Netherlands Twin Register; the result for “maximum number of cigarettes per day” was included (9). In the earliest study, the authors carried out a 2-stage genome scan, and only the result from stage 1 was used since stage 2 was a follow up genome scan in candidate regions (5). Finally, results for two studies (three genome scans) were not available (23, 24). In addition, two studies (15, 16) used the same sample of Finnish twin families, but performed the genome scan on different assessments of smoking behavior (FTND and MaxCigs24). The result from Loukola (16) was included for the primary GSMA on smoking behavior and FTND. The result from Saccone (15) was only used for the secondary GSMA on MaxCigs24. Consequently, the data for this analysis were collected from 12 studies (15 genome scans), including 3404 families with 10,253 individuals.
