Hippocampal Sclerosis of Aging Can Be Segmental: Two Cases and Review of the Literature

Limbic-predominant age-related TDP-43 encephalopathy (LATE-NC): Co-pathologies and genetic risk factors provide clues about pathogenesis

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) is detectable at autopsy in more than one-third of people beyond age 85 years and is robustly associated with dementia independent of other pathologies. Although LATE-NC has a large impact on public health, there remain uncertainties about the underlying biologic mechanisms. Here, we review the literature from human studies that may shed light on pathogenetic mechanisms. It is increasingly clear that certain combinations of pathologic changes tend to coexist in aging brains. Although "pure" LATE-NC is not rare, LATE-NC often coexists in the same brains with Alzheimer disease neuropathologic change, brain arteriolosclerosis, hippocampal sclerosis of aging, and/or age-related tau astrogliopathy (ARTAG). The patterns of pathologic comorbidities provide circumstantial evidence of mechanistic interactions ("synergies") between the pathologies, and also suggest common upstream influences. As to primary mediators of vulnerability to neuropathologic changes, genetics may play key roles. Genes associated with LATE-NC include TMEM106B, GRN, APOE, SORL1, ABCC9, and others. Although the anatomic distribution of TDP-43 pathology defines the condition, important cofactors for LATE-NC may include Tau pathology, endolysosomal pathways, and blood-brain barrier dysfunction. A review of the human phenomenology offers insights into disease-driving mechanisms, and may provide clues for diagnostic and therapeutic targets.

In severe ADNC, hippocampi with comorbid LATE-NC and hippocampal sclerosis have substantially more astrocytosis than those with LATE-NC or hippocampal sclerosis alone

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) and hippocampal sclerosis of aging (HS-A) pathologies are found together at autopsy in ∼20% of elderly demented persons. Although astrocytosis is known to occur in neurodegenerative diseases, it is currently unknown how the severity of astrocytosis is correlated with the common combinations of pathologies in aging brains. To address this knowledge gap, we analyzed a convenience sample of autopsied subjects from the University of Kentucky Alzheimer's Disease Research Center community-based autopsy cohort. The subjects were stratified into 5 groups (n = 51 total): pure ADNC, ADNC + LATE-NC, ADNC + HS-A, ADNC + LATE-NC + HS-A, and low-pathology controls. Following GFAP immunostaining and digital slide scanning with a ScanScope, we measured GFAP-immunoreactive astrocytosis. The severities of GFAP-immunoreactive astrocytosis in hippocampal subfield CA1 and subiculum were compared between groups. The group with ADNC + LATE-NC + HS-A had the most astrocytosis as operationalized by either any GFAP+ or strong GFAP+ immunoreactivity in both CA1 and subiculum. In comparison to that pathologic combination, ADNC + HS or ADNC + LATE-NC alone showed lower astrocytosis. Pure ADNC had only marginally increased astrocytosis in CA1 and subiculum, in comparison to low-pathology controls. We conclude that there appeared to be pathogenetic synergy such that ADNC + LATE-NC + HS-A cases had relatively high levels of astrocytosis in the hippocampal formation.

Characterization of hippocampal sclerosis of aging and its association with other neuropathologic changes and cognitive deficits in the oldest-old

Hippocampal sclerosis of aging (HS-A) is a common age-related neuropathological lesion characterized by neuronal loss and astrogliosis in subiculum and CA1 subfield of hippocampus. HS-A is associated with cognitive decline that mimics Alzheimer's disease. Pathological diagnosis of HS-A is traditionally binary based on presence/absence of the lesion. We compared this traditional measure against our novel quantitative measure for studying the relationship between HS-A and other neuropathologies and cognitive impairment. We included 409 participants from The 90+ study with neuropathological examination and longitudinal neuropsychological assessments. In those with HS-A, we examined digitized H&E and LFB stained hippocampal slides. The length of HS-A in each subfield of hippocampus and subiculum, each further divided into three subregions, was measured using Aperio eSlide Manager. For each subregion, the proportion affected by HS-A was calculated. Using regression models, both traditional/binary and quantitative measures were used to study the relationship between HS-A and other neuropathological changes and cognitive outcomes. HS-A was present in 48 (12%) of participants and was always focal, primarily affecting CA1 (73%), followed by subiculum (9%); overlapping pathology (subiculum and CA1) affected 18% of individuals. HS-A was more common in the left (82%) than the right (25%) hemisphere and was bilateral in 7% of participants. HS-A traditional/binary assessment was associated with limbic-predominant age-related TDP-43 encephalopathy (LATE-NC; OR = 3.45, p < 0.001) and aging-related tau astrogliopathy (ARTAG; OR = 2.72, p = 0.008). In contrast, our quantitative approach showed associations between the proportion of HS-A (CA1/subiculum/combined) and LATE-NC (p = 0.001) and arteriolosclerosis (p = 0.005). While traditional binary assessment of HS-A was associated with impaired memory (OR = 2.60, p = 0.007), calculations (OR = 2.16, p = 0.027), and orientation (OR = 3.56, p < 0.001), our quantitative approach revealed additional associations with impairments in language (OR = 1.33, p = 0.018) and visuospatial domains (OR = 1.37, p = 0.006). Our novel quantitative method revealed associations between HS-A and vascular pathologies and impairment in cognitive domains that were not detected using traditional/binary measures.

A novel histological staging of hippocampal sclerosis that is evident in gray matter loss in vivo

INTRODUCTION

Hippocampal sclerosis of aging (HS) is defined by end-stage histological findings, strongly associated with limbic-predominant age-related TAR DNA-binding protein 43 (TDP-43) encephalopathy (LATE). We aimed to characterize features of early HS to refine the understanding of its role within combined pathology.

METHODS

We studied 159 brain donations from the multimodal Vallecas Alzheimer's Center Study. A staging system (0 to IV) was developed to account for HS progression and analyzed in relation to pre-mortem cognitive and magnetic resonance imaging (MRI) data.

RESULTS

Our HS staging system displayed a significant correlation with disease duration, cognitive performance, and combined neuropathologies, especially with LATE. Two-level assessment along the hippocampal longitudinal axis revealed an anterior-posterior gradient of HS severity. In vivo MRI showed focally reduced hippocampal gray matter density as a function of HS staging.

