Apolipoprotein E epsilon4 and impaired episodic memory in community-dwelling elderly people: a marked sex difference. The Hordaland Health Study

Apolipoprotein E and Its Association With Cognitive Change and Modification of Treatment Effects of Vitamin D3 and Omega-3s on Cognitive Change: Results From the In-Clinic Subset of a Randomized Clinical Trial

BACKGROUND

Apolipoprotein E (APOE)-ε4 allele is associated with cognitive decline; however, its potential to modify effects of vitamin D3 and omega-3s supplementation on later-life cognition is unclear. Our objectives were to estimate among the in-clinic subset of a randomized trial: (1) associations between APOE-ε4 and global and domain-specific cognitive change, with exploration of potential sex and race differences; and (2) modification by APOE-ε4 of effects of vitamin D3 and omega-3s supplementation on cognitive change.

METHODS

From an ancillary study of depression prevention within a completed 2 × 2 factorial trial testing vitamin D3 (2 000 IU per day), omega-3s (1 g per day), and/or placebos, we included 743 older adults with baseline in-person neuropsychiatric assessments and APOE genotyping data. The primary outcome was change in global cognition (averaging z-scores of 9 tests) over 2 years. Secondarily, episodic memory and executive function/attention z-scores were examined. General linear models of response profiles with multiplicative interaction terms were constructed; stratified results were reported.

RESULTS

Mean age (standard deviation) was 67.1 (5.3) years; 50.6% were females; 24.9% were APOE-ε4 carriers. Compared to noncarriers, APOE-ε4 carriers had worse 2-year change in global cognition and episodic memory; differences were more apparent among females than males. There was no variation by race in APOE-ε4 associations with cognition. APOE-ε4 did not significantly modify effects of vitamin D3 or omega-3s, compared to placebo, on change in global cognition, episodic memory, or executive function/attention.

CONCLUSIONS

APOE-ε4 was associated with worse cognition but did not modify overall effects of vitamin D3 or omega-3 supplementation on cognition over 2 years.

Sex significantly predicts medial temporal volume when controlling for the influence of ApoE4 biomarker and demographic variables: A cross-ethnic comparison

OBJECTIVE

To explore the relationship between age, education, sex, and ApoE4 (+) status to brain volume among a cohort with amnestic mild cognitive impairment (aMCI).

METHOD

One hundred and twenty-three participants were stratified into Hispanic (n = 75) and White non-Hispanic (WNH, N = 48). Multiple linear regression analyses were conducted with age, education, sex, and ApoE4 status as predictor variables and left and right combined MRI volumes of the hippocampus, parahippocampus, and entorhinal cortex as dependent variables. Variations in head sizes were corrected by normalization with a total intracranial volume measurement.

RESULTS

Bonferroni-corrected results indicated that when controlling for ApoE4 status, education, and age, sex was a significant predictor of hippocampal volume among the Hispanic group (β = .000464, R2 = .196, p < .01) and the WNH group (β = .000455, R2 = .195, p < .05). Education (β = .000028, R2 = .168, p < .01) and sex (β = .000261, R2 = .168, p < .01) were significant predictors of parahippocampal volume among the Hispanic MCI group when controlling for the effects of ApoE4 status and age. One-way ANCOVAs comparing hippocampal and parahippocampal volume between males and females within groups revealed that females had significantly larger hippocampal volumes (p < .05). Hispanic females had significantly larger hippocampal (p < .001) and parahippocampal (p < .05) volume compared to males. No sex differences in parahippocampal volume were noted among WNHs.

CONCLUSIONS

Biological sex, rather than ApoE4 status, was a greater predictor of hippocampal volume among Hispanic and WNH females. These findings add to the mixed literature on sex differences in dementia research and highlight continued emphasis on ethnic populations to elucidate on neurodegenerative disparities.

The inverse association between the apolipoprotein E ε4 allele and C-reactive protein levels is stronger in persons with obesity and diabetes

BACKGROUND

C-reactive protein (CRP) is lower in patients who carry the apolipoprotein E epsilon 4 allele variant (APOEε4) of the APOE gene. This could however be explained by other factors observed in APOEε4 carriers, such as lower body mass index (BMI), possibly less diabetes and more use of statins, all associated with CRP concentrations.

OBJECTIVES

To assess the association between CRP and APOEε4 stratified by BMI, statin use and diabetes.

METHODS

We included 2700 community-dwelling older adults from the Hordaland health study with genotyping of the APOE gene by a one-step polymerase chain reaction and CRP measured using immuno-MALDI-TOF MS. Differences in CRP concentrations by APOE (ε4 vs no ε4) were assessed using the Mann-Whitney U tests, also stratified by statin use, diabetes and BMI categories. Finally, we performed linear regression with log (CRP) as the outcome and APOEε4 together with statin use, diabetes, BMI and their respective interactions.

RESULTS

CRP was higher in APOEε4 carriers irrespective of BMI, diabetes and statin use. In APOEε4 non-carriers, CRP was elevated with diabetes and obesity as expected. However, this was attenuated or even reversed in APOEε4 carriers. Such differences were not observed for statin use.

CONCLUSIONS

Statin use, obesity or diabetes did not confound the known association between the APOEε4 allele and lower CRP. Our data suggest that CRP is less responsive to inflammatory cues involved in diabetes and obesity in APOEε4 carriers. Epidemiological studies should take note of these relationships, as CRP, APOEε4, diabetes and obesity are both linked to neurodegenerative and cardiovascular disease.

APOE Allele Frequency in Southern Greece: Exploring the Role of Geographical Gradient in the Greek Population

BACKGROUND

the apolipoprotein e4 allele (APOE4) constitutes an established genetic risk factor for Alzheimer's Disease Dementia (ADD). We aimed to explore the frequency of the APOE isoforms in the Greek population of Southern Greece.

METHODS

peripheral blood from 175 Greek AD patients, 113 with mild cognitive impairment (MCI), and 75 healthy individuals. DNA isolation was performed with a High Pure PCR Template Kit (Roche), followed by amplification with a real-time qPCR kit (TIB MolBiol) in Roche's Light Cycler PCR platform.

