Familial Frontotemporal Lobar Degeneration Research Articles

Single-cell dissection of the human motor and prefrontal cortices in ALS and FTLD

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) share many clinical, pathological, and genetic features, but a detailed understanding of their associated transcriptional alterations across vulnerable cortical cell types is lacking. Here, we report a high-resolution, comparative single-cell molecular atlas of the human primary motor and dorsolateral prefrontal cortices and their transcriptional alterations in sporadic and familial ALS and FTLD. By integrating transcriptional and genetic information, we identify known and previously unidentified vulnerable populations in cortical layer 5 and show that ALS- and FTLD-implicated motor and spindle neurons possess a virtually indistinguishable molecular identity. We implicate potential disease mechanisms affecting these cell types as well as non-neuronal drivers of pathogenesis. Finally, we show that neuron loss in cortical layer 5 tracks more closely with transcriptional identity rather than cellular morphology and extends beyond previously reported vulnerable cell types.

Global platform trial design for tau (MAPT) mutation carriers

AbstractBackgroundPathogenic mutations in the MAPT (tau) gene cause familial frontotemporal lobar degeneration (f‐FTLD). No disease‐modifying treatments exist. Tau therapeutics being tested in other tauopathies may be suitable candidates, but the small number of identified mutation carriers prohibits traditional clinical trial designs from achieving adequate power. Platform trial designs permit multiple therapies to be tested in parallel and improve power by sharing placebo groups across treatment arms. We evaluate whether a platform design could improve the likelihood of identifying an effective treatment for MAPT mutation carriers.MethodALLFTD and GENFI observational data were used to simulate MAPT prevention and early symptomatic clinical trials (CDR®+NACC‐FTLD≤1). Only presymptomatic participants (CDR®+NACC‐FTLD = 0) within 2.5 years of expected symptom onset based on disease progression models (DPM) were included. First, we evaluated the time and sample size required to test five treatments using a platform design compared to sequential randomized control trials. Platform designs assumed a max of three treatment arms at any time, with new arms enrolling upon completion of prior arms. Each arm randomized 60 mutations carriers 3:1 treatment to placebo, with a placebo group shared across arms. Minimum follow up was 1.5 years with common close. Sequential trials assumed 90 participants allocated 1:1 treatment to placebo, with three‐month intervals between trials. Using a platform design, we compared a novel method for testing therapeutic effects using DPMs to account for differential rates of expected progression compared to traditional mixed models for repeated measures (MMRM) tests controlling for baseline CDR®+NACC‐FTLD.ResultFive treatments could be tested in a platform design using 300 participants (75% treated) over five years, compared to 450 participants (50% treated) over 13 years using traditional, sequential trials. Platform trial simulations indicated that with 80% power, DPM‐based analytic approach could detect a 25% treatment effect, whereas traditional MMRM could only detect a 40% effect.ConclusionPlatform designs combined with DPM‐based analyses provide a path to testing more treatments with fewer participants. Adequately powered MAPT platform trials are feasible but require a global clinical trial infrastructure.

Characterization of initial symptoms of prodromal familial Frontotemporal Lobar Degeneration: Data from the ALLFTD Consortium

AbstractBackgroundThe ALLFTD Consortium aims to characterize preclinical and prodromal stage of familial Frontotemporal Lobar Degeneration (f‐FTLD) to prepare for clinical trials in FTLD.MethodWe prospectively followed 320 asymptomatic participants of the ALLFTD Consortium who are family members of f‐FTLD with a mutation in MAPT (n = 106), GRN (n = 74), or C9orf72 (n = 140), and describe the ratings on the eight domains of CDR® plus NACC FTLD (FTLD‐CDR) in those who phenoconverted to Mild Behavioral and/or Cognitive Impairment (MBCI). MBCI was diagnosed by the proposed research criteria for MBCI‐FTD (Barker MS, et al. Brain 2022). Participants who were diagnosed as MBCI but returned to asymptomatic at the following visit were excluded from the FTLD‐CDR assessment. ANOVA was used to compare continuous variables, and chi‐square test was used to compare categorical variables across the groups.ResultThirty‐six participants (15 MAPT, 9 GRN, 12 C9orf72) developed MBCI during follow‐up visits, 13 participants (5 MAPT, 3 GRN, 5 C9orf72) were diagnosed as MBCI but were characterized as asymptomatic at the following visit, and 271 participants stayed asymptomatic. Percentage of male in MBCI participants was 50% (MAPT 60%, GRN 33%, C9orf72 50%, p = 0.45). Age at phenoconversion to MBCI was 53.6±13.0 years old, the youngest in MAPT and the oldest in GRN participants (MAPT 44.3±8.3, GRN 63.1±11.3, C9orf72 56.4±10.8, p<0.001). Abnormal rating on each of the eight CDR® plus NACC FTLD domains at the initial visit of MBCI phenoconversion were observed in: “Memory” 36% (MAPT 33%, GRN 33%, C9orf72 44%, p = 0.95); “Orientation” 8% (MAPT 7%, GRN 8%, C9orf72 11%, p = 0.93); “Judgment/Problem Solving” 44% (MAPT 47%, GRN 50%, C9orf72 33%, p = 0.73); “Community Affairs” 22% (MAPT 27%, GRN 17%, C9orf72 22%, p = 0.82); “Home/Hobbies” 25% (MAPT 40%, GRN 8%, C9orf72 22%, p = 0.16); “Personal Care” 0%; “Behavior/Comportment/Personality” 44% (MAPT 60%, GRN 42%, C9orf72 22%, p = 0.19); “Language” 31% (MAPT 13%, GRN 50%, C9orf72 33%, p = 0.12).ConclusionThe three most common FTLD‐CDR domains initially disturbed in the prodromal stage of fFTLD were “Behavior/Comportment/Personality”, “Judgment/Problem Solving”, and “Memory”, while “Orientation” was intact in the majority of the individuals. Memory impairment without disorientation was seen in one‐third of the prodromal fFTLD participants.