DISCUSSION

The association of this staging system with clinical progression and structural differences supports its utility in the characterization and potential in vivo monitoring of HS.

HIGHLIGHTS

The definition of hippocampal sclerosis of aging (HS) is currently limited to an end-stage pathological fingerprint. We characterize early HS histological features to define a complete staging system. The proposed staging displays a parallel but not identical progression to limbic-predominant age-related TAR DNA-binding protein 43 (TDP-43) encephalopathy (LATE). The proposed staging also reflects the expected demographic and cognitive differences associated with HS. In vivo magnetic resonance imaging (MRI) showed focal hippocampal gray matter loss as a function of HS staging.

The unique neuropathological vulnerability of the human brain to aging

Alzheimer's disease (AD)-related neurofibrillary tangles (NFT), argyrophilic grain disease (AGD), aging-related tau astrogliopathy (ARTAG), limbic predominant TDP-43 proteinopathy (LATE), and amygdala-predominant Lewy body disease (LBD) are proteinopathies that, together with hippocampal sclerosis, progressively appear in the elderly affecting from 50% to 99% of individuals aged 80 years, depending on the disease. These disorders usually converge on the same subject and associate with additive cognitive impairment. Abnormal Tau, TDP-43, and α-synuclein pathologies progress following a pattern consistent with an active cell-to-cell transmission and abnormal protein processing in the host cell. However, cell vulnerability and transmission pathways are specific for each disorder, albeit abnormal proteins may co-localize in particular neurons. All these alterations are unique or highly prevalent in humans. They all affect, at first, the archicortex and paleocortex to extend at later stages to the neocortex and other regions of the telencephalon. These observations show that the phylogenetically oldest areas of the human cerebral cortex and amygdala are not designed to cope with the lifespan of actual humans. New strategies aimed at reducing the functional overload of the human telencephalon, including optimization of dream repair mechanisms and implementation of artificial circuit devices to surrogate specific brain functions, appear promising.

LATE-NC staging in routine neuropathologic diagnosis: an update

An international consensus report in 2019 recommended a classification system for limbic-predominant age-related TDP-43 encephalopathy neuropathologic changes (LATE-NC). The suggested neuropathologic staging system and nomenclature have proven useful for autopsy practice and dementia research. However, some issues remain unresolved, such as cases with unusual features that do not fit with current diagnostic categories. The goal of this report is to update the neuropathologic criteria for the diagnosis and staging of LATE-NC, based primarily on published data. We provide practical suggestions about how to integrate available genetic information and comorbid pathologies [e.g., Alzheimer's disease neuropathologic changes (ADNC) and Lewy body disease]. We also describe recent research findings that have enabled more precise guidance on how to differentiate LATE-NC from other subtypes of TDP-43 pathology [e.g., frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS)], and how to render diagnoses in unusual situations in which TDP-43 pathology does not follow the staging scheme proposed in 2019. Specific recommendations are also made on when not to apply this diagnostic term based on current knowledge. Neuroanatomical regions of interest in LATE-NC are described in detail and the implications for TDP-43 immunohistochemical results are specified more precisely. We also highlight questions that remain unresolved and areas needing additional study. In summary, the current work lays out a number of recommendations to improve the precision of LATE-NC staging based on published reports and diagnostic experience.

Limbic-Predominant Age-Related TDP-43 Encephalopathy: LATE-Breaking Updates in Clinicopathologic Features and Biomarkers

PURPOSE OF REVIEW

Limbic-predominant age-related TDP-43 encephalopathy (LATE) is a recently defined neurodegenerative disease characterized by amnestic phenotype and pathological inclusions of TAR DNA-binding protein 43 (TDP-43). LATE is distinct from rarer forms of TDP-43 diseases such as frontotemporal lobar degeneration with TDP-43 but is also a common copathology with Alzheimer's disease (AD) and cerebrovascular disease and accelerates cognitive decline. LATE contributes to clinicopathologic heterogeneity in neurodegenerative diseases, so it is imperative to distinguish LATE from other etiologies.

RECENT FINDINGS

Novel biomarkers for LATE are being developed with magnetic resonance imaging (MRI) and positron emission tomography (PET). When cooccurring with AD, LATE exhibits identifiable patterns of limbic-predominant atrophy on MRI and hypometabolism on 18F-fluorodeoxyglucose PET that are greater than expected relative to levels of local AD pathology. Efforts are being made to develop TDP-43-specific radiotracers, molecularly specific biofluid measures, and genomic predictors of TDP-43. LATE is a highly prevalent neurodegenerative disease distinct from previously characterized cognitive disorders.

Limbic-Predominant Age-Related TDP-43 Encephalopathy: Medical and Pathologic Factors Associated With Comorbid Hippocampal Sclerosis

BACKGROUND AND OBJECTIVES

Limbic-predominant age-related Tar DNA binding protein 43 (TDP-43) encephalopathy neuropathologic change (LATE-NC) is present in ≈25% of older persons' brains and is strongly associated with cognitive impairment. Hippocampal sclerosis (HS) pathology is often comorbid with LATE-NC, but the clinical and pathologic correlates of HS in LATE-NC are not well understood.

METHODS

This retrospective autopsy cohort study used data derived from the National Alzheimer's Coordinating Center Neuropathology Data Set, which included neurologic status, medical histories, and neuropathologic results. All autopsies were performed in 2014 or later. Among participants with LATE-NC, those who also had HS pathology were compared with those without HS with regard to candidate risk factors or common underlying diseases. Statistical significance was set at nominal p < 0.05 in this exploratory study.

RESULTS

A total of 408 participants were included (n = 221 were LATE-NC+/HS-, n = 145 were LATE-NC+/HS+, and n = 42 were LATE-NC-/HS+). Most of the included LATE-NC+ participants were severely impaired cognitively (83.3% with dementia). Compared to HS- participants, LATE-NC+ participants with HS trended toward having worse cognitive status and scored lower on the Personal Care and Orientation domains (both p = 0.03). Among LATE-NC+ participants with Braak neurofibrillary tangle (NFT) stages 0 to IV (n = 88), HS+ participants were more impaired in the Memory and Orientation domains (both p = 0.02). There were no differences (HS+ compared with HS-) in the proportion with clinical histories of seizures, stroke, cardiac bypass procedures, diabetes, or hypertension. The HS+ group lacking TDP-43 proteinopathy (n = 42) was relatively likely to have had strokes (p = 0.03). When LATE-NC+ participants with or without HS were compared, there were no differences in Alzheimer disease neuropathologies (Thal β-amyloid phases or Braak NFT stages) or Lewy body pathologies. However, the HS+ group was less likely to have amygdala-restricted TDP-43 proteinopathy (LATE-NC stage 1) and more likely to have neocortical TDP-43 proteinopathy (LATE-NC stage 3) (p < 0.001). LATE-NC+ brains with HS also tended to have more severe circle of Willis atherosclerosis and arteriolosclerosis pathologies.

