Age-specific incidence rates of Alzheimer's disease: the Baltimore Longitudinal Study of Aging

Unraveling sex differences in Alzheimer's disease and related endophenotypes with brain proteomes

INTRODUCTION

Sex differences exist in Alzheimer's disease (AD), but the underlying mechanisms remain unclear.

METHODS

We examined brain proteomes profiled from the dorsolateral prefrontal cortex of 770 donors (66.2% female).

RESULTS

Proteome-wide differential expression analysis in males and females jointly identified many significant proteins for AD dementia (n = 1228), amyloid beta (n = 1183), tangles (n = 1309), and global cognitive trajectory (n = 2325) at a false discovery rate of <0.05. Sex-stratified analyses also identified many proteins associated with AD or its endophenotypes. Finally, we found 10 proteins with significant sex-by-trait interactions, including one in AD clinical diagnosis (MARCKS), seven in cognitive trajectories (TOGARAM1, PLCD3, SLC22A5, MTFR1L, DCUN1D5, S100A12, and TRIM46), and two in cerebral pathologies (PANK4 and SOS1).

DISCUSSION

The 10 proteins with sex interaction in AD cover a range of functions likely relevant for AD pathogenesis, including estrogen response, inflammation, and mitochondrial biology, and their specific roles in AD ought to be studied. Future work should test their potential as sex-specific AD biomarkers.

HIGHLIGHTS

At the phenotypic level, we found sex differences in baseline cognitive performance, cognitive trajectories, and AD hallmark pathologies. Proteome-wide differential expression analyses identified many brain proteins associated with AD and its endophenotypes in either sex alone or when considered together. We found 10 brain proteins with significant sex interactions in AD and its endophenotypes, which could be investigated as potential sex-specific biomarkers of AD.

Unraveling the mystery of citrate transporters in Alzheimer's disease: An updated review

A key molecule in cellular metabolism, citrate is essential for lipid biosynthesis, energy production, and epigenetic control. The etiology of Alzheimer's disease (AD), a progressive neurodegenerative illness marked by memory loss and cognitive decline, may be linked to dysregulated citrate transport, according to recent research. Citrate transporters, which help citrate flow both inside and outside of cells, are becoming more and more recognized as possible participants in the molecular processes underlying AD. Citrate synthase (CS), a key enzyme in the tricarboxylic acid (TCA) cycle, supports mitochondrial function and neurotransmitter synthesis, particularly acetylcholine (ACh), essential for cognition. Changes in CS activity affect citrate availability, influencing energy metabolism and neurotransmitter production. Choline, a precursor for ACh, is crucial for neuronal function. Lipid metabolism, oxidative stress reactions, and mitochondrial function can all be affected by aberrant citrate transport, and these changes are linked to dementia. Furthermore, the two main pathogenic characteristics of AD, tau hyperphosphorylation and amyloid-beta (Aβ) aggregation, may be impacted by disturbances in citrate homeostasis. The goal of this review is to clarify the complex function of citrate transporters in AD and provide insight into how they contribute to the development and course of the illness. We aim to provide an in-depth idea of which particular transporters are dysregulated in AD and clarify the functional implications of these dysregulated transporters in brain cells. To reduce neurodegenerative processes and restore metabolic equilibrium, we have also discussed the therapeutic potential of regulating citrate transport. Gaining insight into the relationship between citrate transporters and the pathogenesis of AD may help identify new indicators for early detection and creative targets for treatment. This study offers hope for more potent ways to fight this debilitating illness and is a crucial step in understanding the metabolic foundations of AD.

Amyloid-beta peptide toxicity in the aged brain is a one-way journey into Alzheimer's disease

Aging is the primary risk factor for Alzheimer's disease (AD), and the aging brain shares many characteristics with the early stages of AD. This study investigates the interplay between aging and amyloid-beta (Aβ) induced pathology. We developed an AD-like in vivo model, using the stereotactic injection of Aβ1-42 oligomers into the hippocampi of aged mice. Cognitive impairments were assessed using a Y maze. Immunohistochemical and protein analyses were conducted to evaluate neuronal survival, synaptic function and number, levels of tau hyperphosphorylation, microglial activation, autophagy, and mitochondrial function. We compared baseline aging effects in young adult (3 months) and aged (16-18 months) healthy mice. We found that aged mice displayed significant deficits in working memory, synaptic density and neurogenesis, and an increased basal inflammation. In response to acute injury to the hippocampus with Aβ oligomer injection, aged mice suffered sustained deficits, including impaired cognitive function, further reduced neurogenesis and synaptic density, increased microglial activation, astrogliosis, mitochondrial stress, and lysosomal burden. Furthermore, in the weeks following injury, the aged mice show increased amyloid accumulation, microglial activation and phosphorylated tau propagation, expanding from the injection site to adjacent hippocampal regions. In contrast, the young adult mice exhibited only acute effects without long-term progression of pathology or neurodegeneration. We conclude that the aging brain environment increases susceptibility to an acute Aβ injury, creating fertile soil for the progression of AD, whereas younger brains are able to overcome this injury. The processes of aging should be considered as an integral factor in the development of the disease. Targeting aging mechanisms may provide new strategies for AD prevention and treatment, as well as for other neurodegenerative diseases.

Sex/gender differences in the clinical trajectory of Alzheimer's disease: Insights into diagnosis and cognitive reserve

The two-times higher prevalence of Alzheimer's disease (AD) in females versus males is well-known; however, there are also sex/gender differences in clinical presentation and diagnostic accuracy that are less examined but equally important to understand in terms of improving early detection, intervention and disease tracking in each sex/gender. This review explores how these disparities in clinical presentation manifest across the AD continuum, with a focus on the earlier stages of preclinical AD and mild cognitive impairment (MCI). We summarize evidence indicating that female's verbal memory advantage may mask early cognitive decline, leading to delayed MCI diagnosis and limiting opportunities for early intervention. Conversely, females demonstrate steeper cognitive decline at later disease stages compared to males. These patterns align with the cognitive reserve theory, suggesting female's verbal memory strength may act as a domain-specific resilience factor. Lastly, this review emphasizes the need for sex-sensitive diagnostic tools to improve early detection accuracy and equity in clinical practice.

The Dementia SomaSignal Test (dSST): A plasma proteomic predictor of 20-year dementia risk

INTRODUCTION

There is an unmet need for tools to quantify dementia risk during its multi-decade preclinical/prodromal phase, given that current biomarkers predict risk over shorter follow-up periods and are specific to Alzheimer's disease.

METHODS

Using high-throughput proteomic assays and machine learning techniques in the Atherosclerosis Risk in Communities study (n = 11,277), we developed the Dementia SomaSignal Test (dSST).

RESULTS

In addition to outperforming existing plasma biomarkers, the dSST predicted mid-life dementia risk over a 20-year follow-up across two independent cohorts with different ethnic backgrounds (areas under the curve [AUCs]: dSST 0.68-0.70, dSST+age 0.75-0.81). In a separate cohort, the dSST was associated with longitudinal declines across multiple cognitive domains, accelerated brain atrophy, and elevated measures of neuropathology (as evidenced by positron emission tomography and plasma biomarkers).

DISCUSSION

The dSST is a cost-effective, scalable, and minimally invasive protein-based prognostic aid that can quantify risk up to two decades before dementia onset.

HIGHLIGHTS

The Dementia SomaSignal Test (dSST) predicts 20-year dementia risk across two independent cohorts. dSST outperforms existing plasma biomarkers in predicting multi-decade dementia risk. dSST predicts cognitive decline and accelerated brain atrophy in a third cohort. dSST is a prognostic aid that can predict dementia risk over two decades.

Sex differences in the trajectories of plasma biomarkers, brain atrophy, and cognitive decline relative to amyloid onset

INTRODUCTION

The factors that influence the progression of Alzheimer's disease (AD) after individuals become amyloid-positive are poorly understood. This study examines how sex influences the longitudinal trajectories of plasma AD and neurodegenerative biomarkers in the years following a person's estimated onset of amyloid-β.

METHODS

Linear mixed-effects modeling investigated overall and sex-specific longitudinal trajectories of plasma biomarkers, brain volumes, and cognition relative to the estimated age of amyloid onset in a cohort of 78 amyloid-positive Baltimore Longitudinal Study of Aging (BLSA) participants (n = 45 male; follow-up time: 6.8 years [SD 3.31]). Amyloid status was ascertained with 11C-Pittsburgh compound B (PiB) PET imaging.

