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


METHODS
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.
Kieseppä
Tuula
T
Department of Mental Health and Alcohol Research, National Public Health Institute, Helsinki, Finland. tuula.kieseppa@ktl.fi
Tuulio-Henriksson
Annamari
A
Haukka
Jari
J
Van Erp
Theo
T
Glahn
David
D
Cannon
Tyrone D
TD
Partonen
Timo
T
Kaprio
Jaakko
J
Lönnqvist
Jouko
J
D000328:Adult; D001714:Bipolar Disorder / Q000150:complications / Q000235:genetics* / Q000523:psychology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D008569:Memory Disorders / Q000235:genetics / Q000503:physiopathology*; D008606:Mental Processes; D008875:Middle Aged; D009483:Neuropsychological Tests; D013997:Time Factors; D014706:Verbal Learning / Q000502:physiology*