How Personality Traits Tip Over Into Mental Illness

Disorders like depression and ADHD may be genetically linked to personality traits.
Neuroticism has a similar genetic underpinning to clinical depression and anxiety, researchers find.
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Neuroticism has a similar genetic underpinning to clinical depression and anxiety, researchers find.

Psychologists are aware that personality can factor into mental health ― for example, perfectionism leading to clinical depression and anxiety disorders ― but the relationship between certain personality traits and psychiatric illnesses isn’t entirely clear.

A fascinating new study published in Nature Genetics on Dec. 5 takes this association a step further. The findings suggest that personality traits and mental illness exist on a continuum, sharing key influences on a genetic level.

In other words, when innate personality traits are pushed to an extreme by age, adversity or other life experiences, a once-benign quality may turn into mental illness.

“We found genetic overlap between personality and mental illnesses ― some genetic variants influencing personality also contribute to risks of mental illness,” Dr. Chi-Hua Chen, an assistant professor of radiology at the University of California San Diego and the study’s lead author, told The Huffington Post. “Mental illnesses can be viewed as maladaptive or extreme variants of personality traits.”

Chen and her team examined the genetic profiles of 260,000 people using data from 23andMe and the Genetics of Personality Consortium. In their analysis, the researchers were able to identify six regions of the genome linked with major personality domains. The researchers focused on the “big five” personality traits ― extraversion, neuroticism, agreeableness, openness to experience and conscientiousness ― which psychologists have long considered to be the basic dimensions of human personality.

When these personality regions of the genome were compared to areas associated with psychiatric illnesses, some striking overlaps emerged.

For one, they saw that places where gene variations predicted neuroticism ― a trait involving being prone to moodiness, anxiety, sadness and other negative thinking patterns and emotions ― were the same areas where variations predicted clinical depression and generalized anxiety disorder.

“Mental illnesses can be viewed as maladaptive or extreme variants of personality traits.”

While psychologists have previously identified the link between neuroticism and depression and anxiety disorders, a genetic overlap between the personality trait and the disorders hadn’t been shown until now. It seems that when the trait becomes too dominant or unhealthy, it can turn into depression.

“In some ways, it’s not surprising, because clinical and behavioral data have shown links between personality traits and mental illnesses, especially between neuroticism and major depression and anxiety,” Chen said. “However, it’s surprising that these links have such clear genetic underpinning.”

The subsection of the genome where neuroticism was located also comprised genes related to immunity and the nervous system, suggesting that neuroticism could be linked to physical health risks, too. This particular area is considered a “potential hub for cancer and developmental neuropsychiatric disorders,” the researchers noted.

Similar correlations were observed between extraversion and ADHD, and between openness and schizophrenia and bipolar disorder.

The association between openness, schizophrenia and bipolar disorder offer a fascinating window into the creativity-mental illness debate. Openness to experience ― a trait comprised of things like risk-taking, intellectual curiosity and engagement in fantasy and the arts ― is the number-one personality trait predicting artistic and scientific creativity.

Both openness and psychotic disorders are linked with heightened creativity, and also with dopamine activity. A 2010 Swedish study found that dopamine systems in healthy, highly creative adults are similar in certain ways to those found in the brains of people with schizophrenia.

As that study’s author Dr. Fredrik Ullén suggested, creativity and psychotic disorders may lie on two ends of the same spectrum.

“Thinking outside the box,” he said, “might be facilitated by having a somewhat less intact box.”

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