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INTRODUCTION: Alzheimer's disease (AD) is a genetically heterogeneous disease, with various genetic variants potentially influencing disease mechanisms differently. Pathway-based polygenic risk scores (p-PRS) can be used to examine how groups of risk genes with similar biological functions impact disease-related endophenotypes such as cognitive decline. potentially aiding in differentiating pre-clinical dementia from normal age-related cognitive decline.

METHODS: Data from 1,737 participants (53.5% female) from the Betula study were analyzed. AD-weighted p-PRS were calculated for five AD-related pathways: immune response, tau, cholesterol, protein–lipid, and amyloid. The p-PRS were tested for associations with all-cause dementia risk (n = 315 cases), with follow-up analyses restricted to AD (n = 168) or vascular dementia (VD) (n = 110), in comparison to a genome-wide (gw) PRS. Linear mixed effect models were used to examine the same genetic predictors in relation to cognitive decline in subsequently demented and non-demented.

RESULTS: All-cause dementia risk was significantly predicted by the gw- and immune PRS. Hazard ratios for gw-, immune-, tau-, cholesterol-, and amyloid p-PRS were larger for prediction of AD risk and smaller for VD risk relative to all-cause dementia, while the opposite was seen for the protein–lipid p-PRS. Cognitive decline was stronger associated with the immune p-PRS than the gw-PRS, and this effect was driven by participants that remained non-demented (linear age-effects). Amyloid p-PRS showed accelerated age-effect at the oldest age in both non-demented and subsequently demented.

DISCUSSION: Our results show that AD-weighted p-PRS have differential roles on dementia risk and cognitive decline. Specifically, results suggest a broad role of immune p-PRS in both age-related cognitive decline and dementia risk, while amyloid p-PRS influences AD risk and pre-clinical cognitive decline, and protein-lipid p-PRS does not influence AD risk nor cognitive decline but show a potential role in VD. Results are of value for development of precision medicine based on genetic risk profiling. Highlights: All-cause dementia and Alzheimer's disease (AD) risk is strongest predicted by apolipoprotein E (APOE) ε4 and global polygenic risk scores (PRS). Cognitive decline is stronger predicted by immune pathway-based PRS (p-PRS) relative to global PRS. Effect of APOE ε4 on cognitive decline is driven by pre-clinical dementia. Immune p-PRS predicts cognitive decline unrelated to subsequent dementia. Protein–lipid p-PRS may have a stronger role in vascular dementia than AD.

Objectives: Prospective studies suggest that memory deficits are detectable decades before clinical symptoms of dementia emerge. However, individual differences in long-term memory trajectories prior to diagnosis need to be further elucidated. The aim of the current study was to investigate long-term dementia and mortality risk for individuals with different memory trajectory profiles in a well-characterized population-based sample.

Methods: 1062 adults (aged 45–80 years) who were non-demented at baseline were followed over 23–28 years. Dementia and mortality risk were studied for three previously classified episodic memory trajectory groups: maintained high performance (Maintainers; 26%), average decline (Averages; 64%), and accelerated decline (Decliners; 12%), using multistate modeling to characterize individuals’ transitions from an initial non-demented state, possibly to a state of dementia and/or death.

Results: The memory groups showed considerable intergroup variability in memory profiles, starting 10–15 years prior to dementia diagnosis, and prior to death. A strong relationship between memory trajectory group and dementia risk was found. Specifically, Decliners had more than a fourfold risk of developing dementia compared to Averages. In contrast, Maintainers had a 2.6 times decreased dementia risk compared to Averages, and in addition showed no detectable memory decline prior to dementia diagnosis. A similar pattern of association was found for the memory groups and mortality risk, although only among non-demented.

Conclusion: There was a strong relationship between accelerated memory decline and dementia, further supporting the prognostic value of memory decline. The intergroup differences, however, suggest that mechanisms involved in successful memory aging may delay symptom onset.

Background: DNA methylation (DNAm), an epigenetic mark reflecting both inherited and environmental influences, hasshown promise for Alzheimer’s disease (AD) prediction.Objective: Testing long-term predictive ability (>15 years) of existing DNAm-based epigenetic age acceleration (EAA)measures and identifying novel early blood-based DNAm AD-prediction biomarkers.

Methods: EAA measures calculated from Illumina EPIC data from blood were tested with linear mixed-effects models(LMMs) in a longitudinal case-control sample (50 late-onset AD cases; 51 matched controls) with prospective data up to 16years before clinical onset, and post-onset follow-up. NovelDNAmbiomarkers were generated with epigenome-wide LMMs,and Sparse Partial Least Squares Discriminant Analysis applied at pre- (10–16 years), and post-AD-onset time-points.