RESULTS

After amyloid onset, men displayed steeper increases in pTau181, pTau231, and neurofilament light (NfL) compared to women. In this same period, men demonstrated steeper declines in brain volume and cognitive performance.

DISCUSSION

These findings suggest that sex influences the trajectory of AD pathology, neuronal injury, and symptom progression after individuals become amyloid-positive.

HIGHLIGHTS

Steeper rates of increase in pTau and GFAP among amyloid-positive individuals. After amyloid onset, steeper increases in pTau and NfL concentrations in men than in women. Steeper declines in brain volume and cognition in men corroborate biomarker results.

Social patterning of cognitive impairment in Colombia: evidence from the SABE 2015 study

INTRODUCTION

Dementia, an increasingly critical public health concern in low and middle-income countries, is associated with lower socioeconomic status, early cognitive impairment, and elevated dementia-related mortality risk. This study seeks to estimate the prevalence of cognitive impairment, investigate its links with social indicators, and visualize social gradients across different regions in Colombia.

METHODS

Secondary data analysis from the SABE 2015 survey, multinomial regression analyses, and equiplot graphs.

RESULTS

A sample of 23,694 individuals 60 years or older from Colombia. Higher risks were observed among individuals with dark skin color (OR 1.27; 95%CI: 1.10 - 1.47), lower educational levels (OR 3.01; 95%CI:2.04 - 4.42) and reading illiteracy (OR 2.14; 95%CI: 1.87 - 2.46). Inequity patterns were identified by region of residence and income.

DISCUSSION

This study underscores the need for targeted interventions aimed at reducing health inequities. The results highlight the higher prevalence rates of cognitive impairment among socially disadvantaged individuals.

The Landscape of Sex- and APOE Genotype-Specific Transcriptional Changes in Alzheimer's Disease at the Single Cell Level

Alzheimer's disease (AD) is the most common form of dementia, with approximately two-thirds of AD patients are females. Basic and clinical research studies show evidence supporting sex-specific differences contributing to the complexity of AD. There is also strong evidence supporting sex-specific interaction between the primary genetic risk factor of AD, APOE4 and AD-associated neurodegenerative processes. Recent studies by us and others have identified sex and/or APOE4 specific differentially expressed genes in AD based on the bulk tissue RNA-sequencing data of postmortem human brain samples in AD. However, there lacks a comprehensive investigation of the interplay between sex and APOE genotypes at the single cell level. In the current study, we systematically explore sex and APOE genotype differences in single cell transcriptomics in AD. Our work provides a comprehensive overview of sex and APOE genotype-specific transcriptomic changes across 54 high-resolution cell types in AD and highlights individual genes and brain cell types that show significant differences between sexes and APOE genotypes. This study lays the groundwork for exploring the complex molecular mechanisms of AD and will inform the development of effective sex- and APOE-stratified interventions for AD.

Intersectionality of gender with social determinants of health and asymptomatic Alzheimer's disease neuropathology

BACKGROUND

Women comprise approximately two-thirds of Alzheimer's disease cases.

OBJECTIVE

This is the first known study to investigate the role of intersectionality between gender and other social determinants of health (SDOH) in the presentation of cognitive symptoms (i.e., being asymptomatic or symptomatic) among those with pathologically confirmed Alzheimer's disease.

METHODS

We studied 3107 individuals with Alzheimer's disease neuropathology (ADNP) confirmed at autopsy. Asymptomatic ADNP was defined as the absence of a clinical diagnosis of mild cognitive impairment (MCI) or dementia before death (versus symptomatic: diagnosis of MCI/dementia). SDOH included gender, education, ethnoracial group, living alone, and primary language. Multivariable logistic regression tested associations between SDOH and asymptomatic ADNP (versus symptomatic); models were also stratified by gender.

RESULTS

Women, Hispanics, those living alone, and more educated individuals were found to have higher odds of asymptomatic ADNP. Non-English speakers had lower odds of asymptomatic ADNP. Both women and men had higher odds of asymptomatic ADNP if Hispanic or living alone. In only women, non-English speakers had lower odds while in only men, more education was associated with higher odds of asymptomatic ADNP.

CONCLUSIONS

Gender, education, ethnicity, primary language, and living alone, and intersectionality of gender with primary language, may differentially influence MCI and dementia diagnosis prior to death among those with underlying ADNP. These findings emphasize the need for future Alzheimer's disease research to prioritize social determinants of brain health including their intersectionality with gender and how to inform targeted interventions.

The Kynurenine Pathway, Aryl Hydrocarbon Receptor, and Alzheimer's Disease

Alzheimer's disease (AD) is the leading cause of dementia, mainly affecting elderly individuals. AD is characterized by β-amyloid plaques, abnormal tau tangles, neuronal loss, and metabolic disruptions. Recent studies have revealed the involvement of the kynurenine (KP) pathway and the aryl hydrocarbon receptor (AhR) in AD development. The KP pathway metabolizes tryptophan to produce neuroactive substances like kynurenine, kynurenic acid, and quinolinic acid. In AD, high levels of kynurenine and the neurotoxic quinolinic acid are associated with increased neuroinflammation and excitotoxicity; conversely, reduced levels of kynurenic acid, which acts as a glutamate receptor antagonist, compromise neuroprotection. Research has indicated elevated KP metabolites and enzymes in the hippocampus of AD patients and other tissues such as blood, cerebrospinal fluid, and urine. However, the finding that KP metabolites are AD biomarkers in blood, cerebrospinal fluid, and urine has been controversial. This controversy, stemming from the lack of consideration of the specific stage of AD, details of the patient's treatment, cognitive deficits, and psychiatric comorbidities, underscores the need for more comprehensive research. AhR, a ligand-activated transcription factor, regulates immune response, oxidative stress, and xenobiotic metabolism. Various ligands, including tryptophan metabolites, can activate it. Some studies suggest that AhR activation contributes to AD, while others propose that it provides neuroprotection. This discrepancy may be explained by the specific ligands that activate AhR, highlighting the complex relationship between the KP pathway, AhR activation, and AD, where the same pathway can produce both neuroprotective and harmful effects.

Outdoor nighttime light exposure (light pollution) is associated with Alzheimer's disease

Introduction

Alzheimer's disease (AD) prevalence has increased in the last century which can be attributed to increased lifespan, but environment is also important. Exposure to artificial light at night is one environmental factor that may influence AD.

Methods

This study evaluated the relationship between outdoor nighttime light exposure and AD prevalence in the United States using satellite acquired outdoor nighttime light intensity and Medicare data.

Results

Higher outdoor nighttime light was associated with higher prevalence of AD. While atrial fibrillation, diabetes, hyperlipidemia, hypertension, and stroke were associated more strongly with AD prevalence than nighttime light intensity, nighttime light was more strongly associated with AD prevalence than alcohol abuse, chronic kidney disease, depression, heart failure, and obesity. Startlingly, nighttime light exposure more strongly associated with AD prevalence in those under the age of 65 than any other disease factor examined.

Discussion

These data suggest light exposure at night may influence AD, but additional studies are needed.

Proteomics identifies potential immunological drivers of postinfection brain atrophy and cognitive decline

Infections have been associated with the incidence of Alzheimer disease and related dementias, but the mechanisms responsible for these associations remain unclear. Using a multicohort approach, we found that influenza, viral, respiratory, and skin and subcutaneous infections were associated with increased long-term dementia risk. These infections were also associated with region-specific brain volume loss, most commonly in the temporal lobe. We identified 260 out of 942 immunologically relevant proteins in plasma that were differentially expressed in individuals with an infection history. Of the infection-related proteins, 35 predicted volumetric changes in brain regions vulnerable to infection-specific atrophy. Several of these proteins, including PIK3CG, PACSIN2, and PRKCB, were related to cognitive decline and plasma biomarkers of dementia (Aβ42/40, GFAP, NfL, pTau-181). Genetic variants that influenced expression of immunologically relevant infection-related proteins, including ITGB6 and TLR5, predicted brain volume loss. Our findings support the role of infections in dementia risk and identify molecular mediators by which infections may contribute to neurodegeneration.

