SLC6A4 and obesity due to melanocortin 4 receptor deficiency: Additionally, polymorphism of the short allele of SLC6A4 which encodes the SERT has been associated with obesity (Sookoian et al. 2007), and molecular imaging has supported the role of genetics in 5-HT regulation by reporting higher SERT binding in homozygotic carriers of the two long alleles of the SERT within the midbrain (Reimold et al. 2007).