CRTAP and osteogenesis imperfecta: Osteogenesis imperfecta (OI), a rare hereditary connective tissue disorder, is usually caused either by a dominant mutation in one of the collagen type I coding genes, COL1A1 or COL1A2, or by recessive mutations in other genes, such as SERPINF1, CRTAP, WNT1, involved in collagen type I biosynthesis, function, transport, or secretion1,2.