A possible explanation for why consistent findings were only observed in the COGA sample and not in the two other large data sets is that of these three previous studies, the COGA study had the most similar recruitment scheme to ours, as patients were recruited through alcohol treatment programs. This enriches the sample with the most severe AD cases, diagnosed in accordance with DSM. In an attempt to increase the power of the present study, we increased the homogeneity of the patient sample by including male patients with severe AD only. Thus our findings are confined to this specific patient group. Nevertheless, genes identified through systematic screening in clinically homogeneous samples comprised of severely ill patients can provide promising candidates for studies of more heterogeneous samples.