T Cells Trafficking into the Brain in Aging and Alzheimer's Disease

The meninges, choroid plexus (CP) and blood-brain barrier (BBB) are recognized as important gateways for peripheral immune cell trafficking into the central nervous system (CNS). Accumulation of peripheral immune cells in brain parenchyma can be observed during aging and Alzheimer's disease (AD). However, the mechanisms by which peripheral immune cells enter the CNS through these three pathways and how they interact with resident cells within the CNS to cause brain injury are not fully understood. In this paper, we review recent research on T cells recruitment in the brain during aging and AD. This review focuses on the possible pathways through which T cells infiltrate the brain, the evidence that T cells are recruited to the brain, and how infiltrating T cells interact with the resident cells in the CNS during aging and AD. Unraveling these issues will contribute to a better understanding of the mechanisms of aging and AD from the perspective of immunity, and hopefully develop new therapeutic strategies for brain aging and AD.

Sex and Gender Differences in Alzheimer's Disease: Genetic, Hormonal, and Inflammation Impacts

Two-thirds of Americans with Alzheimer's disease are women, indicating a profound variance between the sexes. Variances exist between the sexes in the age and intensity of the presentation, cognitive deficits, neuroinflammatory factors, structural and functional brain changes, as well as psychosocial and cultural circumstances. Herein, we summarize the existing evidence for sexual dimorphism and present the available evidence for these distinctions. Understanding these complexities is critical to developing personalized interventions for the prevention, care, and treatment of Alzheimer's disease.

Proteome-wide analysis identifies plasma immune regulators of amyloid-beta progression

While immune function is known to play a mechanistic role in Alzheimer's disease (AD), whether immune proteins in peripheral circulation influence the rate of amyloid-β (Aβ) progression - a central feature of AD - remains unknown. In the Baltimore Longitudinal Study of Aging, we quantified 942 immunological proteins in plasma and identified 32 (including CAT [catalase], CD36 [CD36 antigen], and KRT19 [keratin 19]) associated with rates of cortical Aβ accumulation measured with positron emission tomography (PET). Longitudinal changes in a subset of candidate proteins also predicted Aβ progression, and the mid- to late-life (20-year) trajectory of one protein, CAT, was associated with late-life Aβ-positive status in the Atherosclerosis Risk in Communities (ARIC) study. Genetic variation that influenced plasma levels of CAT, CD36 and KRT19 predicted rates of Aβ accumulation, including causal relationships with Aβ PET levels identified with two-sample Mendelian randomization. In addition to associations with tau PET and plasma AD biomarker changes, as well as expression patterns in human microglia subtypes and neurovascular cells in AD brain tissue, we showed that 31 % of candidate proteins were related to mid-life (20-year) or late-life (8-year) dementia risk in ARIC. Our findings reveal plasma proteins associated with longitudinal Aβ accumulation, and identify specific peripheral immune mediators that may contribute to the progression of AD pathophysiology.

Group lasso priors for Bayesian accelerated failure time models with left-truncated and interval-censored data

An important task in health research is to characterize time-to-event outcomes such as disease onset or mortality in terms of a potentially high-dimensional set of risk factors. For example, prospective cohort studies of Alzheimer's disease (AD) typically enroll older adults for observation over several decades to assess the long-term impact of genetic and other factors on cognitive decline and mortality. The accelerated failure time model is particularly well-suited to such studies, structuring covariate effects as "horizontal" changes to the survival quantiles that conceptually reflect shifts in the outcome distribution due to lifelong exposures. However, this modeling task is complicated by the enrollment of adults at differing ages, and intermittent follow-up visits leading to interval-censored outcome information. Moreover, genetic and clinical risk factors are not only high-dimensional, but characterized by underlying grouping structures, such as by function or gene location. Such grouped high-dimensional covariates require shrinkage methods that directly acknowledge this structure to facilitate variable selection and estimation. In this paper, we address these considerations directly by proposing a Bayesian accelerated failure time model with a group-structured lasso penalty, designed for left-truncated and interval-censored time-to-event data. We develop an R package with a Markov chain Monte Carlo sampler for estimation. We present a simulation study examining the performance of this method relative to an ordinary lasso penalty and apply the proposed method to identify groups of predictive genetic and clinical risk factors for AD in the Religious Orders Study and Memory and Aging Project prospective cohort studies of AD and dementia.

Adaptive and Maladaptive DNA Breaks in Neuronal Physiology and Alzheimer's Disease

DNA strand breaks excessively accumulate in the brains of patients with Alzheimer's disease (AD). While traditionally considered random, deleterious events, neuron activity itself induces DNA breaks, and these "adaptive" breaks help mediate synaptic plasticity and memory formation. Recent studies mapping the brain DNA break landscape reveal that despite a net increase in DNA breaks in ectopic genomic hotspots, adaptive DNA breaks around synaptic genes are lost in AD brains, and this is associated with transcriptomic dysregulation. Additionally, relationships exist between mitochondrial dysfunction, a hallmark of AD, and DNA damage, such that mitochondrial dysfunction may perturb adaptive DNA break formation, while DNA breaks may conversely impair mitochondrial function. A failure of DNA break physiology could, therefore, potentially contribute to AD pathogenesis.

2024 Alzheimer's disease facts and figures

This article describes the public health impact of Alzheimer's disease (AD), including prevalence and incidence, mortality and morbidity, use and costs of care and the ramifications of AD for family caregivers, the dementia workforce and society. The Special Report discusses the larger health care system for older adults with cognitive issues, focusing on the role of caregivers and non-physician health care professionals. An estimated 6.9 million Americans age 65 and older are living with Alzheimer's dementia today. This number could grow to 13.8 million by 2060, barring the development of medical breakthroughs to prevent or cure AD. Official AD death certificates recorded 119,399 deaths from AD in 2021. In 2020 and 2021, when COVID-19 entered the ranks of the top ten causes of death, Alzheimer's was the seventh-leading cause of death in the United States. Official counts for more recent years are still being compiled. Alzheimer's remains the fifth-leading cause of death among Americans age 65 and older. Between 2000 and 2021, deaths from stroke, heart disease and HIV decreased, whereas reported deaths from AD increased more than 140%. More than 11 million family members and other unpaid caregivers provided an estimated 18.4 billion hours of care to people with Alzheimer's or other dementias in 2023. These figures reflect a decline in the number of caregivers compared with a decade earlier, as well as an increase in the amount of care provided by each remaining caregiver. Unpaid dementia caregiving was valued at $346.6 billion in 2023. Its costs, however, extend to unpaid caregivers' increased risk for emotional distress and negative mental and physical health outcomes. Members of the paid health care and broader community-based workforce are involved in diagnosing, treating and caring for people with dementia. However, the United States faces growing shortages across different segments of the dementia care workforce due to a combination of factors, including the absolute increase in the number of people living with dementia. Therefore, targeted programs and care delivery models will be needed to attract, better train and effectively deploy health care and community-based workers to provide dementia care. Average per-person Medicare payments for services to beneficiaries age 65 and older with AD or other dementias are almost three times as great as payments for beneficiaries without these conditions, and Medicaid payments are more than 22 times as great. Total payments in 2024 for health care, long-term care and hospice services for people age 65 and older with dementia are estimated to be $360 billion. The Special Report investigates how caregivers of older adults with cognitive issues interact with the health care system and examines the role non-physician health care professionals play in facilitating clinical care and access to community-based services and supports. It includes surveys of caregivers and health care workers, focusing on their experiences, challenges, awareness and perceptions of dementia care navigation.

Alzheimer's and neurodegenerative disease biomarkers in blood predict brain atrophy and cognitive decline

BACKGROUND

Although blood-based biomarkers have been identified as cost-effective and scalable alternatives to PET and CSF markers of neurodegenerative disease, little is known about how these biomarkers predict future brain atrophy and cognitive decline in cognitively unimpaired individuals. Using data from the Baltimore Longitudinal Study of Aging (BLSA), we examined whether plasma biomarkers of Alzheimer's disease (AD) pathology (amyloid-β [Aβ42/40], phosphorylated tau [pTau-181]), astrogliosis (glial fibrillary acidic protein [GFAP]), and neuronal injury (neurofilament light chain [NfL]) were associated with longitudinal brain volume loss and cognitive decline. Additionally, we determined whether sex, APOEε4 status, and plasma amyloid-β status modified these associations.

