Processing speed reduced in subgroup of BD patients
MedWire News: Results from a French study indicate that a significant subgroup of patients with bipolar disorder (BD) and their unaffected relatives show impairments in processing speed.
The findings, published in the Journal of Affective Disorders, "support the hypothesis that processing speed may be a valid endophenotype, highly specific for differentiating both euthymic BD patients and unaffected first-degree relatives, from healthy controls," say Claire Daban (Hôpital Albert Chenevier, Créteil) and team.
The researchers studied 53 euthymic BD patients, 50 of their unaffected first-degree relatives, and 60 unrelated mentally healthy controls. There were no significant differences between the groups regarding mean age, premorbid IQ, or gender distribution.
All of the participants were assessed for processing speed using the Digit Symbol Test (DST), which involves a number of straightforward scanning, switching, and writing operations undertaken over a 2-minute period.
The researchers found that, overall, there were significant between-group differences regarding mean DST scores, at 8.96 in BD patients, 9.72 in unaffected relatives, and 11.18 in controls. These differences remained significant after accounting for demographic characteristics and current mood symptoms.
Using a DST cutoff score of 7 (<5th percentile for controls) to define clinically significant impairment or no such impairment, the researchers found that 30.2% of the BD patients and 22.0% of their unaffected relatives had significant processing speed reductions.
Daban and team conclude: "Our findings support the view that a key construct of cognitive operations (ie, processing speed as measured by the DST) may be a valid endophenotype of BD."
They add: "As well as considering the use of the DST in genetic or endophenotype research, it can be argued that it may also be a useful additional screening tool if employed in combination with questionnaires based on clinical symptoms of BD such as the Hypomania Checklist.
"In the future, it would be worthwhile to investigate whether the combination of two instruments performs better than one screening tool used on its own, as they are assessing different aspects of BD."
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By Mark Cowen