The studies consisted of Genome-Wide Association Studies (GWAS) as well as analyses of polymorphisms, expression, and gene methylation, including but not limited to the leptin (LEP) and the leptin receptor (LEPR) genes, the fat mass and obesity-associated gene (FTO), and the oxytocin receptor (OXTR) gene [16, 71–73]. Here, LEPR is linked to obesity due to melanocortin 4 receptor deficiency.