COL1A1 and osteogenesis imperfecta: Type I DGI (DGI-I) is associated with forms of osteogenesis imperfecta (OI) caused by mutations in one of the type I procollagen genes, COL1A1 or COL1A2, whereas the more severe DGI-II and DGI-III are isolated dentin disorders caused by mutations in the DSPP gene.4, 5 Whereas mutations in these genes coding for the most abundant dentin proteins are responsible for the majority of DGI cases, the etiology of other genetic disorders manifesting dentin abnormalities is still unknown.6, 7