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INTRODUCTION Typical Alzheimer's disease (AD) and limbic‐predominant age‐related TAR DNA‐binding protein 43 (TDP‐43) encephalopathy (LATE) are two neurodegenerative diseases that present with a similar initial amnestic clinical phenotype but are associated with distinct proteinopathies. METHODS We investigated white matter (WM) fiber bundle alterations, using fixel‐based analysis, a state‐of‐the‐art diffusion magnetic resonance imaging model, in early AD, presumed LATE, and controls. We also investigated regional cortical atrophy. RESULTS Both amnestic AD and presumed LATE patients exhibited WM alterations in tracts of the temporal and limbic lobes and in callosal fibers connecting superior frontal gyri. In addition, presumed LATE patients showed alterations in callosal fibers connecting the middle frontal gyri and in the cerebello–thalamo–cortical tract. Cortical thickness was reduced in regions connected by the most altered tracts. DISCUSSION These findings, the first to describe WM fiber bundle alterations in presumed LATE, are consistent with results on cortical atrophy and with the staging system of tau or TDP‐43 accumulation. Highlights Fixel‐based analysis revealed white matter (WM) fiber bundle alterations in presumed limbic‐predominant age‐related TAR DNA‐binding protein 43 encephalopathy (LATE) patients identified by isolated episodic/limbic amnesia, the absence of positive Alzheimer's disease (AD) biomarkers, and no other neurological diagnosis after 2 years of follow‐up. Presumed LATE and amnestic AD shared similar patterns of WM alterations in fiber bundles of the limbic and temporal lobes, in congruence with their similar limbic cognitive phenotype. Presumed LATE differed from AD by the alteration of the callosal fibers connecting the middle frontal gyri and of the cerebello–thalamo–cortical tract. WM fiber bundle alterations were consistent with results on regional cortical atrophy. The different anatomical patterns of WM degeneration could provide information on the propagation pathways of distinct proteinopathies.

INTRODUCTION Limbic‐predominant age‐related TAR DNA‐binding protein of 43 kDa encephalopathy neuropathologic change (LATE‐NC) staging criteria were updated in 2023. We evaluated this updated staging using National Alzheimer's Coordinating Center data. METHODS We examined associations of LATE‐NC stages with cognition and other neuropathologic changes (NCs), and with cognition while accounting for other NCs, using multilevel regression models. RESULTS Of 1352 participants, 502 (37%) had LATE‐NC (23% stage 1a, 6% stage 1b, 58% stage 2, 13% stage 3). LATE‐NC stages were associated with cognition, hippocampal sclerosis of aging (HS‐A), Alzheimer's disease NC (ADNC), Lewy bodies (LBs), and hippocampal atrophy. While stage 1b was associated with cognition and HS‐A consistent with other stages, it was not associated with ADNC or LBs. All LATE‐NC stages remained significantly associated with worse cognition when accounting for other NCs. DISCUSSION The updated LATE‐NC staging criteria capture variations in early TDP‐43 pathology spread which are consequential for cognition and associations with other NCs. Highlights We applied the updated limbic‐predominant age‐related TAR DNA‐binding protein of 43 kDa encephalopathy neuropathologic change (LATE‐NC) staging criteria to data from the National Alzheimer's Coordinating Center. LATE‐NC stage 1b was identified in 22% of participants with stage 1. In contrast to other LATE‐NC stages, stage 1b was not associated with Alzheimer's disease neuropathologic change (ADNC) or Lewy bodies. Stages 1a and 1b were significantly associated with dementia and memory impairment. Stages 1b+ were more strongly tied to dementia than all other neuropathologic changes except high likelihood ADNC.

Introduction Limbic‐predominant age‐related TAR DNA‐binding protein 43 (TDP‐43) encephalopathy (LATE) is a recently defined neurodegenerative disease. Currently, there is no effective way to make a prognosis of time to stage‐specific future conversions at an individual level. Methods After using the Kaplan–Meier estimation and log‐rank test to confirm the heterogeneity of LATE progression, we developed a deep learning–based approach to assess the stage‐specific probabilities of time to LATE conversions for different subjects. Results Our approach could accurately estimate the disease incidence and transition to next stages: the concordance index was at least 82% and the integrated Brier score was less than 0.14. Moreover, we identified the top 10 important predictors for each disease conversion scenario to help explain the estimation results, which were clinicopathologically meaningful and most were also statistically significant. Discussion Our study has the potential to provide individualized assessment for future time courses of LATE conversions years before their actual occurrence.

