In vivo diagnosis of TDP-43 proteinopathies: in search of biomarkers of clinical use.

TDP-43 proteinopathies are a heterogeneous group of neurodegenerative disorders that share the presence of aberrant, misfolded and mislocalized deposits of the protein TDP-43, as in the case of amyotrophic lateral sclerosis and some, but not all, pathological variants of frontotemporal dementia. In recent years, many other diseases have been reported to have primary or secondary TDP-43 proteinopathy, such as Alzheimer's disease, Huntington's disease or the recently described limbic-predominant age-related TDP-43 encephalopathy, highlighting the need for new and accurate methods for the early detection of TDP-43 proteinopathy to help on the stratification of patients with overlapping clinical diagnosis. Currently, TDP-43 proteinopathy remains a post-mortem pathologic diagnosis. Although the main aim is to determine the pathologic TDP-43 proteinopathy in the central nervous system (CNS), the ubiquitous expression of TDP-43 in biofluids and cells outside the CNS facilitates the use of other accessible target tissues that might reflect the potential TDP-43 alterations in the brain. In this review, we describe the main developments in the early detection of TDP-43 proteinopathies, and their potential implications on diagnosis and future treatments.

Differences in Symptomatic Presentation and Cognitive Performance Among Participants With LATE-NC Compared to FTLD-TDP.

Transactive response DNA-binding protein 43 kDa (TDP-43) is aberrantly aggregated and phosphorylated in frontotemporal lobar degeneration of the TDP-43 type (FTLD-TDP), and in limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC). We examined data from the National Alzheimer's Coordinating Center to compare clinical features of autopsy-confirmed LATE-NC and FTLD-TDP. A total of 265 LATE-NC and 92 FTLD-TDP participants were included. Cognitive and behavioral symptoms were compared, stratified by level of impairment based on global clinical dementia rating (CDR) score. LATE-NC participants were older at death, more likely to carry APOE ε4, more likely to have Alzheimer disease neuropathology, and had lower (i.e. less severe) final CDR global scores than those with FTLD-TDP. Participants with FTLD-TDP were more likely to present with primary progressive aphasia, or behavior problems such as apathy, disinhibition, and personality changes. Among participants with final CDR score of 2-3, those with LATE-NC were more likely to have visuospatial impairment, delusions, and/or visual hallucinations. These differences were robust after sensitivity analyses excluding older (≥80 years at death), LATE-NC stage 3, or severe Alzheimer cases. Overall, FTLD-TDP was more globally severe, and affected younger participants, whereas psychoses were more common in LATE-NC.

Isolation and characterization of antibody fragments selective for human FTD brain derived TDP-43 variants.

BACKGROUND: Frontotemporal dementia (FTD) is the second leading cause of early onset dementia following Alzheimer's disease. It involves atrophy of the frontal and temporal regions of the brain affecting language, memory, and behavior. Transactive response DNA-binding protein 43 (TDP-43) pathology is found in most FTD and ALS cases. It plays a role in transcription, translation and serves as a shuttle between the nucleus and cytoplasm. Prior to its aggregation, TDP-43 exists as polyubiquitinated, hyperphosphorylated C-terminal fragments that correlate well with FTD disease progression. Because of the importance of TDP-43 in these diseases, reagents that can selectively recognize specific toxic TDP variants associated with onset and progression of FTD can be effective diagnostic and therapeutic tools. RESULTS: We utilized a novel atomic force microscopy (AFM) based biopanning protocol to isolate single chain variable fragments (scFvs) from a phage display library that selectively bind TDP variants present in human FTD but not cognitively normal age matched brain tissue. We then used the scFvs (FTD-TDP1 through 5) to probe post-mortem brain tissue and sera samples for the presence of FTD related TDP variants. The scFvs readily selected the FTD tissue and sera samples over age matched controls. The scFvs were used in immunohistochemical analysis of FTD and control brain slices where the reagents showed strong staining with TDP in FTD brain tissue slice. FTD-TDP1, FTD-TDP2, FTD-TDP4 and FTD-TDP5 all protected neuronal cells against FTD TDP induced toxicity suggesting potential therapeutic value. CONCLUSIONS: These results show existence of different disease specific TDP variants in FTD individuals. We have identified a panel of scFvs capable of recognizing these disease specific TDP variants in postmortem FTD tissue and sera samples over age matched controls and can thus serve as a biomarker tool.

