People with bipolar disorder vary significantly from their unaffected relatives, and from healthy controls, on several measures of personality, a study shows.
Furthermore, genetic analysis revealed suggestive linkage peaks for those traits that were heritable, potentially proving useful for the identification of genes underlying susceptibility to bipolar disorder.
“The results of our analyses suggest that personality dimensions may have utility in dissecting the genetic architecture of BD [bipolar disorder],” the researchers write in the Journal of Affective Disorders.
Personality scores on the Temperament and Character Inventory (TCI) were collected from 428 members of 101 families in which one or more people had a bipolar diagnosis or major depressive disorder. An independent sample of 53 control participants with no personal or family history of mental illness was also recruited.
The TCI is a self-administered true/false questionnaire that assesses personality in seven dimensions. It assesses four temperament dimensions – novelty seeking, harm avoidance, reward dependence and persistence – and three character dimensions – self-directedness, cooperativeness and self-transcendence.
Lead researcher Tiffany Greenwood (University of California, San Diego, USA) and team found significant group differences between patients with bipolar disorder, their first-degree relatives, and independent controls on all personality dimensions apart from reward dependence and persistence.
Bipolar patients had significantly higher scores for novelty seeking, harm avoidance, and self-transcendence and lower scores for self-directedness and cooperativeness than participants with depression, first-degree relatives, and controls.
All personality dimensions except harm avoidance and reward dependence were found to be significantly heritable. Linkage analysis in the subset of 51 families for which genetic data was available produced several suggestive linkage peaks for novelty seeking, persistence, and self-directedness.
The authors identified several genes of potential neuronal significance beneath the suggestive peaks; for example, the glutamate receptor gene GRIK2 lies directly beneath the “persistence peak” on chromosome.
The authors conclude that self-directedness may be a particularly useful measure in studying bipolar disorder, as it was “the most heritable personality dimension in our study, gave the strongest linkage signal, and showed the expected trend of significantly more pathological scores for [bipolar disorder] subjects, followed by their relatives, with the least pathological scores observed for controls.”
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