Mixed dementia: Neglected clinical entity or nosographic artifice?

Prevalence, treatment, and neural correlates of apathy in different forms of dementia: a narrative review

OBJECTIVES

The aim of this review is to provide an overview on prevalence and clinical tools for the diagnosis of apathy, as well as on neurophysiological and neuroimaging findings obtained from studies in patients with apathy in different forms of dementia, including Alzheimer's disease (AD), vascular (VaD) and mixed dementia, frontotemporal dementia (FTD), and Parkinson's disease dementia (PDD).

METHODS

Randomized controlled trials, non-randomized controlled trials, controlled before-after studies, and interrupted time series from four databases (WebOfScience, Scopus, Pubmed, and PsycINFO) addressing apathy in adults or older people aged over 65 years of age affected by dementia were included.

RESULTS

The prevalence of apathy was 26-82% for AD, 28.6-91.7 for VaD, 29-97.5% in PDD, and 54.8-88.0 in FTD. The assessment of apathy was not consistent in the reviewed studies. Methylphenidate was the most successful pharmacological treatment for apathy. Neurobiological studies highlighted the relationship between both structural and functional brain areas and the presence or severity of apathy.

CONCLUSION

Apathy is a very common disorder in all types of dementia, although it is often underdiagnosed and undertreated. Further studies are needed to investigate its diagnosis and management. A consensus on the different evaluation scales should be achieved.

Oral anticoagulants: A plausible new treatment for Alzheimer's disease?

Alzheimer's disease (AD) and cardiovascular disease (CVD) are strongly associated. Both are multifactorial disorders with long asymptomatic phases and similar risk factors. Indeed, CVD signatures such as cerebral microbleeds, micro-infarcts, atherosclerosis, cerebral amyloid angiopathy and a procoagulant state are highly associated with AD. However, AD and CVD co-development and the molecular mechanisms underlying such associations are not understood. Here, we review the evidence regarding the vascular component of AD and clinical studies using anticoagulants that specifically evaluated the development of AD and other dementias. Most studies reported a markedly decreased incidence of composite dementia in anticoagulated patients with atrial fibrillation, with the highest benefit for direct oral anticoagulants. However, sub-analyses by differential dementia diagnosis were scarce and inconclusive. We finally discuss whether anticoagulation could be a plausible preventive/therapeutic approach for AD and, if so, which would be the best drug and strategy to maximize clinical benefit and minimize potential risks. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

Rethinking Dementia Risk Prediction: A Critical Evaluation of a Multimodal Machine Learning Predictive Model

A recent study by Ding et al. explores the integration of artificial intelligence (AI) in predicting dementia risk over a 10-year period using a multimodal approach. While revealing the potential of machine learning models in identifying high-risk individuals through neuropsychological testing, MRI imaging, and clinical risk factors, the imperative of dynamic frailty assessment emerges for accurate late-life dementia prediction. The commentary highlights challenges associated with AI models, including dimensionality and data standardization, emphasizing the critical need for a dynamic, comprehensive approach to reflect the evolving nature of dementia and improve predictive accuracy.

[Use of modern classification systems for complex diagnostics of Alzheimer's disease]

OBJECTIVE

To compare the content of β-amyloid (Aβ) peptides Aβ40, Aβ42, total and threonine phosphorylated 181 tau-protein in cerebrospinal fluid (CSF) of patients with the clinical diagnosis of Alzheimer's disease (AD).

MATERIAL AND METHODS

The study was performed on 64 patients with a diagnosis of dementia and MMSE scores of 24 or lower. All patients underwent lumbar puncture. Aβ40, Aβ42, Aβ42/40 ratio, total tau, phosphorylated tau at threonine 181 were determined in the CSF using a multiplex assay according to the manufacturer's protocol, the concentration was determined in pkg/ml.

RESULTS

The preliminary diagnosis of AD was made in 3 patients (5%). As a result of the study of protein content in the CSF, signs of AD were detected in 48 (75%) people. The findings suggest that the diagnosis of AD is made 10-14 times less frequently than it should be according to the World Health Organization data. The discrepancy between clinical diagnosis and laboratory findings is confirmed by our study.

CONCLUSION

Differences in the therapy of dementias and the development of new drugs targeting specific links in the pathogenesis of different types of dementias require accurate and complete diagnosis of dementias, especially AD, as the most common type of dementia.

Machine-learning-derived heart and brain age are independently associated with cognition

BACKGROUND AND PURPOSE

A heart age biomarker has been developed using deep neural networks applied to electrocardiograms. Whether this biomarker is associated with cognitive function was investigated.

