1, COL1A2, COL2A1, have been well documented in a range of mendelian bone fragility disorders characterized by low bone mass and microarchitectural deterioration of bone tissue, including osteogenesis imperfecta, Ehlers–Danlos syndrome and hypochondrogenesis.