Background: Cognitive deficits seem to be more prevalent in relatives of patients with bipolar disorder type I compared to relatives of BD type II patients. Assessment of cognitive performance in siblings of bipolar disorder from simplex (only one known case of bipolar disorder in first degree relatives) and multiplex (more than one known case of bipolar disorder in first degree relatives) families may provide some light to investigate the biological vulnerability in bipolar disorder. There is limited data pertaining to studies on siblings of patients with bipolar disorder and especially on comparison of effect of Bipolar I Disorder on neurocognitive functions between full biological siblings of patients from simplex and multiplex Families. Materials and Methods: This is a prospective, teaching hospital based, single point non-invasive study of 29 unaffected full biological siblings of patients diagnosed (as per DSM-IV-TR) as bipolar disorder I (BD-I) from Simplex and Multiplex families. Results: The siblings belonging to the multiplex group performed poorly on most domains of the Wisconsin Card Sorting Test (WCST). Comparison of the performance of the siblings belonging to the multiplex sub-group to those of simplex sub-group on the various domains of the Continuous Performance Test (CPT) and Spatial Working Memory Test (SWMT) did not show statistically significant difference. Conclusions: The performance in WCST is significantly affected in siblings from multiplex families than in simplex ones.
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