The SNPs examined in this study represent variants in 16 cholinergic nicotinic receptor genes, with comprehensive coverage of the α5α3β4 cluster on chromosome 15. The COGEND data contain genotypes for 210 SNPs in cholinergic nicotinic receptor genes. Before analysis, genotypic data were thinned using a pair-wise threshold of r2 < 0.95 based on linkage disequilibrium in COGEND to reduce the number of redundant pair-wise tests. This resulted in an analysis dataset of 127 SNPs. The SNPs were not thinned further because a goal of these analyses was to be sensitive to epistasis or other multi-locus effects that might display little to no marginal effects, and whose effects might not be adequately captured using tags with lower correlations.
