Ventral prefrontal executive function impairment as a potential endophenotypic marker for bipolar disorder

Patients with remitted bipolar disorder have cognitive impairments, particularly in executive functions. However, the findings of studies that investigated cognitive functions in unaffected relatives of patients with bipolar disorder are conflicting.

The aim of this study is to investigate executive functions in healthy parents of patients with bipolar I disorder, along with bipolar I disorder patients and matched controls. It has been hypothesized that both patients with bipolar I disorder and their parents would have executive function impairments compared with controls.

25 patients with bipolar I disorder, in full remission, 25 healthy controls that matched the patients with respect to age, gender and education, 50 healthy parents of those patients and 50 healthy controls that matched the parents for age, gender and education were included in the study. All the participants were interviewed with Structured Clinical Interview for DSM-IV-Axis I (SCID-I). Executive functions were assessed using the Verbal Fluency Test (VFT), Trail Making Test (TMT), Wisconsin Card Sorting Test (WCST) and Stroop Test.

Patients performed significantly worse than their matched controls on the VFT, TMT and Stroop tests, but not on the WCST. Parents performed significantly worse than their matched controls on the TMT and Stroop tests, but not on the VFT and WCST.

Our results bring more evidence that deficits in ventral, but not dorsal prefrontal executive functions are associated with familial vulnerability to bipolar disorder and ventral prefrontal executive function impairments may represent a potential endophenotype for bipolar disorder.