RESULTS

APOE4 allele frequency was 20.57% in the ADD group, 17.69% in the MCI group, and 6.67% in the control group. APOE3/3 homozygosity was the most common genotype, while the frequency of APOE4/4 homozygosity was higher in the AD group (8.60%). APOE4 carrier status was associated with higher odds for ADD and MCI (OR: 4.49, 95% CI: [1.90-10.61] and OR: 3.82, 95% CI: [1.59-9.17], respectively).

CONCLUSION

this study examines the APOE isoforms and is the first to report a higher APOE frequency in MCI compared with healthy controls in southern Greece. Importantly, we report the occurrence of the APOE4 allele, related to ADD, as amongst the lowest globally reported, even within the nation, thus enhancing the theory of ethnicity and latitude contribution.

APOE ε4 Allele Distribution and Association With Scores of Subjective Cognitive Decline Questionnaire 9 in a Large Chinese Memory Clinic Cohort

Background

Previous reports on APOE ε4 allele distribution in different populations have been inconclusive. The Subjective Cognitive Decline-Questionnaire 9 (SCD-Q9) was developed to identify those at risk of objective cognitive impairment [OCI; including mild cognitive impairment (MCI) and dementia groups), but its association with APOE ε4 and discriminatory powers for SCD_{with subtle cognitive decline} (SCDs) and OCI in memory clinics are unclear.

Objectives

To investigate demographic distribution of APOE ε4, its association with SCD-Q9 scores, and its ability to discriminate SCDs and OCI groups from normal control (NC).

Methods

A total of 632 participants were recruited (NC = 243, SCDs = 298, OCI = 91). APOE ε4 allele distribution and association with SCD-Q9 scores were calculated and the effects on cognitive impairment were analyzed. Receiver operating characteristic (ROC) analysis was applied to identify discriminatory powers for NC, SCDs, and OCI.

Results

Total APOE ε4 frequency was 13.1%. This did not vary by demography but was higher in patients with OCI. The SCD-Q9 scores were higher in APOE ε4 carriers than non-carriers in the OCI group. The area under the curve (AUC) for discriminating from OCI using APOE ε4 were 0.587 and 0.575, using SCD-Q9 scores were 0.738 and 0.571 for NC and SCDs groups, respectively. When we combined APOE ε4 and SCD-Q9 scores into the model, the AUC increased to 0.747 for discriminating OCI from NC. However, when OCI group was split into MCI and dementia groups, only total SCD-Q9 score was the independent affecting factor of MCI.

Conclusion

This study demonstrated that the distribution of APOE ε4 alleles did not vary with different demographic characteristics in a large-scale cohort from a memory clinic. APOE ε4 alleles may be associated with scores of SCD-Q9 reflecting the degree of cognitive complaints but their additional contribution to SCD-Q9 scores is marginal in discriminating between NC, SCDs, and OCI.

Worry Modifies the Relationship between Locus Coeruleus Activity and Emotional Mnemonic Discrimination

Background: The locus coeruleus (LC) plays a critical role in modulating emotional memory performance via widespread connections to the medial temporal lobe (MTL). Interestingly, both the LC and MTL are affected during aging. Therefore, we aimed to investigate whether worry during cognitive aging changes the relationship between memory performance and the neural activity patterns during an emotional memory task. Methods: Twenty-eight participants aged 60–83 years from the Maastricht Aging study conducted an emotional mnemonic discrimination task during a 7T fMRI-scan. We performed a robust multiple linear regression to examine the association between worry and mnemonic memory performance under different levels of arousal. Subsequently, we examined if worry modifies the relationship between neuronal activity and mnemonic memory performance. Results: We observed that under low arousal, only participants with low compared to high levels of worry benefitted from additional LC activity. Under high arousal, additional LC activity was associated with lower mnemonic memory performance. Conclusion: Our results suggest there might be an optimal involvement of the NA-system for optimal memory discrimination performance, as we observed that under low levels of worry and with lower levels of arousal, higher LC activity might be needed to achieve similar levels of optimal memory performance as achieved under higher arousal when LC activity remained lower.

Early Cognitive Training Rescues Remote Spatial Memory but Reduces Cognitive Flexibility in Alzheimer's Disease Mice

BACKGROUND

Spatial memory dysfunction has been demonstrated in mouse models of Alzheimer's disease (AD) which is consistent with the clinical finding that the early signature of AD includes difficulties in the formation and/or storage of a memory. A stored memory-a long term memory-can be modulated via process called as memory retrieval that can either lead toward memory reconsolidation or even memory extinction.

OBJECTIVE

We aim to shed light on the fate of the spatial memory during memory reactivation and memory extinction using a water maze task.

METHODS

In Set-up I, we trained 3-month-old mice (wild-type mice and mice with cerebral β-amyloidosis) and assessed the fate of remote memory after four months of retention interval (RI). In Set-up II, we performed an early-extensive training at 2 months of age, retrained the same mice at 3 months of age, introduced four months of RI, and finally assessed remote spatial memory at 7 months of age.

RESULTS

We find in β-amyloidosis mice that memory reactivation problems were detectable at 7 months of age and were alleviated by cognitive overtraining. Similarly, forgetting of remote spatial memory was also minimized by cognitive overtraining. Finally, we show that the cognitive training facilitates the recovery of the reactivated spatial memory while reducing the ability to form new spatial memory in AD mice.

CONCLUSION

This result may explain the rationality behind the cognitive reserve observed in AD patients and elderly with severe β-amyloidosis not corresponding to the actual low dementia symptoms.

Apolipoprotein ɛ4 Allele and Subjective Cognitive Functioning in Parents of Adults With Disabilities

OBJECTIVES

Parents of individuals with disabilities face ongoing responsibilities of providing care and support for their children, even during the child's adulthood. Past research has shown that this caregiving role is linked to chronic stress and subsequent adverse health outcomes for parents, including impaired cognition. This study examines the impacts of genetic risk for cognitive impairment (apolipoprotein [APOE] ɛ4 allele) among parents of adults with disabilities and comparison parents whose adult children do not have disabilities.

METHOD

We performed rank order regression analysis of data from the Wisconsin Longitudinal Study (2004-2006 and 2010-2012 surveys and DNA samples). Participants included parents of adults with disabilities (247 mothers and 159 fathers) and comparison parents whose adult children were not disabled (1,482 mothers and 954 fathers).

