Surprising lack of sex differences in normal cognitive aging in twins

The effect of age on executive functions in adults is not sex specific

OBJECTIVE

Numerous studies have shown a decrease in executive functions (EF) associated with aging. However, few investigations examined whether this decrease is similar between sexes throughout adulthood. The present study investigated if age-related decline in EF differs between men and women from early to late adulthood.

METHODS

A total of 302 participants (181 women) aged between 18 and 78 years old completed four computer-based cognitive tasks at home: an arrow-based Flanker task, a letter-based Visual search task, the Trail Making Test, and the Corsi task. These tasks measured inhibition, attention, cognitive flexibility, and working memory, respectively. To investigate the potential effects of age, sex, and their interaction on specific EF and a global EF score, we divided the sample population into five age groups (i.e., 18-30, 31-44, 45-54, 55-64, 65-78) and conducted analyses of covariance (MANCOVA and ANCOVA) with education and pointing device as control variables.

RESULTS

Sex did not significantly affect EF performance across age groups. However, in every task, participants from the three youngest groups (< 55 y/o) outperformed the ones from the two oldest. Results from the global score also suggest that an EF decrease is distinctly noticeable from 55 years old onward.

CONCLUSION

Our results suggest that age-related decline in EF, including inhibition, attention, cognitive flexibility, and working memory, becomes apparent around the age of 55 and does not differ between sexes at any age. This study provides additional data regarding the effects of age and sex on EF across adulthood, filling a significant gap in the existing literature.

Sex-difference in the association between social drinking, structural brain aging and cognitive function in older individuals free of cognitive impairment

Background

We investigated a potential sex difference in the relationship between alcohol consumption, brain age gap and cognitive function in older adults without cognitive impairment from the population-based Mayo Clinic Study of Aging.

Methods

Self-reported alcohol consumption was collected using the food-frequency questionnaire. A battery of cognitive testing assessed performance in four different domains: attention, memory, language, and visuospatial. Brain magnetic resonance imaging (MRI) was conducted using 3-T scanners (Signa; GE Healthcare). Brain age was estimated using the Brain-Age Regression Analysis and Computational Utility Software (BARACUS). We calculated the brain age gap as the difference between predicted brain age and chronological age.

Results

The sample consisted of 269 participants [55% men (n=148) and 45% women (n=121) with a mean age of 79.2 ± 4.6 and 79.5 ± 4.7 years respectively]. Women had significantly better performance compared to men in memory, (1.12 ± 0.87 vs 0.57 ± 0.89, P<0.0001) language (0.66 ± 0.8 vs 0.33 ± 0.72, P=0.0006) and attention (0.79 ± 0.87 vs 0.39 ± 0.83, P=0.0002) z-scores. Men scored higher in visuospatial skills (0.71 ± 0.91 vs 0.44 ± 0.90, P=0.016). Compared to participants who reported zero alcohol drinking (n=121), those who reported alcohol consumption over the year prior to study enrollment (n=148) scored significantly higher in all four cognitive domains [memory: F3,268 = 5.257, P=0.002, Language: F3,258 = 12.047, P<0.001, Attention: F3,260 = 22.036, P<0.001, and Visuospatial: F3,261 = 9.326, P<0.001] after correcting for age and years of education. In addition, we found a significant positive correlation between alcohol consumption and the brain age gap (P=0.03). Post hoc regression analysis for each sex with language z-score revealed a significant negative correlation between brain age gap and language z-scores in women only (P=0.008).

Conclusion

Among older adults who report alcohol drinking, there is a positive association between higher average daily alcohol consumption and accelerated brain aging despite the fact that drinkers had better cognitive performance compared to zero drinkers. In women only, accelerated brain aging is associated with worse performance in language cognitive domain. Older adult women seem to be vulnerable to the negative effects of alcohol on brain structure and on certain cognitive functions.