DISCUSSION

In this cohort skewed toward participants with severe dementia, LATE-NC+ HS pathology was not associated with seizures or with Alzheimer-type pathologies. Rather, the presence of comorbid HS pathology was associated with more widespread TDP-43 proteinopathy and with more severe non-β-amyloid vessel wall pathologies.

Analysis of genes (TMEM106B, GRN, ABCC9, KCNMB2, and APOE) implicated in risk for LATE-NC and hippocampal sclerosis provides pathogenetic insights: a retrospective genetic association study

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) is the most prevalent subtype of TDP-43 proteinopathy, affecting up to 1/3rd of aged persons. LATE-NC often co-occurs with hippocampal sclerosis (HS) pathology. It is currently unknown why some individuals with LATE-NC develop HS while others do not, but genetics may play a role. Previous studies found associations between LATE-NC phenotypes and specific genes: TMEM106B, GRN, ABCC9, KCNMB2, and APOE. Data from research participants with genomic and autopsy measures from the National Alzheimer’s Coordinating Center (NACC; n = 631 subjects included) and the Religious Orders Study and Memory and the Rush Aging Project (ROSMAP; n = 780 included) were analyzed in the current study. Our goals were to reevaluate disease-associated genetic variants using newly collected data and to query whether the specific genotype/phenotype associations could provide new insights into disease-driving pathways. Research subjects included in prior LATE/HS genome-wide association studies (GWAS) were excluded. Single nucleotide variants (SNVs) within 10 kb of TMEM106B, GRN, ABCC9, KCNMB2, and APOE were tested for association with HS and LATE-NC, and separately for Alzheimer’s pathologies, i.e. amyloid plaques and neurofibrillary tangles. Significantly associated SNVs were identified. When results were meta-analyzed, TMEM106B, GRN, and APOE had significant gene-based associations with both LATE and HS, whereas ABCC9 had significant associations with HS only. In a sensitivity analysis limited to LATE-NC + cases, ABCC9 variants were again associated with HS. By contrast, the associations of TMEM106B, GRN, and APOE with HS were attenuated when adjusting for TDP-43 proteinopathy, indicating that these genes may be associated primarily with TDP-43 proteinopathy. None of these genes except APOE appeared to be associated with Alzheimer’s-type pathology. In summary, using data not included in prior studies of LATE or HS genomics, we replicated several previously reported gene-based associations and found novel evidence that specific risk alleles can differentially affect LATE-NC and HS.

Early Detection of Alzheimer's Disease Using Magnetic Resonance Imaging: A Novel Approach Combining Convolutional Neural Networks and Ensemble Learning

Early detection is critical for effective management of Alzheimer's disease (AD) and screening for mild cognitive impairment (MCI) is common practice. Among several deep-learning techniques that have been applied to assessing structural brain changes on magnetic resonance imaging (MRI), convolutional neural network (CNN) has gained popularity due to its superb efficiency in automated feature learning with the use of a variety of multilayer perceptrons. Meanwhile, ensemble learning (EL) has shown to be beneficial in the robustness of learning-system performance via integrating multiple models. Here, we proposed a classifier ensemble developed by combining CNN and EL, i.e., the CNN-EL approach, to identify subjects with MCI or AD using MRI: i.e., classification between (1) AD and healthy cognition (HC), (2) MCIc (MCI patients who will convert to AD) and HC, and (3) MCIc and MCInc (MCI patients who will not convert to AD). For each binary classification task, a large number of CNN models were trained applying a set of sagittal, coronal, or transverse MRI slices; these CNN models were then integrated into a single ensemble. Performance of the ensemble was evaluated using stratified fivefold cross-validation method for 10 times. The number of the intersection points determined by the most discriminable slices separating two classes in a binary classification task among the sagittal, coronal, and transverse slice sets, transformed into the standard Montreal Neurological Institute (MNI) space, acted as an indicator to assess the ability of a brain region in which the points were located to classify AD. Thus, the brain regions with most intersection points were considered as those mostly contributing to the early diagnosis of AD. The result revealed an accuracy rate of 0.84 ± 0.05, 0.79 ± 0.04, and 0.62 ± 0.06, respectively, for classifying AD vs. HC, MCIc vs. HC, and MCIc vs. MCInc, comparable to previous reports and a 3D deep learning approach (3D-SENet) based on a more state-of-the-art and popular Squeeze-and-Excitation Networks model using channel attention mechanism. Notably, the intersection points accurately located the medial temporal lobe and several other structures of the limbic system, i.e., brain regions known to be struck early in AD. More interestingly, the classifiers disclosed multiple patterned MRI changes in the brain in AD and MCIc, involving these key regions. These results suggest that as a data-driven method, the combined CNN and EL approach can locate the most discriminable brain regions indicated by the trained ensemble model while the generalization ability of the ensemble model was maximized to successfully capture AD-related brain variations early in the disease process; it can also provide new insights into understanding the complex heterogeneity of whole-brain MRI changes in AD. Further research is needed to examine the clinical implication of the finding, capability of the advocated CNN-EL approach to help understand and evaluate an individual subject's disease status, symptom burden and progress, and the generalizability of the advocated CNN-EL approach to locate the most discriminable brain regions in the detection of other brain disorders such as schizophrenia, autism, and severe depression, in a data-driven way.

