IntroductionFarnesoid (or farnesol) X receptor (FXR) (or NR1H4) is a member of the same subclass of NR as LXR and , as well as the ecdysone receptor (ECR). FXR heterodimerizes to RXR and binds to DNA sequences consisting of an inverted repeat spaced by one nucleotide (IR-1) . FXR is mainly expressed in the liver, gut, kidney, and adrenal cortex. FXR binds and is activated by several bile acids, including chenodeoxycholic acid, lithocholic acid (LCA), and deoxycholic acid. FXR received its name due to the fact that is activated by a large variety of endogenous isoprenoids, including farnesol. Other endogenous activators include all-trans-retinoic acid, and as mentioned above, fatty acids. This nuclear receptor binds to AA, ALA and DHA with (Ki’s in the low M range ) but has little or no affinity for palmitic or stearic acid .