DSPP and osteogenesis imperfecta: Genetic studies on DI type 1 have confirmed that osteogenesis imperfecta is a separate entity from DI and only a single genetic mutation of the dentin sialophosphoprotein (DSPP) gene located at chromosome 4q21.3 is responsible for causing DI type 2 and DI type 3.66, 67The gene product is a precursor protein that is halved into two dentin-specific proteins: dentin sialoprotein (DSP) and dentin phosphoprotein (DPP).