Verbal ability in postmenopausal women in relation to age, cognitive and reproductive factors

Word-finding difficulties have been associated with age and, in women, lowered sex hormone levels following menopause. However, there is limited understanding of the ways that specific aspects of word-finding are shaped by women's age, reproductive histories, and background factors such as education. The current study investigated the effects of age, cognitive and reproductive factors on word-finding abilities in 53 healthy postmenopausal women aged 48-79. A questionnaire was used to gather demographic information and reproductive history. A battery of verbal fluency, continuous series, and naming tasks was designed to assess word-finding across different sensory modalities and cognitive demands. Category and letter fluency were quantified as total number of correct words produced on each task. For continuous series, switch rates and switch costs were computed. For the naming tasks, accuracy and latency measures were used. There were three key findings. Firstly, there was a consistent positive association between education and all word-finding measures, i.e., verbal fluency, continuous series, and naming. Secondly, age-related declines were seen on tasks heavily dependent on working memory such as the continuous series task. Thirdly, reproductive factors across the lifespan such as age at menarche and reproductive years showed subtle effects on naming abilities, but not on verbal fluency or continuous series. The results highlight that word-finding abilities in healthy postmenopausal women are shaped by factors associated with their early years (education, age at menarche) and later adult life (age, reproductive years). The study also distinguished between the more global effects of education, and the more task-specific associations with age and reproductive variables, on verbal task performance after menopause.

The long-term effects of a polygenetic predisposition to general cognition on healthy cognitive ageing: evidence from the English Longitudinal Study of Ageing

BACKGROUND

As an accelerated cognitive decline frequently heralds onset of severe neuropathological disorders, understanding the source of individual differences in withstanding the onslaught of cognitive ageing may highlight how best cognitive abilities may be retained into advanced age.

METHODS

Using a population representative sample of 5088 adults aged •50 years from the English Longitudinal Study of Ageing, we investigated relationships of polygenic predisposition to general cognition with a rate of change in cognition during a 10-year follow-up period. Polygenic predisposition was measured with polygenic scores for general cognition (GC-PGS). Cognition was measured employing tests for verbal memory and semantic fluency.

RESULTS

The average baseline memory score was 11.1 (s.d. = 2.9) and executive function score was 21.5 (s.d. = 5.8). An increase in GC-PGS by one standard deviation (1-s.d.) was associated with a higher baseline verbal memory by an average 0.27 points (95% CI 0.19-0.34, p < 0.001). Similarly, 1-s.d. increase in GC-PGS was associated with a higher semantic fluency score at baseline in the entire sample (β = 0.45, 95% CI 0.27-0.64, p < 0.001). These associations were significant for women and men, and all age groups. Nonetheless, 1-s.d. increase in GC-PGS was not associated with decreases in verbal memory nor semantic fluency during follow-up in the entire sample, as well stratified models by sex and age.

CONCLUSION

Although common genetic variants associated with general cognition additively are associated with a stable surplus to cognition in adults, a polygenic predisposition to general cognition is not associated with age-related cognitive decline during a 10-year follow-up.

Job Strain and Trajectories of Cognitive Change Before and After Retirement

OBJECTIVES

We examined associations between job strain and trajectories of change in cognitive functioning (general cognitive ability plus verbal, spatial, memory, and speed domains) before and after retirement.

METHODS

Data on indicators of job strain, retirement age, and cognitive factors were available from 307 members of the Swedish Adoption/Twin Study of Aging. Participants were followed up for up to 27 years (mean = 15.4, SD = 8.5).

RESULTS

In growth curve analyses controlling for age, sex, education, depressive symptoms, cardiovascular health, and twinness, greater job strain was associated with general cognitive ability (estimate = -1.33, p = .002), worse memory (estimate = -1.22, p = .007), speed (estimate = -1.11, p = .012), and spatial ability (estimate = -0.96, p = .043) at retirement. Greater job strain was also associated with less improvement in general cognitive ability before retirement and a somewhat slower decline after retirement. The sex-stratified analyses showed that the smaller gains of general cognitive ability before retirement (estimate = -1.09, p = .005) were only observed in women. Domain-specific analyses revealed that greater job strain was associated with less improvement in spatial (estimate = -1.35, p = .010) and verbal (estimate = -0.64, p = .047) ability before retirement in women and a slower decline in memory after retirement in women (estimate = 0.85, p = .008) and men (estimate = 1.12, p = .013). Neither preretirement nor postretirement speed was affected significantly by job strain.

DISCUSSION

Greater job strain may have a negative influence on overall cognitive functioning prior to and at retirement, while interrupting exposure to job strain (postretirement) may slow the rate of cognitive aging. Reducing the level of stress at work should be seen as a potential target for intervention to improve cognitive aging outcomes.

Sex differences and the role of education in cognitive ageing: analysis of two UK-based prospective cohort studies

BACKGROUND

Previous studies have shown an excess risk of Alzheimer's disease and related dementias among women. Education is thought to have a causal association with dementia onset. We aimed to investigate the role of education in influencing sex differences in cognitive ageing.