METHODS

Using 12-lead electrocardiograms, heart age was estimated for a population-based sample (N = 7779, age 40-85 years, 45.3% men). Associations between heart delta age (HDA) and cognitive test scores were studied adjusted for cardiovascular risk factors. In addition, the relationship between HDA, brain delta age (BDA) and cognitive test scores was investigated in mediation analysis.

RESULTS

Significant associations between HDA and the Word test, Digit Symbol Coding Test and tapping test scores were found. HDA was correlated with BDA (Pearson's r = 0.12, p = 0.0001). Moreover, 13% (95% confidence interval 3-36) of the HDA effect on the tapping test score was mediated through BDA.

DISCUSSION

Heart delta age, representing the cumulative effects of life-long exposures, was associated with brain age. HDA was associated with cognitive function that was minimally explained through BDA.

Prevalence of dementia, heart disease and stroke in community-dwelling adults in Canada, 2016-2021: opportunities for joint prevention

INTRODUCTION

This aim of this study is to provide updated estimates on the prevalence of dementia, heart disease, and stroke in Canadian communities. Targeting all three conditions together, at the community level, may be key to disease prevention and health aging in the Canadian population.

METHODS

Using nationwide health survey data, we calculated the age-standardized prevalence of self-reported dementia, heart disease and stroke in adults aged 18 years and over residing in Canadian communities from 2016 to 2021. Poisson regression models were used to detect statistically significant changes in the prevalence of all three conditions from 2016 to 2021.

RESULTS

Less than 1% (~ 175,000 individuals) of adults residing in Canadian communities reported dementia, 5% (~ 1.5 million individuals) reported heart disease, and more than 1% (~ 370,000 individuals) reported stroke annually from 2016 to 2021. Overall, the age-standardized prevalence for stroke decreased minimally from 2016 to 2021 (p = 0.0004). Although the age-standardized prevalence of heart disease and dementia decreased from 2016 to 2018, subsequent increases in prevalence from 2018 to 2021 led to a lack of overall statistically significant changes from 2016 to 2021 (p = 0.10 for heart disease and p = 0.37 for dementia).

CONCLUSION

Recent increases in the prevalence of dementia, heart disease and stroke in Canadian communities threaten to reverse any gains in vascular disease prevention over the past six years. Findings reveal the urgent need for intensified prevention efforts that are community-based with a focus on joint reduction in the shared risk factors contributing to all three diseases.

Predictive value of hypercholesterolemia, vegetarian diet, and hypertension for incident dementia among elderly Taiwanese individuals with low educational levels

Objective

Early management of modifiable dementia-related factors is seen as a novel approach to preventing dementia onset; however, these efforts are often hindered by the complexity of interactions among these factors. In addition, different modifiable dementia-related factors may contribute to different etiologies of dementia.

Design

The current study investigated the effects of common modifiable dementia-related factors on prediction of incident dementia, dementia of the Alzheimer's type (DAT), and vascular dementia (VaD).

Methods

Vascular- and lifestyle-related factors were used as predictors of incident dementia, DAT, and VaD among 1,285 elderly individuals without obvious signs of dementia or mild cognitive impairment. Cox proportional hazard models were used to evaluate the risks associated with each modifiable factor.

Results

After controlling for factors other than stroke-related factors, hypercholesterolemia was correlated with a relatively low risk of all-cause incident dementia and DAT, whereas a vegetarian diet was correlated with an elevated risk of all-cause incident dementia and VaD. Hypertension was correlated with incident VaD. After controlling for stroke-related factors, a vegetarian diet was correlated with an elevated risk of all-cause dementia. A history of myocardiac infarction and the use of anti-platelet medication were, respectively, associated with a reduced risk of DAT and elevated risk of VaD. The use of anti-hypertensives was associated with a reduced risk of all-cause dementia, whereas the use of anti-lipid agents was associated with slow progression DAT (i.e. exceeding the average conversion time). Hypercholesterolemia was associated with an elevated risk for slow progression DAT.

Conclusion

These findings could perhaps be used as clinical markers in predicting and preventing incident dementia, DAT, and VaD.

