CHRNA4 and attention deficit-hyperactivity disorder: Conversely, evidence for the involvement of CHRNA4 in ADHD is strong, as multiple studies have reported an association of ADHD with the gene (Todd et al., 2003; Lee et al., 2008; Wallis et al., 2009; Faraone and Mick, 2010; Mastronardi et al., 2016).