METHODS

We analysed data from two prospective cohort studies in the UK; the English Longitudinal Study of Ageing (ELSA) and the Whitehall II study, to assess sex differences in cognitive performance and cognitive decline by birth cohort (birth year 1930-38, 1939-45, or 1946-55), before and after adjustment for education, and by high and low education level. Memory was assessed using immediate recall, for which data were available from all waves of the ELSA (2002-14) and Whitehall II (1997-2015) studies. Fluency was assessed using a semantic fluency test based on an animal naming task, with data available from all waves of the Whitehall II study and waves one to five (2002-10) and wave seven (2014) of the ELSA study. Cognitive scores were standardised separately in each study based on the mean and SD of the corresponding test among participants aged 50-59 years with secondary education.

FINDINGS

15 924 participants were included from the two studies. In pooled analyses, women had better memory scores than men in all birth cohorts, irrespective of adjustment for education (eg, at age 60 years, birth cohort 1930-38, mean difference between sexes [male scores minus female scores] -0·25 SDs [95% CI -0·32 to -0·19] after adjustment for education), and in both education level groups. Memory decline was faster in men than in women (at age 60 years, birth cohort 1946-55, mean difference in 13-year change -0·15 SDs [-0·20 to -0·09]; after adjustment for education -0·14 SDs [-0·20 to -0·08]). Men had better fluency scores than women in earlier birth cohorts and in the low education group (at age 60 years, birth cohort 1930-38, mean difference 0·20 SDs [95% CI 0·05 to 0·36]); but women had better fluency scores than men in later birth cohorts and in the high education group (at age 60 years, birth cohort 1946-55, mean difference -0·17 SDs [-0·24 to -0·10]). No sex differences were observed for fluency decline.

INTERPRETATION

Our findings suggest that decreasing disparities between sexes in education, due to secular increases in educational opportunities, could attenuate sex differences in dementia risk and cognitive decline in the future.

FUNDING

National Institute on Aging, National Institutes of Health; UK Medical Research Council; British Heart Foundation; and National Institute for Health Research.

Sex differences in cognition and aging and the influence of sex hormones

Sex differences in cognitive functioning have been consistently reported in some cognitive tasks, with varying effect sizes. The most consistent findings in healthy adults are sex differences in the areas of mental rotation and aspects of attention and verbal memory. Sex differences in the vulnerability and manifestation of several psychiatric and neurologic diseases that involve cognitive disruption provide strong justification to continue investigating the social and biologic influences that underpin sex differences in cognitive functioning across health and disease. The biologic influences are thought to include genetic and epigenetic factors, sex chromosomes, and sex hormones. Sex steroid hormones that regulate reproductive function have multiple effects on the development, maintenance, and function of the brain, including significant effects on cognitive functioning. The aim of the current chapter is to provide a theoretical review of sex differences across different cognitive domains in adulthood and aging, as well as provide an overview on the role of sex hormones in cognitive function and cognitive decline.

One-year change in cognitive flexibility and fine motor function in middle-aged male and female marmosets (Callithrix jacchus)

The common marmoset (Callithrix jacchus) is uniquely suited for longitudinal studies of cognitive aging, due to a relatively short lifespan, sophisticated cognitive abilities, and patterns of brain aging that resemble those of humans. We examined cognitive function and fine motor skills in male and female marmosets (mean age ∼5 at study entry) followed longitudinally for 2 years. Each year, monkeys were tested on a reversal learning task with three pairs of stimuli (n = 18, 9 females) and a fine motor task requiring them to grasp small rewards from two staircases (Hill and Valley test, n = 12, 6 females). There was little evidence for a decline in cognitive flexibility between the two time points, in part because of practice effects. However, independent of year of testing, females took longer than males to reach criterion in the reversals, indicating impaired cognitive flexibility. Motivation was unlikely to contribute to this effect, as males refused a greater percentage of trials than females in the reversals. With regards to motor function, females were significantly faster than males in the Hill and Valley task. From Year 1 to Year 2, a slight slowing of motor function was observed in both sexes, but accuracy decreased significantly in males only. This study (1) demonstrates that marmosets exhibit sex differences in cognitive flexibility and fine motor function that resemble those described in humans; (2) that changes in fine motor function can already be detected at middle-age; and (3) that males may experience greater age-related changes in fine motor skills than females. Additional data points will determine whether these sex and age differences persist over time.