Clinical value of CSF TMEM106B in familial and sporadic frontotemporal lobar degeneration

AbstractBackgroundTMEM106B, a lysosomal trafficking protein, is an important genetic susceptibility risk factor for frontotemporal lobar degeneration (FTLD). In GRN mutation carriers, minor allele homozygosity in the TMEM106B rs1990622 SNP modulates the risk of FTLD. TMEM106B is often the main component of amyloid fibrils in FTLD with TDP43 aggregates. TMEM106B has been quantified in human brain specimens, but its role as a fluid biomarker is unknown. Here, we investigate the clinical value of CSF TMEM106B in FTLD.MethodsCSF TMEM106B was quantified with SOMAmer proteomics (v3.0, SomaLogic®) in an original cohort of C9orf72, GRN and MAPT symptomatic and asymptomatic mutation carriers and family non‐carrier controls, recruited through ALLFTD (n = 182), and a validation cohort of sporadic neuropathology‐confirmed FTLD‐tau and FTLD‐TDP43, clinically‐diagnosed progressive supranuclear palsy – Richardson syndrome (PSP‐RS) and age‐matched controls (n = 96). CSF TMEM106B was correlated with disease severity, measured by the Frontotemporal Lobar Degeneration module global scores (CDR+NACC/FTLD); brain volume, measured with Bayesian linear mixed‐effect modeling, using age, sex and total‐intracranial volume‐corrected permutations with threshold‐free cluster enhancement; and CSF neurofilament light chain (NfL) measured with Simoa. TMEM106B SOMAmer specificity was validated in cell culture overexpression systems and human brain specimens with high TMEM106B burden.ResultsIn both cohorts, there were no differences in CSF TMEM106B by sex, phenotype or neuropathological diagnosis, except for lower levels in PSP‐RS compared to controls (‐0.31 Log2‐fold change, p < 0.001). CSF TMEM106B did not correlate with age. Regardless of disease‐causing mutation, lower CSF TMEM106B was associated with worse disease severity (Figure 1 and 2). CSF TMEM106B was lower in homozygous TMEM106B rs1990622 protective allelein C9orf2 and MAPT, but not in GRN mutation carriers (Figures 3). CSF TMEM106B showed a trend for inverse correlation with NfL in the whole sample (r = ‐0.135, p = 0.052), and correlated positively with left frontal volume in symptomatic FTLD mutation gene carriers (p < 0.05).ConclusionCSF TMEM106B is quantifiable in CSF in vivo. CSF TMEM106B levels are affected by an interaction of disease severity and FTLD and TMEM106B genotypes. Further work is needed to determine its value as a clinical biomarker.

Familial FTD in China:progress and prospects

AbstractBackgroundFrontotemporal dementia (FTD) is a set of clinical syndromes characterized by progressive abnormalities in behavior, executive function, language, with a strong genetic background. However, the familiar FTD studies were rare in China. Here we aim to review the previous cross‐sectional reports of Chinese FTD patients with gene mutations, as well as the update status of the longitudinal familiar FTD study by the Chinese Familial Frontotemporal Lobar Degeneration Consortium (CFFC).MethodTo review current status of Chinese FTD patients with gene mutations, we performed a comprehensive electronic searches of Medline, PubMed, and Embase databases were performed by using the combination of a number of medical subject headings, Emtree subject headings, and free‐text terms (“frontotemporal lobar degeneration” or “frontotemporal dementia” for clinical categories; “Chinese” or “China” for ethnics). To start a multi‐center longitudinal cohort of familiar FTD, we established the CFFC in October 2022 by involving 7 top teaching hospitals across China. Patients with MAPT, GRN and C9orf72 mutations were enrolled and followed up according the designed framework.ResultBased on the previous reports, genetic mutations accounted for 5.13%‐27.9% as reported in a few cross‐sectional cohort of Chinese FTD patients. Mostly reported pathogenic variants were MAPT, followed by GRN, TBK1, CHCHD10, C9orf72 repeat expansions, VCP, and SQSTM1. Up till now, there were 26 pedigrees with MAPT mutations, 11 pedigrees with GRN mutations and 9 pedigrees with C9orf72 repeat expansions mutations have been enrolled in the longitudinal multi‐center cohort study by CFFC.ConclusionThe high prevalence of MAPT mutations in Chinese patients with FTD, may implies a genetic heterogeneity between Chinese and other ethnics. Longitudinal studies with larger sample size to modeling the trajectory of biomarkers in genetic mutation carriers for earlier diagnosis and intervention are needed in the future.