RESULTS

Mothers who had adult children with disabilities and who were APOE ɛ4 carriers reported significantly declining levels of subjective cognitive functioning over time, but mothers of adults with disabilities who did not have the APOE ɛ4 allele did not manifest this change. Among comparison group mothers, cognitive change over time was not a function of their APOE ɛ4 carrier status. Fathers' cognitive function did not differ significantly by either parental status or APOE ɛ4 carrier status.

DISCUSSION

The results show that older mothers of adults with disabilities are more susceptible to cognitive impairment than their age peers if they have the genetic risk factor of APOE ɛ4 allele.

APOE ε4 and the Influence of Sex, Age, Vascular Risk Factors, and Ethnicity on Cognitive Decline

We aimed to examine the relationship between Apolipoprotein E ε4 (APOE*4) carriage on cognitive decline, and whether these associations were moderated by sex, baseline age, ethnicity, and vascular risk factors. Participants were 19,225 individuals aged 54-103 years from 15 longitudinal cohort studies with a mean follow-up duration ranging between 1.2 and 10.7 years. Two-step individual participant data meta-analysis was used to pool results of study-wise analyses predicting memory and general cognitive decline from carriage of one or two APOE*4 alleles, and moderation of these associations by age, sex, vascular risk factors, and ethnicity. Separate pooled estimates were calculated in both men and women who were younger (ie, 62 years) and older (ie, 80 years) at baseline. Results showed that APOE*4 carriage was related to faster general cognitive decline in women, and faster memory decline in men. A stronger dose-dependent effect was observed in older men, with faster general cognitive and memory decline in those carrying two versus one APOE*4 allele. Vascular risk factors were related to an increased effect of APOE*4 on memory decline in younger women, but a weaker effect of APOE*4 on general cognitive decline in older men. The relationship between APOE*4 carriage and memory decline was larger in older-aged Asians than Whites. In sum, APOE*4 is related to cognitive decline in men and women, although these effects are enhanced by age and carriage of two APOE*4 alleles in men, a higher numbers of vascular risk factors during the early stages of late adulthood in women, and Asian ethnicity.

Science Runs and the Debate Brakes: Somatic Gene-Editing as a New Tool for Gender-Specific Medicine in Alzheimer's Disease

Gender-specific medicine is a discipline that studies the influence of sex and gender on physiology, pathophysiology, and diseases. One example in light of how a genetic-based disease among other diseases, that impact on sex, can be represented by the risk of developing dementia or Alzheimer's disease. The question that comes into focus is whether gene-editing can represent a new line of investigation to be explored in the development of personalized, gender-specific medicine that guarantees gender equity in health policies. This article aims to discuss the relevance of adopting a gender-specific focus on gene-editing research, considered as a way of contributing to the advance of medicine's understanding, treatment, and prevention of dementia, particularly Alzheimer's disease. The development or improvement of cures could take advantage of the knowledge of the gender diversity in order to ascertain and develop differential interventions also at the genetic level between women and men, and this deserves special attention and deep ethical reflection.

Sex Differences in the Complexity of Healthy Older Adults' Magnetoencephalograms

The analysis of resting-state brain activity recording in magnetoencephalograms (MEGs) with new algorithms of symbolic dynamics analysis could help obtain a deeper insight into the functioning of the brain and identify potential differences between males and females. Permutation Lempel-Ziv complexity (PLZC), a recently introduced non-linear signal processing algorithm based on symbolic dynamics, was used to evaluate the complexity of MEG signals in source space. PLZC was estimated in a broad band of frequencies (2–45 Hz), as well as in narrow bands (i.e., theta (4–8 Hz), alpha (8–12 Hz), low beta (12–20 Hz), high beta (20–30 Hz), and gamma (30–45 Hz)) in a sample of 98 healthy elderly subjects (49 males, 49 female) aged 65–80 (average age of 72.71 ± 4.22 for males and 72.67 ± 4.21 for females). PLZC was significantly higher for females than males in the high beta band at posterior brain regions including the precuneus, and the parietal and occipital cortices. Further statistical analyses showed that higher complexity values over highly overlapping regions than the ones mentioned above were associated with larger hippocampal volumes only in females. These results suggest that sex differences in healthy aging can be identified from the analysis of magnetoencephalograms with novel signal processing methods.

The Role of Sex in Memory Function: Considerations and Recommendations in the Context of Exercise

There is evidence to suggest that biological sex plays a critical role in memory function, with sex differentially influencing memory type. In this review, we detail the current evidence evaluating sex-specific effects on various memory types. We also discuss potential mechanisms that explain these sex-specific effects, which include sex differences in neuroanatomy, neurochemical differences, biological differences, and cognitive and affect-related differences. Central to this review, we also highlight that, despite the established sex differences in memory, there is little work directly comparing whether males and females have a differential exercise-induced effect on memory function. As discussed herein, such a differential effect is plausible given the clear sex-specific effects on memory, exercise response, and molecular mediators of memory. We emphasize that future work should be carefully powered to detect sex differences. Future research should also examine these potential exercise-related sex-specific effects for various memory types and exercise intensities and modalities. This will help enhance our understanding of whether sex indeed moderates the effects of exercise and memory function, and as such, will improve our understanding of whether sex-specific, memory-enhancing interventions should be developed, implemented, and evaluated.

Sexual dimorphism in predisposition to Alzheimer's disease

Clinical studies indicate that Alzheimer's disease (AD) disproportionately affects women in both disease prevalence and rate of symptom progression, but the mechanisms underlying this sexual divergence are unknown. Although some have suggested this difference in risk is a reflection of the known differences in longevity between men and women, mounting clinical and preclinical evidence supports women also having intrinsic susceptibilities toward the disease. Although a number of potential risk factors have been hypothesized to mediate these differences, none have been definitively verified. In this review, we first summarize the epidemiologic studies of prevalence and incidence of AD among the sexes. Next, we discuss the most likely risk factors to date that interact with biological sex, including (1) genetic factors, (2) sex hormones (3) deviations in brain structure, (4) inflammation and microglia, and (5) and psychosocial stress responses. Overall, though differences in life span are likely to account for part of the divide between the sexes in AD prevalence, the abundance of preclinical and clinical evidence presented here suggests an increase in intrinsic AD risk for women. Therefore, future studies focusing on the underlying biological mechanisms for this phenomenon are needed to better understand AD pathogenesis in both sexes, with the eventual goal of sex-specific prevention and treatment strategies.

