Treatment with ALLN (N-acetyl-leucyl-leucyl-norleucinal) to prevent degradation of OASIS cleavage products increased the total OASIS detected in all fibroblast and osteoblast cell lines, as well as the relative proportion of fully cleaved OASIS in normal control, IFAP and KFSD fibroblasts and normal control osteoblasts, more than in OI cells (Fig. 4a). This evidence concerns the gene MBTPS2 and osteogenesis imperfecta.