METHODS

Plasma biomarkers were measured using Quanterix SIMOA assays. Regional brain volumes were measured by 3T MRI, and a battery of neuropsychological tests assessed five cognitive domains. Linear mixed effects models adjusted for demographic factors, kidney function, and intracranial volume (MRI analyses) were completed to relate baseline plasma biomarkers to baseline and longitudinal brain volume and cognitive performance.

RESULTS

Brain volume analyses included 622 participants (mean age ± SD: 70.9 ± 10.2) with an average of 3.3 MRI scans over 4.7 years. Cognitive performance analyses included 674 participants (mean age ± SD: 71.2 ± 10.0) with an average of 3.9 cognitive assessments over 5.7 years. Higher baseline pTau-181 was associated with steeper declines in total gray matter volume and steeper regional declines in several medial temporal regions, whereas higher baseline GFAP was associated with greater longitudinal increases in ventricular volume. Baseline Aβ42/40 and NfL levels were not associated with changes in brain volume. Lower baseline Aβ42/40 (higher Aβ burden) was associated with a faster decline in verbal memory and visuospatial performance, whereas higher baseline GFAP was associated with a faster decline in verbal fluency. Results were generally consistent across sex and APOEε4 status. However, the associations of higher pTau-181 with increasing ventricular volume and memory declines were significantly stronger among individuals with higher Aβ burden, as was the association of higher GFAP with memory decline.

CONCLUSIONS

Among cognitively unimpaired older adults, plasma biomarkers of AD pathology (pTau-181) and astrogliosis (GFAP), but not neuronal injury (NfL), serve as markers of future brain atrophy and cognitive decline.

Plasma p-tau212 antemortem diagnostic performance and prediction of autopsy verification of Alzheimer's disease neuropathology

Blood phosphorylated tau (p-tau) biomarkers, including p-tau217, show high associations with Alzheimer's disease (AD) neuropathologic change and clinical stage. Certain plasma p-tau217 assays recognize tau forms phosphorylated additionally at threonine-212, but the contribution of p-tau212 alone to AD is unknown. We developed a blood-based immunoassay that is specific to p-tau212 without cross-reactivity to p-tau217. Here, we examined the diagnostic utility of plasma p-tau212. In five cohorts (n = 388 participants), plasma p-tau212 showed high performances for AD diagnosis and for the detection of both amyloid and tau pathology, including at autopsy as well as in memory clinic populations. The diagnostic accuracy and fold changes of plasma p-tau212 were similar to those for p-tau217 but higher than p-tau181 and p-tau231. Immunofluorescent staining of brain tissue slices showed prominent p-tau212 reactivity in neurofibrillary tangles that co-localized with p-tau217 and p-tau202/205. These findings support plasma p-tau212 as a peripherally accessible biomarker of AD pathophysiology.

Outdoor Nighttime Light Exposure (Light Pollution) is Associated with Alzheimer's Disease

Alzheimer's disease (AD) prevalence has increased in the last century which can be attributed to increased lifespan, but environment is also important. This study evaluated the relationship between outdoor nighttime light exposure and AD prevalence in the United States. Higher outdoor nighttime light was associated with higher prevalence of AD. While atrial fibrillation, diabetes, hyperlipidemia, hypertension, and stroke were associated more strongly with AD prevalence than nighttime light intensity, nighttime light was more strongly associated with AD prevalence than alcohol abuse, chronic kidney disease, depression, heart failure, and obesity. Startlingly, nighttime light exposure more strongly associated with AD prevalence in those under the age of 65 than any other disease factor examined. These data indicate a need to investigate how nighttime light exposure influences AD pathogenesis.

Longitudinal progression of blood biomarkers reveals a key role of astrocyte reactivity in preclinical Alzheimer's disease

Defining the progression of blood biomarkers of Alzheimer's disease (AD) is essential for targeting treatments in patients most likely to benefit from early intervention. We delineated the temporal ordering of blood biomarkers a decade prior to the onset of AD symptoms in participants in the Baltimore Longitudinal Study of Aging. We show that increased astrocyte reactivity, assessed by elevated glial fibrillary acidic protein (GFAP) levels is an early event in the progression of blood biomarker changes in preclinical AD. In AD-converters who are initially cognitively unimpaired (N=158, 377 serial plasma samples), higher plasma GFAP levels are observed as early as 10-years prior to the onset of cognitive impairment due to incident AD compared to individuals who remain cognitively unimpaired (CU, N=160, 379 serial plasma samples). Plasma GFAP levels in AD-converters remain elevated 5-years prior to and coincident with the onset of cognitive impairment due to AD. In participants with neuropathologically confirmed AD, plasma GFAP levels are elevated relative to cognitively normal individuals and intermediate in those who remain cognitively unimpaired despite significant AD pathology (asymptomatic AD). Higher plasma GFAP levels at death are associated with greater severity of both neuritic plaques and neurofibrillary tangles. In the 5XFAD transgenic model of AD, we observed greater GFAP levels in the cortex and hippocampus of transgenic mice relative to wild-type prior to the development of cognitive impairment. Reactive astrocytosis, an established biological response to neuronal injury, may be an early initiator of AD pathogenesis and a promising therapeutic target.

Women and the risk of Alzheimer's disease

Purpose of the review

This review will elucidate reasons to explain why women may be at greater risk for Alzheimer's disease.

Recent findings

Potential mechanisms to explain sex and gender differences in Alzheimer dementia include: differences in risk associated with the apolipoprotein E 4 allele; telomere shortening- which is linked with neurodegeneration, higher incidence of depression and insomnia in women as psychiatric co-morbidities which are linked with an increased Alzheimer disease risk, disorders of pregnancy including gestational hypertension and preeclampsia and psychosocial factors such as educational level which may contribute to differences in cognitive reserve.

Summary

The sex and gender differences in Alzheimer's disease can be explained by biological and psychosocial factors.

Whole Transcriptome Sequencing of Peripheral Blood Identifies the Alzheimer's Disease-Related circRNA-miRNA-lncRNA Pathway

BACKGROUND

Previous studies on transcriptional profiles suggested dysregulation of multiple RNA species in Alzheimer's disease. However, despite recent investigations revealing various aspects of circular RNA (circRNA)-associated competing endogenous RNA (ceRNA) networks in Alzheimer's Disease (AD) pathogenesis, few genome-wide studies have explored circRNA-associated profiles in AD patients exhibiting varying degrees of cognitive loss.

OBJECTIVE

To investigate the potential pathogenesis-related molecular biological changes in the various stages of AD progression.

METHODS

Whole transcriptome sequencing was performed on the peripheral blood of 7 normal cognition (NC) subjects, 8 patients with mild cognitive impairment, 8 AD patients with mild dementia (miD), and 7 AD patients with moderate dementia (moD). Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were conducted to predict the potential functions of the maternal genes of microRNAs (miRNAs), circRNAs and long non-coding RNAs (lncRNAs). The construction of ceRNA network was performed between the NC group and each diseased group based on the differently expressed RNAs.

RESULTS

In total, 3568 messenger RNAs (mRNAs), 142 miRNAs, 990 lncRNAs, and 183 circRNAs were identified as significantly differentially expressed across the four groups. GO and KEGG enrichment analysis revealed the significant roles of GTPase activity and the MAPK signaling pathway in AD pathogenesis. A circRNA-miRNA-lncRNA ceRNA pathway, characterized by the downregulated hsa-miR-7-5p and upregulated hsa_circ_0001170, was identified based on the differentially expressed RNAs between the NC group and the moD group.

CONCLUSION

The study suggests that circRNAs may be independent of mRNAs in AD pathogenesis and holds promise as potential biomarkers for AD clinical manifestations and pathological changes.

