P3H1 and osteogenesis imperfecta: Recently, mutations in the endoplasmic reticulum (ER)-resident proteins Prolyl-3-hydroxylase-1 (P3H1, also known as LEPRE1) or its binding partner CRTAP were found to be causative in a subset of autosomal recessive forms of OI in humans and/or mice [3]–[5].