Genome-Wide Association Studies (GWAS) performed on the TD phenotype suggested that the GLI family zinc finger 2 (GLI2), heparan sulfate proteoglycan 2 (HSPG2), dipeptidyl-peptidase 6 (DPP6), and GABA pathway genes could putatively be considered susceptibility genes for TD19–23. This evidence concerns the gene DPP6 and thanatophoric dysplasia.