Executive dysfunctions as potential markers of familial vulnerability to bipolar disorder and schizophrenia

Attentional and executive impairments have been found both in patients with schizophrenia and in their unaffected first-degree relatives, suggesting that they might be considered as familial vulnerability markers. Several studies have shown that the performance of bipolar patients does not significantly differ from that of schizophrenic patients, so that executive and attentional deficits might not be specific to schizophrenia. In the present study, we aimed to identify executive dysfunctions in schizophrenia and bipolar disorder that might be vulnerability trait markers specific to one or common to both of these diseases. We assessed cognitive performance of euthymic bipolar and schizophrenic patients, their unaffected first-degree relatives and a healthy control group, using neuropsychological tasks to test different components of executive function: the Verbal Fluency Test, the Stroop Word Colour Test, the Wisconsin Card Sorting Test and the Trail Making Test. The two groups of patients and their unaffected relatives demonstrated disproportionately increased slowness on the Stroop test in comparison to the normal healthy group. Patients with schizophrenia performed poorly on all the tests in comparison to the normal healthy subjects, while no other impairment was observed in the bipolar patients and in the relatives of schizophrenic and bipolar patients. Enhanced susceptibility to interference and reduced inhibition could be transnosographical markers for a shared familial vulnerability common to schizophrenia and bipolar disorders.