Specifically, a complex responsible for 3-prolyl-hydroxylation composed of cartilage-associated protein (CRTAP)/prolyl-3-hydroxylase (P3H1, encoded by the LEPRE1 gene)/cyclophilin B (PPIB) has been implicated in causing recessive OI.(1–4) Furthermore, mutations in all three proteins now have been shown to cause recessive forms of OI in part by leading to loss of hydroxylation at proline residue 986 of the α1(I) triple-helical domain and subsequent collagen overmodification. This evidence concerns the gene P3H3 and osteogenesis imperfecta.