Sex Differences and the Influence of Sex Hormones on Cognition through Adulthood and the Aging Process

Hormones of the hypothalamic-pituitary-gonadal (HPG) axis that regulate reproductive function have multiple effects on the development, maintenance and function of the brain. Sex differences in cognitive functioning have been reported in both health and disease, which may be partly attributed to sex hormones. The aim of the current paper was to provide a theoretical review of how sex hormones influence cognitive functioning across the lifespan as well as provide an overview of the literature on sex differences and the role of sex hormones in cognitive decline, specifically in relation to Alzheimer’s disease (AD). A summary of current hormone and sex-based interventions for enhancing cognitive functioning and/or reducing the risk of Alzheimer’s disease is also provided.

Genetic and Environmental Influences on Language Ability in Older Adults: Findings from the Older Australian Twins Study

We used a sub-sample from the Older Australian Twins Study to estimate the heritability of performance on three tests of language ability: Boston Naming Test (BNT), Letter/Phonemic Fluency (FAS) and Category/Semantic Fluency (CFT) Tests. After adjusting for age, sex, education, mood, and global cognition (GC), heritability estimates obtained for the three tests were 0.35, 0.59, and 0.20, respectively. Multivariate analyses showed that the genetic correlation were high for BNT and CFT (0.61), but low for BNT and FAS (0.17), and for FAS and CFT (0.28). Genetic modelling with Cholesky decomposition indicated that the covariation between the three measures could be explained by a common genetic factor. Environmental correlations between the language ability measures were low, and there were considerable specific environmental influences for each measure. Future longitudinal studies with language performance and neuroimaging data can further our understanding of genetic and environmental factors involved in the process of cognitive aging.

Visuospatial Reasoning Trajectories and Death in a Study of the Oldest Old: A Formal Evaluation of Their Association

OBJECTIVES

To model trajectories of visuospatial reasoning measured using Kohs Block Design test under realistic missing data assumptions and evaluate their association with hazard of death.

METHODS

A joint longitudinal-survival model was used to estimate trajectories of visuospatial reasoning under a missing not at random assumption of participants from the Origins of Variance in the Old-Old: Octogenarian Twins study. Sensitivity analyses to missing data assumptions were conducted.

RESULTS

Visuospatial reasoning declined at constant rate. Baseline age, dementia status, education, and history of stroke were associated with visuospatial reasoning performance, but only dementia was associated with its rate of decline. Importantly, our results demonstrated an association between poorer visuospatial reasoning and increased hazard of death. Baseline age and sex were associated with risk of death.

DISCUSSION

We confirmed an association between visuospatial reasoning and death under plausible missing data assumptions.

Gender-Specific Degeneration of Dementia-Related Subcortical Structures Throughout the Lifespan

Age-related changes in brain structure are a question of interest to a broad field of research. Structural decline has been consistently, but not unambiguously, linked to functional consequences, including cognitive impairment and dementia. One of the areas considered of crucial importance throughout this process is the medial temporal lobe, and primarily the hippocampal region. Gender also has a considerable effect on volume deterioration of subcortical grey matter (GM) structures, such as the hippocampus. The influence of age×gender interaction on disproportionate GM volume changes might be mediated by hormonal effects on the brain. Hippocampal volume loss appears to become accelerated in the postmenopausal period. This decline might have significant influences on neuroplasticity in the CA1 region of the hippocampus highly vulnerable to pathological influences. Additionally, menopause has been associated with critical pathobiochemical changes involved in neurodegeneration. The micro- and macrostructural alterations and consequent functional deterioration of critical hippocampal regions might result in clinical cognitive impairment-especially if there already is a decline in the cognitive reserve capacity. Several lines of potential vulnerability factors appear to interact in the menopausal period eventually leading to cognitive decline, mild cognitive impairment, or Alzheimer's disease. This focused review aims to delineate the influence of unmodifiable risk factors of neurodegenerative processes, i.e., age and gender, on critical subcortical GM structures in the light of brain derived estrogen effects. The menopausal period appears to be of key importance for the risk of cognitive decline representing a time of special vulnerability for molecular, structural, and functional influences and offering only a narrow window for potential protective effects.