Vascular dementia subtypes, pathophysiology, genetics, neuroimaging, biomarkers, and treatment updates along with its association with Alzheimer's dementia and diabetes mellitus

Dementia is a chronic progressive cognitive decline illness that results in functional impairment. Vascular dementia (VaD), second only to Alzheimer's disease (AD), is one of the most prevalent forms of dementia in the elderly (aged over 65 years), with a varied presentation and unpredictable disease development caused by cerebrovascular or cardiovascular illness. To get a better understanding of the changes occurring in the brain and to drive therapy efforts, new biomarkers for early and precise diagnosis of AD and VaD are required. In this review, Firstly, we describe the subtypes of vascular dementia, their clinical features, pathogenesis, genetics implemented, and their associated neuroimaging and biomarkers, while describing extensively the recent biomarkers discovered in the literature. Secondly, we describe some of the well-documented and other less-defined risk factors and their association and pathophysiology in relation to vascular dementia. Finally, we follow recent updates in the management of vascular dementia along with its association and differentiation from Alzheimer's disease. The aim of this review is to gather the scattered updates and the most recent changes in blood, CSF, and neuroimaging biomarkers related to the multiple subtypes of vascular dementia along with its association with Alzheimer's dementia and diabetes mellitus.

Beneath the Top of the Iceberg: Financial Capacity Deficits in Mixed Dementia with and without Depression

Nowadays, controversy exists regarding the influence of comorbid depression on cognition in old age. Additionally, we still know little about the influence of depression in mixed dementia (MD), that is, in cases where there is the co-existence of Alzheimer's disease and vascular dementia (VaD). Given that the assessment of financial capacity is pivotal for independent living as well as in the prevention of financial exploitation and abuse in old age, in this pilot study, we aimed to examine whether comorbid depression in MD patients can influence financial capacity performance. A total of 115 participants were recruited. They were divided into four groups: MD patients with and without depressive symptoms and healthy elderly without depression as well as older adults suffering from depression. Participants were examined with a number of neuropsychological tests, including the Mini-Mental State Examination (MMSE), Geriatric Depression Scale (GDS-15), and Legal Capacity for Property Law Transactions Assessment Scale (LCPLTAS). The results of this study suggested that financial capacity as measured with LCPLTAS in MD patients was severely impaired when depression co-existed compared to patients suffering only from depression and healthy controls. Deficits in financial capacity in MD and comorbid depression should be a point on which healthcare professionals should focus during neuropsychological assessment in order to prevent financial exploitation.

Strategies for Treatment of Disease-Associated Dementia Beyond Alzheimer's Disease: An Update

Memory, cognition, dementia, and neurodegeneration are complexly interlinked processes with various mechanistic pathways, leading to a range of clinical outcomes. They are strongly associated with pathological conditions like Alzheimer's disease, Parkinson's disease, schizophrenia, and stroke and are a growing concern for their timely diagnosis and management. Several cognitionenhancing interventions for management include non-pharmacological interventions like diet, exercise, and physical activity, while pharmacological interventions include medicinal agents, herbal agents, and nutritional supplements. This review critically analyzed and discussed the currently available agents under different drug development phases designed to target the molecular targets, including cholinergic receptor, glutamatergic system, GABAergic targets, glycine site, serotonergic targets, histamine receptors, etc. Understanding memory formation and pathways involved therein aids in opening the new gateways to treating cognitive disorders. However, clinical studies suggest that there is still a dearth of knowledge about the pathological mechanism involved in neurological conditions, making the dropouts of agents from the initial phases of the clinical trial. Hence, a better understanding of the disease biology, mode of drug action, and interlinked mechanistic pathways at a molecular level is required.

Residential greenness and risk of incident dementia: A prospective study of 375,342 participants

INTRODUCTION

Incorporation of greenspace may be a novel environmental policy that might result in positive health effects; hence, this study aimed to investigate the association between residential greenness and dementia incidence. The effects of particulate air pollution on mediating dementia were also determined.

METHODS

A prospective cohort study involving 375,342 UK biobank participants was conducted, in which Cox regression models were used to determine the association of greenspace exposure with the risks of all-cause dementia (ACD), Alzheimer's disease (AD) and vascular dementia (VD). Sociodemographic variables, lifestyle or dietary characteristics and apolipoprotein E4 status were controlled using two levels of adjusted models. Mediation analyses were performed to determine the mediation effects of PMs.

