Neurocognitive functions in siblings of patients with bipolar disorder

Some studies suggest that there are deficits in neurocognitive functions in the euthymic phase of bipolar disorder and healthy relatives of patients with bipolar disorder and that these neurocognitive disorders may be the endophenotype for bipolar disorder. This study aimed to evaluate the neurocognitive functions of unaffected siblings of patients with bipolar disorder compared with the healthy controls. The study included the unaffected siblings of patients with bipolar disorder (n = 75) and healthy volunteers without a family history of bipolar disorder (n = 50). The Structured Clinical Interview for DSM-IV (SCID-I) was administered to each individual to investigate the diagnosis of Axis-I psychiatric disorders according to DSM-IV. The Judgment of Line Orientation Test, the Auditory Verbal Learning Test, the Serial Digit Learning Test, the Stroop Color Word Test, and the Trail Making Test were used to evaluate neurocognitive functions. Our study found no difference between the groups regarding processing speed, set-shifting, and mental flexibility. However, unaffected siblings of patients with bipolar disorder had significantly worse performance than healthy controls in verbal learning and memory, response inhibition, and visuospatial function. This study suggests that visuospatial function, response inhibition, verbal learning, and memory may be endophenotypic markers for bipolar disorder. •Patients' siblings performed worse than healthy controls in verbal learning and memory, response inhibition, and visuospatial function.•The study found no differences between the groups regarding processing speed, set-shifting, and mental flexibility.•There were no significant differences in neuropsychological tests between subgroups of unaffected siblings.