Differential genetic influence for components of memory in aging adult twins.
OBJECTIVE
To investigate the relative proportion of genetic and environmental contributions to verbal memory in community-dwelling World War II veteran twins.


METHODS
The California Verbal Learning Test (CVLT) was administered to 94 monozygotic (MZ) and 89 dizygotic (DZ) elderly male twin pair participants in the fourth examination of the National Heart, Lung, and Blood Institute Twin Study.


METHODS
Subjects voluntarily participated on an outpatient basis at a research or medical center facility in 1 of 4 sites in the United States.


METHODS
Subjects had a mean age of 71.8 years (SD, 2.9 years), a mean educational level of 13.6 years (SD, 2.8 years), and no history of stroke and/or a Mini-Mental State Examination score of 23 or greater.


METHODS
Twin pair similarity in performance on 4 factor analytically derived components of the CVLT measuring verbal learning and memory, response discrimination, learning strategy, and recognition memory.


RESULTS
The MZ intraclass correlation was significantly larger than the DZ correlation for verbal learning and memory (I<.001) but not for the other 3 components of memory. Using maximum likelihood methods, the best-fitting genetic model indicated that verbal learning and memory has a substantial genetic component (56% of total variance), whereas response discrimination has a much smaller, although still detectable, genetic component (24% of total variance). There is no evidence of genetic influence on learning strategy or recognition memory.


CONCLUSIONS
Differential contribution of genetic and environmental influences to specific components of memory suggest that, in this group of elderly male twin pairs, some components may be more amenable to intervention than others.
Swan
G E
GE
Center for Health Sciences, SRI International, Menlo Park, Calif 94024, USA. gswan@unix.sri.com
Reed
T
T
Jack
L M
LM
Miller
B L
BL
Markee
T
T
Wolf
P A
PA
DeCarli
C
C
Carmelli
D
D
D000368:Aged; D004193:Discrimination Learning; D006801:Humans; D007859:Learning Disabilities / Q000235:genetics; D008297:Male; D008568:Memory; D011939:Mental Recall; D009483:Neuropsychological Tests; D014427:Twins / Q000235:genetics*; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics; D014706:Verbal Learning