C9orf72 Mutation Research Articles

Meta-analysis of human and mouse ALS astrocytes reveals multi-omic signatures of inflammatory reactive states.

Astrocytes contribute to motor neuron death in amyotrophic lateral sclerosis (ALS), but whether they adopt deleterious features consistent with inflammatory reactive states remains incompletely resolved. To identify inflammatory reactive features in ALS human induced pluripotent stem cell (hiPSC)–derived astrocytes, we examined transcriptomics, proteomics, and glutamate uptake in VCP-mutant astrocytes. We complemented this by examining other ALS mutations and models using a systematic meta-analysis of all publicly-available ALS astrocyte sequencing data, which included hiPSC-derived astrocytes carrying SOD1, C9orf72, and FUS gene mutations as well as mouse ALS astrocyte models with SOD1G93A mutation, Tardbp deletion, and Tmem259 (also known as membralin) deletion. ALS astrocytes were characterized by up-regulation of genes involved in the extracellular matrix, endoplasmic reticulum stress, and the immune response and down-regulation of synaptic integrity, glutamate uptake, and other neuronal support processes. We identify activation of the TGFB, Wnt, and hypoxia signaling pathways in both hiPSC and mouse ALS astrocytes. ALS changes positively correlate with TNF, IL1A, and complement pathway component C1q-treated inflammatory reactive astrocytes, with significant overlap of differentially expressed genes. By contrasting ALS changes with models of protective reactive astrocytes, including middle cerebral artery occlusion and spinal cord injury, we uncover a cluster of genes changing in opposing directions, which may represent down-regulated homeostatic genes and up-regulated deleterious genes in ALS astrocytes. These observations indicate that ALS astrocytes augment inflammatory processes while concomitantly suppressing neuronal supporting mechanisms, thus resembling inflammatory reactive states and offering potential therapeutic targets.

Suppression of mutant C9orf72 expression by a potent mixed backbone antisense oligonucleotide.

Expansions of a G4C2 repeat in the C9ORF72 gene are the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), two devastating adult-onset neurodegenerative disorders. Using C9-ALS/FTD patient-derived cells and C9ORF72 BAC transgenic mice, we generated and optimized antisense oligonucleotides (ASOs) that selectively blunt expression of G4C2 repeat-containing transcripts and effectively suppress tissue levels of poly(GP) dipeptides. ASOs with reduced phosphorothioate content showed improved tolerability without sacrificing efficacy. In a single patient harboring mutant C9ORF72 with the G4C2 repeat expansion, repeated dosing by intrathecal delivery of the optimal ASO was well tolerated, leading to significant reductions in levels of cerebrospinal fluid poly(GP). This report provides insight into the effect of nucleic acid chemistry on toxicity and, to our knowledge, for the first time demonstrates the feasibility of clinical suppression of the C9ORF72 gene. Additional clinical trials will be required to demonstrate safety and efficacy of this therapy in patients with C9ORF72 gene mutations.

Emerging Mechanisms Underpinning Neurophysiological Impairments in C9ORF72 Repeat Expansion-Mediated Amyotrophic Lateral Sclerosis/Frontotemporal Dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are characterized by degeneration of upper and lower motor neurons and neurons of the prefrontal cortex. The emergence of the C9ORF72 hexanucleotide repeat expansion mutation as the leading genetic cause of ALS and FTD has led to a progressive understanding of the multiple cellular pathways leading to neuronal degeneration. Disturbances in neuronal function represent a major subset of these mechanisms and because such functional perturbations precede degeneration, it is likely that impaired neuronal function in ALS/FTD plays an active role in pathogenesis. This is supported by the fact that ALS/FTD patients consistently present with neurophysiological impairments prior to any apparent degeneration. In this review we summarize how the discovery of the C9ORF72 repeat expansion mutation has contributed to the current understanding of neuronal dysfunction in ALS/FTD. Here, we discuss the impact of the repeat expansion on neuronal function in relation to intrinsic excitability, synaptic, network and ion channel properties, highlighting evidence of conserved and divergent pathophysiological impacts between cortical and motor neurons and the influence of non-neuronal cells. We further highlight the emerging association between these dysfunctional properties with molecular mechanisms of the C9ORF72 mutation that appear to include roles for both, haploinsufficiency of the C9ORF72 protein and aberrantly generated dipeptide repeat protein species. Finally, we suggest that relating key pathological observations in C9ORF72 repeat expansion ALS/FTD patients to the mechanistic impact of the C9ORF72 repeat expansion on neuronal function will lead to an improved understanding of how neurophysiological dysfunction impacts upon pathogenesis.

