C. elegans (Davies et al., 2003). Because KCNMA1 has been implicated in nicotine- and alcohol-related disorders in other studies (Davies et al., 2003; Hu & Agarwal, 2009; Schuckit et al., 2005; Ye et al., 2004) and several potassium voltage-gated ion channels were present in our top-30 results for ND it is likely that these ion channels play a role in the liability for ND and AD. A second group is formed by the genes coding for cell adhesion molecules. Several of these genes were also detected in previous GWAS to addiction phenotypes; PCDH15 (Uhl et al., 2008b), DSCAM (Liu et al., 2006; Uhl et al., 2008a), CNTN5 (Bice et al., 2009), CNTN4 (Bice et al., 2009). CNTNAP2 is a member of the neurexin family which act as cell adhesion molecules and receptors in synaptic signalling. Several neurexins are associated with addictive behaviors (e.g., NRXN3 (Hishimoto et al., 2007; Lachman et al., 2007; Novak et al., 2009)), and CNTNAP2 is previously associated with autism (Alarcon et al., 2008; Arking et al., 2008), schizophrenia (Friedman et al., 2008) and openness to experience (Terracciano et al., 2008).
