contain genes contributing independently to NW vulnerability. Across societies, women were significantly more likely to report depressed mood as a symptom of nicotine withdrawal than men, which appears to be a common phenomenon (Pergadia et al., 2006a). One other notable difference in the Finnish sample was that women were also more likely to report impairment related to nicotine withdrawal relative to men. Previous analyses of the individual symptoms of NW found: that most items were familial (even after controlling for regular smoking), variation within the items could be accounted for by a single factor, and that additive genetic variance significantly influenced categorically defined DSM-IV NW (accounting for over 45% of the variance; Pergadia et al., 2006a). Thus, our approach in this study was to conduct genetic linkage using only the categorical measure of DSM-IV NW. This approach also circumvented multiple testing.