Lipopolysaccharide triggers exacerbated microglial activation, excessive cytokine release and behavioural disturbances in mice with truncated Fused-in-Sarcoma Protein (FUS)

CNS inflammation, including microglial activation, in response to peripheral infections are known to contribute to the pathology of both familial and sporadic neurodegenerative disease. The relationship between Fused-in-Sarcoma Protein (FUS)-mediated disease in the transgenic FUS[1–359] animals and the systemic inflammatory response have not been explored. Here, we investigated microglial activation, inflammatory gene expression and the behavioural responses to lipopolysaccharide-induced (LPS; 0.1 mg/kg) systemic inflammation in the FUS[1–359] transgenic mice. The pathology of these mice recapitulates the key features of mutant FUS-associated familial frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). Here, pre-symptomatic 8-week-old mutant or wild type controls were challenged with LPS or with saline and sucrose intake, novel cage exploration, marble burying and swimming behaviours were analyzed. The level of pro-inflammatory gene expression was also determined, and microglial activation was evaluated. In chronic experiments, to discover whether the LPS challenge would affect the onset of ALS-like paralysis, animals were evaluated for clinical signs from 5 to 7 weeks post-injection. Compared to controls, acutely challenged FUS[1–359]-tg mice exhibited decreased sucrose intake and increased floating behaviours. The FUS[1–359]-tg mice exhibited an increase in immunoreactivity for Iba1-positive cells in the prefrontal cortex and ventral horn of the spinal cord, which was accompanied by increased expression of interleukin-1β, tumour necrosis factor, cyclooxygenase-(COX)-1 and COX-2. However, the single LPS challenge did not alter the time to development of paralysis in the FUS[1–359]-tg mice. Thus, while the acute inflammatory response was enhanced in the FUS mutant animals, it did not have a lasting impact on disease progression.

Insight into Tetramolecular DNA G-Quadruplexes Associated with ALS and FTLD: Cation Interactions and Formation of Higher-Ordered Structure.

The G4C2 hexanucleotide repeat expansion in the c9orf72 gene is a major genetic cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), with the formation of G-quadruplexes directly linked to the development of these diseases. Cations play a crucial role in the formation and structure of G-quadruplexes. In this study, we investigated the impact of biologically relevant potassium ions on G-quadruplex structures and utilized 15N-labeled ammonium cations as a substitute for K+ ions to gain further insights into cation binding and exchange dynamics. Through nuclear magnetic resonance spectroscopy and molecular dynamics simulations, we demonstrate that the single d(G4C2) repeat, in the presence of 15NH4+ ions, adopts a tetramolecular G-quadruplex with an all-syn quartet at the 5'-end. The movement of 15NH4+ ions through the central channel of the G-quadruplex, as well as to the bulk solution, is governed by the vacant cation binding site, in addition to the all-syn quartet at the 5'-end. Furthermore, the addition of K+ ions to G-quadruplexes folded in the presence of 15NH4+ ions induces stacking of G-quadruplexes via their 5'-end G-quartets, leading to the formation of stable higher-ordered species.

Concomitant Neuronal Tau Deposition and FKBP52 Decrease Is an Early Feature of Different Human and Experimental Tauopathies.

Pathological tau proteins constitute neurofibrillary tangles that accumulate in tauopathies including Alzheimer's disease (AD), progressive supranuclear palsy (PSP), and familial frontotemporal lobar degeneration (FTLD-Tau). We previously showed that the FKBP52 immunophilin interacts functionally with tau and strongly decreases in AD brain neurons in correlation with tau deposition. We also reported that FKBP52 co-localizes with autophagy-lysosomal markers and an early pathological tau isoform in AD neurons, suggesting its involvement in autophagic tau clearance. Our objective was to evaluate if differences in neuronal FKBP52 expression levels and subcellular localization might be detected in AD, PSP, familial FTLD-Tau, and in the hTau-P301 S mouse model compared to controls. Cell by cell immunohistofluorescence analyses and quantification of FKBP52 were performed on postmortem brain samples of some human tauopathies and on hTau-P301 S mice spinal cords. We describe a similar FKBP52 decrease and its localization with early pathological tau forms in the neuronal autophagy-lysosomal pathway in various tauopathies and hTau-P301 S mice. We find that FKBP52 decreases early during the pathologic process as it occurs in rare neurons with tau deposits in the marginally affected frontal cortex region of AD Braak IV brains and in the spinal cord of symptomless 1-month-old hTau-P301 S mice. As FKBP52 plays a significant role in cellular signaling and conceivably in tau clearance, our data support the idea that the prevention of FKBP52 decrease or the restoration of its normal expression at early pathologic stages might represent a new potential therapeutic approach in tauopathies including AD, familial FTLD-Tau, and PSP.

