ABCC9 gene polymorphism is associated with hippocampal sclerosis of aging pathology

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.

Genetic variants in Alzheimer disease - molecular and brain network approaches

Genetic studies in late-onset Alzheimer disease (LOAD) are aimed at identifying core disease mechanisms and providing potential biomarkers and drug candidates to improve clinical care of AD. However, owing to the complexity of LOAD, including pathological heterogeneity and disease polygenicity, extraction of actionable guidance from LOAD genetics has been challenging. Past attempts to summarize the effects of LOAD-associated genetic variants have used pathway analysis and collections of small-scale experiments to hypothesize functional convergence across several variants. In this Review, we discuss how the study of molecular, cellular and brain networks provides additional information on the effects of LOAD-associated genetic variants. We then discuss emerging combinations of these omic data sets into multiscale models, which provide a more comprehensive representation of the effects of LOAD-associated genetic variants at multiple biophysical scales. Furthermore, we highlight the clinical potential of mechanistically coupling genetic variants and disease phenotypes with multiscale brain models.

"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.

Update on Hippocampal Sclerosis

The diagnostic hallmarks of hippocampal sclerosis (HS) are severe volume loss of the hippocampus, severe neuronal loss, and reactive gliosis involving primarily two especially vulnerable fields, CA1 and the subiculum. Occasionally, HS may be the only neuropathological change detected in older individuals with dementia and is known as pure HS. In the majority of cases, HS occurs in the setting of other degenerative changes, usually Alzheimer's disease (AD). In these cases, it is classified as combined HS. Although a clinical profile for HS has been identified, its similarities with AD make the diagnosis during life quite challenging; thus, the diagnosis is often made postmortem. The pathogenesis of HS is not completely understood, but the strong association with transactive response DNA-binding protein 43 (TDP-43), in approximately 90%, and the recent discovery of genetic risk factors are important contributions to a better understanding of the disease process.

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).

Higher Prevalence of TDP-43 Proteinopathy in Cognitively Normal Asians: A Clinicopathological Study on a Multiethnic Sample

Transactive response DNA binding protein 43 (TDP-43) proteinopathy is the major hallmark of frontotemporal lobar degeneration and amyotrophic lateral sclerosis. It is also present in a subset of Alzheimer's disease cases. Recently, few reports showed TDP-43 changes in cognitively normal elderly. In Caucasians, TDP-43 proteinopathy independently correlate with cognitive decline. However, it is challenging to establish direct links between cognitive and/or neuropsychiatric symptoms and protein inclusions in neurodegenerative diseases because individual cognitive reserves modify the threshold for clinical disease expression. Cognitive reserve is influenced by demographic, environmental and genetic factors. We investigated the relationships between demographic, clinical and neuropathological variables and TDP-43 proteinopathy in a large multiethnic sample of cognitively normal elderly. TDP-43 proteinopathy was identified in 10.5%, independently associated with older age (P = 0.03) and Asian ethnicity (P = 0.002). Asians showed a higher prevalence of TDP-43 proteinopathy than Caucasians, even after adjustment for sex, age, Braak stage and schooling (odds ratio = 3.50, confidence interval 1.41-8.69, P = 0.007). These findings suggested that Asian older adults may be protected from the clinical manifestation of brain TDP-43 proteinopathy. Future studies are needed to identify possible race-related protective factors against clinical expression of TDP-43 proteinopathies.

