These genes are all expressed in osteoblasts, and most of them are directly involved in collagen type I metabolism, even though some of these genes seem to play a role in other aspects of osteoblast function such as Wnt signaling.1 Defects in the newer OI‐related genes usually lead to recessive forms of OI, but two genes (IFITM5, P4HB) are associated with dominant OI, and two genes (PLS3, MBTPS2) lead to X‐linked bone fragility. This evidence concerns the gene MBTPS2 and osteogenesis imperfecta.