Phenoconversion and disease progression observed in mutation carriers of familial Frontotemporal Lobar Degeneration in the ALLFTD Consortium

AbstractBackgroundThe ARTFL‐LEFFTDS Longitudinal Frontotemporal Lobar Degeneration (ALLFTD) study is designed to characterize both sporadic and familial FTLD (f‐FTLD) through annual detailed clinical, neuropsychological, biomarker, and neuroimaging assessments to capture disease onset and trajectory in preparation for therapeutic trails in FTLD. Transitions from asymptomatic to mild disease, or from mild to overt, may reveal critical windows for intervention.Method169 f‐FTLD participants carrying mutations in the main FTLD‐associated genes (79 C9orf72; 37 GRN; 53 MAPT) with at least two clinical assessments were included for analysis of phenoconversion from asymptomatic or mild disease. [CDRÒ + NACC FTLD global scores (Miyagawa et al, 2020) were used to define baseline status at first visit: “asymptomatic” = 0 and “mild” = 0.5. Conversion was defined as “partial” (asymptomatic to mild), “definite” (asymptomatic to overt [CDRÒ + NACC FTLD > = 1) and “mild to overt” (0.5 to > = 1).ResultDefinite conversion occurred most often in MAPT mutation carriers, with 5/43 asymptomatic carriers transitioning through mild to overt across multiple visits. Definite conversion was also seen in 2/65 C9orf72 expansion carriers and 1/30 GRN mutation carriers. All definite converters were assessed as mild (CDRÒ + NACC FTLD = 0.5) for at least one intermediate visit; definite conversion was observed from 2‐4 years from initial assessment. Partial conversions also occurred in all three genetic groups (MAPT: 6; C9orf72: 5; GRN: 5). Further conversion is expected to be observed in these participants in additional follow‐up visits. C9orf72 expansion carriers were less likely to progress from a baseline of mild to overt (3/14) than GRN carriers (4/6) or MAPT (7/10).ConclusionLongitudinal assessment through natural history studies can capture early phenoconversion in carriers of FTLD‐associated genetic mutations; corresponding imaging, cognitive, and biomarker profiles captured may provide insights into disease mechanisms and trajectories.

Memory Performance in Asymptomatic and Prodromal Familial Frontotemporal Lobar Degeneration: Findings from the ALLFTD Consortium (P13-6.001)

Memory Performance in Asymptomatic and Prodromal Familial Frontotemporal Lobar Degeneration: Findings from the ALLFTD Consortium (P13-6.001)

Characterization of CDR® plus NACC FTLD at Phenoconversion from Asymptomatic to Mild Behavioral and/or Cognitive Impairment in Familial Frontotemporal Lobar Degeneration: Data from the ALLFTD Consortium

AbstractBackgroundThe three most common genes responsible for the familial Frontotemporal Lobar Degeneration (f‐FTLD) are MAPT, GRN, and C9orf72, with the C9orf72 mutation being the most common cause of f‐FTLD. The ALLFTD Consortium targets to characterize f‐FTLD, including its preclinical stage, to prepare for clinical trials in FTLD. We sought to investigate the initial symptoms and clinical picture of f‐FTLD and compare them among the common pathogenic genes using longitudinal CDR® plus NACC FTLD.MethodWe longitudinally assessed the CDR® plus NACC FTLD among 292 asymptomatic participants of the ALLFTD Consortium who are family members of f‐FTLD caused by MAPT (n = 99), GRN (n = 67), or C9orf72 (n = 126) mutations, and described the detailed profiles of the CDR® plus NACC FTLD in the participants who developed Mild Behavioral and/or Cognitive Impairment (MBCI).ResultForty‐one participants (17 MAPT, 11 GRN, 13 C9orf72) developed MBCI during follow‐up visits . Age at the diagnosis of MBCI was 52.3±13.0 years (GRN 63.2±11.8, MAPT 43.5±8.6, C9orf72 54.7±10.7). Frequencies of abnormal rating on the eight CDR® plus NACC FTLD domains at the time of MBCI diagnosis were: “Memory” 44% (MAPT 47%, GRN 55%, C9orf72 31%); “Orientation” 7% (MAPT 6%, GRN 9%, C9orf72 8%); “Judgment and Problem Solving” 39% (MAPT 41%, GRN 55%, C9orf72 23%); “Community Affairs” 22% (MAPT 24%, GRN 18%, C9orf72 23%); “Home and Hobbies” 22% (MAPT 35%, GRN 0%, C9orf72 23%); “Personal Care” 0%; “Behavior/Comportment/Personality” 51% (MAPT 59%, GRN 55%, C9orf72 38%); “Language” 29% (MAPT 18%, GRN 55%, C9orf72 23%).ConclusionInitial symptoms and clinical picture of f‐FTLD in MBCI stage differ among responsible FTLD genes, which could be useful in detecting very early features of f‐FTLD in pathogenic mutation carriers.

