From an initial proband diagnosed with AD, we identified members of a set of extended pedigrees in which AD segregates living in a relatively isolated region of Northern Hunan Province, China. The study was approved by ethics committees at Hunan Normal University and the Yale University School of Medicine and written informed consent was obtained from each participant. Members of the identified set of pedigrees were interviewed locally by trained interviewers with clinical experience (XYW, TQL, and WH) using the Chinese version of the Diagnostic Interview for Genetic Studies (DIGS 2.0; Berney et al. 2002), to assess AD and related psychiatric phenotypes based on Diagnostic and Statistical Manual of Mental Disorders version IV (DSM-IV) criteria (American Psychiatric Association 2000). The DIGS was developed to ascertain psychiatric diagnoses including substance use disorders, and has been used for genetics studies of schizophrenia (Hwu et al. 2005; Tang et al. 2007) and heroin dependence (Glatt et al. 2008) in Chinese samples.
