In contrast to the human genetics studies examining an association between CHRNB2 and ND, the work with CHRNA4 has been more consistent. Feng and colleagues initially reported an association between rs1044396 and rs1044397 and ND in Chinese males (Feng et al. 2004a). Since this report, additional studies have reported associations between ND and CHRNA4 variation (Breitling et al. 2009; Chu et al. 2011; Han et al. 2011; Li et al. 2005; Saccone et al. 2009; Saccone et al. 2010; Xie et al. 2011).