In Thai Nationals, the ApoE4 Allele Affects Multiple Domains of Neuropsychological, Biobehavioral, and Social Functioning Thereby Contributing to Alzheimer's Disorder, while the ApoE3 Allele Protects Against Neuropsychiatric Symptoms and Psychosocial Deficits

The apolipoprotein E epsilon 4 (ApoE4) allele is the strongest genetic risk factor for Alzheimer's disorder (AD) and is associated with semantic and episodic memory deficits. The aim of this study was to examine the associations between ApoE alleles (E2, E3, E4) and genotypes and neuropsychological tests, behavioral functions, and dementia symptoms as assessed using Consortium to Establish a Registry for Alzheimer's Disease (CERAD). This study included 60 patients with Alzheimer's disorder (AD), 60 with mild cognitive disorder (MCI), and 62 normal volunteers. ApoE4 carriers and individuals with E3/E4 and E4/E4 genotypes show an increased incidence of AD, but not MCI. ApoE4 carriers and especially E4/E4 homozygotes show a worse outcome on the CERAD total score, Blessed Dementia Scale, and Short Blessed Test and lower scores on the Verbal Fluency Test, Boston Naming Test, Constructional Praxis Recall, and Word List Memory, Recall, and Recognition. ApoE4 carriers and E4/E3 heterozygotes show higher scores on the Clock Drawing Test. ApoE4 carriers show a worse outcome on the CERAD clinical history scores of memory, language, personality, ADL, orientation, and social skills, while allele AopE3 carriers show better scores on activities of daily living (ADL) and social skills. ApoE3 carriers show lower total weighted, irritability/aggression, and behavioral dysregulation scores on the Behavior Rating Scale for Dementia. The results show that in Thai individuals, the presence of ApoE4 allele is accompanied by a multifarious decline in neurocognitive functions and behavioral features and that ApoE3 may convey protection against neuropsychiatric symptoms and a decline in social skills. ApoE4 and especially the E4/E4 genotype may affect multiple domains of cognitive, biobehavioral, and social functioning thereby contributing to AD phenomenology.

Apolipoprotein E Genotype and Sex Risk Factors for Alzheimer Disease: A Meta-analysis

Importance

It is unclear whether female carriers of the apolipoprotein E (APOE) ε4 allele are at greater risk of developing Alzheimer disease (AD) than men, and the sex-dependent association of mild cognitive impairment (MCI) and APOE has not been established.

Objective

To determine how sex and APOE genotype affect the risks for developing MCI and AD.

Data Sources

Twenty-seven independent research studies in the Global Alzheimer's Association Interactive Network with data on nearly 58 000 participants.

Study Selection

Non-Hispanic white individuals with clinical diagnostic and APOE genotype data.

Data Extraction and Synthesis

Homogeneous data sets were pooled in case-control analyses, and logistic regression models were used to compute risks.

Main Outcomes and Measures

Age-adjusted odds ratios (ORs) and 95% confidence intervals for developing MCI and AD were calculated for men and women across APOE genotypes.

Results

Participants were men and women between ages 55 and 85 years. Across data sets most participants were white, and for many participants, racial/ethnic information was either not collected or not known. Men (OR, 3.09; 95% CI, 2.79-3.42) and women (OR, 3.31; CI, 3.03-3.61) with the APOE ε3/ε4 genotype from ages 55 to 85 years did not show a difference in AD risk; however, women had an increased risk compared with men between the ages of 65 and 75 years (women, OR, 4.37; 95% CI, 3.82-5.00; men, OR, 3.14; 95% CI, 2.68-3.67; P = .002). Men with APOE ε3/ε4 had an increased risk of AD compared with men with APOE ε3/ε3. The APOE ε2/ε3 genotype conferred a protective effect on women (OR, 0.51; 95% CI, 0.43-0.61) decreasing their risk of AD more (P value = .01) than men (OR, 0.71; 95% CI, 0.60-0.85). There was no difference between men with APOE ε3/ε4 (OR, 1.55; 95% CI, 1.36-1.76) and women (OR, 1.60; 95% CI, 1.43-1.81) in their risk of developing MCI between the ages of 55 and 85 years, but women had an increased risk between 55 and 70 years (women, OR, 1.43; 95% CI, 1.19-1.73; men, OR, 1.07; 95% CI, 0.87-1.30; P = .05). There were no significant differences between men and women in their risks for converting from MCI to AD between the ages of 55 and 85 years. Individuals with APOE ε4/ε4 showed increased risks vs individuals with ε3/ε4, but no significant differences between men and women with ε4/ε4 were seen.

Conclusions and Relevance

Contrary to long-standing views, men and women with the APOE ε3/ε4 genotype have nearly the same odds of developing AD from age 55 to 85 years, but women have an increased risk at younger ages.

Age, APOE and sex: Triad of risk of Alzheimer's disease

Age, apolipoprotein E ε4 (APOE) and chromosomal sex are well-established risk factors for late-onset Alzheimer's disease (LOAD; AD). Over 60% of persons with AD harbor at least one APOE-ε4 allele. The sex-based prevalence of AD is well documented with over 60% of persons with AD being female. Evidence indicates that the APOE-ε4 risk for AD is greater in women than men, which is particularly evident in heterozygous women carrying one APOE-ε4 allele. Paradoxically, men homozygous for APOE-ε4 are reported to be at greater risk for mild cognitive impairment and AD. Herein, we discuss the complex interplay between the three greatest risk factors for Alzheimer's disease, age, APOE-ε4 genotype and chromosomal sex. We propose that the convergence of these three risk factors, and specifically the bioenergetic aging perimenopause to menopause transition unique to the female, creates a risk profile for AD unique to the female. Further, we discuss the specific risk of the APOE-ε4 positive male which appears to emerge early in the aging process. Evidence for impact of the triad of AD risk factors is most evident in the temporal trajectory of AD progression and burden of pathology in relation to APOE genotype, age and sex. Collectively, the data indicate complex interactions between age, APOE genotype and gender that belies a one size fits all approach and argues for a precision medicine approach that integrates across the three main risk factors for Alzheimer's disease.

