By Mark Cowen
Patients with bipolar I disorder (BD I) and their unaffected siblings show increased levels of impulsivity, researchers report.
The team found that BD I patients had significantly higher total scores on the Barratt Impulsiveness Scale, version 11 (BIS-11) than unrelated mentally healthy controls, as well as higher scores on all three BIS-11 subscales (attentional, motor, and non-planning).
The unaffected siblings of BD I patients also had higher total BIS-11 scores than controls, as well as higher motor and non-planning subscale scores.
"Our results suggest that the BIS-11 is a candidate endophenotype for BD I and suggest that increased impulsivity is associated with familial liability for developing bipolar disorder," comment David Glahn (Institute of Living, Hartford, Connecticut, USA) and colleagues.
The BIS-11 is a 30-item self-report questionnaire that measures three components of impulsiveness: attentional (tendency to make rapid decisions), motor (acting without thinking), and nonplanning (lacking forethought). Higher scores indicate increased impulsiveness.
In total, 54 euthymic BD I patients, 57 of their unaffected siblings, and 49 unrelated controls completed the questionnaire. They also completed the Global Assessment of Functioning (GAF), with higher scores indicating better functioning.
The team found that BD I patients had significantly higher total BIS-11 scores than their siblings and controls, at 72.9 versus 58.9 and 52.8, respectively, and significantly higher attentional (18.7 vs 13.9 and 12.3), motor (26.1 vs 22.3 and 19.8), and nonplanning (28.0 vs 22.6 and 20.3) subscale scores.
The difference between unaffected siblings and controls was significant for total BIS-II scores and for the motor and non-planning subscale scores.
In the BD I patients, BIS-11 total score negatively correlated with GAF score, and this association was similar but attenuated in the sibling and control groups.
"Our data support previous findings of increased trait impulsivity in individuals with bipolar I disorder in a state of euthymia compared to healthy controls, and extends these findings by demonstrating that impulsivity is also increased in the unaffected full siblings of bipolar probands," conclude Glahn et al in Bipolar Disorders.
They add: "The use of quantitative endophenotypes should improve our ability to identify genes that influence risk for bipolar disorder, which in turn could provide new treatment targets for this debilitating illness."
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