Genomewide linkage survey of nicotine dependence phenotypes

BackgroundA comprehensive understanding of the etiology and neurobiology of nicotine dependence is not available. We sought to identify genomic regions that might contain etiologically-relevant loci using genomewide univariate and bivariate linkage analyses.MethodsWe conducted secondary data analyses of 626 all possible sibling pairs ascertained in Ireland and Northern Ireland on the basis of alcohol dependence. A set of 1020 short tandem repeat genetic markers were genotyped in all subjects. The phenotypes analyzed were the Fagerström Test for Nicotine Dependence (FTND), a history of nicotine dependence, the number of symptoms of alcohol dependence (AlcSx), and a history of alcohol dependence. Genomewide linkage analyses were conducted with non-parametric and variance components methods.FindingsFor the bivariate variance component analysis of the continuous FTND and AlcSx scores, multipoint LOD scores were >4 in two genomic regions—an 11 cM region on chr7 (D7S2252–D7S691, empirical p = 0.0006) and an 8 cM region on chr18 flanking D18S63 (empirical p = 0.0007). These findings did not exceed a conservative estimate of study-wide significance. The remaining sets of findings had considerably smaller or less consistent peak signals. Notably, strong linkage signal at D4S1611 for AlcSx from a prior report (PMID 16534506) was not found when jointly analyzed with FTND.InterpretationReplication is required. However, chromosomes 7 and 18 may contain genetic loci relevant to the etiology of nicotine-related phenotypes.