VDR and Alzheimer disease: Of the ligands for RA receptors investigated as AD therapeutics the most interest has been directed towards bexarotene, an agonist of retinoid X receptors (RXR) which are related to the RARs but with a wider range of action because they heterodimerize with many nuclear receptors including PPAR, thyroid hormone receptor, vitamin D receptors and others, including RAR.