Initial Reports of ALLFTD Participant Internet and Social Media Usage Survey

AbstractBackgroundThe ARTFL LEFFTDS Longitudinal Frontotemporal Lobar Degeneration (ALLFTD) Study, is the unification of prior FTD research studies, ARTFL and LEFFTDS. ALLFTD aims to evaluate sporadic (s‐) and familial (f‐) frontotemporal lobar degeneration (FTLD) patients and asymptomatic family members of f‐FTLD patients, characterizing the cohorts longitudinally and informing clinical trial design.MethodALLFTD participants completed the ALLFTD‐specific, Internet and Social Media (ISM) Usage Survey. This survey was created to learn more about participants’ ISM habits. The survey asks participants to report on the frequency with which they use ISM for personal reasons and contains additional questions about reasons for use and general gaming and social media habits.ResultIn conjunction with their scheduled ALLFTD visit, 194 participants completed the ALLFTD ISM Usage Survey. Fifty one percent of participants identified as female. The mean age was 56.6 (SD 14.61), and the mean education level was 15.9 (SD 3.53). Most participants reported using ISM 1‐5 hours per day (56.7%). Participants also reported using ISM at less common frequencies: more than 5 hours per day (12.9%), less than 1 hour per day (13.9%), weekly (3.1%), 2‐3 times a week (2.1%), 2‐3 times a month (2.1%), and never (9.3%). “Moderate and Severely impaired” participants (CDR© + NACC FTLD > = 2) reported using ISM less frequently than “mildly symptomatic” participants (CDR© + NACC FTLD = 1, p<0.0001), and those who are “normal and questionably impaired” CDR© + NACC FTLD < = 0.5, p<0.0001). Those who are mildly symptomatic reported using ISM at a similar frequency to those who are normal or questionably impaired (p<0.01). When reporting on personal use, most participants stated that they used the internet for email (45.5%), news (37.5%), social media (32.4%), and entertainment (33.5%). Additionally, most participants reported playing games (56.2%) and using social media (59.8%). Participants predominantly indicated that they use social media to connect with family and friends (90.5%). Comparison of ISM usage frequency to reported anxiety, agitation, or depression on the NPI‐Q found evidence of a difference in ISM usage frequency; directional comparison studies are forthcoming.ConclusionFrequency of ISM usage is consistent between ALLFTD participants. Additional analyses of ISM usage are forthcoming.

The Neurofilament Surveillance Project (NSP): A biomarker study to sample blood quarterly in familial frontotemporal lobar degeneration

AbstractBackgroundIn familial frontotemporal lobar degeneration (f‐FTLD), plasma levels of neurofilament light (NfL) are elevated at least two years prior to symptom onset and predict future clinical status. The Neurofilament Surveillance Project (NSP), an actively recruiting observational study, seeks to obtain higher resolution data of temporal changes in plasma NfL to better understand its clinical utility in f‐FTLD interventional trials. The NSP is a pre‐competitive collaboration sponsored by the Bluefield Project to Cure FTD and funded by biotechnology and pharmaceutical companies and nonprofit organizations.MethodParticipants must be members of families with disease‐causing mutations in C9orf72, MAPT or GRN and enrolled in the ALLFTD natural history study. Up to 335 participants, with roughly equal representation across mutation type, provide plasma quarterly for 3 years (4355 samples total) to enable the observation of peripheral NfL levels longitudinally during disease onset and progression. Plasma is collected by certified mobile research nurses during remote visits, and NfL is measured in batch at least every 6 months. NfL measurements from one plasma aliquot per draw will be correlated with annual assessments obtained in the ALLFTD study, including measures of disease severity (CDRÒ+NACC‐FTLD, CGI, etc.), cognitive function from the UDS Neuropsychology Battery, and volumetric MRI data. Additional plasma aliquots are reserved for future analyses of other biomarkers during the course of the study; another subset of aliquots is reserved to share with interested investigators after the study ends.ResultAs of 1/19/22, the NSP had enrolled 161 participants, including 62 from C9orf72 kindreds, 60 from MAPT kindreds, and 28 from GRN kindreds. One‐hundred forty‐five participants had completed their initial visit, and 109 had completed more than 3, and up to 5, quarterly blood draws. Enrollment and study visits are ongoing despite COVID‐related limitations.ConclusionThe quarterly blood sampling from this study, combined with annual comprehensive clinical assessments through the ALLFTD natural history study, will enable a more detailed understanding of when and how NfL levels change during phenoconversion and/or disease progression in f‐FTLD mutation carriers. These data will be especially informative in the context of the targeted investigational therapeutics for f‐FTLD now entering clinical trials.

Pathological 25 kDa C-Terminal Fragments of TDP-43 Are Present in Lymphoblastoid Cell Lines and Extracellular Vesicles from Patients Affected by Frontotemporal Lobar Degeneration and Neuronal Ceroidolipofuscinosis Carrying a GRN Mutation.

