The absence of CRTAP, P3H1 and CyPB, associated with complete lack or reduced α1(I)3-Hyp986, delays collagen type I folding, causing overmodification of the helical region and decreased collagen secretion at least in OI dermal fibroblasts (Marini et al., 2007). Here, P3H1 is linked to osteogenesis imperfecta.