Probands, siblings, and parents were interviewed by clinically trained research interviewers, most of whom had extensive clinical experience with alcoholism. The assessment included demographic characteristics, lifetime history of AD and other comorbid conditions, alcohol-related traits, personality features, and clinical records. All participants provided informed consent. Controls were recruited in the Northern Ireland from volunteers donating at the Northern Ireland Blood Transfusion Service and in the Republic from the Garda Siochana (the national police force) and the Forsa Cosanta Aituil (the army reserve). Controls were screened and their samples excluded if they reported a history of heavy drinking or problem alcohol use. In the present case–control study design, we included 545 independent AD cases and 509 controls with an ample yield of high-quality DNA for genotyping. The selection of cases was random with respect to AD severity and comorbid phenotypes.
