Genetic studies have identified over 26 susceptibility loci associated with DD, including those linked to WNT signaling (e.g., Wnt Family Member 4 = WNT4, Secreted Frizzled-Related Protein 4 = SFRP4 and R-spondin 2 = RSPO2) and extracellular matrix (ECM) remodeling [8,9]. This evidence concerns the gene SFRP4 and dentin dysplasia.