In an interesting pattern for this factor, multiple independent SNPs within two Cadherin genes (CDH13 and CDH23) have the strongest association with Extraversion, though none of these effects were replicated in the two independent samples. The Cadherin genes encode for cell-cell adhesion proteins that form complexes crucial in regulating synapse formation, function, and plasticity (63-65). CDH23 is expressed in neurosensory epithelium and linked to some instances of deafness (66). CDH13 is expressed in the heart and several brain tissues, where it is thought to act as a regulator of neural cell growth (67). For rs904208 we found a trend (P = .065) in the replication samples consistent with the effect found in Sardinia. For rs2813838 there was a consistent effect in the two follow-up samples, but unfortunately the effect in the Sardinia GWA was in the opposite direction (see signs of Z scores in Table 1). In addition to the SNPs shown in Table 1, a further interesting association is with rs11030064 (P = 8.05 × 10−5), a SNP lying close to the brain-derived neurotrophic factor (BDNF) gene, and an