Frontotemporal lobar degeneration (FTLD) is a complex disease, characterized by progressive degeneration of frontal and temporal lobes. Mutations in progranulin (GRN) gene have been found in up to 50% of patients with familial FTLD. Abnormal deposits of post-translationally-modified TAR DNA-binding protein of 43 kDa (TDP-43) represent one of the main hallmarks of the brain pathology. To investigate in peripheral cells the presence of the different TDP-43 forms, especially the toxic 25 kDa fragments, we analyzed lymphoblastoid cell lines (LCLs) and the derived extracellular vesicles (EVs) from patients carrying a GRN mutation, together with wild-type (WT) healthy controls. After characterizing EV sizes and concentrations by nanoparticle tracking analysis, we investigated the levels of different forms of the TDP-43 protein in LCLs and respective EVs by Western blot. Our results showed a trend of concentration decreasing in EVs derived from GRN-mutated LCLs, although not reaching statistical significance. A general increase in p-TDP-43 levels in GRN-mutated LCLs and EVs was observed. In particular, the toxic 25 kDa fragments of p-TDP-43 were only present in GRN-mutated LCLs and were absent in the WT controls. Furthermore, these fragments appeared to be more concentrated in EVs than in LCLs, suggesting a relevant role of EVs in spreading pathological molecules between cells.

Distinguishing Frontotemporal Lobar Degeneration Tau From TDP-43 Using Plasma Biomarkers

Biomarkers are lacking that can discriminate frontotemporal lobar degeneration (FTLD) associated with tau (FTLD-tau) or TDP-43 (FTLD-TDP). To test whether plasma biomarkers glial fibrillary acidic protein (GFAP), neurofilament light chain (NfL), or their ratio (GFAP/NfL) differ between FTLD-tau and FTLD-TDP. This retrospective cross-sectional study included data from 2009 to 2020 from the University of Pennsylvania Integrated Neurodegenerative Disease Database, with a median (IQR) follow-up duration of 2 (0.3-4.2) years. The training sample was composed of patients with autopsy-confirmed and familial FTLD; nonimpaired controls were included as a reference group. The independent validation sample included patients with FTD with a clinical diagnosis of progressive supranuclear palsy syndrome (PSPS) associated with tau (PSPS-tau) or amytrophic lateral sclerosis (ALS) associated with TDP-43 (ALS-TDP). In patients with FTLD with autopsy-confirmed or variant-confirmed pathology, receiver operating characteristic (ROC) curves tested the GFAP/NfL ratio and established a pathology-confirmed cut point. The cut point was validated in an independent sample of patients with clinical frontotemporal dementia (FTD). Data were analyzed from February to July 2022. Clinical, postmortem histopathological assessments, and plasma collection. ROC and area under the ROC curve (AUC) with 90% CIs evaluated discrimination of pure FTLD-tau from pure FTLD-TDP using plasma GFAP/NfL ratio; the Youden index established optimal cut points. Sensitivity and specificity of cut points were assessed in an independent validation sample. Of 349 participants with available plasma data, 234 met inclusion criteria (31 controls, 141 in the training sample, and 62 in the validation sample). In the training sample, patients with FTLD-tau were older than patients with FTLD-TDP (FTLD-tau: n = 46; mean [SD] age, 65.8 [8.29] years; FTLD-TDP: n = 95; mean [SD] age, 62.3 [7.82] years; t84.6 = 2.45; mean difference, 3.57; 95% CI, 0.67-6.48; P = .02) but with similar sex distribution (FTLD-tau: 27 of 46 [59%] were male; FTLD-TDP: 51 of 95 [54%] were male; χ21 = 0.14; P = .70). In the validation sample, patients with PSPS-tau were older than those with ALS-TDP (PSPS-tau: n = 31; mean [SD] age, 69.3 [7.35] years; ALS-TDP: n = 31; mean [SD] age, 54.6 [10.17] years; t54.6 = 6.53; mean difference, 14.71; 95% CI, 10.19-19.23; P < .001) and had fewer patients who were male (PSPS-tau: 9 of 31 [29%] were male; ALS-TDP: 22 of 31 [71%] were male; χ21 = 9.3; P = .002). ROC revealed excellent discrimination of FTLD-tau from FTLD-TDP by plasma GFAP/NfL ratio (AUC = 0.89; 90% CI, 0.82-0.95; sensitivity = 0.73; 90% CI, 0.65-0.89; specificity = 0.89; 90% CI, 0.78-0.98), which was higher than either GFAP level alone (AUC = 0.65; 90% CI, 0.54-0.76) or NfL levels alone (AUC = 0.75; 90% CI, 0.64-0.85). In the validation sample, there was sensitivity of 0.84 (90% CI, 0.66-0.94) and specificity of 0.81 (90% CI, 0.62-0.91) when applying the autopsy-derived plasma GFAP/NfL threshold. The plasma ratio of GFAP/NfL may discriminate FTLD-tau from FTLD-TDP.