Validation of machine learning models to detect amyloid pathologies across institutions.

Semi-quantitative scoring schemes like the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) are the most commonly used method in Alzheimer's disease (AD) neuropathology practice. Computational approaches based on machine learning have recently generated quantitative scores for whole slide images (WSIs) that are highly correlated with human derived semi-quantitative scores, such as those of CERAD, for Alzheimer's disease pathology. However, the robustness of such models have yet to be tested in different cohorts. To validate previously published machine learning algorithms using convolutional neural networks (CNNs) and determine if pathological heterogeneity may alter algorithm derived measures, 40 cases from the Goizueta Emory Alzheimer's Disease Center brain bank displaying an array of pathological diagnoses (including AD with and without Lewy body disease (LBD), and / or TDP-43-positive inclusions) and levels of Aß pathologies were evaluated. Furthermore, to provide deeper phenotyping, amyloid burden in gray matter vs whole tissue were compared, and quantitative CNN scores for both correlated significantly to CERAD-like scores. Quantitative scores also show clear stratification based on AD pathologies with or without additional diagnoses (including LBD and TDP-43 inclusions) vs cases with no significant neurodegeneration (control cases) as well as NIA Reagan scoring criteria. Specifically, the concomitant diagnosis group of AD + TDP-43 showed significantly greater CNN-score for cored plaques than the AD group. Finally, we report that whole tissue computational scores correlate better with CERAD-like categories than focusing on computational scores from a field of view with densest pathology, which is the standard of practice in neuropathological assessment per CERAD guidelines. Together these findings validate and expand CNN models to be robust to cohort variations and provide additional proof-of-concept for future studies to incorporate machine learning algorithms into neuropathological practice.

Limbic Predominant Age-Related TDP-43 Encephalopathy (LATE): Clinical and Neuropathological Associations.

Recently, a consensus working group provided new terminology for a common disease entity, limbic predominant age-related TDP-43 encephalopathy (LATE), and its neuropathological substrate (LATE-NC). LATE-NC not only often co-occurs with Alzheimer disease neuropathological change (ADNC), but also may present in isolation. The present study aimed to investigate potential risk factors and neuropathological characteristics associated with LATE-NC. A sample of 616 autopsied participants (>75 years at death), with TDP-43 immunohistochemical studies performed, was obtained from the National Alzheimer's Coordinating Center. Logistic regression analyses examined associations between demographic, clinical and neuropathological characteristics and LATE-NC (TDP-43 in amygdala, hippocampus, or entorhinal/inferior temporal cortex) (alpha = 0.05). Adjusted models indicated that ADNC, hippocampal sclerosis (HS), arteriolosclerosis, and limbic or amygdala-predominant Lewy body disease (LBD), but not other LBD subtypes, were associated with higher odds of LATE-NC, whereas congestive heart failure (CHF) and motor problems as first predominant symptom were associated with lower odds of LATE-NC. Our findings corroborate previous studies indicating associations between LATE-NC and ADNC, HS, and arteriolosclerosis. Novel findings suggest the association with LATE-NC is restricted to amygdala/limbic-predominant subtype of LBD, and a possible protective (or competing risk) association with CHF. This study may inform future hypothesis-driven research on LATE-NC, a common brain disease of aging.

Perfusion alterations converge with patterns of pathological spread in transactive response DNA-binding protein 43 proteinopathies.

Amyotrophic lateral sclerosis (ALS) and the behavioral variant of frontotemporal dementia (bvFTD) commonly share the presence of transactive response DNA-binding protein 43 (TDP-43) inclusions. Structural magnetic resonance imaging studies demonstrated evidence for TDP-43 pathology spread, but while structural imaging usually reveals overt neuronal loss, perfusion imaging may detect more subtle neural activity alterations. We evaluated perfusion as an early marker for incipient pathology-associated brain alterations in TDP-43 proteinopathies. Cortical thickness (CT) and perfusion measurements were obtained in ALS (N = 18), pathologically and/or genetically confirmed bvFTD-TDP (N = 12), and healthy controls (N = 33). bvFTD showed reduced frontotemporal CT, hypoperfusion encompassing orbitofrontal and temporal cortices, and hyperperfusion in motor and occipital regions. ALS did not show reduced CT, but exhibited hypoperfusion in motor and temporal regions, and hyperperfusion in frontal and occipital cortices. Frontotemporal hypoperfusion and reduced CT correlated with cognitive and behavioral impairments as investigated using Mini-Mental State Examination and Philadelphia Brief Assessment of Cognition in bvFTD, and hypoperfusion in motor regions correlated with motor disability as measured by the ALS Functional Rating Scale-Revised in ALS. Hypoperfusion marked early pathologically involved regions, while hyperperfusion characterized regions of late pathological involvement. Distinct perfusion patterns may provide early markers of pathology distribution in TDP-43 proteinopathies.

