Neuropsychological performance of monozygotic twins discordant for bipolardisorder

Background: A paradigm that involves cognitive assessment of monozygotic (M Z) twins discordant for a neuropsychiatric disorder there bipolar illness) allows for the examination of bath disease-specific impairments tin the com parison of affected to unaffected twins) and risk factors tin the compariso n of unaffected twins to normal twins), Methods: Neuropsychological functions were evaluated in seven MZ twin pairs discordant for bipolar illness and seven pairs of normal MZ twins in an at tempt to highlight cognitive abilities associated with manifestations of di sease and genetic risk factors. Ar the time of testing, 3 of the affected t wins were euthymic, 2 had depressive symptoms, and 2 had manic symptoms; al l were receiving medication. All twins receive neuropsychological tests to evaluate intelligence, attention, visuospatial skills, language, learning a nd memory, and problem solving. Results: Statistical analyses revealed that the affected twins were signifi cantly impaired as compared to the unaffected land normal) twins on some me asures of visuospatial functioning and some verbal memory measures. In cont rast to a sample of MZ twins discordant for schizophrenia studied previousl y, the cognitive impairments we observed in bipolar twins were mild in natu re and fairly circumscribed. The unaffected twins performed significantly w orse than normal controls on a Brown-Petersen memory task, verbal list lear ning, and overall Wechsler Memory Quotient. Conclusions: These data suggest that while some visuospatial deficits and v erbal memory deficits may be features of bipolar disorder related to diseas e parameters, mild attenuations in overall memory or retrieval function may be related to genetic factors associated with the illness, Biol Psychiatry 1999;45:639-646 (C) 1999 Society of Biological Psychiatry.