CHRNA4 and major depressive disorder: Corroborating our finding, previous studies showed the association of the CHRNA4 rs1044396 T allele with a protective effect in different phenotypes, such as: lower levels of depression, anxiety, and emotional instability, and lower propensity for ND (Feng et al., 2004; Breitling et al., 2009; Markett et al., 2011; Tsai et al., 2012).