Prevalence of transactive response DNA-binding protein 43 (TDP-43) proteinopathy in cognitively normal older adults: systematic review and meta-analysis.

OBJECTIVE: To perform a systematic review and meta-analysis on the prevalence of transactive response DNA-binding protein 43 (TDP-43) proteinopathy in cognitively normal older adults. METHODS: We systematically reviewed and performed a meta-analysis on the prevalence of TDP-43 proteinopathy in older adults with normal cognition, evaluated by the Mini-Mental State Examination or the Clinical Dementia Rating. We estimated the overall prevalence of TDP-43 using random-effect models, and stratified by age, sex, sample size, study quality, antibody used to assess TDP-43 aggregates, analysed brain regions, Braak stage, Consortium to Establish a Registry for Alzheimer's Disease score, hippocampal sclerosis and geographic location. RESULTS: A total of 505 articles were identified in the systematic review, and 7 were included in the meta-analysis with 1196 cognitively normal older adults. We found an overall prevalence of TDP-43 proteinopathy of 24%. Prevalence of TDP-43 proteinopathy varied widely across geographic location (North America: 37%, Asia: 29%, Europe: 14%, and Latin America: 11%). Estimated prevalence of TDP-43 proteinopathy also varied according to study quality (quality score >7: 22% vs. quality score <7: 42%), antibody used to assess TDP-43 proteinopathy (native: 18% vs. hyperphosphorylated: 24%) and presence of hippocampal sclerosis (without 24% vs. with hippocampal sclerosis: 48%). Other stratified analyses by age, sex, analysed brain regions, sample size and severity of AD neuropathology showed similar pooled TDP-43 prevalence. CONCLUSIONS: Different methodology to access TDP-43, and also differences in lifestyle and genetic factors across different populations could explain our results. Standardization of TDP-43 measurement, and future studies about the impact of genetic and lifestyle characteristics on the development of neurodegenerative diseases are needed.

Cortical influences drive amyotrophic lateral sclerosis.

The early motor manifestations of sporadic amyotrophic lateral sclerosis (ALS), while rarely documented, reflect failure of adaptive complex motor skills. The development of these skills correlates with progressive evolution of a direct corticomotoneuronal system that is unique to primates and markedly enhanced in humans. The failure of this system in ALS may translate into the split hand presentation, gait disturbance, split leg syndrome and bulbar symptomatology related to vocalisation and breathing, and possibly diffuse fasciculation, characteristic of ALS. Clinical neurophysiology of the brain employing transcranial magnetic stimulation has convincingly demonstrated a presymptomatic reduction or absence of short interval intracortical inhibition, accompanied by increased intracortical facilitation, indicating cortical hyperexcitability. The hallmark of the TDP-43 pathological signature of sporadic ALS is restricted to cortical areas as well as to subcortical nuclei that are under the direct control of corticofugal projections. This provides anatomical support that the origins of the TDP-43 pathology reside in the cerebral cortex itself, secondarily in corticofugal fibres and the subcortical targets with which they make monosynaptic connections. The latter feature explains the multisystem degeneration that characterises ALS. Consideration of ALS as a primary neurodegenerative disorder of the human brain may incorporate concepts of prion-like spread at synaptic terminals of corticofugal axons. Further, such a concept could explain the recognised widespread imaging abnormalities of the ALS neocortex and the accepted relationship between ALS and frontotemporal dementia.

Survival in the pre-senile dementia frontotemporal lobar degeneration with TDP-43 proteinopathy: effects of genetic, demographic and neuropathological variables.