No Association between Variation in Longevity Candidate Genes and Aging-related Phenotypes in Oldest-old Danes

In this study we explored the association between aging-related phenotypes previously reported to predict survival in old age and variation in 77 genes from the DNA repair pathway, 32 genes from the growth hormone 1/ insulin-like growth factor 1/insulin (GH/IGF-1/INS) signalling pathway and 16 additional genes repeatedly considered as candidates for human longevity: APOE, APOA4, APOC3, ACE, CETP, HFE, IL6, IL6R, MTHFR, TGFB1, SIRTs 1, 3, 6; and HSPAs 1A, 1L, 14. Altogether, 1,049 single nucleotide polymorphisms (SNPs) were genotyped in 1,088 oldest-old (age 92-93 years) Danes and analysed with phenotype data on physical functioning (hand grip strength), cognitive functioning (mini mental state examination and a cognitive composite score), activity of daily living and self-rated health. Five SNPs showed association to one of the phenotypes; however, none of these SNPs were associated with a change in the relevant phenotype over time (7 years of follow-up) and none of the SNPs could be confirmed in a replication sample of 1,281 oldest-old Danes (age 94-100). Hence, our study does not support association between common variation in the investigated longevity candidate genes and aging-related phenotypes consistently shown to predict survival. It is possible that larger sample sizes are needed to robustly reveal associations with small effect sizes.

Are the effects of APOE ϵ4 on cognitive function in nonclinical populations age- and gender-dependent?

APOE ϵ4 - one of three possible allelic variants (ϵ2, ϵ3 and ϵ4) of the polymorphic protein APOE - is well characterized in its role as the strongest risk factor (after old age) for sporadic Alzheimer's disease (AD). Perhaps less well known, and certainly less well characterized, is that this ϵ4 variant of the APOE gene also is a significant risk factor for age-related cognitive decline in nonclinical populations. This article considers APOE ϵ4 effects on cognition in people without dementia, the extent to which such effects may depend on age and on gender and other interactive biological systems that change across the lifespan.

Greater memory impairment in dementing females than males relative to sex-matched healthy controls

Previously we demonstrated sex differences in episodic memory in healthy elderly and suggested that normative data be separated by sex. The present study extended the exploration of sex differences on memory measures into two clinical populations, mild cognitive impairment (MCI) and Alzheimer's disease (AD). Seventy-six subjects with MCI and 101 subjects with AD diagnosed by a multidisciplinary team were included. These two groups were also compared to a group of 177 healthy elderly control participants. Sex differences on the Rey Auditory Verbal Learning Test (RAVLT; total and delayed recall) raw scores and Brief Visuospatial Memory Test-Revised (BVMT-R) were demonstrated within the healthy but not the MCI or AD groups. Calculating z scores by sex for both dementing groups based on the healthy controls suggested a larger performance gap between healthy and dementing women than between healthy and dementing men. MCI females were on average 0.48 standard deviations lower for total verbal learning compared to healthy female controls than were MCI males when compared to healthy male controls. For verbal delayed recall the gap was even larger (SD = 1.09). Similarly, on the BVMT-R, a measure of visual memory, the difference was 0.60 standard deviations for total visual learning and 0.99 standard deviations for delayed recall. This same sex difference, with females showing greater impairment compared to the controls group than did the males, was also present within the AD group. The greater memory impairment in dementing females rather than males when compared to sex-matched healthy controls was unlikely to be due to more severe illness since females performed equivalently to males on the Clinical Dementia Rating Scale, Mini-Mental Status Examination, and Dementia Rating Scale, and were also similar for age, education, and apolipoprotein status. The present study suggested relatively greater memory impairment in females with MCI or AD than in controls.

Differential contributions of ApoE4 and female sex to BACE1 activity and expression mediate Aβ deposition and learning and memory in mouse models of Alzheimer's disease

Alzheimer’s disease (AD), the most common form of dementia, disproportionately affects women in both prevalence and severity. This increased vulnerability to AD in women is strongly associated with age-related ovarian hormone loss and apolipoprotein E 4 allele (ApoE4), the most important genetic risk factor for sporadic AD. Up to date, the mechanism involved in the interaction between ApoE4 and sex/gender in AD is still unclear. This study evaluated the sex-dependent ApoE4 effects on learning and memory, Aβ deposition and potential mechanisms, using mice bearing both sporadic (ApoE4) and familial (APP_Swe, PS1_M146V, tau_P301L; 3xTg) AD risk factors and compared with sex- and age-matched 3xTg or nonTg mice. Compared to nonTg mice, transgenic mice of both sexes showed spatial learning and memory deficits in the radial arm water maze and novel arm discrimination tests at 20 months of age. However, at 10 months, only ApoE4/3xTg mice showed significant learning and memory impairment. Moreover, molecular studies of hippocampal tissue revealed significantly higher protein levels of Aβ species, β-site APP cleavage enzyme (BACE1) and Sp1, a transcription factor of BACE1, in female ApoE4/3xTg when compared with female nonTg, female 3xTg, and male ApoE4/3xTg mice. Significantly increased BACE1 enzymatic activities were observed in both male and female mice carrying ApoE4; however, only the females showed significant higher BACE1 expressions. Together, these data suggest that ApoE4 allele is associated with increased BACE1 enzymatic activity, while female sex plays an important role in increasing BACE1 expression. The combination of both provides a molecular basis for high Aβ pathology and the resultant hippocampus-dependent learning and memory deficits in female ApoE4 carriers.

Spatial pattern separation differences in older adult carriers and non-carriers for the apolipoprotein E epsilon 4 allele

We examined the performance of healthy young (n=57) and older adults (n=43) genotyped as apolipoprotein E-ε4 (APOE-ε4) carriers or APOE-ε4 non-carriers on a delayed match-to-sample task involving varying degrees of spatial interference hypothesized to assess spatial pattern separation. Older adult ε4 carriers were further divided into "impaired" and "unimpaired" groups based on their performance on a standardized test of verbal memory. We found that performance on the spatial pattern separation test increased as a function of decreased spatial interference across all groups. The older ε4 carriers in the impaired group performed significantly worse (p<.05) than unimpaired ε4 carriers, ε4 non-carriers, and young adults. The data suggest that spatial pattern separation may be less efficient in a subset of healthy older adults with subtle memory decline who are carriers of the ε4 allele. However, pattern separation performance may be comparable to that of young adults in a subset of older adult ε4 carriers and more broadly among non-carriers. Our findings offer additional evidence that pattern separation may vary in older adults, and they provide novel insight into pattern separation efficiency in ε4-positive older adults.