ABCC9/SUR2 in the brain: Implications for hippocampal sclerosis of aging and a potential therapeutic target

The ABCC9 gene and its polypeptide product, SUR2, are increasingly implicated in human neurologic disease, including prevalent diseases of the aged brain. SUR2 proteins are a component of the ATP-sensitive potassium ("KATP") channel, a metabolic sensor for stress and/or hypoxia that has been shown to change in aging. The KATP channel also helps regulate the neurovascular unit. Most brain cell types express SUR2, including neurons, astrocytes, oligodendrocytes, microglia, vascular smooth muscle, pericytes, and endothelial cells. Thus it is not surprising that ABCC9 gene variants are associated with risk for human brain diseases. For example, Cantu syndrome is a result of ABCC9 mutations; we discuss neurologic manifestations of this genetic syndrome. More common brain disorders linked to ABCC9 gene variants include hippocampal sclerosis of aging (HS-Aging), sleep disorders, and depression. HS-Aging is a prevalent neurological disease with pathologic features of both neurodegenerative (aberrant TDP-43) and cerebrovascular (arteriolosclerosis) disease. As to potential therapeutic intervention, the human pharmacopeia features both SUR2 agonists and antagonists, so ABCC9/SUR2 may provide a "druggable target", relevant perhaps to both HS-Aging and Alzheimer's disease. We conclude that more work is required to better understand the roles of ABCC9/SUR2 in the human brain during health and disease conditions.

Brain pathologies in extreme old age

With an emphasis on evolving concepts in the field, we evaluated neuropathologic data from very old research volunteers whose brain autopsies were performed at the University of Kentucky Alzheimer's Disease Center, incorporating data from the Georgia Centenarian Study (n = 49 cases included), Nun Study (n = 17), and University of Kentucky Alzheimer's Disease Center (n = 11) cohorts. Average age of death was 102.0 (range: 98-107) years overall. Alzheimer's disease pathology was not universal (62% with "moderate" or "frequent" neuritic amyloid plaque densities), whereas frontotemporal lobar degeneration was absent. By contrast, some hippocampal neurofibrillary tangles (including primary age-related tauopathy) were observed in every case. Lewy body pathology was seen in 16.9% of subjects and hippocampal sclerosis of aging in 20.8%. We describe anatomic distributions of pigment-laden macrophages, expanded Virchow-Robin spaces, and arteriolosclerosis among Georgia Centenarians. Moderate or severe arteriolosclerosis pathology, throughout the brain, was associated with both hippocampal sclerosis of aging pathology and an ABCC9 gene variant. These results provide fresh insights into the complex cerebral multimorbidity, and a novel genetic risk factor, at the far end of the human aging spectrum.

Association of DNA methylation in the brain with age in older persons is confounded by common neuropathologies

DNA methylation plays a crucial role in the regulation of gene expression, cell differentiation and development. Previous studies have reported age-related alterations of methylation levels in the human brain across the lifespan, but little is known about whether the observed association with age is confounded by common neuropathologies among older persons. Using genome-wide DNA methylation data from 740 postmortem brains, we interrogated 420,132 CpG sites across the genome in a cohort of individuals with ages from 66 to 108 years old, a range of ages at which many neuropathologic indices become quite common. We compared the association of DNA methylation prior to and following adjustment for common neuropathologies using a series of linear regression models. In the simplest model adjusting for technical factors including batch effect and bisulfite conversion rate, we found 8156 CpGs associated with age. The number of CpGs associated with age dropped by more than 10% following adjustment for sex. Notably, after adjusting for common neuropathologies, the total number of CpGs associated with age was reduced by approximately 40%, compared to the sex-adjusted model. These data illustrate that the association of methylation changes in the brain with age is inflated if one does not account for age-related brain pathologies. This article is part of a Directed Issue entitled: Epigenetics dynamics in development and disease.

Late-onset dementia: a mosaic of prototypical pathologies modifiable by diet and lifestyle

