Results from a US study show that patients with mood disorders exhibit increased levels of impulsivity, even during periods of euthymia.
The researchers also found that the unaffected relatives of mood disorder patients have higher levels of attentional impulsivity and lower levels of non-planning impulsivity than mentally healthy individuals without a family history of mood disorders.
"These observations, together with evidence that a positive family history of BD [bipolar disorder] is a strong predictor of future bipolar illness, suggest the possibility that increased attentional impulsivity and decreased non-planning impulsivity in unaffected relatives might represent a risk factor for future development of mood disorder," say Elaine Henna (University of Texas-Houston Medical School) and team.
"Alternatively, decreased non-planning impulsivity may be an adaptation that protects the unaffected relatives from expressing the illness," they add.
The findings come from a study of 54 euthymic BD patients, 25 euthymic unipolar depression (UD) patients, 14 unaffected relatives, and 136 mentally healthy individuals without a family history of mood disorders (controls).
All of the participants were assessed for attentional, motor, and non-planning impulsivity using the Barratt Impulsiveness Scale version 11A (BIS-11A).
The team found that BD and UD patients had significantly higher total BIS-11A scores than unaffected relatives and controls, at 73.9 and 67.4 versus 54.6 and 53.2, respectively.
However, BD and UD patients and their unaffected relatives had significantly higher BIS-11A scores for attentional impulsivity than controls, at 21.1, 19.0, and 19.8 versus 14.0, respectively.
Conversely, unaffected relatives had significantly lower non-planning impulsivity scores than BD and UD patients and controls, at 15.0 versus 26.6, 25.7, and 19.7, respectively.
The researchers also found that impulsivity levels were significantly higher among mood disorder patients with than without a history of substance abuse, while there was no significant difference between those with and without a history of suicide attempts.
Henna and team write: "Trait impulsivity was elevated in patients with BD and UD, confirming that impulsivity is relatively independent of mood state, and was higher in past substance users.
"Attentional impulsivity was elevated in unaffected relatives, which might signal a vulnerability to develop affective disorders."
They add: "This result should be replicated in larger samples, including the offspring of patients with UD, to assess the predictive value of impulsivity for the development of mood disorders."
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