PBX1 and obesity due to melanocortin 4 receptor deficiency: Upregulation of the RA pathway (including Crabp-II, Ppar, Rbp and RxR) together with a putative increase in the synthesis of its main agonist (RA) via the HOX-PBX1 complex, suggest an epigenetic regulation mechanism whereby abnormal blood glucose levels, high SBP and obesity could be prevented or reversed.