CHRNA5 and nicotine dependence: For instance, Siemińska et al. showed, that the variant allele A of rs169969968 of the alpha-5 nicotinic receptor subunit gene (CHRNA5), a polymorphism which is strongly associated with nicotine dependence was significantly less frequent in comparison to the HapMap CEU reference population (www.hapmap.org) [26, 27, 35–37].