RESULTS

The results indicated that there were 4929 ACD, 2132 AD, and 1184 VD incidents throughout the 8-year study. In the multi-adjusted model, each interquartile increment in greenspace (buffer 300m) conferred the lower risks of ACD (HR = 0.968, 95% confidence intervals [CI]: 0.938-1.000]) and VD (HR = 0.926, 95% CI: 0.867-0.989). The fourth greenspace quartile conferred also reduced risks of ACD (HR = 0.891, 95% CI: 0.804-0.989) and VD (HR = 0.778, 95% CI: 0.630-0.960) in reference to the first quartile. With regard to 1000m catchment, each interquartile increment conferred a 5.0% (95% CI: 1.8-8.1) lower risk of ACD, and the fourth greenspace quartile conferred a 10.9% (95% CI: 0.9-19.8) lower risk of ACD compared to the first quartile. The protective effect of greenness might be mediated based on the reduction of PM_2.5 and PM₁₀ (P_{indirect effect}<0.05).

CONCLUSIONS

Increasing greenness reduces the risk of dementia. This study suggests that greenspace is an environmental strategy that helps prevent dementia.

Liver Enzymes in a Cohort of Community-Dwelling Older Persons: Focus on Sex Contribution

Dysfunctions in liver metabolic activities may increase the risk of cognitive impairment and dementia. In a cohort of community-dwelling older persons investigated for a suspected cognitive decline, we studied the association between liver status and dementia, considering sex and frailty contribution. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) concentrations, and the AST/ALT ratio were used to assess liver function in 419 older adults (248 persons with dementia and 171 age- and sex-matched subjects without cognitive decline). Although the serum concentrations of the liver enzymes were in the physiologic range, patients with dementia showed lower ALT concentrations (p = 0.005) and higher AST/ALT ratios (p = 0.003) compared to controls. The same differences were found when comparing men with and without dementia (ALT, p = 0.009; AST/ALT ratio, p = 0.003) but disappeared in women. Curiously, comparing women and men with the same diagnosis, the ALT concentrations were lower (p = 0.008), and the AST/ALT ratio was higher (p = 0.001) in control women than men, whereas no significant difference was found between persons with dementia. In conclusion, in our cohort of older people living in the community, the association between serum aminotransferases and dementia was remarked. Moreover, our results support attention to sex difference in liver function, suggesting a role in the pathogenesis of dementia.

Blood Analytes as Biomarkers of Mechanisms Involved in Alzheimer’s Disease Progression

Alzheimer’s disease (AD) is the leading cause of dementia, but the pathogenetic factors are not yet well known, and the relationships between brain and systemic biochemical derangements and disease onset and progression are unclear. We aim to focus on blood biomarkers for an accurate prognosis of the disease. We used a dataset characterized by longitudinal findings collected over the past 10 years from 90 AD patients. The dataset included 277 observations (both clinical and biochemical ones, encompassing blood analytes encompassing routine profiles for different organs, together with immunoinflammatory and oxidative markers). Subjects were grouped into four severity classes according to the Clinical Dementia Rating (CDR) Scale: mild (CDR = 0.5 and CDR = 1), moderate (CDR = 2), severe (CDR = 3) and very severe (CDR = 4 and CDR = 5). Statistical models were used for the identification of potential blood markers of AD progression. Moreover, we employed the Pathfinder tool of the Reactome database to investigate the biological pathways in which the analytes of interest could be involved. Statistical results reveal an inverse significant relation between four analytes (high-density cholesterol, total cholesterol, iron and ferritin) with AD severity. In addition, the Reactome database suggests that such analytes could be involved in pathways that are altered in AD progression. Indeed, the identified blood markers include molecules that reflect the heterogeneous pathogenetic mechanisms of AD. The combination of such blood analytes might be an early indicator of AD progression and constitute useful therapeutic targets.

A new generation of AD biomarkers: 2019 to 2021

Alzheimer's disease (AD) is the most common form of dementia and cases are rising worldwide. The effort to fight this disease is hampered by a lack of disease-modifying treatments and the absence of an early, accurate diagnostic tool. Neuropathology begins years or decades before symptoms occur and, upon onset of symptoms, diagnosis can take a year or more. Such delays postpone treatment and make research into the early stages of the disease difficult. Ideally, clinicians require a minimally invasive test that can detect AD in its early stages, before cognitive symptoms occur. Advances in proteomic technologies have facilitated the study of promising biomarkers of AD. Over the last two years (2019-2021) studies have identified and validated many species which can be measured in cerebrospinal fluid (CSF), plasma, or in both fluids, and which have a high predictive value for AD. We herein discuss proteins which have been highlighted as promising biomarkers of AD in the last two years, and consider implications for future research within the research framework of the amyloid (A), tau (T), neurodegeneration (N) scoring system. We review recently identified species of amyloid and tau which may improve diagnosis when used in combination with current measures such as amyloid-beta-42 (Aβ42), total tau (t-tau) and phosphorylated tau (p-tau). In addition, several proteins have been identified as likely proxies for neurodegeneration, including neurofilament light (NfL), synaptosomal-associated protein 25 (SNAP-25) and neurogranin (NRGN). Finally, proteins originating from diverse processes such as neuroinflammation, lipid transport and mitochondrial dysfunction could aid in both AD diagnosis and patient stratification.

