Results from a Taiwanese study suggest that aggression may be a trait marker for bipolar II disorder (BD II).
Yuan-Hwa Chou (National Yang Ming University, Taipei) and team found that BD II patients have increased levels of aggression, even during periods of euthymia, compared with mentally healthy individuals (controls).
They also found that although there was no significant difference in brain serotonin transporter (SERT) availability between BD II patients and controls, SERT availability in the midbrain and aggression scores were significantly correlated in BD II patients.
"This may reflect the role of SERT availability in aggression per se," they comment.
The findings come from a study of 24 euthymic BD II patients and 38 age-matched controls who were assessed for aggression using the Overt Aggression Scale (OAS). There were no significant differences between the groups regarding gender distribution, education, and body mass index.
The participants were also assessed for SERT availability using single photon emission computed tomography.
The researchers found that total OAS scores were significantly higher in BD II patients than controls, at 15.0 versus 2.5, as were scores for all three OAS sub-items, at 10.5 versus 0.6 for aggression, 3.5 versus 1.8 for irritability, and 1.0 versus 0 for suicidality.
There were no significant differences in SERT availability between BD II patients and controls in the midbrain, the thalamus, or the striatum.
However, there was a significant correlation between SERT availability in the midbrain and total OAS score, as well as all OAS sub-item scores, in BD II patients.
There was no such association in controls, and no associations between SERT availability and OAS scores in other brain regions in either BD II patients or controls.
Chou and team conclude in the Journal of Affective Disorders: "The higher total scores of OAS in euthymic BD II patients than in HCs [healthy controls] support the idea that aggression might be a trait marker for BD.
"Although SERT availability in euthymic BD II patients and in HCs did not differ significantly, the correlation of SERT availability and total OAS provides the possible explanation of aggression in BD II."
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