The gene group analysis that we performed provides one way to summarize the statistical evidence for association between a trait and multiple genetic variants across groups of genes that share sequence similarity and function. Nicotinic cholinergic receptors and voltage-dependent calcium-activated potassium channels were significantly associated with CPD (gene group P<0.01). We have previously discussed nicotinic receptor findings above. The association of rs7050529 (IVS3+286 of TRPC5) with CPD (Table 2) is notable as a closely related family member, TRPC7, was previously significantly associated with nicotine dependence [59]. The transient receptor potential cation family is a superfamily of 28 genes coding for cationic ion channels responding to temperature, endogenous and exogenous organic compounds, Ca2+ flux, and mechanical stimuli, and are expressed in nearly every tissue [78]. This study, the NICSNP study and Feng et al., 2006 [79] have identified significant associations between five Transient Receptor Family Potential (TRP) subfamily members and nicotine related behaviors in the canonical (this study Table 2, [59] Table 1, and [79]) and vanilloid subfamilies (this study Table 3, and Saccone et al., 2007, Supplementary Material [50]). Recently,