Blood pressure interacts with APOE ε4 to predict memory performance in a midlife sample

OBJECTIVE

Elevated blood pressure and the Apolipoprotein ε4 allele (APOE ε4) are independent risk factors for Alzheimer's disease. We sought to determine whether the combined presence of the APOE ε4 allele and elevated blood pressure is associated with lower cognitive performance in cognitively healthy middle-aged adults.

METHODS

A total of 975 participants aged 30-54 (mean age = 44.47) were genotyped for APOE. Cardiometabolic risk factors including blood pressure, lipids, and glucose were assessed and cognitive function was measured using the Trail Making Test and the Visual Reproduction and Logical Memory subtests from the Wechsler Memory Scale.

RESULTS

Multivariable regression analysis showed that the association between APOE ε4 and episodic memory performance varied as a function of systolic blood pressure (SBP), such that elevated SBP was predictive of poorer episodic memory performance only in APOE ε4 carriers (β = -.092; t = -2.614; p = .009). Notably, this association was apparent at prehypertensive levels (≥130 mmHg), even after adjusting for physical activity, depression, smoking, and other cardiometabolic risk factors.

CONCLUSIONS

The joint presence of APOE ε4 and elevated SBP, even at prehypertensive levels, is associated with lower cognitive performance in healthy, middle-aged adults. Results of this study suggest that the combination of APOE ε4 and elevated SBP may synergistically compromise memory function well before the appearance of clinically significant impairments. Interventions targeting blood pressure control in APOE ε4 carriers during midlife should be studied as a possible means to reduce the risk of cognitive decline in genetically susceptible samples.

Apolipoprotein E, gender, and Alzheimer's disease: an overlooked, but potent and promising interaction

Alzheimer's disease (AD) is an increasingly prevalent, fatal neurodegenerative disease that has proven resistant, thus far, to all attempts to prevent it, forestall it, or slow its progression. The ε4 allele of the Apolipoprotein E gene (APOE4) is a potent genetic risk factor for sporadic and late-onset familial AD. While the link between APOE4 and AD is strong, many expected effects, like increasing the risk of conversion from MCI to AD, have not been widely replicable. One critical, and commonly overlooked, feature of the APOE4 link to AD is that several lines of evidence suggest it is far more pronounced in women than in men. Here we review previous literature on the APOE4 by gender interaction with a particular focus on imaging-related studies.

A combined effect of two Alzheimer's risk genes on medial temporal activity during executive attention in young adults

A recent history of failed clinical trials suggests that waiting until even the early stages of onset of Alzheimer's disease may be too late for effective treatment, pointing to the importance of early intervention in young people. Early intervention will require markers of Alzheimer's risk that track with genotype but are capable of responding to treatment. Here, we sought to identify a functional MRI signature of combined Alzheimer's risk imparted by two genetic risk factors. We used a task of executive attention during fMRI in participants genotyped for two Alzheimer's risk alleles: APOE-ε4 and CLU-C. Executive attention is a sensitive indicator of the progression of Alzheimer's even in the early stages of mild cognitive impairment, but has not yet been investigated as a marker of Alzheimer's risk in young adults. Functional MRI revealed that APOE-ε4 and CLU-C had an additive effect on brain activity such that increased combined genetic risk was associated with decreased brain activity during executive attention, including in the medial temporal lobe, a brain area affected early in Alzheimer's pathogenesis.

Cognitive function in an elderly population: interaction between vitamin B12 status, depression, and apolipoprotein E ε4: the Hordaland Homocysteine Study

OBJECTIVE

To investigate the cross-sectional relation between metabolic markers of vitamin B(12) status and cognitive performance, and possible effect modification by the presence of depression and apolipoprotein E (ApoE) ε4.

METHODS

This is a population-based study of 1935 participants, aged 71 to 74 years, from Norway. Participants were administered a cognitive test battery, and vitamin B(12) status was assessed by measurements of plasma vitamin B(12), holotranscobalamin (holoTC), methylmalonic acid (MMA), and total homocysteine.

RESULTS

The geometric mean (95% confidence interval) for vitamin B(12) was 348 pM (341-354), whereas 5.9% of participants had vitamin B(12) levels lower than 200 pM. In linear regression analyses, holoTC (p = .039) and the holoTC/vitamin B(12) ratio (p = .013) were positively related, whereas MMA (p = .010) was inversely related, to global cognition, after adjustment for sex, education, ApoE status, plasma creatinine, and history of diabetes, cardiovascular disease, hypertension, and depression. Among those positive for ApoE ε4, but not among those without the ε4 allele, plasma vitamin B(12) was positively associated with global cognition (p = .015), whereas MMA was inversely related to global cognition (p = .036) and executive function (p = .014). In participants with depression, MMA was inversely associated with global cognition (p < .001) and episodic memory (p = .001).

CONCLUSIONS

Among the well-nourished elderly, low vitamin B(12) status is associated with cognitive deficit, particularly in those with the ApoE ε4 allele or with depression.

Gender modulates the APOE ε4 effect in healthy older adults: convergent evidence from functional brain connectivity and spinal fluid tau levels

We examined whether the effect of the apolipoprotein E (APOE) genotype on functional brain connectivity is modulated by gender in healthy older human adults. Our results confirm significantly decreased connectivity in the default mode network in healthy older APOE ε4 carriers compared with ε3 homozygotes. More important, further testing revealed a significant interaction between APOE genotype and gender in the precuneus, a major default mode hub. Female ε4 carriers showed significantly reduced default mode connectivity compared with either female ε3 homozygotes or male ε4 carriers, whereas male ε4 carriers differed minimally from male ε3 homozygotes. An additional analysis in an independent sample of healthy elderly using an independent marker of Alzheimer's disease, i.e., spinal fluid levels of tau, provided corresponding evidence for this gender-by-APOE interaction. Together, these results converge with previous work showing a higher prevalence of the ε4 allele among women with Alzheimer's disease and, critically, demonstrate that this interaction between APOE genotype and gender is detectable in the preclinical period.

