In conclusion, this is the first time that it has been described that the expression of LXRα, ABCA1, ABCG1, and Ob-Rb in PBMCs was decreased in patients with MO before and after RYGB and was associated with several variables related to obesity, inflammation, and liver function. Here, ABCG1 is linked to obesity due to melanocortin 4 receptor deficiency.