Therefore, we speculated that the combined mutations in COL1A1 and the COL5A1 C-terminal propeptide domain could result in the hybrid EDS-OI phenotype of the proband III-1 and her mother, both of whom exclusively carry the COL5A1 (c.5335A>G) mutation within the family. The gene discussed is COL5A1; the disease is osteogenesis imperfecta.