Aug 29 2013
By Joanna Lyford, Senior medwireNews Reporter
People with bipolar disorder type I are significantly more impulsive than the general population, while their siblings show an intermediate level of impulsivity, a study by Brazilian researchers shows.
The finding indicates that impulsivity may be a vulnerability marker for bipolar disorder, say Karla de Almeida (University of São Paolo) and study co-authors, writing in Comprehensive Psychiatry.
Noting that bipolar disorder is highly heritable and that impulsive behavior may also be genetically determined, the researchers hypothesized that people with bipolar disorder and their unaffected relatives would share an impulsive trait that represents “the behavioral expression of a specific genetic diathesis for bipolar disorder.”
To investigate, they recruited 67 euthymic outpatients with bipolar disorder type 1, 67 of their psychiatrically healthy siblings, and 70 healthy controls matched for age and gender.
All participants were assessed using the Barratt Impulsiveness Scale (BIS), which features 30 items in three domains: attentional (inattention and cognitive instability), motor (motor impulsiveness and lack of perseverance), and nonplanning impulsivity.
Mean scores on the BIS differed significantly between the three groups, report de Almeida et al. Total scores were 69.16 in patients, 59.94 in their unaffected siblings, and 57.13 in healthy controls.
People with bipolar disorder scored significantly higher than siblings and controls on all three BIS subscales. However, siblings scored significantly higher than healthy controls only on the motor impulsivity domain; scores were 22.48, 19.15, and 16.94 in probands, siblings, and controls, respectively.
The researchers say their findings suggest that motor impulsivity might be a vulnerability trait in bipolar disorder and could “contribute to further improve preventive strategies in subjects at high risk for bipolar disorder.”
They note, however, that more than 50% of siblings had suffered at least one Axis I disorder in their lifetime, potentially confounding the results.
“Further studies are needed to investigate motor impulsivity as a vulnerability factor for [bipolar disorder] in subjects at high genetic risk for this condition as well as to elucidate the influence of other Axis I diagnosis on the scores of motor impulsivity of relatives of patients with [bipolar disorder],” they conclude.
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