Objective: Most psychiatric disorders are complex genetic traits involving both genetic and environmental risk factors. Some authors have advocated the use of the endophenotype approach to circumvent this problem. . Several cognitive functions have been suggested to be potential endophenotypes for bipolar disorder (BD), and the strongest evidence is for verbal learning/memory, verbal working memory as well as sustained attention, information processing speed and executive functioning, particularly set shifting and response inhibition. The aim of the present study was to assess cognitive functions in unaffected siblings of patients with BD comparing with the healthy subjects with a negative family history.
Method: The unaffected siblings of patients with BD (n=75) and healthy volunteers with a negative family (n=50) were enrolled in the study. The sociodemographic and clinical features of the patients and the control subjects were recorded and SCID-I was administered to determine the existence of any psychiatric morbidity. Visuospatial abilities were evaluated by using the Judgment of Line Orientation Test (JLOT). The Auditory Verbal Learning Test (AVLT) and the Serial Digit Learning Test (SDLT) were used to assess verbal learning and memory. The Stroop Test was used to assess response inhibition and selective attention. Psychomotor speed and set shifting were evaluated by the Trail Making Test (TMT).
Results: There was no difference in TMT and SDLT between unaffected siblings of patients with BD and control subjects. The unaffected siblings of patients with BD showed significantly poorer performance on the AVLT, the JLOT and the Stroop Test compared with control group.
Conclusion: This study suggests that visuospatial ability, response inhibition, selective attention, long delay free recall and recognition memory may be endophenotypic markers for BD. Longitudinal studies using more comprehensive tests with larger population are need.