Cognitive deficit, and neuropathological correlates, in the oldest-old

Several disorders are usually involved in the cognitive deficit of the oldest old. Alzheimer disease is the commonest. It is usually characterized by progressive memory impairment - neocortical symptoms occurring much later in the course of the disease. Alzheimer disease should not be considered any more as the single cause of a cognitive deficit in a very old patient. Vascular alterations, possibly causing microinfarcts, are commonly associated, especially in cerebral amyloid angiopathy. A slowly progressive memory deficit with negative CSF biomarkers of Alzheimer's disease may be due to hippocampal sclerosis that may be the consequence of multiple causes: in most of the cases, it is associated with neuronal TDP-43 inclusions. Recently, a distribution of these inclusions to a territory more extensive than the hippocampus has been reported and attributed to a new entity, called Limbic-predominant Age-related TDP-43 Encephalopathy (LATE) with or without hippocampal sclerosis. The presence of cortical Lewy bodies may cause an intellectual deficit or contribute to it. The prevalence of dementia with cortical Lewy bodies in the oldest old is discussed. Tau inclusions in cortical glia have also been shown to participate to the intellectual deficit. Association of neurodegenerative and vascular changes is the most frequent situation in the very old patients. Systemic diseases such as diabetes or heart failure, prescription drugs (when misused), or toxic such as alcohol may also contribute to the cognitive impairment and be amenable to treatment.

Hippocampal Sclerosis, Argyrophilic Grain Disease, and Primary Age-Related Tauopathy

PURPOSE OF REVIEW

Hippocampal sclerosis, argyrophilic grain disease, and primary age-related tauopathy are common Alzheimer disease mimics that currently lack clinical diagnostic criteria. Increased understanding of these pathologic entities is important for the neurologist who may encounter patients with an unusually slowly progressive degenerative dementia that may appear to meet criteria for Alzheimer disease but who progress to develop symptoms that are unusual for classic Alzheimer disease RECENT FINDINGS: Hippocampal sclerosis has traditionally been associated with hypoxic/ischemic injury and poorly controlled epilepsy, but it is now recognized that hippocampal sclerosis may also be associated with a unique degenerative disease of aging or may be an associated pathologic finding in many cases of frontotemporal lobar degeneration. Argyrophilic grain disease has been recognized as an enigma in the field of pathology for over 30 years, but recent discoveries suggest that it may overlap with other tau-related disorders within the spectrum of frontotemporal lobar degeneration. Primary age-related tauopathy has long been recognized as a distinct clinical entity that lies on the Alzheimer pathologic spectrum, with the presence of neurofibrillary tangles that lack the coexistent Alzheimer plaque development; thus, it is thought to represent a distinct pathologic entity.

SUMMARY

Despite advances in dementia diagnosis that suggest that we have identified and unlocked the mysteries of the major degenerative disease states responsible for cognitive decline and dementia in the elderly, diseases such as hippocampal sclerosis, argyrophilic grain disease, and primary age-related tauopathy demonstrate that we remain on the frontier of discovery and that our diagnostic repertoire of diseases responsible for such clinical symptoms remains in its infancy. Understanding such diagnostic confounds is important for the neurologist in assigning appropriate diagnoses and selecting appropriate therapeutic management strategies for patients with mild cognitive impairment and dementia.

Hippocampal Sclerosis in the Oldest Old: A Finnish Population-Based Study

Background:

There are only few population-based studies that have systemically investigated the prevalence of hippocampal sclerosis (HS) in the very old. The frequency of unilateral versus bilateral HS has been rarely studied.

Objective:

We investigated the prevalence and laterality of HS and its association with other neurodegenerative and vascular pathologies in a population-based sample of very elderly. Furthermore, the concomitant presence of immunoreactivity for TDP-43, p62, and HPtau was studied.

Methods:

The population-based Vantaa 85+ study includes all inhabitants of the city of Vantaa, who were >85 years in 1991 (n = 601). Neuropathological assessment was possible in 302 subjects. Severity of neuronal loss of CA sectors and subiculum was determined bilaterally by HE- staining. Immunohistochemistry performed using antibodies for TDP-43, p62, and HPtau.

Results:

Neuronal loss and pathological changes in the hippocampus sector CA1 and subiculum were observed in 47 of the 302 individuals (16%), and 51% of these changes were bilateral. HS without comorbid neurodegenerative pathology was found in 1/47 subjects with HS (2%). Dementia (p < 0.001) and TDP-43 immunopositivity of the granular cell layer of the dentate fascia (p < 0.001) were strongly associated with HS. The CERAD score, immunopositivity for HPtau and p62 in the granular cell layer of the fascia dentate were also associated.

Conclusion:

HS is prevalent (16%) in the oldest old population, but HS without any comorbid neurodegenerative pathology is rare. The high frequency of unilateral HS (49%) implied that bilateral sampling of hippocampi should be routine practice in neuropathological examination.

Limbic-predominant age-related TDP-43 encephalopathy (LATE): consensus working group report

We describe a recently recognized disease entity, limbic-predominant age-related TDP-43 encephalopathy (LATE). LATE neuropathological change (LATE-NC) is defined by a stereotypical TDP-43 proteinopathy in older adults, with or without coexisting hippocampal sclerosis pathology. LATE-NC is a common TDP-43 proteinopathy, associated with an amnestic dementia syndrome that mimicked Alzheimer's-type dementia in retrospective autopsy studies. LATE is distinguished from frontotemporal lobar degeneration with TDP-43 pathology based on its epidemiology (LATE generally affects older subjects), and relatively restricted neuroanatomical distribution of TDP-43 proteinopathy. In community-based autopsy cohorts, ∼25% of brains had sufficient burden of LATE-NC to be associated with discernible cognitive impairment. Many subjects with LATE-NC have comorbid brain pathologies, often including amyloid-β plaques and tauopathy. Given that the 'oldest-old' are at greatest risk for LATE-NC, and subjects of advanced age constitute a rapidly growing demographic group in many countries, LATE has an expanding but under-recognized impact on public health. For these reasons, a working group was convened to develop diagnostic criteria for LATE, aiming both to stimulate research and to promote awareness of this pathway to dementia. We report consensus-based recommendations including guidelines for diagnosis and staging of LATE-NC. For routine autopsy workup of LATE-NC, an anatomically-based preliminary staging scheme is proposed with TDP-43 immunohistochemistry on tissue from three brain areas, reflecting a hierarchical pattern of brain involvement: amygdala, hippocampus, and middle frontal gyrus. LATE-NC appears to affect the medial temporal lobe structures preferentially, but other areas also are impacted. Neuroimaging studies demonstrated that subjects with LATE-NC also had atrophy in the medial temporal lobes, frontal cortex, and other brain regions. Genetic studies have thus far indicated five genes with risk alleles for LATE-NC: GRN, TMEM106B, ABCC9, KCNMB2, and APOE. The discovery of these genetic risk variants indicate that LATE shares pathogenetic mechanisms with both frontotemporal lobar degeneration and Alzheimer's disease, but also suggests disease-specific underlying mechanisms. Large gaps remain in our understanding of LATE. For advances in prevention, diagnosis, and treatment, there is an urgent need for research focused on LATE, including in vitro and animal models. An obstacle to clinical progress is lack of diagnostic tools, such as biofluid or neuroimaging biomarkers, for ante-mortem detection of LATE. Development of a disease biomarker would augment observational studies seeking to further define the risk factors, natural history, and clinical features of LATE, as well as eventual subject recruitment for targeted therapies in clinical trials.