Plasma p-tau212: antemortem diagnostic performance and prediction of autopsy verification of Alzheimer's disease neuropathology

Blood phosphorylated tau (p-tau) biomarkers, including p-tau217, show high associations with Alzheimer's disease (AD) neuropathologic change and clinical stage. Certain plasma p-tau217 assays recognize tau forms phosphorylated additionally at threonine-212, but the contribution of p-tau212 alone to AD is unknown. We developed a blood-based immunoassay that is specific to p-tau212 without cross-reactivity to p-tau217. Thereafter, we examined the diagnostic utility of plasma p-tau212. In five cohorts (n=388 participants), plasma p-tau212 showed high performances for AD diagnosis and for the detection of both amyloid and tau pathology, including at autopsy as well as in memory clinic populations. The diagnostic accuracy and fold changes of plasma p-tau212 were similar to those for p-tau217 but higher than p-tau181 and p-tau231. Immunofluorescent staining of brain tissue slices showed prominent p-tau212 reactivity in neurofibrillary tangles that co-localized with p-tau217 and p-tau202/205. These findings support plasma p-tau212 as a novel peripherally accessible biomarker of AD pathophysiology.

Application and validation of an algorithmic classification of early impairment in cognitive performance

OBJECTIVE

Due to the long prodromal period for dementia pathology, approaches are needed to detect cases before clinically recognizable symptoms are apparent, by which time it is likely too late to intervene. This study contrasted two theoretically-based algorithms for classifying early cognitive impairment (ECI) in adults aged ≥50 enrolled in the Baltimore Longitudinal Study of Aging.

METHOD

Two ECI algorithms were defined as poor performance (1 standard deviation [SD] below age-, sex-, race-, and education-specific means) in: (1) Card Rotations or California Verbal Learning Test (CVLT) immediate recall and (2) ≥1 (out of 2) memory or ≥3 (out of 6) non-memory tests. We evaluated concurrent criterion validity against consensus diagnoses of mild cognitive impairment (MCI) or dementia and global cognitive scores using receiver operating characteristic (ROC) curve analysis. Predictive criterion validity was evaluated using Cox proportional hazards models to examine the associations between algorithmic status and future adjudicated MCI/dementia.

RESULTS

Among 1,851 participants (mean age = 65.2 ± 11.8 years, 50% women, 74% white), the two ECI algorithms yielded comparably moderate concurrent criterion validity with adjudicated MCI/dementia. For predictive criterion validity, the algorithm based on impairment in Card Rotations or CVLT immediate recall was the better predictor of MCI/dementia (HR = 3.53, 95%CI: 1.59-7.84) over 12.3 follow-up years.

CONCLUSIONS

Impairment in visuospatial ability or memory may be capable of detecting early cognitive changes in the preclinical phase among cognitively normal individuals.

APOE genotype and sex modulate Alzheimer's disease pathology in aged EFAD transgenic mice

Increasing evidence supports that age, APOE and sex interact to modulate Alzheimer's disease (AD) risk, however the underlying pathways are unclear. One way that AD risk factors may modulate cognition is by impacting amyloid beta (Aβ) accumulation as plaques, and/or neuroinflammation Therefore, the goal of the present study was to evaluate the extent to which age, APOE and sex modulate Aβ pathology, neuroinflammation and behavior in vivo. To achieve this goal, we utilized the EFAD mice, which express human APOE3 or APOE4 and have five familial AD mutations (FAD) that result in Aβ42 overproduction. We assessed Aβ levels, reactive glia and Morris water maze performance in 6-, 10-, 14-, and 18-month-old EFAD mice. Female APOE4 mice had the highest Aβ deposition, fibrillar amyloid deposits and neuroinflammation as well as earlier behavior deficits. Interestingly, we found that female APOE3 mice and male APOE4 mice had similar levels of pathology. Collectively our data support that the combination of APOE4 and female sex is the most detrimental combination for AD, and that at older ages, female sex may be equivalent to APOE4 genotype.

Cognitive impairment indicator for the neuropsychological test batteries in the Canadian Longitudinal Study on Aging: definition and evidence for validity

BACKGROUND

Prevalence of overall cognitive impairment based on each participant's performance across a neuropsychological battery is challenging; consequently, we define and validate a dichotomous cognitive impairment/no cognitive indicator (CII) using a neuropsychological battery administered in a population-based study. This CII approximates the clinical practice of interpretation across a neuropsychological battery and can be applied to any neuropsychological dataset.

METHODS

Using data from participants aged 45-85 in the Canadian Longitudinal Study on Aging receiving a telephone-administered neuropsychological battery (Tracking, N = 21,241) or a longer in-person battery (Comprehensive, N = 30,097), impairment was determined for each neuropsychological test based on comparison with normative data. We adjusted for the joint probability of abnormally low scores on multiple neuropsychological tests using baserates of low scores demonstrated in the normative samples and created a dichotomous CII (i.e., cognitive impairment vs no cognitive impairment). Convergent and discriminant validity of the CII were assessed with logistic regression analyses.

RESULTS

Using the CII, the prevalence of cognitive impairment was 4.3% in the Tracking and 5.0% in the Comprehensive cohorts. The CII demonstrated strong convergent and discriminant validity.

CONCLUSIONS

The approach for the CII is a feasible method to identify participants who demonstrate cognitive impairment on a battery of tests. These methods can be applied in other epidemiological studies that use neuropsychological batteries.

Sex differences in dementia risk and risk factors: Individual-participant data analysis using 21 cohorts across six continents from the COSMIC consortium

INTRODUCTION

Sex differences in dementia risk, and risk factor (RF) associations with dementia, remain uncertain across diverse ethno-regional groups.

METHODS

A total of 29,850 participants (58% women) from 21 cohorts across six continents were included in an individual participant data meta-analysis. Sex-specific hazard ratios (HRs), and women-to-men ratio of hazard ratios (RHRs) for associations between RFs and all-cause dementia were derived from mixed-effect Cox models.

RESULTS

Incident dementia occurred in 2089 (66% women) participants over 4.6 years (median). Women had higher dementia risk (HR, 1.12 [1.02, 1.23]) than men, particularly in low- and lower-middle-income economies. Associations between longer education and former alcohol use with dementia risk (RHR, 1.01 [1.00, 1.03] per year, and 0.55 [0.38, 0.79], respectively) were stronger for men than women; otherwise, there were no discernible sex differences in other RFs.

DISCUSSION

Dementia risk was higher in women than men, with possible variations by country-level income settings, but most RFs appear to work similarly in women and men.

Comparative neurogenetics of dog behavior complements efforts towards human neuropsychiatric genetics

Domestic dogs display a wide array of heritable behaviors that have intermediate genetic complexity thanks to a long history of human-influenced selection. Comparative genetics in dogs could address the scarcity of non-human neurogenetic systems relevant to human neuropsychiatric disorders, which are characterized by mental, emotional, and behavioral symptoms and involve vastly complex genetic and non-genetic risk factors. Our review describes the diverse behavioral "phenome" of domestic dogs, past and ongoing sources of behavioral selection, and the state of canine behavioral genetics. We highlight two naturally disordered behavioral domains that illustrate how dogs may prove useful as a comparative, forward neurogenetic system: canine age-related cognitive dysfunction, which can be examined more rapidly given the attenuated lifespan of dogs, and compulsive disorders, which may have genetic roots in purpose-bred behaviors. Growing community science initiatives aimed at the companion dog population will be well suited to investigating such complex behavioral phenotypes and offer a comparative resource that parallels human genomic initiatives in scale and dimensionality.

Divergent patterns of healthy aging across human brain regions at single-cell resolution reveal links to neurodegenerative disease

Age is a major common risk factor underlying neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Previous studies reported that chronological age correlates with differential gene expression across different brain regions. However, prior datasets have not disambiguated whether expression associations with age are due to changes in cell numbers and/or gene expression per cell. In this study, we leveraged single nucleus RNA-sequencing (snRNAseq) to examine changes in cell proportions and transcriptomes in four different brain regions, each from 12 donors aged 20-30 years (young) or 60-85 years (old). We sampled 155,192 nuclei from two cortical regions (entorhinal cortex and middle temporal gyrus) and two subcortical regions (putamen and subventricular zone) relevant to neurodegenerative diseases or the proliferative niche. We found no changes in cellular composition of different brain regions with healthy aging. Surprisingly, we did find that each brain region has a distinct aging signature, with only minor overlap in differentially associated genes across regions. Moreover, each cell type shows distinct age-associated expression changes, including loss of protein synthesis genes in cortical inhibitory neurons, axonogenesis genes in excitatory neurons and oligodendrocyte precursor cells, enhanced gliosis markers in astrocytes and disease-associated markers in microglia, and genes critical for neuron-glia communication. Importantly, we find cell type-specific enrichments of age associations with genes nominated by Alzheimer's disease and Parkinson's disease genome-wide association studies (GWAS), such as apolipoprotein E (APOE), and leucine-rich repeat kinase 2 (LRRK2) in microglia that are independent of overall expression levels across cell types. We present this data as a new resource which highlights, first, region- and cell type-specific transcriptomic changes in healthy aging that may contribute to selective vulnerability and, second, provide context for testing GWAS-nominated disease risk genes in relevant subtypes and developing more targeted therapeutic strategies. The data is readily accessible without requirement for extensive computational support in a public website, https://brainexp-hykyffa56a-uc.a.run.app/.

