In the past years, genome-wide association (GWA) studies to smoking behavior revealed several regions and candidate genes (17–20). However, none of these GWA studies reported genome-wide significant results because of the limited sample sizes. It is now recognized that a well-powered GWA needs to include ten thousands and possibly hundred-thousands of subjects. In 2010, three large consortia, the Oxford-GlaxoSmithKline (Ox-GSK), Tobacco and Genetics Consortium (TAG) and ENGAGE consortium, each carried out meta-analyses for smoking phenotypes. They also combined their analyses for smoking initiation and cigarettes per day (21–24). The most significant finding was the association between the number of cigarettes per day and a cluster of nicotinic receptor genes on chromosome 15 (21–24).
