For both log-transformed pack years and quantitative cannabis use, sex and age were significantly associated and consequently, were regressed out. Men reported greater smoking in pack years (β=−0.11, se=0.05) and a higher frequency of cannabis use (β=−0.14, se=0.02) while older individuals reported more pack years smoked (β=0.03, se=0.002) but reported less cannabis use (β=−0.14, se=0.02). For the binary traits, with the exception of self-reported history of drug-related problems (N=2 affected MZ twins), we were able to use both DZ pairs and a single MZ from a concordant affected pair (in a case-control framework) to test for association. For current smoking status, 270 DZ (89 concordant affected) pairs and 176 (84 concordant affected) representative members from a concordant MZ pair were available. No significant association was noted in the within-family analysis of smoking or illicit drug use measures and SNPs in GABRA2. However, in the MZ only sample of unrelated cases and controls, current smoking status in people who have ever smoked was associated with 7 SNPs in GABRA2 (see Table 4), the same that were associated with quantitative measures of
