Genetic and epidemiological studies have demonstrated that nicotine dependence (ND) is a complex disorder that is influenced by genetic and environmental factors. Our meta-analysis based on reported twin studies indicated that the weighted mean heritability for ND is 56% in adult smokers. To identify susceptibility loci for ND, six genome-wide linkage studies have been reported, including the one reported by this group. However, when the regions identified in these studies are compared, one would find that only a few loci have been replicated in more than one study. During the past few years, we have conducted linkage analyses on ND in two independent samples, i.e., Framingham Heart Study (FHS) and Mid-South Tobacco family (MSTF; recruited by us from Mid-South States in 1999-2004) cohorts. By comparing the identified linkage regions for ND between these two cohorts, we found that the four genomic regions located on chromosomes 1, 9,11 and 17 have been detected in both samples, suggesting these regions are more likely to harbor susceptibility genes for ND. Additionally, we identified another significant linkage (LOD=3.64) on chromosome 12 in the MSTF cohort. To identify susceptibility genes for ND in this renewal application, we propose to perform fine mapping of these five regions that either showed significant linkage to ND in the MSTF samples or had been identified in two independent cohorts (MSTF and FHS) by typing more SNPs within these regions in the MSTF cohort (Aim 1). Two thousand appropriate SNPs have been selected on the basis of their location, frequency, distance between SNPs and haplotype information. To address the concern of low replication rates across studies and genetic differences between ethnic groups on nicotine metabolism and other smoking related behavior, in Aim 2 we propose to recruit 750 smokers and 750 nonsmoker controls in each of two ethnic populations (total of 3000 subjects); i.e., Caucasian- and African-Americans.
In Aim 3, we will use the newly recruited case-control samples from Aim 2 to confirm our fine mapping results obtained with the MSTF cohort in Aim 1. To have complete coverage, we propose type approximately 1 SNP per 10 kb of nucleotide sequence within each gene or region of interest. Various association methods required to analyze the data generated from Aims 1 and 3 are provided in detail in Section D.4 of the proposal.
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