A total of 56,034 subjects from 41 datasets spanning nine countries were included in a meta-analysis. Sample sizes for each SNP and the two phenotypes differ (age of tobacco initiation N ~ 12,662, age of onset of regular smoking N ~ 55,317) depending on which of the studies, listed in Table 1, had contributed information. All but 11 of these datasets consisted of unrelated ever-smokers of European descent. Details regarding individual study characteristics are provided in supplementary Table S1. Eight (Dental Caries, VA-Twin, NAG-FIN, NAG-OZALC, NTR1, NTR2, QIMR, and STR) were subsets of unrelated subjects selected from family-based datasets. The Add Health, NYS-FS, and SMOFAM datasets included family members of European descent. Informed consent was obtained from all participants and was approved by the local institutional review boards. Inclusion into this study required ever smokers to be assessed for (1) Age of tobacco initiation (AOI); and/or (2) Age of onset of regular smoking (AOS). Mean AOI and AOS values are shown in Table 1. Phrasing of AOI and AOS questions is provided in supplementary Table S1.
