Psychological Medicine



Memory and verbal learning functions in twins with bipolar-I disorder, and the role of information-processing speed


TUULA KIESEPPÄ a1c1, ANNAMARI TUULIO-HENRIKSSON a1, JARI HAUKKA a1, THEO VAN ERP a1, DAVID GLAHN a1, TYRONE D. CANNON a1, TIMO PARTONEN a1, JAAKKO KAPRIO a1 and JOUKO LÖNNQVIST a1
a1 Department of Mental Health and Alcohol Research, National Public Health Institute, Helsinki, Finland; Department of Public Health, University of Helsinki, Helsinki, Finland; Department of Psychology, UCLA, California, USA; Department of Psychiatry and Research Imaging Center, University of Texas, San Antonio, Texas, USA

Article author query
kieseppa t   [PubMed][Google Scholar] 
tuulio-henriksson a   [PubMed][Google Scholar] 
haukka j   [PubMed][Google Scholar] 
van erp t   [PubMed][Google Scholar] 
glahn d   [PubMed][Google Scholar] 
cannon td   [PubMed][Google Scholar] 
partonen t   [PubMed][Google Scholar] 
kaprio j   [PubMed][Google Scholar] 
lonnqvist j   [PubMed][Google Scholar] 

Abstract

Background. Euthymic bipolar-I disorder (BP I) patients and their siblings have shown impairments in verbal learning and memory functions compared with controls, suggesting that these impairments may be genetic in origin. Reduced information-processing speed has been associated with impaired memory in the elderly, and recently in schizophrenia. The authors compared verbal learning and memory functioning in twins with BP I and co-twins to control twins, and examined whether the observed deficits are related to information-processing speed.

Method. Finnish Medical and Population Registers and Twin Cohorts were used to identify the BP I and control twins. Neuropsychological tests assessing verbal learning and memory, working memory, facial recognition, visual memory, and information-processing speed were administered to 26 BP I twins, 19 non-bipolar co-twins, and 114 controls. Group differences were analyzed by generalized estimation equation modeling.

Results. BP I patients, but not co-twins, showed impairments in all memory tests compared with controls. Female co-twins showed impairment in verbal learning and memory. Information-processing speed had a significant effect on encoding and learning efficiency.

Conclusions. This study showed for the first time that information-processing speed is related to memory functioning and verbal learning in BP I in a population-based, representative and euthymic sample. Furthermore, the data support the view that defects in verbal memory may be related to the genetic factors predisposing to BP I in females.


Correspondence:
c1 Dr Tuula Kieseppä, Department of Mental Health and Alcohol Research, National Public Health Institute, Mannerheimintie 166, 00300 Helsinki 30, Finland. (Email: tuula.kieseppa@ktl.fi)


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