Idiopathic late-onset dementia (ILOD) describes impairments of memory, reasoning and/or social abilities in the elderly that compromise their daily functioning. Dementia occurs in several major prototypical neurodegenerative disorders that are currently defined by neuropathological criteria, most notably Alzheimer’s disease (AD), Lewy body dementia (LBD), frontotemporal dementia (FTD) and hippocampal sclerosis of aging (HSA). However, people who die with ILOD commonly exhibit mixed pathologies that vary within and between brain regions. Indeed, many patients diagnosed with probable AD exhibit only modest amounts of disease-defining amyloid β-peptide plaques and p-Tau tangles, and may have features of FTD (TDP-43 inclusions), Parkinson’s disease (α-synuclein accumulation), HSA and vascular lesions. Here I argue that this ‘mosaic neuropathological landscape’ is the result of commonalities in aging-related processes that render neurons vulnerable to the entire spectrum of ILODs. In this view, all ILODs involve deficits in neuronal energy metabolism, neurotrophic signaling and adaptive cellular stress responses, and associated dysregulation of neuronal calcium handling and autophagy. Although this mosaic of neuropathologies and underlying mechanisms poses major hurdles for development of disease-specific therapeutic interventions, it also suggests that certain interventions would be beneficial for all ILODs. Indeed, emerging evidence suggests that the brain can be protected against ILOD by lifelong intermittent physiological challenges including exercise, energy restriction and intellectual endeavors; these interventions enhance cellular stress resistance and facilitate neuroplasticity. There is also therapeutic potential for interventions that bolster neuronal bioenergetics and/or activate one or more adaptive cellular stress response pathways in brain cells. A wider appreciation that all ILODs share age-related cellular and molecular alterations upstream of aggregated protein lesions, and that these upstream events can be mitigated, may lead to implementation of novel intervention strategies aimed at reversing the rising tide of ILODs.

Dissecting Complex and Multifactorial Nature of Alzheimer's Disease Pathogenesis: a Clinical, Genomic, and Systems Biology Perspective

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by loss of memory and other cognitive functions. AD can be classified into familial AD (FAD) and sporadic AD (SAD) based on heritability and into early onset AD (EOAD) and late onset AD (LOAD) based on age of onset. LOAD cases are more prevalent with genetically complex architecture. In spite of significant research focused on understanding the etiological mechanisms, search for diagnostic biomarker(s) and disease-modifying therapy is still on. In this article, we aim to comprehensively review AD literature on established etiological mechanisms including role of beta-amyloid and apolipoprotein E (APOE) along with promising newer etiological factors such as epigenetic modifications that have been associated with AD suggesting its multifactorial nature. As genomic studies have recently played a significant role in elucidating AD pathophysiology, a systematic review of findings from genome-wide linkage (GWL), genome-wide association (GWA), genome-wide expression (GWE), and epigenome-wide association studies (EWAS) was conducted. The availability of multi-dimensional genomic data has further coincided with the advent of computational and network biology approaches in recent years. Our review highlights the importance of integrative approaches involving genomics and systems biology perspective in elucidating AD pathophysiology. The promising newer approaches may provide reliable means of early and more specific diagnosis and help identify therapeutic interventions for LOAD.

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

Hippocampal sclerosis of aging (HS-Aging) is a neurodegenerative disease that mimics Alzheimer disease (AD) clinically and has a prevalence rivaling AD in advanced age. Whereas clinical biomarkers are not yet optimized, HS-Aging has distinctive pathological features that distinguish it from other diseases with "hippocampal sclerosis" pathology, such as epilepsy, cerebrovascular perturbations, and frontotemporal lobar degeneration. By definition, HS-Aging brains show neuronal cell loss and gliosis in the hippocampal formation out of proportion to AD-type pathology; it is strongly associated with aberrant TDP-43 pathology and arteriolosclerosis. Here, we describe 2 cases of "segmental" HS-Aging in which "sclerosis" in the hippocampus was evident only in a subset of brain sections by hematoxylin and eosin (H&E) stain. In these cases, TDP-43 pathology was more widespread on immunostained sections than the neuronal cell loss and gliosis seen in H&E stains. The 2 patients were cognitively intact at baseline and were tracked longitudinally over a decade using cognitive studies with at least 1 neuroimaging scan. We discuss the relevant HS-Aging literature, which indicates the need for a clearer consensus-based delineation of "hippocampal sclerosis" and TDP-43 pathologies in aged subjects.