Evaluation of TDP-43 proteinopathy and hippocampal sclerosis in relation to APOE ε4 haplotype status: a community-based cohort study

BACKGROUND

Transactive response DNA-binding protein of 43 kDa (TDP-43) proteinopathy in older adults frequently coexists with Alzheimer's disease pathology and hippocampal sclerosis. It is unclear whether there is a link between APOE ε4 and TDP-43 proteinopathy, and the role of APOE ε4 in the association of TDP-43 proteinopathy with hippocampal sclerosis remains to be examined. We investigated the relationships of TDP-43 proteinopathy and hippocampal sclerosis with APOE ε4.

METHODS

We used data from two community-based cohort studies of ageing and dementia: the Religious Orders Study (ROS) and the Rush Memory and Aging Project (MAP). A battery of cognitive tests examining multiple cognitive domains is given to ROS-MAP participants each year, and a measure of annual global cognitive function for each participant is derived by averaging Z scores of these tests. The final clinical diagnosis is assigned after death by a neurologist using all available clinical data without access to post-mortem pathology. Amyloid-β, paired helical filament tau, Lewy bodies, TDP-43, and hippocampal sclerosis were microscopically evaluated in the midbrain, medial temporal, and neocortical regions that capture the progression of each neuropathology. TDP-43 proteinopathy topographic stage was recorded as an ordinal variable, and TDP-43 burden was defined by averaging a semi-quantitative six-point scale across six brain regions. The relationships among APOE ε4, TDP-43 proteinopathy, and hippocampal sclerosis were tested with regression models controlled for sex and age at death, and they were further explored with a mediation analysis using the quasi-Bayesian Monte Carlo method.

FINDINGS

ROS began data collection in 1994, and MAP began data collection in 1997. The data included in this study were analysed from Jan 16, 2017, to July 12, 2017. When analysis began in January, 2017, a total of 1059 ROS-MAP participants who were deceased had APOE genotype and complete pathological measures for amyloid-β, paired helical filament tau, and TDP-43 proteinopathy stage. After excluding 15 participants with other pathological diagnoses, 1044 participants, 1042 of whom also had measures of Lewy body pathology, were included in this study (470 from ROS and 574 from MAP). APOE ε4 count was associated with higher TDP-43 proteinopathy stage (odds ratio [OR] 2·0, 95% CI 1·6-2·6; p=1·9 × 10^-9) and TDP-43 burden (0·40, 0·28-0·52; p=1·2 × 10^-10). Amyloid-β, paired helical filament tau, or Lewy body pathology did not fully explain this association. APOE ε4 increased the odds of hippocampal sclerosis (OR 2·1, 95% CI 1·4-3·0; p=1·7 × 10^-4); this effect was largely mediated by TDP-43 burden (mediated effect p<1·0 × 10^-4) but not directly by APOE ε4 (direct effect p=0·40). APOE ε4 was associated with worse global cognition proximate to death even after adjusting for amyloid-β and paired helical filament tau (estimated effect -0·18, 95% CI -0·31 to -0·04; p=0·010), but this association was attenuated by additionally adjusting for TDP-43 burden (-0·09, -0·22 to 0·04; p=0·18).

INTERPRETATION

APOE ε4 seems to increase TDP-43 burden, and this effect in turn was associated with higher odds of hippocampal sclerosis, a pathology potentially downstream of TDP-43 proteinopathy. TDP-43 proteinopathy contributes to the detrimental effect of APOE ε4 on late-life cognition through mechanisms independent of Alzheimer's disease pathology, and future research should consider that TDP-43 proteinopathy might be an integral component of APOE-related neurodegeneration.

FUNDING

US National Institute on Aging and Alzheimer's Association.

Combined neuropathological pathways account for age-related risk of dementia

OBJECTIVE

Our objectives were to characterize the inter-relation of known dementia-related neuropathologies in one comprehensive model and quantify the extent to which accumulation of neuropathologies accounts for the association between age and dementia.

METHODS

We used data from 1,362 autopsied participants of three community-based clinicopathological cohorts: the Religious Orders Study, the Rush Memory and Aging Project, and the Minority Aging Research Study. We estimated a series of structural equation models summarizing a priori hypothesized neuropathological pathways between age and dementia risk individually and collectively.

RESULTS

At time of death (mean age, 89 years), 44% of our sample had a clinical dementia diagnosis. When considered individually, our vascular, amyloid/tau, neocortical Lewy body, and TAR DNA-binding protein 43 (TDP-43)/hippocampal sclerosis pathology pathways each accounted for a substantial proportion of the association between age and dementia. When considered collectively, the four pathways fully accounted for all variance in dementia risk previously attributable to age. Pathways involving amyloid/tau, neocortical Lewy bodies, and TDP-43/hippocampal sclerosis were interdependent, attributable to the importance of amyloid beta plaques in all three. The importance of the pathways varied, with the vascular pathway accounting for 32% of the association between age and dementia, wheraes the remaining three inter-related degenerative pathways together accounted for 68% (amyloid/tau, 24%; the Lewy body, 1%; and TDP-43/hippocampal sclerosis, 43%).

INTERPRETATION

Age-related increases in dementia risk can be attributed to accumulation of multiple pathologies, each of which contributes to dementia risk. Multipronged approaches may be necessary if we are to develop effective therapies. Ann Neurol 2018;84:10-22.

