We know from twin and family studies that our personality is to a large degree – probably around 40 per cent – inherited. Geneticists are busy trying to find the specific gene variants involved, but because each one on its own only exerts a modest influence, this is challenging research requiring huge samples. A new study in Nature Genetics has made a significant contribution, using the technique of Genome Wide Analysis to look for genetic variants that correlate with personality. The researchers led by Min-Tzu Lo at the University of California, San Diego have identified variations in six genetic loci that correlate with different personality trait scores, five of which were previously unknown. In a separate analysis, the researchers also showed that many of the genetic variants involved in personality overlap with those involved in the risk of developing mental health disorders.
The researchers analysed the genomes of hundreds of thousands of people, including clients of 23andMe – a commercial service that promises to inform customers about their ancestry and health based on their DNA (usefully for present purposes, the company also asks its clients to complete personality questionnaires). Among the genetic loci the researchers identified as being linked with personality, the most influential correlated with Neuroticism scores and was on a region of chromosome 8 (specifically 8p23.1) that is known to be involved in nervous system development and developmental neuropsychiatric disorders. Another that was linked with extraversion scores was on a region of chromosome 12 (specifically 12q23.3) that has also been highlighted in genetic research into bipolar disorder.
The researchers also compared the gene/personality correlations in their massive data sets with similar records previously obtained by the Psychiatric Genetics Consortium to look for genetic influences on mental health disorders. This showed substantial genetic correlations between personality and psychiatric disorders – that is, many of the genetic influences on personality are also implicated in the risk of developing various mental health disorders. This makes sense given what we already know about the influence of personality on mental health – for instance, high scorers on Neuroticism are at increased risk of anxiety and depression, while high scorers on Extraversion and Openness to Experience are more likely than others to be diagnosed with bipolar disorder.
The genetic findings largely matched this picture. For instance, in terms of shared genetic influences, the trait of Openness to Experience, bipolar disorder and schizophrenia tended to cluster together, as did Neuroticism and Depression, and Extraversion and ADHD.
Another test the researchers were able to do was to see what proportion of the variation in the participants’ personality traits could be traced to differences in their genome – in other words to estimate the genetic heritability for each of the Big Five traits. Based on an analysis of over one million genetic variants (single-nucleotide polymorphisms; SNPs) present in the 59,000+ clients of 23andMe, the researchers found that Extraversion was the most strongly heritable trait with 18 per cent of variation in this trait traceable to differences in the genome (the estimates for Agreeableness, Conscientiousness, Neuroticism and Openness were 8 per cent, 9 per cent, 11 per cent and 10 per cent, respectively). As expected, these heritability estimates for personality are lower than those found in twin and family studies – among the reasons for this is the fact the researchers were only able to look at a fraction of the genetic variants that may play a role in personality, and were unable to explore ways that genes interact with the environment.
The researchers said that overall their results are consistent with the idea that “maladaptive or extreme variants of personality may contribute to the persistence of, or vulnerability to, psychiatric disorders and comorbidity”. They ended with a note about keeping things in perspective. “Personality traits are probably influenced by many genetic variants and gene-environment interactions,” they said. “Researchers are only beginning to understand the genetics of personality and their relation to psychiatric disorders.” In other words, these are important findings, but they are just one small piece in a growing genetic jigsaw puzzle that might one day contribute to improving people’s mental health.