top signals from the GWA analyses were typed in two independent samples. Although replication attempts clearly failed to find consistent effects for most SNPs we examined, a few provided more convincing evidence. In particular, the association of Agreeableness with the CLOCK gene variant was consistent across the Sardinia and the two follow-up samples, but it was not in a third follow-up sample. For Neuroticism, the top SNPs in Sardinia were not among the top signals identified in the previous GWA scan (15), but we found some evidence for a role of SNAP25, and another SNP, rs1849710, maps in the 12q region where one of the most convincing linkage peaks has been reported (4, 7).
