The use of the chemical chaperone 4-PBA, approved by Food and Drug Administration, reduced ER stress and restored cell homeostasis in human fibroblasts of OI patients carrying dominant mutations in α1 and α2 collagen type I chains [17] as well as recessive mutations in cartilage-associated protein (CRTAP), prolyl-3-hydroxylase 1 (P3H1) and cyclophilin B (PPIB) impairing prolyl-3 hydroxylation of collagen type I [18]. This evidence concerns the gene CRTAP and osteogenesis imperfecta.