Given this literature, early human genetic studies of the genes coding for nAChR subunits focused on CHRNA4 and CHRNB2. For CHRNB2, results of association studies have been mixed. Early studies that were limited in sample size did not find association between CHRNB2 variants and ND (Etter et al. 2009; Feng et al. 2004a; Li et al. 2005; Lueders et al. 2002; Silverman et al. 2000). However, more recent work examining other nicotine-related phenotypes (such as smoking initiation, subjective effects, abstinence rates) have detected evidence for association (Conti et al. 2008; Ehringer et al. 2007; Greenbaum et al. 2006; Hoft et al. 2011; King et al. 2012; Perkins et al. 2009). Furthermore, common and rare genetic variants in CHRNB2 have been associated with ND in individuals seeking smoking cessation treatment (Wessel et al. 2010).
