This article is more than 5 years old. Information may no longer be current.

Different genes underlie normative personality, personality disorder

Twin study findings published in The American Journal of Psychiatry indicated that a proportion of the genetic influence underlying DSM-IV personality disorders is not shared with the constructs of those that underlie normative personality.

“Similarities in the extent of genetic influences have fueled speculation that largely the same etiological factors may underlie both normal personality and personality disorders,” Nikolai Czajkowski, PhD, of the department of psychology in the Institute of Clinical Medicine at University of Oslo in Norway, and colleagues wrote. “However, to our knowledge, no study has had the appropriate data for directly assessing the extent of overlapping genetic etiology in normative personality and DSM personality disorders.”

Researchers examined the phenotypic similarity between normative and pathological personality, as well as how genetic and environmental stimuli that trigger individual variance in normative personality account for symptom differences across the 10 personality disorders in DSM-IV.

Using data from two waves of a longitudinal population-based study of adult twins with mental illness in Norway, the investigators examined personality disorders via structured interviews. At wave two, participants completed the Big Five Inventory, a self-report instrument that measures the five prominent domains of normative personality — extraversion, agreeableness, conscientiousness, neuroticism and openness. Then, they assessed the proportion of genetic and environmental factors not shared with the five Big Five Inventory domains — in other words, factors unique to each personality disorder measure.

At wave one, the Big Five domain construct with the largest median phenotypic correlation across all 10 personality disorders was neuroticism followed by conscientiousness, agreeableness, extraversion and openness; at wave two, the domain with the largest median correlation also was neuroticism and the smallest link was also openness. Researchers found that the highest correlations were between neuroticism and borderline, avoidant and dependent personality disorder measures and the lowest correlations were for antisocial, narcissistic, histrionic and obsessive personality disorder measures.

Based on the first wave data, the percentage of genetic variance in personality disorder traits not shared with the Big Five domains ranged from 22% for avoidant to 79% for schizotypal (median, 64%), whereas the percentage of unique environmental differences ranged from 89% for avoidant to 99% for schizoid (median, 97%).

At wave two, the proportion of genetic differences not shared with the five domains ranged from 18% for avoidant to 58% for obsessive, and the percentage of unique environmental variance at wave two ranged from 79% for avoidant to 98% for obsessive. For the wave one data, the domain with the highest median genetic correlation across all personality disorder traits was agreeableness and the lowest was extraversion; whereas, the median genetic correlations across the six personality disorders measured at wave two — in decreasing order of magnitude — was neuroticism, conscientiousness, agreeableness, extraversion and openness.

“Our results suggest that although the observed association between DSM personality disorder criteria and normative personality is largely due to common genetic influences rather than environmental influences, a substantial proportion of the genetic risk underlying the endorsement of personality disorder criteria appears not to be shared with normative personality,” Czajkowski and colleagues wrote. - by Savannah Demko

Disclosures: Czajkowski reports no relevant financial disclosures. Please see the full study for all other authors’ relevant financial disclosures.