Genetic modulation of personality traits: a systematic review of the literature.

The heritability of human personality traits is by now well established. However, since the first reports on associations between specific genetic variants and personality traits, only modest progress has been made in identifying loci that robustly support these associations. The aim of this study was to provide a summary of literature data on association studies focused on the genetic modulation of personality, according to the Cloninger, Eysenck and Costa and McCrae models. PubMed was searched for papers investigating the association between any gene variant and personality traits, which were grouped into five clusters: (a) anxiety, (b) impulsivity, (c) determination-activity, (d) socialization and (e) spirituality, in healthy individuals, populations and psychiatric patients. A total of 369 studies were included. No clear consensus on the role of any individual gene variant in personality modulation emerged, although SLC6A4 haplotypes and the DRD4 rs1800955 promoter variant seemed to be more reliably related to anxiety and impulsivity-related traits, respectively. Because conflicting results emerged from the literature, plausibly as a result of the combined influence of many loci of small effects on personality, larger sample sizes and more narrow and specific phenotype will be the minimum requirements for future genetic studies on personality. Moreover, gene × gene and gene × environment interaction studies deserve further attention.