Concurrent tau pathologies in frontotemporal lobar degeneration with TDP-43 pathology.

AimsAccumulating evidence suggests that patients with frontotemporal lobar degeneration (FTLD) can have pathologic accumulation of multiple proteins, including tau and TDP‐43. This study aimed to determine the frequency and characteristics of concurrent tau pathology in FTLD with TDP‐43 pathology (FTLD‐TDP).MethodsThe study included 146 autopsy‐confirmed cases of FTLD‐TDP and 55 cases of FTLD‐TDP with motor neuron disease (FTLD‐MND). Sections from the basal forebrain were screened for tau pathology with phosphorylated‐tau immunohistochemistry. For cases with tau pathology on the screening section, additional brain sections were studied to establish a diagnosis. Genetic analysis of C9orf72, GRN and MAPT was performed on select cases.ResultsWe found 72 cases (36%) with primary age‐related tauopathy (PART), 85 (42%) with ageing‐related tau astrogliopathy (ARTAG), 45 (22%) with argyrophilic grain disease (AGD) and 2 cases (1%) with corticobasal degeneration (CBD). Patients with ARTAG or AGD were significantly older than those without these comorbidities. One of the patients with FTLD‐TDP and CBD had C9orf72 mutation and relatively mild tau pathology, consistent with incidental CBD.ConclusionThe coexistence of TDP‐43 and tau pathologies was relatively common, particularly PART and ARTAG. Although rare, patients with FTLD can have multiple neurodegenerative proteinopathies. The absence of TDP‐43‐positive astrocytic plaques may suggest that CBD and FTLD‐TDP were independent disease processes in the two patients with both tau and TDP‐43 pathologies. It remains to be determined if mixed cases represent a unique disease process or two concurrent disease processes in an individual.

Differential synaptic marker involvement in the different genetic forms of frontotemporal dementia

AbstractBackgroundApproximately a third of frontotemporal dementia (FTD) is genetic with mutations in three genes accounting for the majority of the inheritance: C9orf72, GRN and MAPT. Synaptic dysfunction is a common mechanism in all of them and the use of fluid biomarkers could be helpful to improve the diagnostic accuracy and useful as a readout of cellular dysfunction within therapeutic trials.MethodA total of 193 cerebrospinal fluid samples from the GENetic FTD Initiative including 77 presymptomatic (31 C9orf72, 23 GRN, 23 MAPT), 55 symptomatic mutation carriers (26 C9orf72, 17 GRN, 12 MAPT) and 61 mutation‐negative controls were measured using a microflow LC PRM‐MS set‐up targeting 15 synaptic proteins: 14‐3‐3 proteins (eta, zeta/delta and epsilon), AP‐2 complex subunit beta, beta‐synuclein, gamma‐synuclein, complexin‐2, neurogranin, neuronal pentraxin receptor (NPTXR), neuronal pentraxin 1 (NPTX1), neuronal pentraxin 2 (NPTX2), phosphatidylethanolamine‐binding protein 1 (PEBP‐1), rab GDP dissociation inhibitor α (rab GDIα), syntaxin‐1B and syntaxin‐7. Mutation carrier groups were compared to each other and to controls using a bootstrapped linear regression model, adjusting for age and sex.ResultEight proteins were increased only in symptomatic MAPT mutation carriers (compared with controls) and not in symptomatic C9orf72 or GRN mutation carriers: 14‐3‐3‐eta, beta‐synuclein, gamma‐synuclein, neurogranin, PEBP‐1, rab GDIα, syntaxin‐1B and syntaxin‐7. In contrast, NPTX1 and NPTX2 were affected in all three genetic groups (decreased compared to controls), with NPTXR being affected in C9orf72 and GRN mutation carriers only (decreased compared to controls). No changes were seen in presymptomatic mutation carriers in these proteins. Figure 1 contains p‐values for all significant changes.ConclusionDifferential involvement of synaptic markers is seen in the genetic forms of FTD, with impairment particularly in those with MAPT mutations, with only the neuronal pentraxins affected in GRN and C9orf72 mutation carriers. Further work is needed to explore correlations with clinical and imaging biomarkers, whether there are changes in the late presymptomatic period, and how these markers change over time.