Novel human ABCC9/SUR2 brain-expressed transcripts and an eQTL relevant to hippocampal sclerosis of aging

ABCC9 genetic polymorphisms are associated with increased risk for various human diseases including hippocampal sclerosis of aging. The main goals of this study were 1 > to detect the ABCC9 variants and define the specific 3' untranslated region (3'UTR) for each variant in human brain, and 2 > to determine whether a polymorphism (rs704180) associated with risk for hippocampal sclerosis of aging pathology is also associated with variation in ABCC9 transcript expression and/or splicing. Rapid amplification of ABCC9 cDNA ends (3'RACE) provided evidence of novel 3' UTR portions of ABCC9 in human brain. In silico and experimental studies were performed focusing on the single nucleotide polymorphism, rs704180. Analyses from multiple databases, focusing on rs704180 only, indicated that this risk allele is a local expression quantitative trait locus (eQTL). Analyses of RNA from human brains showed increased ABCC9 transcript levels in individuals with the risk genotype, corresponding with enrichment for a shorter 3' UTR which may be more stable than variants with the longer 3' UTR. MicroRNA transfection experiments yielded results compatible with the hypothesis that miR-30c causes down-regulation of SUR2 transcripts with the longer 3' UTR. Thus we report evidence of complex ABCC9 genetic regulation in brain, which may be of direct relevance to human disease. ABCC9 gene variants are associated with increased risk for hippocampal sclerosis of aging (HS-Aging--a prevalent brain disease with symptoms that mimic Alzheimer's disease). We describe novel ABCC9 variants in human brain, corresponding to altered 3'UTR length, which could lead to targeting by miR-30c. We also determined that the HS-Aging risk mutation is associated with variation in ABCC9 transcript expression.

The TMEM106B locus and TDP-43 pathology in older persons without FTLD

OBJECTIVE

To determine the independent association of the TMEM106B variants with transactive response DNA binding protein 43 (TDP-43) pathology in older persons without frontotemporal lobar degeneration (FTLD) and to explore functional pathways that link the risk variants to the pathology, including a GRN mRNA pathway.

METHODS

Data came from 544 autopsied participants without FTLD in 2 community-based studies of aging. Participants underwent uniform neuropathologic evaluations, including TDP-43 cytoplasmic inclusions. We examined the association of TMEM106B variants with a semiquantitative measure of TDP-43 pathology in a series of regression analysis. We explored potential pathways by leveraging genetic, brain DNA methylation, miRNA, and transcriptomic data collected from this same group of participants.

RESULTS

TDP-43 pathology was identified in 51.7% of the participants. The index single-nucleotide polymorphism (SNP), rs1990622(A), was associated with more advanced TDP-43 pathology. Top hits from fine mapping of the locus were in linkage disequilibrium of the index SNP. The association remained significant after adjustment for other neuropathologies including Alzheimer disease and hippocampal sclerosis (odds ratio = 1.351, 95% confidence interval = 1.068-1.709, p = 0.012). GRN expression was upregulated in rs1990622(AA/AG) carriers, and was associated with more advanced TDP-43 pathology. The TMEM106B variants were associated with lower level of DNA methylation in an active enhancer in GRN.

CONCLUSIONS

Common variants in TMEM106B serve as a distinct risk factor for TDP-43 pathology in older persons without FTLD. The role of GRN expression and epigenetic mechanisms associating TMEM106B in the accumulation of TDP-43 in older persons require further study.