Sex differences in cognitive trajectories in clinically normal older adults

Age effects on cognitive functioning are well-documented, but effects of sex on trajectories of cognitive aging are less clear. We examined cognitive ability across a variety of measures for 1,065 to 2,127 participants (mean baseline age 64.1 to 69.7 years) from the Baltimore Longitudinal Study of Aging who were repeatedly tested over a mean follow-up interval of 3.0 to 9.0 years with a mean of 2.3 to 4.4 assessments. Memory and other cognitive tests were administered at each visit, assessing mental status, verbal learning and memory, figural memory, language, attention, perceptuomotor speed and integration, executive function, and visuospatial ability. Importantly, participants free from cognitive impairment at all time points were used in the analyses. Results showed that for all tests, higher age at baseline was significantly associated with lower scores, and performance declined over time. In addition, advancing age was associated with accelerated longitudinal declines in performance (trend for mental status). After adjusting for age, education, and race, sex differences were observed across most tests of specific cognitive abilities examined. At baseline, males outperformed females on the 2 tasks of visuospatial ability, and females outperformed males in most other tests of cognition. Sex differences in cognitive change over time indicated steeper rates of decline for men on measures of mental status, perceptuomotor speed and integration, and visuospatial ability, but no measures on which women showed significantly steeper declines. Our results highlight greater resilience to age-related cognitive decline in older women compared with men.

Gender Differences in Cognitive Performance in Old Age

Objective: To examine gender differences in level and change of cognitive performance in the oldest old while accounting for gender differences in longevity. Method: 574 individuals, aged 80 years and older, from the OCTO Twin Study. Five cognitive domains were administered at five occasions at 2-year intervals. Results: There were no cognitive differences between men and women, with the exception that men showed a steeper rate of decline in semantic memory. This effect was driven by men who had developed dementia and declined at a faster rate than women. Conclusion: Our results support previous findings showing minor to nonexisting gender differences in cognition among nondemented individuals in very old age when taking gender differences in longevity into account.

Rate of cognitive decline in relation to sex after 60 years-of-age: a systematic review

Some studies have shown differences in specific cognitive ability domains between the sexes at 60 years-of-age. However is important to analyze whether the rate of cognitive decline is also similar between the sexes after this age. The present study examined previously published literature to investigate whether cognitive decline is distinct between men and women after the age of 60 years. A systematic review was carried out with the PubMed, LILACS and PsycINFO databases (2001-2011) using the following search terms: aging, aged, cognitive function, mild cognitive impairment, mental health and cognition. We analyzed longitudinal research that used neuropsychological tests for evaluating cognitive function, showed results separated by sex and that excluded participants with dementia. Elderly women showed better performance in tests of episodic memory, whereas elderly men had a better visuospatial ability. Only one study detected distinct rates of cognitive decline in specific tests between the sexes. Despite differences observed in some domains, most of the studies showed that this rate is similar between the sexes until the age of 80 years. It is unclear whether sex influences the rate of cognitive decline after the age of 80 years. The present review observed that sex does not determine the rate of cognitive decline between 60 and 80 years-of-age. The contextual and cultural factors that involve men and women might determine a distinct decline between them, rather than sex alone.

Regional specificity of sex effects on subcortical volumes across the lifespan in healthy aging

When conceptualizing age-specific onsets and sex-specific characteristics of neuropsychiatric diseases in a neurobiological context, it may be crucially important to consider differential trajectories of aging. Here, we investigated effects of age, sex, and their interactions on absolute and relative volumes of subcortical structures with known involvement in psychiatric disorders, including the basal ganglia, thalamus, hippocampus, and amygdala. Structural MRI data of 76 healthy subjects (38 males, 19-70 years) from the ICBM database were analyzed. Age-related absolute atrophy was generally found in the basal ganglia and thalamus, while in the hippocampus decline was only observed in males, and was generally absent in the amygdala. Disproportionate degeneration in the basal ganglia and thalamus, exceeding cortical decline was specific for females. When allowing higher-order models, a quadratic model could better describe the negative relation of absolute volume and age in the basal ganglia in males, and generally in the hippocampus and amygdala. We could show that negative age-relations are highly specific for certain subcortical structures in either gender. Importantly these findings also emphasize the significant impact of analytical strategies when deciding for correction of subcortical volumes to the whole-brain decline. Specifically, in the basal ganglia disproportionate shrinkage in females was suggested by the relative analysis while absolute volume analysis rather stressed an accelerating decline in older males. Given strong involvement of the basal ganglia in both cognitive aging and emotional regulation, our findings may be crucial for studies investigating the onset and prevalence of dementia and depressive symptoms in male and female aging.