Sex differences in the association of the apolipoprotein E epsilon 4 allele with incidence of dementia, cognitive impairment, and decline

We examined longitudinal associations between the apolipoprotein E ε4 allele (ApoE4(+) status) and several cognitive outcomes and tested effect modification by sex. Data on 644 non-Hispanic Caucasian adults, from the Baltimore Longitudinal Study of Aging (BLSA) were used. Dementia onset, cognitive impairment and decline were assessed longitudinally. After 27.5 years median follow-up, 113 participants developed dementia. ApoE4(+) predicted dementia significantly (hazard ratio [HR] = 2.89; 95% confidence interval [CI], 1.93-4.33), with nonsignificant sex differences. Taking all time points for predicting cognition, women had significantly stronger positive associations than men between ApoE4(+) status and impairment or decline on the California Verbal Learning Test (CVLT; delayed recall and List A total recall) and on Verbal Fluency Test-Categories. This ApoE4 × sex interaction remained significant with Bonferroni correction only for CVLT-delayed recall. Taking time points prior to dementia for cognitive predictions, the positive association between impairment in CVLT-delayed recall and ApoE4(+) status remained stronger among women, though only before Bonferroni correction. While ApoE4(+) status appears to be a sex neutral risk factor for dementia, its association with verbal memory and learning decline and impairment was stronger among women.

Butyrylcholinesterase genotype and gender influence Alzheimer's disease phenotype

Retrospective data are presented to support a spectrum of early Alzheimer's disease (AD) along a continuum defined by gender and genotype. The putative neurodegenerative mechanisms driving distinct phenotypes at each end of the spectrum are glial hypoactivity associated with early failure of synaptic cholinergic neurotransmission and glial overactivation associated with loss of neural network connectivity due to accelerated age-related breakdown of myelin. In early AD, male butyrylcholinesterase K-variant carriers with one or two apolipoprotein ɛ4 alleles have prominent medial temporal atrophy, synaptic failure, cognitive decline, and accumulation of aggregated beta-amyloid peptide. Increasing synaptic acetylcholine in damaged but still functional cholinergic synapses improves cognitive symptoms, whereas increasing the ability of glia to support synapses and to clear beta-amyloid peptide might be disease-modifying. Conversely, chronic glial overactivation can also drive degenerative processes and in butyrylcholinesterase K-variant negative females generalized glial overactivation may be the main driver from mild cognitive impairment to AD. Females are more likely than males to have accelerated age-related myelin breakdown, more widespread white matter loss, loss of neural network connectivity, whole brain atrophy, and functional decline. Increasing extracellular acetylcholine levels blocks glial activation, reduces myelin loss and damage to neural network connectivity, and is disease-modifying. Between extremes characterized by gender, genotype, and age, pathophysiology may be mixed and this spectrum may explain much of the heterogeneity of amnestic mild cognitive impairment. Preservation of the functional integrity of the neural network may be an important component of strengthening cognitive reserve and significantly delaying the onset and progression of dementia, particularly in females. Prospective confirmation of these hypotheses is required. Implications for future research and therapeutic opportunities are discussed.

Intake of vitamin K1 and K2 and risk of hip fractures: The Hordaland Health Study

BACKGROUND

Evidence of the effect of vitamin K on bone health is conflicting. The aim was to investigate the association between intake of vitamins K1 and K2 and subsequent risk of hip fracture in a general population sample, as well as potential effect modification by apolipoprotein E gene (APOE) status by presence of the E4 allele.

METHODS

1238 men and 1569 women 71-75 years of age were included in the community-based Hordaland Health Study 1997-1999 in Western Norway. Information on hip fracture was obtained from hospitalizations in the region from enrolment until 31 December 2009. Information on intake of vitamins K1 and K2 collected at baseline was used as potential predictors of hip fracture in Cox proportional hazards regression analyses.

RESULTS

Participants in the lowest compared to the highest quartile of vitamin K1 intake had increased risk of suffering a hip fracture (hazard ratio (HR)=1.57 [95% CI 1.09, 2.26]). Vitamin K2 intake was not associated with hip fracture. Presence of APOE4-allele did not increase the risk of hip fracture, nor was there any effect modification with vitamin K1 in relation to risk of hip fracture.

CONCLUSIONS

A low intake of vitamin K1, but not K2, was associated with an increased risk of hip fractures.

Use of genetic variation as biomarkers for mild cognitive impairment and progression of mild cognitive impairment to dementia

Cognitive impairment is prevalent in the elderly. The high estimates of conversion to dementia have spurred the interest in identification of genetic risk factors associated with development of cognitive impairment and or its progression. However, despite notable achievements in human genetics over the years, in particular technological advances in gene mapping and in statistical methods that relate genetic variants to disease, to date only a small proportion of the genetic contribution to late-life cognitive impairment can be explained. A likely explanation for the difficulty in gene identification is that it is a multifactorial disorder with both genetic and environmental components, in which several genes with small effects each are likely to contribute to the quantitative traits associated with the disease. The motivation for identifying the underlying genetic risk factors elderly is clear. Not only could it shed light on disease pathogenesis, but it may also provide potential targets for effective treatment, screening, and prevention. In this article we review the current knowledge on underlying genetic variants and the usefulness of genetic variation as diagnostic tools and biomarkers. In addition, we discuss the potentials and difficulties researchers face in designing appropriate studies for gene discovery.

Use of genetic variation as biomarkers for Alzheimer's disease

Late-onset Alzheimer's disease (LOAD) is the most common cause of late-onset dementia in western societies. Despite remarkable achievements in human genetics throughout the years, in particular technological advances in gene mapping and in statistical methods that relate genetic variants to disease, to date only a small proportion of the genetic contribution to LOAD can be explained leaving several remaining genetic risk factors to be identified. A possible explanation for the difficulty in gene identification is that LOAD is a multifactorial complex disorder with both genetic and environmental components. Multiple genes with small effects each ("quantitative trait loci"[QTLs]) are likely to contribute to the quantitative traits associated with the disease, such as memory performance, amyloid/tau pathology, or hippocampal atrophy. The motivation for identifying the genetics of LOAD is clear. Not only could it shed light on disease pathogenesis, but it may also provide potential targets for effective treatment, screening, and prevention. Here, we review the usefulness of genetic variation as diagnostic tools and biomarkers in LOAD and discuss the potentials and difficulties researchers face in designing appropriate studies for gene discovery.