The Amygdala as a Locus of Pathologic Misfolding in Neurodegenerative Diseases

Over the course of most common neurodegenerative diseases the amygdala accumulates pathologically misfolded proteins. Misfolding of 1 protein in aged brains often is accompanied by the misfolding of other proteins, suggesting synergistic mechanisms. The multiplicity of pathogenic processes in human amygdalae has potentially important implications for the pathogenesis of Alzheimer disease, Lewy body diseases, chronic traumatic encephalopathy, primary age-related tauopathy, and hippocampal sclerosis, and for the biomarkers used to diagnose those diseases. Converging data indicate that the amygdala may represent a preferential locus for a pivotal transition from a relatively benign clinical condition to a more aggressive disease wherein multiple protein species are misfolded. Thus, understanding of amygdalar pathobiology may yield insights relevant to diagnoses and therapies; it is, however, a complex and imperfectly defined brain region. Here, we review aspects of amygdalar anatomy, connectivity, vasculature, and pathologic involvement in neurodegenerative diseases with supporting data from the University of Kentucky Alzheimer's Disease Center autopsy cohort. Immunohistochemical staining of amygdalae for Aβ, Tau, α-synuclein, and TDP-43 highlight the often-coexisting pathologies. We suggest that the amygdala may represent an "incubator" for misfolded proteins and that it is possible that misfolded amygdalar protein species are yet to be discovered.

Hippocampal sclerosis, hippocampal neuron loss patterns and TDP-43 in the aged population

Hippocampal neuron loss is a common neuropathological feature in old age with various underlying etiologies. Hippocampal sclerosis of aging (HS-Aging) is neuropathologically characterized by severe CA1 neuronal loss and frequent presence of transactive response DNA-binding protein of 43 kDa (TDP-43) aggregations. Its etiology is unclear and currently no standardized approaches to measure HS-Aging exist. We developed a semi-quantitative protocol, which captures various hippocampal neuron loss patterns, and compared their occurrence in the context of HS-Aging, TDP-43, vascular and tau pathology in 672 brains (TDP-43 staining n = 642/672, 96%) donated for the population-based Cambridge City over-75s Cohort and the Cognitive Function and Ageing Study. HS-Aging was first evaluated independently from the protocol using the most common criteria defined in literature, and then described in detail through examination of neuron loss patterns and associated pathologies. 34 (5%) cases were identified, with a maximum of five pyramidal neurons in each of over half CA1 fields-of-view (x200 magnification), no vascular damage, no neuron loss in CA2-CA4, but consistent TDP-43 neuronal solid inclusions and neurites. We also report focal CA1 neuron loss with vascular pathology to affect predominantly CA1 bordering CA2 (Fisher's exact, P = 0.009), whereas neuron loss in the subicular end of CA1 was associated with TDP-43 inclusions (Fisher's exact, P < 0.001) and high Braak stage (Fisher's exact, P = 0.001). Hippocampal neuron loss in CA4-CA2 was not associated with TDP-43. We conclude that hippocampal neuron loss patterns are associated with different etiologies within CA1, and propose that these patterns can be used to form objective criteria for HS-Aging diagnosis. Finally, based on our results we hypothesize that neuron loss leading to HS-Aging starts from the subicular end of CA1 when it is associated with TDP-43 pathology, and that this neurodegenerative process is likely to be significantly more common than "end-stage" HS-Aging only.

Hippocampal Sclerosis in Older Patients: Practical Examples and Guidance With a Focus on Cerebral Age-Related TDP-43 With Sclerosis

CONTEXT

- Autopsy studies of the older population (≥65 years of age), and particularly of the "oldest-old" (≥85 years of age), have identified a significant proportion (∼20%) of cognitively impaired patients in which hippocampal sclerosis is the major substrate of an amnestic syndrome. Hippocampal sclerosis may also be comorbid with frontotemporal lobar degeneration, Alzheimer disease, and Lewy body disease. Until recently, the terms hippocampal sclerosis of aging or hippocampal sclerosis dementia were applied in this context. Recent discoveries have prompted a conceptual expansion of hippocampal sclerosis of aging because (1) cellular inclusions of TAR DNA-binding protein 43 kDa (TDP-43) are frequent; (2) TDP-43 pathology may be found outside hippocampus; and (3) brain arteriolosclerosis is a common, possibly pathogenic, component.

OBJECTIVE

- To aid pathologists with recent recommendations for diagnoses of common neuropathologies in older persons, particularly hippocampal sclerosis, and highlight the recent shift in diagnostic terminology from HS-aging to cerebral age-related TDP-43 with sclerosis (CARTS).

DATA SOURCES

- Peer-reviewed literature and 5 autopsy examples that illustrate common age-related neuropathologies, including CARTS, and emphasize the importance of distinguishing CARTS from late-onset frontotemporal lobar degeneration with TDP-43 pathology and from advanced Alzheimer disease with TDP-43 pathology.

CONCLUSIONS

- In advanced old age, the substrates of cognitive impairment are often multifactorial. This article demonstrates common and frequently comorbid neuropathologic substrates of cognitive impairment in the older population, including CARTS, to aid those practicing in this area of pathology.

Gene-based association study of genes linked to hippocampal sclerosis of aging neuropathology: GRN, TMEM106B, ABCC9, and KCNMB2

Hippocampal sclerosis of aging (HS-Aging) is a common neurodegenerative condition associated with dementia. To learn more about genetic risk of HS-Aging pathology, we tested gene-based associations of the GRN, TMEM106B, ABCC9, and KCNMB2 genes, which were reported to be associated with HS-Aging pathology in previous studies. Genetic data were obtained from the Alzheimer's Disease Genetics Consortium, linked to autopsy-derived neuropathological outcomes from the National Alzheimer's Coordinating Center. Of the 3251 subjects included in the study, 271 (8.3%) were identified as an HS-Aging case. The significant gene-based association between the ABCC9 gene and HS-Aging appeared to be driven by a region in which a significant haplotype-based association was found. We tested this haplotype as an expression quantitative trait locus using 2 different public-access brain gene expression databases. The HS-Aging pathology protective ABCC9 haplotype was associated with decreased ABCC9 expression, indicating a possible toxic gain of function.