Polygenic coronary artery disease association with brain atrophy in the cognitively impaired

While a number of low-frequency genetic variants of large effect size have been shown to underlie both cardiovascular disease and dementia, recent studies have highlighted the importance of common genetic variants of small effect size, which, in aggregate, are embodied by a polygenic risk score. We investigate the effect of polygenic risk for coronary artery disease on brain atrophy in Alzheimer's disease using whole-brain volume and put our findings in context with the polygenic risk for Alzheimer's disease and presumed small vessel disease as quantified by white-matter hyperintensities. We use 730 subjects from the Alzheimer's disease neuroimaging initiative database to investigate polygenic risk score effects (beyond APOE) on whole-brain volumes, total and regional white-matter hyperintensities and amyloid beta across diagnostic groups. In a subset of these subjects (N = 602), we utilized longitudinal changes in whole-brain volume over 24 months using the boundary shift integral approach. Linear regression and linear mixed-effects models were used to investigate the effect of white-matter hyperintensities at baseline as well as Alzheimer's disease-polygenic risk score and coronary artery disease-polygenic risk score on whole-brain atrophy and whole-brain atrophy acceleration, respectively. All genetic associations were examined under the oligogenic (P = 1e-5) and the more variant-inclusive polygenic (P = 0.5) scenarios. Results suggest no evidence for a link between the polygenic risk score and markers of Alzheimer's disease pathology at baseline (when stratified by diagnostic group). However, both Alzheimer's disease-polygenic risk score and coronary artery disease-polygenic risk score were associated with longitudinal decline in whole-brain volume (Alzheimer's disease-polygenic risk score t = 3.3, P _FDR = 0.007 over 24 months in healthy controls) and surprisingly, under certain conditions, whole-brain volume atrophy is statistically more correlated with cardiac polygenic risk score than Alzheimer's disease-polygenic risk score (coronary artery disease-polygenic risk score t = 2.1, P _FDR = 0.04 over 24 months in the mild cognitive impairment group). Further, in our regional analysis of white-matter hyperintensities, Alzheimer's disease-polygenic risk score beyond APOE is predictive of white-matter volume in the occipital lobe in Alzheimer's disease subjects in the polygenic regime. Finally, the rate of change of brain volume (or atrophy acceleration) may be sensitive to Alzheimer's disease-polygenic risk beyond APOE in healthy individuals (t = 2, P = 0.04). For subjects with mild cognitive impairment, beyond APOE, a more inclusive polygenic risk score including more variants, shows coronary artery disease-polygenic risk score to be more predictive of whole-brain volume atrophy, than an oligogenic approach including fewer larger effect size variants.

[Cerebrovascular disease with neurocognitive impairment]

In the International Classification of Diseases 11th revision in the section «Diseases of the nervous system», it is proposed to distinguish «Cerebrovascular disorder with neurocognitive impairment», which corresponds to both discirculatory encephalopathy (DEP) or chronic cerebral ischemia (CCI) accepted in our country, and also vascular cognitive impairments. The terminology, prevalence, risk factors and pathological basis of the disease are discussed, in particular multiple infarctions, strategic infarctions, cerebral small vessel disease, specific microangiopathies, intracerebral hemorrhage and global hypoperfusion. Post-stroke cognitive impairments are discussed in detail. The article presents relevant data on the pathogenesis of the disease, highlights the issues of clinical and neuroimaging diagnostics. Based on the data presented in the article, we can conclude that the diagnosis of DEP, CCI should be based on the presence of cerebrovascular disease with neurocognitive impairment, which implies the verification of vascular cognitive impairments and reliable neuroimaging signs of cerebrovascular pathology while excluding other causes. Early diagnosis and effective treatment of cerebrovascular disease with neurocognitive impairment (DEP, CCI) is becoming increasingly important, since treatment can slow the progression of the disease and lead to a decrease in the incidence of stroke and dementia.

