Type I collagen is a member of group I collagen found in most connective tissues such as skin, bone and tendon. Collagen type I is produced from procollagen when two teloterminal propeptides are digested from the procursor and released into the circulation. Type I collagen is a heterotrimer that consists of two alpha 1 chains and one alpha 2 chain. Mutations in the COL1A1 gene encoding the alpha 1 chain are associated with osteogenesis imperfecta types I-IV, Ehlers-Danlos syndrome type VIIA, Ehlers-Danlos syndrome Classical type, Caffey Disease and idiopathic osteoporosis. Mutations in the COL1A2 gene encoding the alpha 2 chain are associated with osteogenesis imperfecta types I-IV, Ehlers-Danlos syndrome type VIIB, recessive Ehlers-Danlos syndrome Classical type, idiopathic osteoporosis, and atypical Marfan syndrome.