Racial, ethnic and neighborhood socioeconomic differences in incidence of dementia: A regional retrospective cohort study

BACKGROUND

Evidence on the effects of neighborhood socioeconomic disadvantage on dementia risk in racially and ethically diverse populations is limited. Our objective was to evaluate the relative extent to which neighborhood disadvantage accounts for racial/ethnic variation in dementia incidence rates. Secondarily, we evaluated the spatial relationship between neighborhood disadvantage and dementia risk.

METHODS

In this retrospective study using electronic health records (EHR) at two regional health systems in Northeast Ohio, participants included 253,421 patients aged >60 years who had an outpatient primary care visit between January 1, 2005 and December 31, 2015. The date of the first qualifying visit served as the study baseline. Cumulative incidence of composite dementia outcome, defined as EHR-documented dementia diagnosis or dementia-related death, stratified by neighborhood socioeconomic deprivation (as measured by Area Deprivation Index) was determined by competing-risk regression analysis, with non-dementia-related death as the competing risk. Fine-Gray sub-distribution hazard ratios were determined for neighborhood socioeconomic deprivation, race/ethnicity, and clinical risk factors. The degree to which neighborhood socioeconomic position accounted for racial/ethnic disparities in the incidence of composite dementia outcome was evaluated via mediation analysis with Poisson rate models.

RESULTS

Increasing neighborhood disadvantage was associated with increased risk of EHR-documented dementia diagnosis or dementia-related death (most vs. least disadvantaged ADI quintile HR = 1.76, 95% confidence interval = 1.69-1.84) after adjusting for age and sex. The effect of neighborhood disadvantage on this composite dementia outcome remained after accounting for known medical risk factors of dementia. Mediation analysis indicated that neighborhood disadvantage accounted for 34% and 29% of the elevated risk for composite dementia outcome in Hispanic and Black patients compared to White patients, respectively.

CONCLUSION

Neighborhood disadvantage is related to the risk of EHR-documented dementia diagnosis or dementia-related death and accounts for a portion of racial/ethnic differences in dementia burden, even after adjustment for clinically important confounders.

Unbiased proteomics and multivariable regularized regression techniques identify SMOC1, NOG, APCS, and NTN1 in an Alzheimer's disease brain proteomic signature

Advancements in omics methodologies have generated a wealth of high-dimensional Alzheimer's disease (AD) datasets, creating significant opportunities and challenges for data interpretation. In this study, we utilized multivariable regularized regression techniques to identify a reduced set of proteins that could discriminate between AD and cognitively normal (CN) brain samples. Utilizing eNetXplorer, an R package that tests the accuracy and significance of a family of elastic net generalized linear models, we identified 4 proteins (SMOC1, NOG, APCS, NTN1) that accurately discriminated between AD (n = 31) and CN (n = 22) middle frontal gyrus (MFG) tissue samples from Religious Orders Study participants with 83 percent accuracy. We then validated this signature in MFG samples from Baltimore Longitudinal Study of Aging participants using leave-one-out logistic regression cross-validation, finding that the signature again accurately discriminated AD (n = 31) and CN (n = 19) participants with a receiver operating characteristic curve area under the curve of 0.863. These proteins were strongly correlated with the burden of neurofibrillary tangle and amyloid pathology in both study cohorts. We additionally tested whether these proteins differed between AD and CN inferior temporal gyrus (ITG) samples and blood serum samples at the time of AD diagnosis in ROS and BLSA, finding that the proteins differed between AD and CN ITG samples but not in blood serum samples. The identified proteins may provide mechanistic insights into the pathophysiology of AD, and the methods utilized in this study may serve as the basis for further work with additional high-dimensional datasets in AD.

Can accelerated ageing models inform us on age-related tauopathies?

Ageing is the greatest risk factor of late-onset neurodegenerative diseases. In the realm of sporadic tauopathies, modelling the process of biological ageing in experimental animals forms the foundation of searching for the molecular origin of pathogenic tau and developing potential therapeutic interventions. Although prior research into transgenic tau models offers valuable lessons for studying how tau mutations and overexpression can drive tau pathologies, the underlying mechanisms by which ageing leads to abnormal tau accumulation remains poorly understood. Mutations associated with human progeroid syndromes have been proposed to be able to mimic an aged environment in animal models. Here, we summarise recent attempts in modelling ageing in relation to tauopathies using animal models that carry mutations associated with human progeroid syndromes, or genetic elements unrelated to human progeroid syndromes, or have exceptional natural lifespans, or a remarkable resistance to ageing-related disorders.

2023 Alzheimer's disease facts and figures

This article describes the public health impact of Alzheimer's disease, including prevalence and incidence, mortality and morbidity, use and costs of care, and the overall impact on family caregivers, the dementia workforce and society. The Special Report examines the patient journey from awareness of cognitive changes to potential treatment with drugs that change the underlying biology of Alzheimer's. An estimated 6.7 million Americans age 65 and older are living with Alzheimer's dementia today. This number could grow to 13.8 million by 2060 barring the development of medical breakthroughs to prevent, slow or cure AD. Official death certificates recorded 121,499 deaths from AD in 2019, and Alzheimer's disease was officially listed as the sixth-leading cause of death in the United States. In 2020 and 2021, when COVID-19 entered the ranks of the top ten causes of death, Alzheimer's was the seventh-leading cause of death. Alzheimer's remains the fifth-leading cause of death among Americans age 65 and older. Between 2000 and 2019, deaths from stroke, heart disease and HIV decreased, whereas reported deaths from AD increased more than 145%. This trajectory of deaths from AD was likely exacerbated by the COVID-19 pandemic in 2020 and 2021. More than 11 million family members and other unpaid caregivers provided an estimated 18 billion hours of care to people with Alzheimer's or other dementias in 2022. These figures reflect a decline in the number of caregivers compared with a decade earlier, as well as an increase in the amount of care provided by each remaining caregiver. Unpaid dementia caregiving was valued at $339.5 billion in 2022. Its costs, however, extend to family caregivers' increased risk for emotional distress and negative mental and physical health outcomes - costs that have been aggravated by COVID-19. Members of the paid health care workforce are involved in diagnosing, treating and caring for people with dementia. In recent years, however, a shortage of such workers has developed in the United States. This shortage - brought about, in part, by COVID-19 - has occurred at a time when more members of the dementia care workforce are needed. Therefore, programs will be needed to attract workers and better train health care teams. Average per-person Medicare payments for services to beneficiaries age 65 and older with AD or other dementias are almost three times as great as payments for beneficiaries without these conditions, and Medicaid payments are more than 22 times as great. Total payments in 2023 for health care, long-term care and hospice services for people age 65 and older with dementia are estimated to be $345 billion. The Special Report examines whether there will be sufficient numbers of physician specialists to provide Alzheimer's care and treatment now that two drugs are available that change the underlying biology of Alzheimer's disease.