INTRODUCTION Research‐oriented autopsy cohorts provide critical insights into dementia pathobiology. However, different studies sometimes report disparate findings, partially because each study has its own recruitment biases. We hypothesized that a straightforward metric, related to the percentage of research volunteers cognitively normal at recruitment, would predict other inter‐cohort differences. METHODS The National Alzheimer's Coordinating Center (NACC) provided data on N = 7178 autopsied participants from 28 individual research centers. Research cohorts were grouped based on the proportion of participants with normal cognition at initial clinical visit. RESULTS Cohorts with more participants who were cognitively normal at recruitment contained more individuals who were older, female, had lower frequencies of apolipoprotein E ε4, Lewy body disease, and frontotemporal dementia, but higher rates of cerebrovascular disease. Alzheimer's disease (AD) pathology was little different between groups. DISCUSSION The percentage of participants recruited while cognitively normal predicted differences in findings in autopsy research cohorts. Most differences were in non‐AD pathologies. Highlights Systematic differences exist between autopsy cohorts that serve dementia research. We propose a metric to use for gauging a research‐oriented autopsy cohort. It is essential to consider the characteristics of autopsy cohorts.

Hippocampal atrophy on magnetic resonance imaging is an important biomarker in Alzheimer's disease (AD). While hippocampal atrophy was thought to result from tau tangles in AD, different neuropathologies can lead to hippocampal atrophy, especially TAR DNA‐binding protein 43 (TDP‐43) pathology. In this narrative review, we evaluate existing studies on the relative contribution of tau and TDP‐43 pathology to medial temporal lobe (MTL) atrophy. We report a clear association of both tau and TDP‐43 neuropathology with MTL atrophy, even after correcting for other neuropathologies. Next, we discuss a potential synergism between tau and TDP‐43 and the relative timing of the effects of both neuropathologies. Finally, avenues for future research will be discussed. A better understanding of the interplay between tau and TDP‐43 neuropathologies and their effect on atrophy will help with the development of more specific biomarkers for limbic‐predominant age‐related TDP‐43 encephalopathy and pinpointing of the optimal timing for testing anti‐tau and anti‐TDP‐43 treatments in trials. Highlights Both tau and TAR DNA‐binding protein 43 (TDP‐43) pathology contribute to medial temporal lobe atrophy. There is a positive association between tau and TDP‐43 and potentially a synergism. It is unclear if tau and TDP‐43 have an additive or synergistic effect on atrophy. The relative timing of the tau and TDP‐43 effects on atrophy remains unclear. Clarifying the interplay between tau and TDP‐43 will help improve magnetic resonance imaging biomarkers.

Based on the anatomic proximity, connectivity, and functional similarities between the anterior insula and amygdala, we tested the hypothesis that the anterior insula is an important focus in the progression of TDP-43 pathology in LATE-NC. Blinded to clinical and neuropathologic data, phospho-TDP (pTDP) inclusion pathology was assessed in paired anterior and posterior insula samples in 105 autopsied patients with Alzheimer disease, Lewy body disease, LATE-NC and hippocampal sclerosis (HS), amyotrophic lateral sclerosis (ALS), and other conditions. Insular pTDP pathology was present in 34.3% of the study cohort, most commonly as neuronal inclusions and/or short neurites in lamina II, and less commonly as subpial processes resembling those described in the amygdala region. Among positive samples, pTDP pathology was limited to the anterior insula (41.7%), or occurred in both anterior and posterior insula (58.3%); inclusion density was greater in anterior insula across all diseases (p < .001). pTDP pathology occurred in 46.7% of ALS samples, typically without a widespread TDP-43 proteinopathy. In LATE-NC, it was seen in 30.4% of samples (mostly LATE-NC stages 2 and 3), often co-occurring with basal forebrain pathology and comorbid HS, suggesting this is an important step in the evolution of this pathology beyond the medial temporal lobe.

Purpose of ReviewLimbic-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 FindingsNovel 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.