Factors associated with survival were studied in 84 neuropathologically documented cases of the pre-senile dementia frontotemporal dementia lobar degeneration (FTLD) with transactive response (TAR) DNA-binding protein of 43 kDa (TDP-43) proteinopathy (FTLD-TDP). Kaplan-Meier survival analysis estimated mean survival as 7.9 years (range: 1-19 years, SD = 4.64). Familial and sporadic cases exhibited similar survival, including progranulin (GRN) gene mutation cases. No significant differences in survival were associated with sex, disease onset, Braak disease stage, or disease subtype, but higher survival was associated with lower post-mortem brain weight. Survival was significantly reduced in cases with associated motor neuron disease (FTLD-MND) but increased with Alzheimer's disease (AD) or hippocampal sclerosis (HS) co-morbidity. Cox regression analysis suggested that reduced survival was associated with increased densities of neuronal cytoplasmic inclusions (NCI) while increased survival was associated with greater densities of enlarged neurons (EN) in the frontal and temporal lobes. The data suggest that: (1) survival in FTLD-TDP is more prolonged than typical in pre-senile dementia but shorter than some clinical subtypes such as the semantic variant of primary progressive aphasia (svPPA), (2) MND co-morbidity predicts poor survival, and (3) NCI may develop early and EN later in the disease. The data have implications for both neuropathological characterization and subtyping of FTLD-TDP.

Chronic Traumatic Encephalopathy Presenting as Alzheimer's Disease in a Retired Soccer Player.

The relationship between soccer and chronic traumatic encephalopathy (CTE) is not well established. We report clinicopathological correlations in an 83-year-old retired center-back soccer player, with no history of concussion, manifesting typical Alzheimer-type dementia. Examination revealed mixed pathology including widespread CTE, moderate Alzheimer's disease, hippocampal sclerosis, and TDP-43 proteinopathy. This case adds to a few CTE cases described in soccer players. Furthermore, it corroborates that CTE may present clinically as typical Alzheimer-type dementia. Further studies investigating the extent to which soccer is a risk for CTE are needed.

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.

Cortical degeneration in frontotemporal lobar degeneration with TDP-43 proteinopathy caused by progranulin gene mutation.

Familial frontotemporal lobar degeneration with transactive response (TAR) DNA-binding protein of 43 kDa (TDP-43) proteinopathy (FTLD-TDP) is most commonly caused by progranulin (GRN) gene mutation. To characterize cortical degeneration in these cases, changes in density of the pathology across the cortical laminae of the frontal and temporal lobe were studied in seven cases of FTLD-TDP with GRN mutation using quantitative analysis and polynomial curve fitting. In 50% of gyri studied, neuronal cytoplasmic inclusions (NCI) exhibited a peak of density in the upper cortical laminae. Most frequently, neuronal intranuclear inclusions (NII) and dystrophic neurites (DN) exhibited a density peak in lower and upper laminae, respectively, glial inclusions (GI) being distributed in low densities across all laminae. Abnormally enlarged neurons (EN) were distributed either in the lower laminae or were more uniformly distributed across the cortex. The distribution of all neurons present varied between cases and regions, but most commonly exhibited a bimodal distribution, density peaks occurring in upper and lower laminae. Vacuolation primarily affected the superficial laminae and density of glial cell nuclei increased with distance across the cortex from pia mater to white matter. The densities of the NCI, GI, NII, and DN were not spatially correlated. The laminar distribution of the pathology in GRN mutation cases was similar to previously reported sporadic cases of FTLD-TDP. Hence, pathological changes initiated by GRN mutation, and by other causes in sporadic cases, appear to follow a parallel course resulting in very similar patterns of cortical degeneration in FTLD-TDP.

[Genetics of amyotrophic lateral sclerosis]. / Genetik der amyotrophen Lateralsklerose.

Amyotrophic lateral sclerosis (ALS) is an aggressive rapidly progressing degeneration of both upper and lower motor neurons. Clinically, ALS is characterized by rapidly progressing atrophy and paresis of the muscles of the extremities. The genetics of ALS have become more complex in the last 5 years. The SOD gene is still very important; however, in recent years mutations in the genes for TDP-43 and FUS were discovered and also a most interesting intronic repeat expansion of the hexanucleotide repeat in C9ORF72 has been shown to be the most common in ALS. There are other quantitatively less relevant genes, which, however, are meaningful for pathogenetic aspects. It is also necessary to know that the phenotypes associated with ALS genetics have expanded.

Progressive supranuclear palsy presenting as primary lateral sclerosis but lacking parkinsonism, gaze palsy, aphasia, or dementia.