Working memory deficits in healthy APOE epsilon 4 carriers

Studies on the cognitive effects of APOE allele variation in healthy persons have mainly focused on episodic memory performance as most sensitive to genetic effects. The present study focuses on working memory performance, measured both in an experimental paradigm, the AX-Continuous Performance Task (AX-CPT), and in neuropsychological test paradigms of span capacity and interference control. In a highly functioning healthy group (N=186) of mean age 64.5 years we found evidence of reduced working memory performance in APOE epsilon4 carriers, with sex and epsilon4 dose as modifying variables. Several aspects of capacity and control in working memory were affected, while genetic effects were not present for measures of episodic memory. The pattern of results suggests that response inhibition is sensitive to genetic effects. In healthy individuals the broad range of neurobiological mechanisms associated with APOE is consistent with effects on non-memory cognitive subsystems, and gender effects may be modulated by interaction of APOE with myelination, androgen mechanisms, or broad patterns of age-related changes in gene expression.

Endophenotypes in normal brain morphology and Alzheimer's disease: a review

Late-onset Alzheimer's disease is a common complex disorder of old age. Though these types of disorders can be highly heritable, they differ from single-gene (Mendelian) diseases in that their causes are often multifactorial with both genetic and environmental components. Genetic risk factors that have been firmly implicated in the cause are mutations in the amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes, which are found in large multi-generational families with an autosomal dominant pattern of disease inheritance, the apolipoprotein E (APOE)epsilon4 allele and the sortilin-related receptor (SORL1) gene. Environmental factors that have been associated with late-onset Alzheimer's disease include depressive illness, various vascular risk factors, level of education, head trauma and estrogen replacement therapy. This complexity may help explain their high prevalence from an evolutionary perspective, but the etiologic complexity makes identification of disease-related genes much more difficult. The "endophenotype" approach is an alternative method for measuring phenotypic variation that may facilitate the identification of susceptibility genes for complexly inherited traits. The usefulness of endophenotypes in genetic analyses of normal brain morphology and, in particular for Alzheimer's disease will be reviewed as will the implications of these findings for models of disease causation. Given that the pathways from genotypes to end-stage phenotypes are circuitous at best, identifying endophenotypes more proximal to the effects of genetic variation may expedite the attempts to link genetic variants to disorders.

The effects of apolipoprotein E on non-impaired cognitive functioning: a meta-analysis

Nearly twice as many participants are represented in the current literature than were available at the time of the last major meta-analytic neurocognitive examination of apolipoprotein E (ApoE) epsilon allele combinations [Small, B.J., Rosnick, C.B., Fratiglioni, L., Backman, L., 2004. Apolipoprotein E and cognitive performance: a meta-analysis. Psychol. Aging 19, 592-600]. The meta-analysis in the current study sought to specifically examine (1) small effects and (2) possible moderating variables associated with ApoE allele combinations that may have been undiscoverable in previous examinations of smaller data sets. A total of 77 studies, representing 40,942 cognitively healthy adults were identified for inclusion in the current meta-analysis (random effects design). Results were congruent with the previous meta-analytic findings indicating that carriers of ApoE allele 4 (ɛ4) perform significantly worse on measures of episodic memory, executive functioning, and overall global cognitive ability. In addition, the current analysis revealed a small effect suggesting that ApoE allele 4 adversely impacts perceptual speed. In contrast to earlier studies, the results also indicate that increases in age result in significantly larger differences between ApoE ɛ4 carriers and ApoE non-ɛ4 carriers on measures of episodic memory and global cognitive ability. ApoE ɛ4 exerts broad, but specific, adverse small effects on a range of neurocognitive functions in cognitively healthy adults.

Evidence that the gene encoding insulin degrading enzyme influences human lifespan

Studies in model organisms have demonstrated that components of insulin and insulin-like signaling pathways are involved in the regulation of lifespan but the relevance of those findings to humans has remained obscure. Here we provide evidence suggesting that variants of the gene encoding insulin-degrading enzyme (IDE) may be influencing human lifespan. We have employed a variety of models and diverse samples that reproducibly indicate the relative change in IDE genotype frequency across the age spectrum as well as allow the detection of association with age-at-death. A tenable molecular basis of this is suggested by the observation of genetic association with both fasting plasma insulin levels and IDE mRNA expression. Across populations the emergent genetic model is indicative of over-dominance, where heterozygotes of critical markers have increased IDE mRNA expression and insulin levels, and this is reflected in diminished heterozygosity at advanced age. A critical and replicating feature of this study is that change in IDE genotype frequency with advancing age appears to be occurring only in men, and this is supported in that insulin levels are only associated with IDE in men. Results suggest a relationship between a gene that is intimately involved in insulin metabolism and the determination of lifespan in humans, but over-dominance and gender specificity will be important parameters to consider clarifying the biological importance of these findings.

Gene expression profile of the PDAPP mouse model for Alzheimer's disease with and without Apolipoprotein E

The APOE epsilon 4 allele is a strong risk factor for Alzheimer's disease (AD). However, the molecular basis for this effect remains unclear. We examined expression of approximately 12,000 genes and expressed sequence tags in the hippocampus and cortex of PDAPP (APP(V717)) mice modeling AD that show extensive amyloid beta (A beta) deposition, and in PDAPP mice lacking murine APOE expression, which show marked attenuation of A beta deposition in the brain. Wild type and APOE knockout animals were also examined. Expression levels were determined at the initial stage of A beta deposition, as well as in older animals showing extensive neuropathological changes. Fifty-four transcripts were identified using our statistical analysis as differentially regulated between the PDAPP and PDAPP/APOE ko mice, whereas 31 transcripts were classified as differentially regulated among PDAPP mice and WT animals, and seven transcripts were identified as regulated between the PDAPP/APOE ko animals and the APOE ko animals. Interestingly, many of the differentially regulated genes we detected can be related to biological processes previously shown to be important in AD pathophysiology, including inflammation, calcium homeostasis, cholesterol transport and uptake, kinases and phosphatases involved in tau phosphorylation and dephosphorylation, mitochondrial energy metabolism, protein degradation, neuronal growth, endoplasmic reticulum (ER) stress related proteins, antioxidant activity, cytoskeletal organization, and presenilin binding proteins. Regulated genes also included some not directly associated with AD in the past but likely to be involved in known AD pathophysiologic mechanisms, and others that may represent completely novel factors in the pathogenesis of AD. These results provide a global molecular profile of hippocampal and cortical gene expression during the initial and intermediate stages Abeta deposition, and the effects of APOE deletion on this process.