This review also discussed the deep involvement of the PPAR family, a master regulator of lipid metabolism, in NAFLD, and the possibility that PPARs function as heterodimers with RXRs, and that in NAFLD and other liver disorders, retinoic acid deficiency due to abnormal retinoid metabolism could be one trigger, resulting in abnormal regulation of PPAR-RXR activity. This evidence concerns the gene PPARA and liver disorder.