Type I collagen defects—While most pathogenic defects in the pro-α1- and pro-α2-chains of type I collagen, encoded by the COL1A1 and COL1A2 genes, respectively, result in the brittle bone disorder osteogenesis imperfecta, some specific defects are associated with rare EDS types. The gene discussed is COL1A2; the disease is Ehlers-Danlos syndrome.