Response inhibition deficits may indicate familial liability for psychotic BD I
MedWire News: Patients with bipolar I disorder (BD I) who have a history of psychotic symptoms and their unaffected first-degree relatives exhibit impairments in response inhibition, researchers have found.
"The reporting of executive functioning deficits in BD patients and their unaffected relatives compared to controls adds to the accumulating evidence that such deficits are promising candidate endophenotypic markers for BD I," explain Muriel Walshe (King's College London, UK) and team.
However, they add that a number of studies have not found executive functioning deficits in the relatives of BD patients. This may possibly be due to "methodological heterogeneity, eg, differences in sample sizes or the use of different instruments that vary in how well they assess different domains of executive functioning; and/or clinical heterogeneity, ie, combining clinical subtypes across the bipolar spectrum."
To investigate further, the team studied executive function in a "relatively homogeneous" group of 44 BD I patients who had experienced psychotic symptoms, 42 of their unaffected first-degree relatives, and 47 unrelated mentally healthy controls.
All participants were Caucasian and aged between 18 and 65 years, were similar in years of education and parental social class, and did not have a substance use disorder (excluding nicotine) or a history of head injury.
Response inhibition was assessed using the Hayling Sentence Completion Test (HSCT), verbal working memory was assessed using the Wechsler Adult Intelligence Scale-Revised (WAIS-R) and spatial working memory and cognitive set shifting were both evaluated using the Cambridge Neuropsychological Test Automated Battery (CANTAB).
Analysis of the findings revealed that BD I patients and their unaffected relatives had significantly poorer response inhibition than controls, with overall HSCT scores of 5.31 and 5.62 versus 6.43, respectively.
There were no significant differences between the three groups regarding test results for working memory or cognitive set shifting.
Analysis that excluded the eight relatives and eight controls with an Axis I diagnosis of nonpsychotic, nonbipolar disorder did not affect the overall findings, the researchers note.
Walshe et al conclude in the journal Bipolar Disorders: "Both patients and their relatives showed significant executive functioning deficits in response inhibition but not in set shifting or working memory when compared to controls.
"These findings indicate that components of executive functioning may be promising candidate endophenotypes for psychotic BD I."
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By Mark Cowen