Nine loci have been associated with extreme obesity at the genome-wide level, five of them influencing BMI / waist circumference as well as risk for extreme obesity (FTO, MC4R, TMEM18, MSRA, NPC1) [102, 104, 107-110], four loci being more specific of genetic risk for extreme obesity (MAF, PTER, PRL, SDCCAG8) [107, 109] (Table 1). This evidence concerns the gene MC4R and obesity due to melanocortin 4 receptor deficiency.