When we examined the GO categories with an excess of hits within genes displaying high scores on our AD factor score (results presented in Appendix, Tables A3 and A4), there was a surprising lack of neurotransmitter or receptor based GO categories. Nonetheless, we did observe several GO categories that could potentially be involved in the molecular mechanisms of AD such as tolerance and withdrawal. Thus, the analysis in the EA sample identified cellular mechanisms including responses to hormonal stimuli, anatomical structural homeostasis, phosphorylation, and NADPH oxidase complex, glucocorticoid stimulus, cellular response to insulin stimulus, insulin receptor signaling pathway, and sulfation. Some of these categories suggest a role in the general biology underlying addictive behavior; when the genes were considered individually, we observed signals in genes related to calcium and potassium signaling and glutamate receptor subunits which may have a direct role in addiction, including AD. ALIGATOR analysis helped to highlight processes related to underlying mechanisms; the Australian/Dutch GWAS (Lind et al. 2010) also reported results with genes encoding transporters, cell adhesion molecules and cytoskeleton proteins. Structural homeostasis has been shown
