ABCG8 and Parkinson disease: In the ileum of PD and controls, we examined the transcript levels of nuclear receptors that regulate bile acid and cholesterol homeostasis (FXR and LXR), bile acid-sensing receptor (TGR5), transporters for bile reabsorption (ASBT, OSTα/OSTβ, FABP6), and transporters for cholesterol reabsorption and efflux (NPC1L1 and ABCG5/ABCG8, respectively).