The most notable finding is the association of Agreeableness with several SNPs within or close to the CLOCK gene (see Figure 1). The strongest signal was with rs6832769 (P = 8.71 × 10−6). The two follow-up samples showed similar effects that reached statistical significance when meta-analytically combined (P = .022). Based on the initial replication, we genotyped rs6832769 in an additional sample of 1,822 individuals. In this third follow-up sample we failed to replicate the association of the rs6832769 CLOCK variant with Agreeableness (P = 0.47). Still, in the combined SardiNIA GWA and the three follow-up samples (N = 7,875) the P value was 2 × 10−5. CLOCK encodes for a transcription factor that is essential for circadian rhythm (72, 73), which in turn has large influences on human behavior, cognition, and emotion. Agreeableness has been linked to morningness preference (74), and have similar maturational trends. Younger adults tend to be more evening type and antagonistic, and older people are more agreeable (75) and more likely to be “morning types” (76). Mixed findings have been reported for a CLOCK variant