Molecular imaging biomarkers in familial frontotemporal lobar degeneration: Progress and prospects

Familial frontotemporal lobar degeneration (FTLD) is a pathologically heterogeneous group of neurodegenerative diseases with diverse genotypes and clinical phenotypes. Three major mutations were reported in patients with familial FTLD, namely, progranulin (GRN), microtubule-associated protein tau (MAPT), and the chromosome 9 open reading frame 72 (C9orf72) repeat expansion, which could cause neurodegenerative pathological changes years before symptom onset. Noninvasive quantitative molecular imaging with PET or single-photon emission CT (SPECT) allows for selective visualization of the molecular targets in vivo to investigate brain metabolism, perfusion, neuroinflammation, and pathophysiological changes. There was increasing evidence that several molecular imaging biomarkers tend to serve as biomarkers to reveal the early brain abnormalities in familial FTLD. Tau-PET with 18F-flortaucipir and 11C-PBB3 demonstrated the elevated tau position in patients with FTLD and also showed the ability to differentiate patterns among the different subtypes of the mutations in familial FTLD. Furthermore, dopamine transporter imaging with the 11C-DOPA and 11C-CFT in PET and the 123I-FP-CIT in SPECT revealed the loss of dopaminergic neurons in the asymptomatic and symptomatic patients of familial FTLD. In addition, PET imaging with the 11C-MP4A has demonstrated reduced acetylcholinesterase (AChE) activity in patients with FTLD, while PET with the 11C-DAA1106 and 11C-PK11195 revealed an increased level of microglial activation associated with neuroinflammation even before the onset of symptoms in familial FTLD. 18F-fluorodeoxyglucose (FDG)-PET indicated hypometabolism in FTLD with different mutations preceded the atrophy on MRI. Identifying molecular imaging biomarkers for familial FTLD is important for the in-vivo assessment of underlying pathophysiological changes with disease progression and future disease-modifying therapy. We review the recent progress of molecular imaging in familial FTLD with focused on the possible implication of these techniques and their prospects in specific mutation types.

Differences in Motor Features of C9orf72, MAPT, or GRN Variant Carriers With Familial Frontotemporal Lobar Degeneration.

Familial frontotemporal lobar degeneration (f-FTLD) is a phenotypically heterogeneous spectrum of neurodegenerative disorders most often caused by variants within chromosome 9 open reading frame 72 (C9orf72), microtubule-associated protein tau (MAPT), or granulin (GRN). The phenotypic association with each of these genes is incompletely understood. We hypothesized that the frequency of specific clinical features would correspond with different genes. We screened the Advancing Research and Treatment in Frontotemporal Lobar Degeneration (ARTFL)/Longitudinal Evaluation of Familial Frontotemporal Dementia Subjects (LEFFTDS)/ARTFL LEFFTDS Longitudinal Frontotemporal Lobar Degeneration Consortium for symptomatic carriers of pathogenic variants in C9orf72, MAPT, or GRN. We assessed for clinical differences among these 3 groups based on data recorded as part of a detailed neurologic examination, the Progressive Supranuclear Palsy Rating Scale, Progressive Supranuclear Palsy-Quality of Life Rating Scale, Unified Parkinson's Disease Rating Scale Part III (motor items), and the Amyotrophic Lateral Sclerosis Functional Rating Scale, revised version. Data were analyzed using Kruskal-Wallis and Wilcoxon rank-sum tests and Fisher exact test. We identified 184 symptomatic participants who had a single pathogenic variant in C9orf72 (n = 88), MAPT (n = 53), or GRN (n = 43). Motor symptom age at onset was earliest in the MAPT participants followed by C9orf72, whereas the GRN pathogenic variant carriers developed symptoms later. C9orf72 participants more often had fasciculations, muscle atrophy, and weakness, whereas parkinsonism was less frequent. Vertical oculomotor abnormalities were more common in the MAPT cohort, whereas apraxia and focal limb dystonia occurred more often in participants with GRN variants. We present a large comparative study of motor features in C9orf72, MAPT, and GRN pathogenic variant carriers with symptomatic f-FTLD. Our findings demonstrate characteristic phenotypic differences corresponding with specific gene variants that increase our understanding of the genotype-phenotype relationship in this complex spectrum of neurodegenerative disorders. NCT02365922, NCT02372773, and NCT04363684.

Behavioral Variant Frontotemporal Dementia.

This article reviews many of the complex facets of behavioral variant frontotemporal dementia (bvFTD) and frontotemporal lobar degeneration (FTLD). A particular focus is on improving diagnostic accuracy to reduce the arduous diagnostic odyssey that so many patients and families endure. Strategies to promote diagnostic accuracy and approach the management of problematic symptoms are also discussed. Although the International Consensus Criteria for bvFTD were published more than a decade ago and clinicopathologic studies have confirmed their utility, diagnostic confusion continues. This article presents updated data along with illustrative cases to emphasize the clinical pearls that are most useful for clinicians. Although accurate prediction of the underlying proteinopathy remains a challenge, the ability to differentiate bvFTD from atypical Alzheimer disease, psychiatric disorders, and other mimickers has improved. Knowledge about the genetic underpinnings in a significant minority of individuals with familial FTLD is enabling early and accurate diagnosis. Therapeutic optimism has also increased, particularly in familial FTLD, with a few clinical trials in progress and several more planned, some of which are designed to slow progression or delay the onset of symptoms, or both. The diagnosis and management of bvFTD is challenging for clinicians and particularly for patients and their families. Although much progress has been gained over recent years, several key research questions persist. Treatments that significantly improve symptoms or alter the course of FTLD remain elusive, but optimism is increasing as pathobiology is better understood and novel therapies are being developed.