Association between C-reactive protein and cognitive deficits in elderly men and women: a meta-analysis

BACKGROUND

Certain risk factors for cognitive decline appear modifiable. A potentially modifiable marker of inflammation, C-reactive protein may be associated with cognitive deficits, although not all studies have found a relationship between C-reactive protein and cognitive ability. Further, few research papers have examined whether gender may affect any association between C-reactive protein and cognitive deficit.

METHODS

To better understand the association between C-reactive protein, cognitive deficit, and gender in elderly people, we meta-analyzed cross-sectional studies that reported cognitive ability assessed by the Mini-Mental State Examination or an equivalent measure, C-reactive protein concentrations, and gender.

RESULTS

While we identified no studies containing only male subjects, the two identified studies containing both female and male subjects (n = 2,525) showed an effect size for cognition of -0.1809 (95% confidence interval, -0.2652 to -0.0967, p = 0.000025) between high and low C-reactive-protein groups. In contrast, the two identified studies containing only female subjects (n = 1,754) showed an effect size for cognition of 0.0345 (95% confidence interval, -0.0594 to 0.1285, not significant).

CONCLUSIONS

In the context of a small number of source studies and lack of an all-male group, these results suggest that any association between C-reactive protein and cognitive deficits may be stronger in elderly men than in elderly women.

Both odor identification and ApoE-ε4 contribute to normative cognitive aging

Research indicates that apoliprotein E (ApoE) plays a role in the development of Alzheimer's disease (AD) and possibly in the cognitive decline associated with normative aging. More recently, researchers have shown that ApoE is expressed in olfactory brain structures, and a relationship among ApoE, AD, and olfactory function has been proposed. In the current analyses, we investigated the contribution of ApoE and odor identification in decline trajectories associated with normative cognitive aging in various domains, using longitudinal data on cognitive performance available from the Swedish Adoption/Twin Study of Aging. Data on both ApoE status and olfactory functioning were available from 455 individuals ranging in age from 50 to 88 years at the first measurement occasion. Odor identification was measured via a mailed survey. Cognitive performance was assessed in up to 5 waves of in-person testing covering a period of 16 years. Latent growth curve analyses incorporating odor identification and ApoE status indicated a main effect of odor identification on the performance level in three cognitive domains: verbal, memory, and speed. A main effect of ApoE on rates of decline after age 65 was found for verbal, spatial, and speed factors. The consistency of results across cognitive domains provides support for theories that posit central nervous system-wide origins of the olfaction-cognition-ApoE relationship; however, olfactory errors and APOE ε4 show unique and differential effects on cognitive trajectory features.

Genetic influences on cognitive functions in the elderly: a selective review of twin studies

In this review, we examined the published reports on the heritability of cognitive functioning in old age. Twenty-four papers from five study centers, comprising of participants with a mean age of 65 years and above were examined. The comparability of findings from different studies was compromised by the use of different measures for the same cognitive domain, and with large scale twin studies in cognitive aging limited to a few Scandinavian countries. While the results from cross-sectional samples appear to lend support for the notion that heritability of cognitive functions decreases in the elderly, the findings are best considered inconclusive. Longitudinal reports show little evidence for genetic effects, but an increase in unique environmental influences on the rate of cognitive change as age increases. In relation to the two prominent theories of cognitive aging, the genetic influence on processing speed as a major contributor to cognitive aging has been indicated in three reports, whereas the genetic relationship between executive functions and other cognitive functions has not been explored. Only two studies have focused on sex difference and did not find sex-specific genetic influence in cognitive abilities. This review indicates that there are complex relationships between heritability, environmental influence, and cognitive functions in the elderly. It highlights the need for more research, with consistent and appropriate cognitive measures, with data obtained from larger and more geographically and culturally diverse twin samples.

Heritability of neurocognitive functioning in the elderly: evidence from an Italian twin study

BACKGROUND

the genetic and environmental origins of individual differences in specific cognitive abilities in the elderly are poorly understood. One reason is the lack of studies performed in cohorts with normal cognitive functions.

OBJECTIVE

to estimate the relative contributions of genetic and environmental factors in determining inter-individual variation in neurocognitive abilities in the Italian population.

DESIGN

cross-sectional analysis of twin data.

SETTING

a sample of older twins with normal cognition from the population-based Italian Twin Registry (ITR).

