This conclusion was supported by subsequent analyses in which the alcohol dependence diagnosis was included in the linkage analysis of nicotine dependence first as a covariate and then as a second phenotype in a bivariate analysis. For the reported peak on chromosome 2 at 184 cM, a slight increase in the initial LOD score was observed when the alcohol dependence diagnosis was added as a covariate (from 3.54 to 3.57), whereas a drop in the LOD score was observed for the bivariate analysis (from 3.54 to 2.17) that probably occurred because of corrections for the inclusion of additional parameters. This result suggests this region confers risk towards nicotine but not alcohol dependence (see Figure 2). Similar conclusions were made regarding the remaining peaks of interest (see Table 3 for complete results).