A cognitive composite for genetic frontotemporal dementia: GENFI‐cog

AbstractBackgroundDevelopment of endpoints for clinical trials in frontotemporal dementia (FTD) is increasingly urgent. In other neurodegenerative diseases composite scores are often used as outcome measures but are, as of yet, lacking in FTD. The aim of this study was to create gene‐specific cognitive composite scores for MAPT, GRN and C9orf72 mutation carriers and provide recommendations on recruitment and trial duration.Method69 C9orf72, 41 GRN, 28 MAPT mutation carriers with a CDR® plus NACC‐FTLD global score ≥0.5 and 275 controls completed a neuropsychological battery covering five cognitive domains. Logistic regression was used to identify the combination of tests that discriminated best between mutation carrier groups and controls. Weighted averages of the test scores in the models were calculated based on the regression coefficients (GENFI‐cog). Sample size estimates were calculated for individual tests and composite. The treatment effect was estimated as the mean difference between CDR® plus NACC‐FTLD 0.5 and 1 groups. Time‐to‐event analysis was used to determine the fraction of patients within GENFI that converted from CDR® plus NACC‐FTLD 0.5 to ≥1.ResultThe most sensitive model in C9orf72 mutation carriers included a combination of executive, social cognitive and visuoconstructive tests (Table 1). A combination of executive, social cognitive, semantic and memory tests was most sensitive in GRN mutation carriers, and a combination of social cognitive, attention, semantic and memory tests in MAPT mutation carriers, resulted in the most sensitive model. The estimated sample size to detect a treatment effect was lower for the composite than for most individual tests (Table 2). A Kaplan‐Meier curve (Figure 1) showed that after three years 50% of individuals convert from CDR® plus NACC‐FTLD global score 0.5 to 1 or more.ConclusionWe created gene‐specific cognitive composite scores for C9orf72, GRN and MAPT mutation carriers (GENFI‐cog) which resulted in substantially lower estimated sample sizes to detect a treatment effect than most individual cognitive tests. Only 50% of patients with a CDR® plus NACC‐FTLD of 0.5 convert to ≥1 in a three‐year period. GENFI‐cog has potential as a cognitive endpoint for upcoming trials and the results from this study provide important information concerning trial duration and sample sizes.

Early detection of neuropsychiatric, language and motor symptoms in genetic frontotemporal dementia (FTD): Defining prodromal FTD

AbstractBackgroundThe prodromal stage of genetic frontotemporal dementia (FTD) is currently poorly defined. Whilst the majority of people with genetic FTD develop behavioural symptoms, a number of people present with primary progressive aphasia (PPA), neuropsychiatric symptoms, parkinsonism, including corticobasal syndrome (CBS) or progressive supranuclear palsy (PSP), or amyotrophic lateral sclerosis (ALS). Such variable phenotypes pose a barrier to clearer definitions of prodromal FTD.Methods1139 people have been recruited to the Genetic FTD Initiative (GENFI), a deep phenotyping international multicentre cohort study of FTD. Clinical data on symptoms within the language, neuropsychiatric and motor domains have been collected on presymptomatic and symptomatic mutation carriers, as well as mutation‐negative controls using the GENFI Symptom Scales.Results Language: In the symptomatic phase, 19 participants met Gorno‐Tempini diagnostic criteria for primary progressive aphasia (PPA), the majority (17) of whom had a progranulin (GRN) mutation. The phenotype in these cases was either nonfluent variant (8) or did not meet criteria for a specific variant (9). Additionally, 42 presymptomatic participants had subtle early language problems. Neuropsychiatric: Symptoms were reported most frequently in symptomatic C9orf72 mutation carriers (91.7% of all symptomatic C9orf72 carriers) and to a lesser extent in GRN and MAPT mutation carriers. Depression and anxiety were common in mutation‐negative controls (14%) as well as mutation carriers. Motor: ALS and FTD‐ALS were most frequent in C9orf72‐associated FTD (12.5% of all symptomatic C9orf72 carriers). Parkinsonism (including PSP and CBS) was present to a lesser extent in C9orf72, GRN, and MAPT mutation carriers.ConclusionsLanguage, neuropsychiatric and motor features are common in genetic FTD and will need to be included in any prodromal staging system. Improved, operationalised measurement of such symptoms will allow improved stratification of individuals, and aid clinical trials. Future work should unravel the temporal trajectory of such symptoms within each form of genetic FTD.