Olfactory Bulb Proteomics Reveals Widespread Proteostatic Disturbances in Mixed Dementia and Guides for Potential Serum Biomarkers to Discriminate Alzheimer Disease and Mixed Dementia Phenotypes

The most common form of mixed dementia (MixD) is constituted by abnormal protein deposits associated with Alzheimer's disease (AD) that coexist with vascular disease. Although olfactory dysfunction is considered a clinical sign of AD-related dementias, little is known about the impact of this sensorial impairment in MixD at the molecular level. To address this gap in knowledge, we assessed olfactory bulb (OB) proteome-wide expression in MixD subjects (n = 6) respect to neurologically intact controls (n = 7). Around 9% of the quantified proteins were differentially expressed, pinpointing aberrant proteostasis involved in synaptic transmission, nucleoside monophosphate and carbohydrate metabolism, and neuron projection regeneration. In addition, network-driven proteomics revealed a modulation in cell-survival related pathways such as ERK, AKT, and the PDK1-PKC axis. Part of the differential OB protein set was not specific of MixD, also being deregulated across different tauopathies, synucleinopathies, and tardopathies. However, the comparative functional analysis of OB proteome data between MixD and pure AD pathologies deciphered commonalities and differences between both related phenotypes. Finally, olfactory proteomics allowed to propose serum Prolow-density lipoprotein receptor-related protein 1 (LRP1) as a candidate marker to differentiate AD from MixD phenotypes.

Identification of vascular dementia and Alzheimer's disease hub genes expressed in the frontal lobe and temporal cortex by weighted co-expression network analysis and construction of a protein-protein interaction

Background: It is difficult to distinguish cognitive decline due to AD from that sustained by cerebrovascular disease in view of the great overlap. It is uncertain in the molecular biological pathway behind AD and VaD.Objective: Our study aimed to explore the hub molecules and their associations with each other to identify potential biomarkers and therapeutic targets for the AD and VaD.Methods: We screened the differentially expressed genes of AD and VaD, used weighted gene co-expression network analysis and then constructed a VaD-AD-specific protein-protein interaction network with functional annotation to their related metabolic pathways. Finally, we performed a ROC curve analysis of hub proteins to get an idea about their diagnostic value.Results: In the frontal lobe and temporal cortex, hub genes were identified. With regard to VaD, there were only three hub genes which encoded the neuropeptides, SST, NMU and TAC1. The AUC of these genes were 0.804, 0.768 and 0.779, respectively. One signature was established for these three hub genes with AUC of 0.990. For the identification of AD and VaD, all hub genes were receptors. These genes included SH3GL2, PROK2, TAC3, HTR2A, MET, TF, PTH2R CNR1, CHRM4, PTPN3 and CRH. The AUC of these genes were 0.853, 0.859, 0.796, 0.775, 0.706, 0.677, 0.696, 0.668 and 0.652, respectively. The other signature was built for eleven hub genes with AUC of 0.990.Conclusion: In the frontal lobe and temporal cortex regions, hub genes are used as diagnostic markers, which may provide insight into personalized potential biomarkers and therapeutic targets for patients with VaD and AD.

microRNA-Based Biomarkers in Alzheimer's Disease (AD)

Alzheimer's disease (AD) is a multifactorial, age-related neurological disease characterized by complex pathophysiological dynamics taking place at multiple biological levels, including molecular, genetic, epigenetic, cellular and large-scale brain networks. These alterations account for multiple pathophysiological mechanisms such as brain protein accumulation, neuroinflammatory/neuro-immune processes, synaptic dysfunction, and neurodegeneration that eventually lead to cognitive and behavioral decline. Alterations in microRNA (miRNA) signaling have been implicated in the epigenetics and molecular genetics of all neurobiological processes associated with AD pathophysiology. These changes encompass altered miRNA abundance, speciation and complexity in anatomical regions of the CNS targeted by the disease, including modified miRNA expression patterns in brain tissues, the systemic circulation, the extracellular fluid (ECF) and the cerebrospinal fluid (CSF). miRNAs have been investigated as candidate biomarkers for AD diagnosis, disease prediction, prognosis and therapeutic purposes because of their involvement in multiple brain signaling pathways in both health and disease. In this review we will: (i) highlight the significantly heterogeneous nature of miRNA expression and complexity in AD tissues and biofluids; (ii) address how information may be extracted from these data to be used as a diagnostic, prognostic and/or screening tools across the entire continuum of AD, from the preclinical stage, through the prodromal, i.e., mild cognitive impairment (MCI) phase all the way to clinically overt dementia; and (iii) consider how specific miRNA expression patterns could be categorized using miRNA reporters that span AD pathophysiological initiation and disease progression.