Hydroxychloroquine lowers Alzheimer's disease and related dementias risk and rescues molecular phenotypes related to Alzheimer's disease

We recently nominated cytokine signaling through the Janus-kinase-signal transducer and activator of transcription (JAK/STAT) pathway as a potential AD drug target. As hydroxychloroquine (HCQ) has recently been shown to inactivate STAT3, we hypothesized that it may impact AD pathogenesis and risk. Among 109,124 rheumatoid arthritis patients from routine clinical care, HCQ initiation was associated with a lower risk of incident AD compared to methotrexate initiation across 4 alternative analyses schemes addressing specific types of biases including informative censoring, reverse causality, and outcome misclassification (hazard ratio [95% confidence interval] of 0.92 [0.83-1.00], 0.87 [0.81-0.93], 0.84 [0.76-0.93], and 0.87 [0.75-1.01]). We additionally show that HCQ exerts dose-dependent effects on late long-term potentiation (LTP) and rescues impaired hippocampal synaptic plasticity prior to significant accumulation of amyloid plaques and neurodegeneration in APP/PS1 mice. Additionally, HCQ treatment enhances microglial clearance of Aβ_1-42, lowers neuroinflammation, and reduces tau phosphorylation in cell culture-based phenotypic assays. Finally, we show that HCQ inactivates STAT3 in microglia, neurons, and astrocytes suggesting a plausible mechanism associated with its observed effects on AD pathogenesis. HCQ, a relatively safe and inexpensive drug in current use may be a promising disease-modifying AD treatment. This hypothesis merits testing through adequately powered clinical trials in at-risk individuals during preclinical stages of disease progression.

Global incidence of young-onset dementia: A systematic review and meta-analysis

INTRODUCTION

Reliable data on the incidence rates for young-onset dementia (YOD) are lacking, but are necessary for research on disease etiology and to raise awareness among health care professionals.

METHODS

We performed a systematic review and meta-analysis on population-based studies on the incidence of YOD, published between January 1, 1990 and February 1, 2022, according to Meta-analyses of Observational Studies in Epidemiology (MOOSE) guidelines. Data were analyzed using random-effects meta-analyses. Results were age-standardized, and heterogeneity was assessed by subgroup analyses and meta-regression.

RESULTS

Sixty-one articles were included. Global age-standardized incidence rates increased from 0.17/100,000 in age 30 to 34 years, to 5.14/100,000 in age 60 to 64 years, giving a global total age-standardized incidence rate of 11 per 100,000 in age 30 to 64. This corresponds to 370,000 new YOD cases annually worldwide. Heterogeneity was high and meta-regression showed geographic location significantly influenced this heterogeneity.

DISCUSSION

This meta-analysis shows the current best estimate of YOD incidence. New prospective cohort studies are needed.

Application and validation of an algorithmic classification of early impairment in cognitive performance

Objective

Due to the long prodromal period for dementia pathology, approaches are needed to detect cases before clinically recognizable symptoms are apparent, by which time it is likely too late to intervene. This study contrasted two theoretically-based algorithms for classifying early cognitive impairment (ECI) in adults aged ≥50 enrolled in the Baltimore Longitudinal Study of Aging.

Method

Two ECI algorithms were defined as poor performance (1 standard deviation [SD] below age-, sex-, race-, and education-specific means) in: (1) Card Rotations or California Verbal Learning Test (CVLT) immediate recall and (2) ≥1 (out of 2) memory or ≥3 (out of 6) non- memory tests. We evaluated concurrent criterion validity against consensus diagnoses of mild cognitive impairment (MCI) or dementia and global cognitive scores using receiver operating characteristic (ROC) curve analysis. Predictive criterion validity was evaluated using Cox proportional hazards models to examine the associations between algorithmic status and future adjudicated MCI/dementia.

Results

Among 1,851 participants (mean age=65.2±11.8 years, 50% women, 74% white), the two ECI algorithms yielded comparably moderate concurrent criterion validity with adjudicated MCI/dementia. For predictive criterion validity, the algorithm based on impairment in Card Rotations or CVLT immediate recall was the better predictor of MCI/dementia (HR=3.53, 95%CI: 1.59-7.84) over 12.3 follow-up years.

Conclusions

Impairment in visuospatial ability or memory may be capable of detecting early cognitive changes in the preclinical phase among cognitively normal individuals.

Association between testosterone and cognitive performance in postmenopausal women: a systematic review of observational studies

This review was conducted to explore the association between endogenous testosterone blood concentrations and cognitive performance among community dwelling postmenopausal women. We searched Ovid MEDLINE, EMBASE, PsycINFO and Web of Science databases for observational studies with at least 100 postmenopausal participants. The results were categorized by study design, reporting of total or free testosterone and risk of bias assessments, narratively. Ten of the 26 articles retrieved for full-text review met the inclusion criteria, six provided cross-sectional data, seven provided longitudinal data and one provided case-control data. Cognitive performance tests differed between studies. Eight studies measured testosterone by immunoassay, one by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and one did not specify their methodology. Eleven different cognitive domains were tested by 37 different instruments. Irrespective of the study design, the findings were inconsistent and inconclusive. Both positive and inverse associations were reported for each of global cognition and immediate and delayed verbal recall. The majority of studies reported no association between total or free testosterone and cognitive performance. Although this review did not demonstrate an association between testosterone and cognitive performance in postmenopausal women, the findings should be considered inconclusive due to the imprecision of testosterone measurement and the methodological heterogeneity of the included studies.

Genetic Polymorphisms in Oxidative Stress and Inflammatory Pathways as Potential Biomarkers in Alzheimer's Disease and Dementia

Oxidative stress and neuroinflammation are important processes involved in Alzheimer's disease (AD) and mild cognitive impairment (MCI). Numerous risk factors, including genetic background, can affect the complex interplay between those mechanisms in the aging brain and can also affect typical AD hallmarks: amyloid plaques and neurofibrillary tangles. Our aim was to evaluate the association of polymorphisms in oxidative stress- and inflammation-related genes with cerebrospinal fluid (CSF) biomarker levels and cognitive test results. The study included 54 AD patients, 14 MCI patients with pathological CSF biomarker levels, 20 MCI patients with normal CSF biomarker levels and 62 controls. Carriers of two polymorphic IL1B rs16944 alleles had higher CSF Aβ_1-42 levels (p = 0.025), while carriers of at least one polymorphic NFE2L2 rs35652124 allele had lower CSF Aβ_1-42 levels (p = 0.040). Association with IL1B rs16944 remained significant in the AD group (p = 0.029). Additionally, MIR146A rs2910164 was associated with Aβ_42/40 ratio (p = 0.043) in AD. Significant associations with cognitive test scores were observed for CAT rs1001179 (p = 0.022), GSTP1 rs1138272 (p = 0.005), KEAP1 rs1048290 and rs9676881 (both p = 0.019), as well as NFE2L2 rs35652124 (p = 0.030). In the AD group, IL1B rs1071676 (p = 0.004), KEAP1 rs1048290 and rs9676881 (both p = 0.035) remained associated with cognitive scores. Polymorphisms in antioxidative and inflammation genes might be associated with CSF biomarkers and cognitive test scores and could serve as additional biomarkers contributing to early diagnosis of dementia.

Molecular Imaging of Neuroinflammation in Alzheimer's Disease and Mild Cognitive Impairment

Alzheimer's disease (AD) is the most prevalent neurocognitive disorder. Due to the ineffectiveness of treatments targeting the amyloid cascade, molecular biomarkers for neuroinflammation are attracting attention with increasing knowledge about the role of neuroinflammation in the pathogenesis of AD. This chapter will explore the results of studies using molecular imaging for diagnosing AD and mild cognitive impairment (MCI). Because it is critical to interpreting the data to understand which substances are targeted in molecular imaging, this chapter will discuss the two most significant targets, microglia and astrocytes, as well as the best-known radioligands for each. Then, neuroimaging results with PET neuroinflammation imaging will be reviewed for AD and MCI. Although a growing body of evidence has suggested that these molecular imaging biomarkers for neuroinflammation may have a role in the diagnosis of AD and MCI, the findings are inconsistent or cross-sectional, which indicates that it is difficult to apply the contents in practice due to the need for additional study. In particular, because the results of multiple interventions targeting neuroinflammation were inconclusive, molecular imaging markers for neuroinflammation can be used in combination with conventional markers to select appropriate patients for early intervention for neuroinflammation rather than as a single marker.

Female APOE ɛ4 Carriers with Slow Rates of Biological Aging Have Better Memory Performances Compared to Female ɛ4 Carriers with Accelerated Aging

BACKGROUND

Evidence suggests that APOE ɛ4 carriers have worse memory performances compared to APOE ɛ4 non-carriers and effects may vary by sex and age. Estimates of biological age, using DNA methylation may enhance understanding of the associations between sex and APOE ɛ4 on cognition.