Reassessment of risk genotypes (GRN, TMEM106B, and ABCC9 variants) associated with hippocampal sclerosis of aging pathology

Hippocampal sclerosis of aging (HS-Aging) is a common high-morbidity neurodegenerative condition in elderly persons. To understand the risk factors for HS-Aging, we analyzed data from the Alzheimer's Disease Genetics Consortium and correlated the data with clinical and pathologic information from the National Alzheimer's Coordinating Center database. Overall, 268 research volunteers with HS-Aging and 2,957 controls were included; detailed neuropathologic data were available for all. The study focused on single-nucleotide polymorphisms previously associated with HS-Aging risk: rs5848 (GRN), rs1990622 (TMEM106B), and rs704180 (ABCC9). Analyses of a subsample that was not previously evaluated (51 HS-Aging cases and 561 controls) replicated the associations of previously identified HS-Aging risk alleles. To test for evidence of gene-gene interactions and genotype-phenotype relationships, pooled data were analyzed. The risk for HS-Aging diagnosis associated with these genetic polymorphisms was not secondary to an association with either Alzheimer disease or dementia with Lewy body neuropathologic changes. The presence of multiple risk genotypes was associated with a trend for additive risk for HS-Aging pathology. We conclude that multiple genes play important roles in HS-Aging, which is a distinctive neurodegenerative disease of aging.

Hippocampal sclerosis in Lewy body disease is a TDP-43 proteinopathy similar to FTLD-TDP Type A

Hippocampal sclerosis (HpScl) is frequent in frontotemporal lobar degeneration with TDP-43 pathology (FTLD-TDP), but it also occurs in dementia of the elderly with or without accompanying Alzheimer type pathology. HpScl has been hypothesized to be a neurodegenerative process given its association with TDP-43 pathology, but this is still controversial. TDP-43 pathology is found in Lewy body disease (LBD), but no study has focused on the pathologic and genetic characteristics of HpScl in LBD. We found HpScl in 5.2% of 669 LBD cases (289 transitional and 380 diffuse). Older age, higher Braak neurofibrillary tangle (NFT) stage, and presence of TDP-43 pathology were associated with HpScl. There was no difference in the frequency of HpScl between transitional and diffuse LBD, suggesting that Lewy-related pathology appears to have no direct association with HpScl. All HpScl cases had TDP-43 pathology consistent with Type A pattern. HpScl cases harbored genetic variation in TMEM106B that has been previously associated with FTLD-TDP. Interestingly, the severity of TDP-43-positive fine neurites in CA1 sector, a possible pathologic precursor of HpScl, was associated with the TMEM106B variant. These results demonstrate HpScl in LBD is a TDP-43 proteinopathy and is similar to FTLD-TDP Type A. Furthermore, a subset of LBD cases without HpScl ("pre-HpScl") had similar pathologic and genetic characteristics to typical HpScl, suggesting that the spectrum of HpScl pathology may be wider than previously thought. Some cases with many extracellular NFTs also had a similar profile. We suggest that HpScl is "masked" in these cases.

Differential clinicopathologic and genetic features of late-onset amnestic dementias

Hippocampal sclerosis of the elderly (HpScl) and Alzheimer's disease (AD), especially the limbic-predominant subtype (LP-AD), are amnestic syndromes that can be difficult to distinguish. To complicate matters, a subset has concomitant HpScl and AD (HpScl-AD). We examined a large cohort of autopsy-confirmed cases of HpScl, HpScl-AD, LP-AD, and typical AD to identify distinct clinical, genetic, and pathologic characteristics. HpScl cases were significantly older at death and had a substantially slower rate of cognitive decline than the AD subtypes. Genetic analysis revealed that the AD groups (AD, LP-AD, and HpScl-AD) were more likely to be APOE ε4 carriers. In contrast, the HpScl groups (HpScl and HpScl-AD) were more likely to exhibit genetic variants in GRN and TMEM106B that are associated with frontotemporal lobar degeneration. The HpScl groups had a high frequency of TDP-43 pathology that was most often Type A morphology and distribution, while typical AD and LP-AD had a significantly lower frequency of TDP-43 pathology that was most often Type B. These results suggest that HpScl and AD are pathologically and genetically distinct and non-synergistic neurodegenerative processes that present with amnestic dementia. Pure HpScl and HpScl with concomitant AD occur most often in elderly individuals.