Type I collagen is the most abundant form of collagen in the human body and is synthesized mainly by fibroblasts, osteoblasts, odontoblasts and chondroblasts.It is located in the extracellular matrix of many tissues of the body including cartilage, bone, tendon, skin and the sclera of the eye.Type I collagen is composed of two pro-α1(I) chains, produced from the COL1A1 gene, and one pro-α2(I) chain, produced from the COL1A2 gene.Mutations in the genes that produce collagen type I are responsible for causing various health conditions including Ehlers-Danlos syndrome, osteogenesis imperfecta, osteoporosis and Caffey disease.