SUBJECTS

twin pairs resident in Rome and born between 1926 and 1940, identified through the ITR in 2002. The final study population included 93 twin pairs.

METHODS

subjects underwent neuropsychological tests providing information about different cognitive domains. The contributions of genetic and environmental effects were assessed using standard univariate twin modelling based on linear structural equations.

RESULTS

the best-fitting model incorporated additive genetic (A) and unique environmental (E) sources of variance for the following tests: Mini-Mental State Examination (A = 55%), Raven (A = 56%), Attentional Matrices (A = 79%), Copying Drawings (A = 69%) and Story Recall (A = 54%). For Phonological and Semantic Verbal Fluency, the best model included non-additive (D) and unique environmental influences (D = 62 and 54%, respectively). Cigarette smoking was estimated to be negatively associated with the score of Phonological Verbal Fluency. For Token test, the inter-individual variance was entirely due to environmental factors not shared by the twins.

CONCLUSION

our data showed that most of the specific cognitive abilities are moderately to highly heritable, and that the environmental factors of relevance for these abilities are those causing within-family differences.

A phenotype for genetic studies of successful cognitive aging

Survival from Alzheimer's disease (AD) and other dementias into late old age may be a useful phenotype for genetic studies of successful cognitive aging. To support molecular genetics studies for successful cognitive aging, we conducted a two-stage study to determine an optimal age phenotype for successful cognitive aging. First, risk of AD was evaluated, through informant interviews, in 4,794 parents and siblings of 976 elderly nondemented probands who were divided into three different proband age groups: those aged 60-74, 75-89, and 90+. Relatives of probands aged 90+ had a significantly lower risk than the relatives of the other two proband groups. Second, this sample was combined with an earlier sample (combined nondemented elderly probands: n = 2,025; relatives: n = 10,506), and a series of proband age groups (i.e., 75-79, 80-84, 85-89, 90+) were used to determine which optimally identifies a group of relatives with low AD risk. Using the relatives of the nondemented proband aged 60-74 as the reference group, there were reductions in cumulative risk among relatives of probands aged 85-89 and 90+, but only the latter group also showed significant reductions to the relatives of probands aged 75-79, 80-84, and 85-89. This pattern of results varied little by sex. Finally, cumulative AD risk curves were similar between relatives of probands aged 90-94 and 95+. These results suggest that age 90 is an optimal age threshold to use for both men and women in genetic studies seeking to identify genes associated with successful cognitive aging.

Female CREBalphadelta- deficient mice show earlier age-related cognitive deficits than males

Age-related changes in the hippocampus increase vulnerability to impaired learning and memory. Our goal is to understand how a genetic vulnerability to cognitive impairment can be modified by aging and sex. Mice with a mutation in the cAMP response element binding (CREB) protein gene (CREB(alphadelta-) deficient mice) have a mild cognitive impairment and show test condition-dependent learning and memory deficits. We tested three ages of CREB(alphadelta-) deficient and wild-type (WT) mice in two Morris water maze (MWM) protocols: four trials per day with a 3-5 min inter-trial interval (ITI) (MWM4) and two trials per day with a 1 min ITI (MWM2). All CREB(alphadelta-) deficient mice performed well in the easier MWM4, except for the aged females that performed poorly. In the harder MWM2, young male and female and middle-aged male CREB(alphadelta-) deficient mice performed well, but aged male and all middle-aged and aged female CREB(alphadelta-) deficient mice were impaired. These results show that mice with a genetic vulnerability to impaired learning and memory exhibit increased vulnerability with age that is most apparent among females. Thus, a genetic predisposition to cognitive impairment may render females more vulnerable than males to such deficits with age.

Cohort Differences in Trajectories of Cognitive Aging

To separate age and cohort effects on decline in normal cognitive aging, we applied growth curve models to longitudinal data from the Swedish Adoption/Twin Study of Aging. Data from up to five measurement waves covering a 16-year period were available from 806 participants (age 50 to 88 at the first wave). We divided the sample into two cohorts by birth year: 1900-1925 and 1926-1948. We generated components to tap four cognitive domains: verbal and spatial ability, memory, and speed. We tested cohort differences by using two growth models: quadratic and two linear slopes. Results indicated significant cohort differences in average performance at age 67.5 for all components except speed. When we compared linear slopes during the same age range (age 62-78), we found no cohort differences. Trajectories of change with age in these four domains were fundamentally the same in middle-old age for individuals born during the first half of the 20th century.