Disease progression models of familial frontotemporal lobar degeneration and the temporal ordering of biomarker changes in an international cohort

AbstractBackgroundClinical trials are underway to treat familial frontotemporal lobar degeneration (f‐FTLD). This is a rare disease, and a limited number of mutation carriers have been identified; thus, efficient trial design is critical. Multimodal, latent disease progression models (DPM) can estimate time to symptom onset and define the temporal ordering of biomarker changes. DPMs can also be leveraged to select endpoints and potentially supplement analyses by integrating historical data. Recent draft FDA guidance for gene therapy trials in neurological disease supports these novel approaches to clinical trials.MethodParticipants included 1,049 members of families affected by f‐FTLD, due to mutations in GRN, MAPT, or C9orf72 genes, who were enrolled in ALLFTD or GENFI. A Bayesian repeated measures model incorporated multimodal data to estimate disease progression, conditional on latent disease age (proximity to symptom onset), in 677 mutations carriers (GRN (n=233), MAPT (n=151) and C9orf72 (n=293)). Family members without pathogenic mutations were used as the reference group. Mean follow‐up was 1.1 (SD=1.1) years. Jointly modeled longitudinal variables included neuropsychological scores, CDR®+NACC‐FTLD Box Score, MRI volumes of brain regions affected by f‐FTLD, and plasma levels of neurofilament light chain (NfL).ResultDisease progression curves were similar across ALLFTD and GENFI cohorts. Plasma NfL elevations occurred earliest, up to 10 years before symptom onset, and NfL was the most powerful endpoint in the asymptomatic stage. MRI abnormalities occurred next, closer to symptom onset. The earliest MRI changes relative to symptom onset were observed in C9orf72+. GRN mutation carriers showed the most rapid acceleration in all biomarkers, and this acceleration occurred in close proximity to symptom onset. Neuropsychological measures and CDR®+NACC‐FTLD Box Score were among the most promising endpoints in the symptomatic stage. Trial simulations indicated that using latent disease age as an enrollment criterion would allow some asymptomatic mutation carriers to be enrolled without sacrificing power.ConclusionSimilarity in disease progression across ALLFTD and GENFI participants suggests these models will apply to international trials. Model‐derived estimates of disease progression curves indicate that endpoint selection should be specific to disease stage and mutation, and DPMs would facilitate greater participant enrollment.

Clinical value of CSF tau, p‐tau181, neurogranin and neurofilaments in familial frontotemporal lobar degeneration

AbstractBackgroundBlood neurofilament light chain (NfL) is a robust predictor of phenoconversion in familial frontotemporal lobar degeneration (fFTLD). The comparative value of CSF NfL and other CSF markers of degeneration in fFTLD remains unexplored.MethodFLTD‐causing mutation carriers were recruited through ALLFTD (n = 113, 56.6% female, mean age 48.1 ± 13 years; 29 C9orf72, 16 GRN, 34 MAPT, 34 mutation non‐carriers) and prospectively evaluated for 3 years. Baseline CSF was analyzed for NfL, phosphorylated neurofilament heavy chain (p‐NfH), tau, phosphorylated tau181 (p‐tau) and neurogranin using fit‐for‐purpose immunoassays. Mixed effect linear models, with random slopes, corrected for age, sex, genotype and total intracranial volume related CSF biomarkers to longitudinal clinical variables.ResultNfL (β = 0.64, p &lt; 0.001), p‐NfH (β = 0.68, p &lt; 0.001) and tau (β = 0.46, p &lt; 0.001) correlated with age. There were no differences in biomarker concentrations by phenotype or severity, except for higher NfL and p‐NfH in full phenotype, compared to prodromal disease and asymptomatic carriers. Low neurogranin (β = ‐0.39, p &lt; 0.001), low p‐tau (β = ‐0.33, p &lt; 0.001) and high NfL (β = 0.42, p &lt; 0.001) correlated with worse baseline disease severity measured by the CDR® Dementia Staging Instrument plus behavior and language domains from the National Alzheimer’s Disease Coordinating Center FTLD module sum of boxes (CDR®+NACC‐FTLDsb), and with other measures of global cognition, instrumental and daily function, and frontal and temporal brain volumes. Regardless of genotype, the predicted annualized rate of CDR®+NACC‐FTLDsb score worsenings per higher baseline CSF biomarker Log pg/mL were tau: 3.0 ± 0.2, NfL: 2.8 ± 0.2 and p‐NfH: 2.8 ± 0.2. High tau, NfL and p‐NfH also predicted worsening in other measures of global cognition and instrumental and daily function. Neurogranin and p‐tau did not predict clinical decline.ConclusionCSF tau, p‐tau, neurogranin, NfL and p‐NfH reflect important aspects of disease severity in fFTLD. In contrast to Alzheimer’s disease, low p‐tau and neurogranin are inversely related to clinical severity, which suggests a distinctive pathophysiological process and has implications for therapeutic development. CSF NfL, p‐NfH and tau have strong prognostic value in fFTLD.