Overlapping but distinct TDP-43 and tau pathologic patterns in aged hippocampi

Intracellular proteinaceous aggregates (inclusion bodies) are almost always detectable at autopsy in brains of elderly individuals. Inclusion bodies composed of TDP-43 and tau proteins often coexist in the same brain, and each of these pathologic biomarkers is associated independently with cognitive impairment. However, uncertainties remain about how the presence and neuroanatomical distribution of inclusion bodies correlate with underlying diseases including Alzheimer's disease (AD). To address this knowledge gap, we analyzed data from the University of Kentucky AD Center autopsy series (n = 247); none of the brains had frontotemporal lobar degeneration. A specific question for this study was whether neurofibrillary tangle (NFT) pathology outside of the Braak NFT staging scheme is characteristic of brains with TDP-43 pathology but lacking AD, that is those with cerebral age-related TDP-43 with sclerosis (CARTS). We also tested whether TDP-43 pathology is associated with comorbid AD pathology, and whether argyrophilic grains are relatively likely to be present in cases with, vs. without, TDP-43 pathology. Consistent with prior studies, hippocampal TDP-43 pathology was associated with advanced AD - Braak NFT stages V/VI. However, argyrophilic grain pathology was not more common in cases with TDP-43 pathology in this data set. In brains with CARTS (TDP-43[+]/AD[-] cases), there were more NFTs in dentate granule neurons than were seen in TDP-43[-]/AD[-] cases. These dentate granule cell NFTs could provide a proxy indicator of CARTS pathology in cases lacking substantial AD pathology. Immunofluorescent experiments in a subsample of cases found that, in both advanced AD and CARTS, approximately 1% of dentate granule neurons were PHF-1 immunopositive, whereas ∼25% of TDP-43 positive cells showed colocalized PHF-1 immunoreactivity. We conclude that NFTs in hippocampal dentate granule neurons are often present in CARTS, and TDP-43 pathology may be secondary to or occurring in parallel with tauopathy.

Hippocampal Sclerosis of Aging, a Common Alzheimer's Disease 'Mimic': Risk Genotypes are Associated with Brain Atrophy Outside the Temporal Lobe

Hippocampal sclerosis of aging (HS-Aging) is a common brain disease in older adults with a clinical course that is similar to Alzheimer's disease. Four single-nucleotide polymorphisms (SNPs) have previously shown association with HS-Aging. The present study investigated structural brain changes associated with these SNPs using surface-based analysis. Participants from the Alzheimer's Disease Neuroimaging Initiative cohort (ADNI; n = 1,239), with both MRI scans and genotype data, were used to assess the association between brain atrophy and previously identified HS-Aging risk SNPs in the following genes: GRN, TMEM106B, ABCC9, and KCNMB2 (minor allele frequency for each is >30%). A fifth SNP (near the ABCC9 gene) was evaluated in post-hoc analysis. The GRN risk SNP (rs5848_T) was associated with a pattern of atrophy in the dorsomedial frontal lobes bilaterally, remarkable since GRN is a risk factor for frontotemporal dementia. The ABCC9 risk SNP (rs704180_A) was associated with multifocal atrophy whereas a SNP (rs7488080_A) nearby (∼50 kb upstream) ABCC9 was associated with atrophy in the right entorhinal cortex. Neither TMEM106B (rs1990622_T), KCNMB2 (rs9637454_A), nor any of the non-risk alleles were associated with brain atrophy. When all four previously identified HS-Aging risk SNPs were summed into a polygenic risk score, there was a pattern of associated multifocal brain atrophy in a predominately frontal pattern. We conclude that common SNPs previously linked to HS-Aging pathology were associated with a distinct pattern of anterior cortical atrophy. Genetic variation associated with HS-Aging pathology may represent a non-Alzheimer's disease contribution to atrophy outside of the hippocampus in older adults.

Tauopathy with hippocampal 4-repeat tau immunoreactive spherical inclusions: a report of three cases

Tauopathies are a major group of neurodegenerative proteinopathies characterized by the accumulation of abnormal and hyperphosphorylated tau proteins in the brain. Tau pathology is characterized as 3R (repeat) or 4R predominant or mixed 3R and 4R type. Here we report three cases lacking mutations in the microtubule associated protein tau (MAPT) gene with unusual tau pathology. The age at onset and duration of illness, respectively, were 63 and 20 years (male), 67 and 5 years (female) and 72 and 20 years (female). The clinical presentation was compatible with a diagnosis of progressive supranuclear palsy (PSP) in two subjects and with cognitive decline in all three subjects. Common neuropathological features included neuronal loss in the hippocampus and dentate gyrus associated with spherical basophilic Pick body-like inclusions showing 4R tau immunoreactivity, which was supported by the detection of predominantly 4R tau species by Western blot examination. In addition, accumulation of tau immunoreactive argyrophilic astrocytes in the hippocampus and amygdala and oligodendroglial coiled bodies in the hippocampal white matter were observed. These morphologies appeared in combination with Alzheimer disease-related pathology and subcortical tau pathology compatible with PSP. Together with a single case report in the literature, our observations on these three cases expand the spectrum of previously described tauopathies. We suggest that this tauopathy variant with hippocampal 4R tau immunoreactive spherical inclusions might contribute to the cognitive deficits in the patients reported here. The precise definition of the clinicopathological relevance of these unusual tau pathologies merits further study.

Risk factors and global cognitive status related to brain arteriolosclerosis in elderly individuals

Risk factors and cognitive sequelae of brain arteriolosclerosis pathology are not fully understood. To address this, we used multimodal data from the National Alzheimer's Coordinating Center and Alzheimer's Disease Neuroimaging Initiative data sets. Previous studies showed evidence of distinct neurodegenerative disease outcomes and clinical-pathological correlations in the "oldest-old" compared to younger cohorts. Therefore, using the National Alzheimer's Coordinating Center data set, we analyzed clinical and neuropathological data from two groups according to ages at death: < 80 years (n = 1008) and ≥80 years (n = 1382). In both age groups, severe brain arteriolosclerosis was associated with worse performances on global cognition tests. Hypertension (but not diabetes) was a brain arteriolosclerosis risk factor in the younger group. In the ≥ 80 years age at death group, an ABCC9 gene variant (rs704180), previously associated with aging-related hippocampal sclerosis, was also associated with brain arteriolosclerosis. A post-hoc arterial spin labeling neuroimaging experiment indicated that ABCC9 genotype is associated with cerebral blood flow impairment; in a convenience sample from Alzheimer's Disease Neuroimaging Initiative (n = 15, homozygous individuals), non-risk genotype carriers showed higher global cerebral blood flow compared to risk genotype carriers. We conclude that brain arteriolosclerosis is associated with altered cognitive status and a novel vascular genetic risk factor.

