OI types caused by mutations in the collagen prolyl 3-hydroxylation complex, and in a few other genes encoding proteins involved in collagen folding and PTMs (i.e. FKBP10, MESD, and PLOD), are the more common among the recessive OI forms, representing more than 880 individuals (65). The gene discussed is MESD; the disease is osteogenesis imperfecta.