GWAS (Genome-wide association studies) have indicated that SNPs (single nucleotide polymorphisms) on a chromosome 16 locus encompassing FTO, as well as IRX3, 5, 6, FTM and FTL are robustly associated with human obesity, with carriers of the risk alleles reported to have increased appetite [1–3]. Here, FTL is linked to obesity due to melanocortin 4 receptor deficiency.