Interestingly, the administration of 4 phenyl butyrate (4PBA), a chemical chaperone known to release ER stress in presence of collagen accumulation in dominant (23, 35) and some OI recessive forms (36), reduced Hsp47 signal in both mutants compared to controls supporting its positive role in restoring cell homeostasis also in presence of tmem38b mutations (Figures 4D-F). This evidence concerns the gene SERPINH1 and osteogenesis imperfecta.