OBJECTIVE

To investigate whether associations between APOE ɛ4 status and memory vary according to rates of biological aging, using a DNA methylation age biomarker, in older men and women without dementia.

METHODS

Data were obtained from 1,771 adults enrolled in the 2016 wave of the Health and Retirement Study. A series of ANCOVAs were used to test the interaction effects of APOE ɛ4 status and aging rates (defined as 1 standard deviation below (i.e., slow rate), or above (i.e., fast rate) their sex-specific mean rate of aging on a composite measure of verbal learning and memory.

RESULTS

APOE ɛ4 female carriers with slow rates of GrimAge had significantly better memory performances compared to fast and average aging APOE ɛ4 female carriers. There was no effect of aging group rate on memory in the female non-carriers and no significant differences in memory according to age rate in either male APOE ɛ4 carriers or non-carriers.

CONCLUSION

Slower rates of aging in female APOE ɛ4 carriers may buffer against the negative effects of the ɛ4 allele on memory. However, longitudinal studies with larger sample sizes are needed to evaluate risk of dementia/memory impairment based on rates of aging in female APOE ɛ4 carriers.

The Contribution of the Locus Coeruleus-Noradrenaline System Degeneration during the Progression of Alzheimer's Disease

Alzheimer's disease (AD), which is characterized by extracellular accumulation of amyloid-beta peptide and intracellular aggregation of hyperphosphorylated tau, is the most common form of dementia. Memory loss, cognitive decline and disorientation are the ultimate consequences of neuronal death, synapse loss and neuroinflammation in AD. In general, there are many brain regions affected but neuronal loss in the locus coeruleus (LC) is one of the earliest indicators of neurodegeneration in AD. Since the LC is the main source of noradrenaline (NA) in the brain, degeneration of the LC in AD leads to decreased NA levels, causing increased neuroinflammation, enhanced amyloid and tau burden, decreased phagocytosis and impairment in cognition and long-term synaptic plasticity. In this review, we summarized current findings on the locus coeruleus-noradrenaline system and consequences of its dysfunction which is now recognized as an important contributor to AD progression.

Relationships of Low Cognitive Performance and Sleep Disorder With Functional Disabilities Among Older Adults

Objectives

This study examined the relationships of low cognitive performance and sleep disorder with functional disabilities among older adults. Methods: NHANES 2011–2014 data on 3179 individuals [Mage=69.71] were analyzed. Functional domains included: activities of daily living (ADL), instrumental ADL (IADL) and leisure and social activities (LSA). Animal Fluency Test and the Digit Symbol Substitution Test assessed cognitive performance. Participants self-reported having physician-diagnosed sleep disorder. Results: Participants with both low cognitive performance and sleep disorder had 4- to 10-times greater odds for ADL, IADL, and LSA difficulties compared to the participants with no low cognitive performance/sleep disorder. Participants with only low cognitive performance and those with only sleep disorder were two to three times more likely to experience these difficulties. Discussion: Low cognitive performance and sleep disorder together or independently were associated with functional disabilities. Participants with both low cognitive performance and sleep disorder had higher odds of functional disabilities.

Consideration of sex and gender in Alzheimer's disease and related disorders from a global perspective

Sex or gender differences in the risk of Alzheimer's disease and related dementias (ADRD) differ by world region, suggesting that there are potentially modifiable risk factors for intervention. However, few epidemiological or clinical ADRD studies examine sex differences; even fewer evaluate gender in the context of ADRD risk. The goals of this perspective are to: (1) provide definitions of gender, biologic sex, and sexual orientation. and the limitations of examining these as binary variables; (2) provide an overview of what is known with regard to sex and gender differences in the risk, prevention, and diagnosis of ADRD; and (3) discuss these sex and gender differences from a global, worldwide perspective. Identifying drivers of sex and gender differences in ADRD throughout the world is a first step in developing interventions unique to each geographical and sociocultural area to reduce these inequities and to ultimately reduce global ADRD risk. HIGHLIGHTS: The burden of dementia is unevenly distributed geographically and by sex and gender. Scientific advances in genetics and biomarkers challenge beliefs that sex is binary. Discrimination against women and sex and gender minority (SGM) populations contributes to cognitive decline. Sociocultural factors lead to gender inequities in Alzheimer's disease and related dementias (ADRD) worldwide.

BACE1 Aptamer-Modified Tetrahedral Framework Nucleic Acid to Treat Alzheimer's Disease in an APP-PS1 Animal Model

Alzheimer's disease is a neurodegenerative disease caused by excessive amyloid β protein-induced neurotoxicity. However, drugs targeting amyloid β protein production face many problems, such as the low utilization rate of drugs by cells and the difficulty of drugs in penetrating the blood-brain barrier. A tetrahedral framework nucleic acid is a new type of nanonucleic acid structure that functions as a therapy and drug carrier. Here, we synthesized a BACE1 aptamer-modified tetrahedral framework nucleic acid and tested its therapeutic effect on Alzheimer's disease in vitro and in vivo. Our results demonstrated that the tetrahedral framework nucleic acid could be used as a carrier to deliver the BACE1 aptamer to the brain to reduce the production of amyloid β proteins. It also played an antiapoptotic role by reducing the production of reactive oxygen species. Thus, this nanomaterial is a potential drug for Alzheimer's disease.

The COVID-19 pandemic and Alzheimer's disease: mutual risks and mechanisms

Coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a life-threatening disease, especially in elderly individuals and those with comorbidities. The predominant clinical manifestation of COVID-19 is respiratory dysfunction, while neurological presentations are increasingly being recognized. SARS-CoV-2 invades host cells primarily via attachment of the spike protein to the angiotensin-converting enzyme 2 (ACE2) receptor expressed on cell membranes. Patients with Alzheimer's disease (AD) are more susceptible to SARS-CoV-2 infection and prone to severe clinical outcomes. Recent studies have revealed some common risk factors for AD and COVID-19. An understanding of the association between COVID-19 and AD and the potential related mechanisms may lead to the development of novel approaches to treating both diseases. In the present review, we first summarize the mechanisms by which SARS-CoV-2 invades the central nervous system (CNS) and then discuss the associations and potential shared key factors between COVID-19 and AD, with a focus on the ACE2 receptor, apolipoprotein E (APOE) genotype, age, and neuroinflammation.

Risk of Alzheimer's disease and related dementia by sex and race/ethnicity: The Multiethnic Cohort Study

INTRODUCTION

Data are limited for comparison of sex- and race/ethnicity-specific risks of Alzheimer's disease and related dementia (ADRD).

METHODS

In the population-based Multiethnic Cohort, we estimated the age-standardized diagnostic incidence rate (ASDIR) and relative risk of late-onset ADRD (n = 16,410) among 105,796 participants based on Medicare claims (1999-2014) by sex and race/ethnicity.

RESULTS

The ASDIR for ADRD was higher for women (17.0 per 1000 person-years) than for men (15.3) and varied across African Americans (22.9 in women, 21.5 in men), Native Hawaiians (19.3, 19.4), Latinos (16.8, 14.7), Whites (16.4, 15.5), Japanese Americans (14.8, 13.8), and Filipinos (12.5, 9.7). Similar risk patterns were observed for AD. Adjustment for education and cardiometabolic diseases attenuated the differences. Accounting for deaths from competing causes increased the sex difference, while reducing the racial/ethnic differences. Less racial/ethnic disparity was detected among apolipoprotein E (APOE) e4 carriers.

DISCUSSION

More research is needed to understand the sex and racial/ethnic differences in ADRD.

Sex and gender differences in dementia

The dementia landscape has undergone a striking paradigm shift. The advances in understanding of neurodegeneration and proteinopathies has changed our approach to patients with cognitive impairment. Firstly, it has recently been shown that the various proteinopathies that are the cause of the dementia begin to build up long before the appearance of any obvious symptoms. This has cemented the idea that there is an urgency in diagnosis as it occurs very late in the pathophysiology of these diseases. Secondly, that accurate diagnosis is required to deliver targeted therapies, that is precision medicine. With this latter point, the realization that various factors of a person need to be considered as they may impact the presentation and progression of disease has risen to the forefront. Two of these factors aside from race and age are biological sex and gender (social construct), as both can have tremendous impact on manifestation of disease. This chapter will cover what is known and remains to be known on the interaction of sex and gender with some of the major causes of dementia.