Impairment of executive functions and memory in unaffected siblings of patients with bipolar disorder

Abstract

Objective: Neurocognitive impairments in bipolar patients as a possible endophenotype is a growing field of research. Impairments in executive functions and memory have been reported in relatives of patients with bipolar disorder, suggesting that they could be potential endophenotypes for genetic studies. In this study, neuropsychological performance in unaffected siblings of patients diagnosed as bipolar I disorder is compared to that of matched healthy controls. Method: We evaluated 35 unaffected siblings of probands with bipolar I disorder and 35 healthy controls using tests of verbal fluency, attention, executive functions and memory. Rey Auditory Verbal Learning Test (RAVLT), Wechsler Memory Scale-Revised (WMS-R) visual memory test, Stroop Colour-Word Interference test (SCWIT), Trail Making Test-A and B, Wechsler Adult Intelligence Scale-Revised Digit Span test, categoric verbal fluency test (Isaac SET Test) , and clock drawing tests were performed. Results: Unaffected siblings of patients with bipolar disorder performed poorly on the RAVLT, SCWIT, forward Digit Span Test, TMT-A and B, visual recall test. Using stepwise logictic regression TMT-B alone could highly differentiate siblings from controls. Conclusion: We found significant impairment of set shifting task measured with TMT-B in siblings of patients with BD. Our study suggests that set shifting/cognitive flexibility could be a potential cognitive endophenotype for bipolar disorder.