Genomics and CSF analyses implicate thyroid hormone in hippocampal sclerosis of aging

We report evidence of a novel pathogenetic mechanism in which thyroid hormone dysregulation contributes to dementia in elderly persons. Two single nucleotide polymorphisms (SNPs) on chromosome 12p12 were the initial foci of our study: rs704180 and rs73069071. These SNPs were identified by separate research groups as risk alleles for non-Alzheimer's neurodegeneration. We found that the rs73069071 risk genotype was associated with hippocampal sclerosis (HS) pathology among people with the rs704180 risk genotype (National Alzheimer's Coordinating Center/Alzheimer's Disease Genetic Consortium data; n = 2113, including 241 autopsy-confirmed HS cases). Furthermore, both rs704180 and rs73069071 risk genotypes were associated with widespread brain atrophy visualized by MRI (Alzheimer's Disease Neuroimaging Initiative data; n = 1239). In human brain samples from the Braineac database, both rs704180 and rs73069071 risk genotypes were associated with variation in expression of ABCC9, a gene which encodes a metabolic sensor protein in astrocytes. The rs73069071 risk genotype was also associated with altered expression of a nearby astrocyte-expressed gene, SLCO1C1. Analyses of human brain gene expression databases indicated that the chromosome 12p12 locus may regulate particular astrocyte-expressed genes induced by the active form of thyroid hormone, triiodothyronine (T3). This is informative biologically, because the SLCO1C1 protein transports thyroid hormone into astrocytes from blood. Guided by the genomic data, we tested the hypothesis that altered thyroid hormone levels could be detected in cerebrospinal fluid (CSF) obtained from persons with HS pathology. Total T3 levels in CSF were elevated in HS cases (p < 0.04 in two separately analyzed groups), but not in Alzheimer's disease cases, relative to controls. No change was detected in the serum levels of thyroid hormone (T3 or T4) in a subsample of HS cases prior to death. We conclude that brain thyroid hormone perturbation is a potential pathogenetic factor in HS that may also provide the basis for a novel CSF-based clinical biomarker.

"New Old Pathologies": AD, PART, and Cerebral Age-Related TDP-43 With Sclerosis (CARTS)

The pathology-based classification of Alzheimer's disease (AD) and other neurodegenerative diseases is a work in progress that is important for both clinicians and basic scientists. Analyses of large autopsy series, biomarker studies, and genomics analyses have provided important insights about AD and shed light on previously unrecognized conditions, enabling a deeper understanding of neurodegenerative diseases in general. After demonstrating the importance of correct disease classification for AD and primary age-related tauopathy, we emphasize the public health impact of an underappreciated AD "mimic," which has been termed "hippocampal sclerosis of aging" or "hippocampal sclerosis dementia." This pathology affects >20% of individuals older than 85 years and is strongly associated with cognitive impairment. In this review, we provide an overview of current hypotheses about how genetic risk factors (GRN, TMEM106B, ABCC9, and KCNMB2), and other pathogenetic influences contribute to TDP-43 pathology and hippocampal sclerosis. Because hippocampal sclerosis of aging affects the "oldest-old" with arteriolosclerosis and TDP-43 pathologies that extend well beyond the hippocampus, more appropriate terminology for this disease is required. We recommend "cerebral age-related TDP-43 and sclerosis" (CARTS). A detailed case report is presented, which includes neuroimaging and longitudinal neurocognitive data. Finally, we suggest a neuropathology-based diagnostic rubric for CARTS.

Hippocampal Sclerosis but Not Normal Aging or Alzheimer Disease Is Associated With TDP-43 Pathology in the Basal Forebrain of Aged Persons

Transactivating responsive sequence (TAR) DNA-binding protein 43-kDa (TDP-43) pathology has been described in various brain diseases, but the full anatomical distribution and clinical and biological implications of that pathology are incompletely characterized. Here, we describe TDP-43 neuropathology in the basal forebrain, hypothalamus, and adjacent nuclei in 98 individuals (mean age, 86 years; median final mini-mental state examination score, 27). On examination blinded to clinical and pathologic diagnoses, we identified TDP-43 pathology that most frequently involved the ventromedial basal forebrain in 19 individuals (19.4%). As expected, many of these brains had comorbid pathologies including those of Alzheimer disease (AD), Lewy body disease (LBD), and/or hippocampal sclerosis of aging (HS-Aging). The basal forebrain TDP-43 pathology was strongly associated with comorbid HS-Aging (odds ratio = 6.8, p = 0.001), whereas there was no significant association between basal forebrain TDP-43 pathology and either AD or LBD neuropathology. In this sample, there were some cases with apparent preclinical TDP-43 pathology in the basal forebrain that may indicate that this is an early affected area in HS-Aging. We conclude that TDP-43 pathology in the basal forebrain is strongly associated with HS-Aging. These results raise questions about a specific pathogenetic relationship between basal forebrain TDP-43 and non-HS-Aging comorbid diseases (AD and LBD).

Oxidative stress and hippocampal synaptic protein levels in elderly cognitively intact individuals with Alzheimer's disease pathology

Neuritic amyloid plaques and neurofibrillary tangles are hallmarks of Alzheimer's disease (AD) and are major components used for the clinical diagnosis of this disorder. However, many individuals with no cognitive impairment (NCI) also present at autopsy with high levels of these AD pathologic hallmarks. In this study, we evaluated 15 autopsy cases from NCI individuals with high levels of AD-like pathology (high pathology no cognitive impairment) and compared them to age- and postmortem-matched cohorts of individuals with amnestic mild cognitive impairment and NCI cases with low AD-like pathology (low pathology no cognitive impairment [LPNCI]). Individuals classified as high pathology no cognitive impairment or amnestic mild cognitive impairment had a significant loss of both presynaptic and postsynaptic proteins in the hippocampus compared with those in the LPNCI cohort. In addition, these 2 groups had a significant increase in 3 different markers of oxidative stress compared with that in the LPNCI group. The changes in levels of synaptic proteins are strongly associated with levels of oxidative stress. These data suggest that cognitively older subjects without dementia but with increased levels of AD-like pathology may represent a very early preclinical stage of AD.