TDP‐43 proteinopathy in the retina of patients with frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a clinically and pathologically heterogeneous disease. The distinct underlying pathologies include aggregation of TDP-43, tau and FUS. Currently, no ante-mortem biomarkers are available to distinguish between the different pathological subtypes, providing challenges for diagnosis and therapeutic interventions. As an extension of the brain, the retina displays similarities in terms of anatomy and functionality. The accessibility of the retina provides a 'window' into the brain and a great potential for noninvasive imaging of neurodegenerative changes in patients. The aim of this study is to assess the presence of TDP-43 in the retina.Post-mortem retina tissue was obtained from donors with FTLD-TDP (n=6), of which 3 donors carried a C9orf72 repeat expansion, one progranulin (PRGN) mutation and two sporadic donors. We also included donors with FTLD-tau (n=5), FTLD-FUS (n=1) , AD with limbic TDP-43 depositions (n=2), and donors with ALS-TDP (n=2). Immunohistochemical stainings were performed for panTDP-43, phosphorylated TDP-43 (pTDP-43), p62, and dipeptides (polyGA and polyGP).In C9orf72 and PRGN mutation carriers, as well as one sporadic FTLD-TDP donor, TDP-43 inclusions were observed in the outer plexiform layer of the retina. One sporadic donor showed granular TDP-43 deposits in amacrine cells. No TDP-43 inclusions were observed in FTLD-tau, ALS and AD donors. Interestingly, all C9orf72 mutation carriers showed abundant presence of p62 and dipeptide inclusions in the inner nuclear layer of the retina.Manifestations of TDP-43 and dipeptide pathology are present in the retina of patients with FTLD-TDP. No TDP-43 inclusions are present in the retina of ALS or AD patients with limbic TDP-43 pathology, suggesting that retinal TDP-43 pathology is specific for FTLD-TDP. With the advances in ocular imaging techniques these findings provide opportunities for non-invasive retinal imaging for diagnosis and monitoring progression of FTLD-TDP.

Dual pathogenic mutations in SQSTM1 and C9orf72 as a cause of frontotemporal dementia

AbstractBackgroundHexanucleotide repeat expansions in the C9orf72 gene have been found to be the leading genetic cause of both familial frontotemporal dementia (FTD) and motor neuron disease (MND). However there are a number of other genetic causes of both FTD and MND including, less commonly, mutations in sequestosome 1 (SQSTM1) which codes for the cargo protein p62. Occasionally, people with FTD or MND have been described with dual pathogenic mutations, although this is rare.MethodWe describe the clinical and imaging features of a woman who presented with FTD and motor neurone involvement who was found to carry both a pathogenic C9orf72 expansion and a deleterious c.1185dup, p.Glu396* heterozygous SQSTM1 mutation.ResultSymptoms started at the age of 60 with change in personality and impaired behaviour followed at the age of 63 by prosopagnosia and semantic impairment. Brain magnetic resonance imaging showed right‐sided predominant temporal more than frontal lobe atrophy, and she was initially diagnosed with behavioural variant FTD. However at the age of 66 she developed asymmetrical limb weakness and stiffness, with upper motor neurone features only on examination, suggestive of primary lateral sclerosis (PLS). She deteriorated rapidly over the next couple of years, although never developed lower motor neurone features when subsequently examined. She died at the age of 69.ConclusionThe co‐presence of both a SQSTM1 mutation and C9orf72 expansion is rare. It remains unclear which mutation accounts for which of the features seen. Focal right temporal lobe atrophy is more common with SQSTM1 mutations, but PLS is uncommon with both mutations. It may be therefore that it is the dual mutations together that explain the altered phenotype. It is paramount to better understand the roles which SQSTM1 and C9orf72 mutations have on cellular pathways and how their combination results in rare phenotypes.