Results: EAA did not differentiate cases from controls during the follow-up time (p > 0.05). Three new DNA biomarkersshowed in-sample predictive ability on average 8 years pre-onset, after adjustment for age, sex, and white blood cell proportions(p-values: 0.022-<0.00001). Our longitudinally-derived panel replicated nominally (p = 0.012) in an external cohort (n = 146cases, 324 controls). However, its effect size and discriminatory accuracy were limited compared to APOE 4-carriership(OR = 1.38 per 1 SD DNAmscore increase versus OR= 13.58 for 4-allele carriage; AUCs = 77.2% versus 87.0%). Literaturereview showed low overlap (n = 4) across 3275 AD-associated CpGs from 8 published studies, and no overlap with ouridentified CpGs.

Conclusion: The limited predictive value of EAA for AD extends prior findings by considering a longer follow-up time, andwith appropriate control for age, sex, APOE, and blood-cell proportions. Results also highlight challenges with replicatingdiscriminatory or predictive CpGs across studies.

BACKGROUND: The Apolipoprotein E (APOE) ɛ4 allele has been linked to increased tau phosphorylation and tangle formation. APOE ɛ4 carriers with elevated tau might be at the higher risk for Alzheimer's disease (AD) progression. Previous studies showed that tau pathology begins early in areas of the medial temporal lobe. Similarly, APOE ɛ4 carriers showed altered hippocampal functional integrity. However, it remains unknown whether the influence of elevated tau accumulation on hippocampal functional changes would be more pronounced for APOE ɛ4 carriers.

OBJECTIVE: We related ɛ4 carriage to levels of plasma phosphorylated tau (p-tau181) up to 15 years prior to AD onset. Furthermore, elevated p-tau181 was explored in relation to longitudinal changes in hippocampal function and connectivity.

METHODS: Plasma p-tau181 was analyzed in 142 clinically defined AD cases and 126 matched controls. The longitudinal analysis involved 87 non-demented individuals (from population-based study) with two waves of plasma samples and three waves of functional magnetic resonance imaging during rest and memory encoding.

RESULTS: Increased p-tau181 was observed for both ɛ4 carriers and non-carriers close to AD onset, but exclusively for ɛ4 carriers in the early preclinical groups (7- and 13-years pre-AD). In ɛ4 carriers, longitudinal p-tau181 increase was paralleled by elevated local hippocampal connectivity at rest and subsequent reduction of hippocampus encoding-related activity.

CONCLUSION: Our findings support an association of APOE ɛ4 and p-tau181 with preclinical AD and hippocampus functioning.

Leukocyte telomere length (LTL) is a proposed biomarker for aging-related disorders, including cognitive decline and dementia. Long-term longitudinal studies measuring intra-individual changes in both LTL and cognitive outcomes are scarce, precluding strong conclusions about a potential aging-related relationship between LTL shortening and cognitive decline. This study investigated associations between baseline levels and longitudinal changes in LTL and memory performance across an up to 20-year follow-up in 880 dementia-free participants from a population-based study (mean baseline age: 56.8 years, range: 40–80; 52% female). Shorter baseline LTL significantly predicted subsequent memory decline (r = .34, 95% confidence interval: 0.06, 0.82), controlling for age, sex, and other relevant covariates. No significant associations were however observed between intra-individual changes in LTL and memory, neither concurrently nor with a 5-year time-lag between LTL shortening and memory decline. These results support the notion of short LTL as a predictive factor for aging-related memory decline, but suggest that LTL dynamics in adulthood and older age may be less informative of cognitive outcomes in aging. Furthermore, the results highlight the importance of long-term longitudinal evaluation of outcomes in biomarker research.

Background: Leukocyte telomere length (LTL) has been shown to predict Alzheimer’s disease (AD), albeit inconsistently. Failing to account for the competing risks between AD, other dementia types, and mortality, can be an explanation for the inconsistent findings in previous time-to-event analyses. Furthermore, previous studies indicate that the association between LTL and AD is non-linear and may differ depending on apolipoprotein E (APOE) ε4 allele carriage, the strongest genetic AD predictor.

Methods: We analyzed whether baseline LTL in interaction with APOE ε4 predicts AD, by following 1306 initially non-demented subjects for 25 years. Gender- and age-residualized LTL (rLTL) was categorized into tertiles of short, medium, and long rLTLs. Two complementary time-to-event models that account for competing risks were used; the Fine-Gray model to estimate the association between the rLTL tertiles and the cumulative incidence of AD, and the cause-specific hazard model to assess whether the cause-specific risk of AD differed between the rLTL groups. Vascular dementia and death were considered competing risk events. Models were adjusted for baseline lifestyle-related risk factors, gender, age, and non-proportional hazards.

Results: After follow-up, 149 were diagnosed with AD, 96 were diagnosed with vascular dementia, 465 died without dementia, and 596 remained healthy. Baseline rLTL and other covariates were assessed on average 8 years before AD onset (range 1–24). APOE ε4-carriers had significantly increased incidence of AD, as well as increased cause-specific AD risk. A significant rLTL-APOE interaction indicated that short rLTL at baseline was significantly associated with an increased incidence of AD among non-APOE ε4-carriers (subdistribution hazard ratio = 3.24, CI 1.404–7.462, P = 0.005), as well as borderline associated with increased cause-specific risk of AD (cause-specific hazard ratio = 1.67, CI 0.947–2.964, P = 0.07). Among APOE ε4-carriers, short or long rLTLs were not significantly associated with AD incidence, nor with the cause-specific risk of AD.

