CRTAP associates in a complex with prolyl 3-hydroxylase 1 and cyclophilin B and this complex functions to both chaperone type I collagen and 3-hydroxylate a single proline residue, Pro986, in the alpha 1(I) chain.4 Mutations in the genes encoding any of the three complex members have since been shown to cause recessive OI (MIM *610339, *123841). Here, CRTAP is linked to osteogenesis imperfecta.