Specific candidate gene approaches have targeted neurotransmitter and neuropeptide systems, and have included a variety of serotonergic, epinephrine/norepinephrine and dopaminergic genes, genes coding for proteins associated with the melanocortin system, and genes for leptin, ghrelin, agouti-related protein, neuropeptide Y, opioids, cannabinoid receptors, potassium channels, brain derived neurotrophic factor, and reproductive hormones. Several reviews have been published detailing the results of these studies [Tozzi et al., 2002; Hinney et al., 2004; Klump and Gobrogge, 2005; Slof-Op ’t Landt et al., 2005; Bulik et al., 2007]. Overall, association studies have yielded sporadically significant and typically non-replicated findings [Bulik et al., 2007] highlighting the methodological and statistical challenges associated with genetic studies of a relatively low prevalence disorder (e.g., small sample sizes, lack of power, multiple testing issues, and varying phenotypic definitions) [Balding, 2006]. As with other, and perhaps all, complex traits, it is likely that susceptibility to disease is comprised of multiple, relatively common genetic variants each of which confers only small to modest risk in conjunction with environmental factors, a model of disease that will require approaches that increase the number
