Furthermore, as other RXR (the main active form of PPARγ is the RXR/PPARγ heterodimer) and PPARγ activators are also present in the environment, additive (acting only through PPARγ) and synergistic (acting through both RXR and PPARγ) effects could occur and further increase the risk of metabolic diseases. This evidence concerns the gene PPARG and metabolic disease.