Additional experimental studies have found that male carriers of the Asp40 allele report higher levels of alcohol craving following alcohol cue exposure, as compared to homozygotes for the Asn40 allele (van den Wildenberg et al., 2007). Likewise, alcohol-dependent Asp40 carriers reported higher alcohol intake and greater craving in response to stress, as compared to Asn40 homozygotes (Pratt and Davidson, 2009). Similar genotype effects on stress-reactivity were not reported in a study of heavy drinkers; however, higher cue-induced alcohol craving was observed among Asp40 carriers (Ray, 2011). More recently, a laboratory study of metyrapone, a stressor which blocks glucocorticoid production in the adrenal cortex, revealed that Asp40 carriers displayed a blunted adrenocorticotropic hormone (ACTH) response to this medication suggesting a greater tonic inhibition of the hypothalamic–pituitary–adrenal (HPA) sites and less cyclical glucocorticoid inhibition among Asp40 carriers (Ducat et al., in press). A laboratory study showed that Asp40 carriers displayed stronger automatic approach tendencies for alcohol and suggested that such approach bias may not be alcohol-specific, as it was observed for other appetitive stimuli (Wiers et al., 2009). A self-report study in