We report an autopsy case of progressive supranuclear palsy (PSP) that clinically showed only slowly progressive and symmetric upper motor neuron syndrome over a disease course of 12 years. A female patient initially exhibited dysarthria at the age of 65, followed by gait disturbance and dysphagia. Neurological examination at age 67 disclosed pseudobulbar palsy, spastic gait, hyperreflexia, and presence of bilateral Hoffmann and Babinski signs. However, muscle atrophy, weakness, evidence of denervation on electromyography, vertical gaze palsy, parkinsonism, gait freezing, aphasia, speech apraxia, or dementia was not noted throughout the course. She was clinically diagnosed as having motor neuron disease consistent with so-called primary lateral sclerosis. Pathological examination disclosed histopathological features of PSP, including argyrophilic and tau-positive tufted astrocytes, neurofibrillary tangles, coiled bodies, and thread-like processes in the motor cortex and superior frontal gyrus, and to a lesser degree, in the basal ganglia and brain stem nuclei. In addition, severe fibrillary gliosis was noted in the precentral gyrus and corticospinal tract, being consistent with upper motor neuron syndrome observed in this case. No TAR-DNA binding protein 43-positive lesion, FUS pathology, Bunina body, or Lewy body-like hyaline inclusion was noted in the motor cortex or lower motor neurons. These findings suggest that when tau pathology is prominent in the motor cortex but is minimal in the basal ganglia and brain stem nuclei, a PSP case can lack all classic clinical features of PSP and show only slowly progressive upper motor syndrome, consistent with clinical picture of primary lateral sclerosis.

Right temporal variant frontotemporal dementia with motor neuron disease.

Patterns of atrophy in frontotemporal dementia (FTD) correlate with the clinical subtypes of behavioral variant FTD (bvFTD), semantic dementia, progressive non-fluent aphasia (PNFA) and FTD with motor neuron disease (FTD-MND). Right temporal variant FTD is associated with behavioral dyscontrol and semantic impairment, with tau abnormalities more common in right temporal bvFTD and TDP-43 accumulation in right temporal semantic dementia. However, no clinical and anatomical correlation has been described for patients with predominant right temporal atrophy and FTD-MND. Therefore, we performed a database screen for all patients diagnosed with FTD-MND at Mayo Clinic and reviewed their MRI scans to identify those with striking, dominant, right temporal lobe atrophy. For cases with volumetric MRI we performed voxel based morphometry and for those with brain tissue we performed pathological examination. Of three such patients identified, each patient had different presenting behavioral and/or aphasic characteristics. MRI, including diffusion tensor imaging in one patient, and FDG positron emission tomography revealed striking and dominant right temporal lobe atrophy, right corticospinal tract degeneration, and right temporal hypometabolism. Archived brain tissue was available in two patients; both demonstrating TDP-43 type 3 pathology (Mackenzie scheme) with predominant neuronal cytoplasmic inclusions. In one case, neurofibrillary tangles (Braak V) and neuritic plaques were also present in keeping with a diagnosis of Alzheimer's disease. There appears to be an association between FTD-MND and severe right temporal lobe atrophy. Until further characterization of such cases are determined, they may be best classified as right temporal variant FTD-MND.

[German consortium for frontotemporal lobar degeneration]. / Konsortium zur Erforschung der frontotemporalen Lobärdegeneration.

Frontotemporal lobar degeneration (FTLD) is an umbrella term for an aetiologically diverse group of neurodegenerative disorders with prominent lobar cortical atrophy. First this disease group was restricted to Pick's disease or Pick's complex. Several updates of the clinical classification systems were performed and discussed. Currently we summarize the following diseases under the FTLD spectrum: frontotemporal dementia (FTD) as a behavioural variant, primary non-fluent aphasia (PNFA) and semantic dementia as language variants, amyotrophic lateral sclerosis with FTD (ALS-FTD), corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP).From the pathophysiological aspect major progress was made. Neuropathologically FTLDs are now defined based on the molecular composition of these protein accumulations. A major distinction of tau-associated (FTLD-tau) and TDP43-associated (FTLD-TDP43) and to a lesser extend FUS-associated (FTLD-FUS) has been made. Additional risk genes were described. However from the therapeutic perspective even symptomatic therapy is under discussion. A major aim of our consortium is to develop parameters allowing an early diagnosis and follow-up, thus providing effective and objective parameters for therapeutic strategies.