Executive functioning in twins with bipolar I disorder and healthy co-twins.

The aims of the study were to compare performance of twins with bipolar disorder (BPD) and healthy co-twins in neuropsychological tests assessing various aspects of executive functioning and to examine the relationship of clinical factors with executive functions. Twenty-six euthymic BPD twins, 19 co-twins, and 114 control twins were examined using the Stroop test, the Wisconsin card sorting test (WCST), the trail making test (TMT), and semantic and phonemic verbal fluency tests. BPD twins and co-twins performed worse than controls in the Stroop test. BPD twins scored lower than controls in semantic fluency. Clinical factors correlated with scores in TMT, WCST, and semantic fluency. Our results suggest that the response inhibition impairment may associate with genetic risk of BPD and represent a potential endophenotype for BPD. The impaired performance in the semantic fluency test among the patients may result from semantic memory retrieval problems.