Conclusions: Our findings from two complementary competing risk time-to-event models indicate that short rLTL may be a valuable predictor of the AD incidence in non-APOE ε4-carriers, on average 8 years before AD onset. More generally, the findings highlight the importance of accounting for competing risks, as well as the APOE status of participants in AD biomarker research.

It is widely known that the apolipoprotein E (APOE) ε4 allele imposes a higher risk for Alzheimer's disease (AD). Recent evidence suggests that exposure to air pollution is also a risk factor for AD, and results from a few studies indicate that the effect of air pollution on cognitive function and dementia is stronger in APOE ε4 carriers than in non-carriers. Air pollution and interaction with APOE ε4 on AD risk thus merits further attention. We studied dementia incidence over a 15-year period from the longitudinal Betula study in Northern Sweden. As a marker for long-term exposure to traffic-related air pollution, we used modelled annual mean nitrogen oxide levels at the residential address of the participants at start of follow-up. Nitrogen oxide correlate well with fine particulate air pollution levels in the study area. We had full data on air pollution, incidence of AD and vascular dementia (VaD), APOE ε4 carrier status, and relevant confounding factors for 1,567 participants. As expected, air pollution was rather clearly associated with dementia incidence. However, there was no evidence for a modifying effect by APOE ε4 on the association (p-value for interaction > 0.30 for both total dementia (AD+VaD) and AD). The results from this study do not imply that adverse effects of air pollution on dementia incidence is limited to, or stronger in, APOE ε4 carriers than in the total population.

Individual differences in cognitive performance increase with advancing age, reflecting marked cognitive changes in some individuals along with little or no change in others. Genetic and lifestyle factors are assumed to influence cognitive performance in ageing by affecting the magnitude and extent of age-related brain changes (i.e., brain maintenance or atrophy), as well as the ability to recruit compensatory processes. The purpose of this review is to present findings from the Betula study and other longitudinal studies, with a focus on clarifying the role of key biological and environmental factors assumed to underlie individual differences in brain and cognitive ageing. We discuss the vital importance of sampling, analytic methods, consideration of non-ignorable dropout, and related issues for valid conclusions on factors that influence healthy neurocognitive ageing.

Most people's cognitive abilities decline with age, with significant and partly genetically driven, individual differences in rate of change. Although APOE 4 and genetic scores for late-onset Alzheimer's disease (LOAD) have been related to cognitive decline during preclinical stages of dementia, there is limited knowledge concerning genetic factors implied in normal cognitive aging. In the present study, we examined three potential genetic predictors of age-related cognitive decline as follows: (1) the APOE 4 allele, (2) a polygenic score for general cognitive ability (PGS-cog), and (3) a polygenic risk score for late-onset AD (PRS-LOAD). We examined up to six time points of cognitive measurements in the longitudinal population-based Betula study, covering a 25-year follow-up period. Only participants that remained alive and non-demented until the most recent dementia screening (1-3 years after the last test occasion) were included (n=1087). Individual differences in rate of cognitive change (composite score) were predicted by the PRS-LOAD and APOE 4, but not by PGS-cog. To control for the possibility that the results reflected a preclinical state of Alzheimer's disease in some participants, we re-ran the analyses excluding cognitive data from the last test occasion to model cognitive change up-until a minimum of 6 years before potential onset of clinical Alzheimers. Strikingly, the association of PRS-LOAD, but not APOE 4, with cognitive change remained. The results indicate that PRS-LOAD predicts individual difference in rate of cognitive decline in normal aging, but it remains to be determined to what extent this reflects preclinical Alzheimer's disease brain pathophysiology and subsequent risk to develop the disease.

Introduction: We investigated neurofilament light (NFL) accumulation in normal aging as well as in preclinical and clinical Alzheimer's disease (AD) and assessed individual differences in NFL load in relation to cognition and brain white-matter integrity.

Methods: We analyzed longitudinal data covering 30 years (1988-2017). Cognitive testing was done up to six times. Plasma NFL was quantified for controls and 142 cases who developed AD over time, and longitudinal changes in NFL were quantified for 100 individuals with three brain-imaging sessions.

Results: Longitudinal analyses revealed age-related NFL increases with marked variability. AD cases had elevated NFL levels, while no significant group differences were seen in the preclinical phase. Variability in NFL levels showed non-significant correlations with cognition but was associated with brain white matter.

Discussion: Our findings suggest that elevated blood NFL, likely reflecting brain white-matter alterations, characterizes clinical AD, while NFL levels do not predict age-related cognitive impairment or impending AD.