A data‐driven disease progression model of fluid biomarkers in genetic FTD

AbstractBackgroundSeveral fluid biomarkers for genetic frontotemporal dementia (FTD) have been proposed, including those reflecting neuroaxonal loss (neurofilament light chain (NfL) and phosphorylated neurofilament heavy chain (pNfH)), synapse dysfunction (neuronal pentraxin 2 (NPTX2)), gliosis (glial fibrillary acidic protein (GFAP)) and complement activation (C3b, C1q). Determining the sequence in which biomarkers become abnormal over the course of disease could facilitate disease staging in FTD and enable us to identify mutation carriers with prodromal or early‐stage FTD, which is especially important as pharmaceutical interventions emerge. We aimed to model the sequence of biomarker abnormalities in presymptomatic and symptomatic genetic FTD using cross‐sectional data from the Genetic Frontotemporal dementia Initiative (GENFI).Method276 presymptomatic and 142 symptomatic carriers of mutations in GRN, C9orf72 or MAPT, as well as 247 non‐carriers, were selected from the GENFI cohort based on availability of one or more of the aforementioned biomarkers. Nine presymptomatic carriers developed symptoms within 18 months of data collection (‘converters’). Sequences of biomarker abnormalities were modelled for the entire group using discriminative event‐based modelling (DEBM) and for each genetic subgroup using co‐initialized DEBM. These models estimate probabilistic biomarker abnormalities in a data‐driven way and do not rely on prior diagnostic information or biomarker cut‐off points. We estimated individual disease severity scores based on the position of subjects along the disease progression timeline through cross‐validation.ResultCerebrospinal fluid (CSF) NPTX2 was the first detectable abnormal biomarker, followed by blood and CSF NfL, blood GFAP, blood pNfH and finally CSF C1q and C3b (Fig. 1). Biomarker orderings did not differ significantly between genetic subgroups. Estimated disease severity scores (Fig. 2) could distinguish symptomatic from presymptomatic carriers and non‐carriers with areas under the curve (AUC) of 0.84 and 0.90 respectively. The AUC to distinguish converters from non‐converting presymptomatic carriers was 0.85.ConclusionIn our data‐driven disease progression models of genetic FTD, NPTX2 and NfL were the first biomarkers to become abnormal. Further research should focus on their utility as candidate selection tools for pharmaceutical trials. Estimating disease stages using DEBM could enable us to identify presymptomatic carriers approaching symptom onset and track the efficacy of therapeutic interventions.

18F]RO948 tau PET in bvFTD due to C9orf72 and GRN mutations

AbstractBackgroundThe behavioral variant of frontotemporal dementia (bvFTD) is characterized by marked changes in personality and behaviour. Approximately 30% of cases are genetic in nature and most commonly due to autosomal dominant mutations in the chromosome 9 open reading frame 72 (C9orf72) and progranulin (GRN) genes resulting in TAR DNA‐binding protein 43 (TDP‐43) pathology. Several tau positron emission tomography (PET) studies using [18F]flortaucipir have shown conflicting results regarding tracer retention in bvFTD due to C9orf72 (bvFTD‐C9orf72) and GRN (bvFTD‐GRN) mutations. To date, no studies in bvFTD due to either mutation have been conducted using the novel tau tracer [18F]RO948.MethodEight patients meeting criteria for definite bvFTD were included from the Swedish BioFINDER‐2 study, including seven C9orf72 expansion carriers and one with a GRN mutation. Standardized uptake value ratio (SUVR) images of [18F]RO948 PET were created using 70‐90 post‐injection data and the inferior cerebellar cortex as reference region. Age and sex matched CU individuals (n=9) and patients with Alzheimer’s disease (AD) dementia (n=9) were included for comparison. [18F]RO948 retention in bvFTD mutation carriers was also assessed relative to a larger Aβ‐negative CU group (n=50) using age‐adjusted voxelwise t‐tests.ResultBvFTD‐C9orf72 patients were on average 63 years of age (range 53‐72) and 57% were female. The bvFTD‐GRN patient was a 69‐year‐old male. Comparison of SUVR images showed that [18F]RO948 retention levels in bvFTD mutation carriers were similar to those seen in Aβ‐negative CU individuals (Figure 1). Voxelwise t‐tests showed no significant differences in comparison to the Aβ‐negative CU group. Similar findings were seen using a composite frontal region of interest (ROI) and when using the brainstem as reference instead of the inferior cerebellar cortex.ConclusionThese preliminary findings suggest that [18F]RO948 signal is specific for AD‐type tau and does not capture TDP‐43 type pathology.

The Cambridge Behavioural Inventory (revised) detects early behavioural and functional impairment in genetic frontotemporal dementia within the GENFI cohort

AbstractBackgroundBehavioural dysfunction is a key feature of genetic frontotemporal dementia (FTD) but validated clinical scales measuring behaviour are lacking at present.MethodWe assessed behaviour using the revised version of the Cambridge Behavioural Inventory (CBI‐R) in 733 participants from the Genetic FTD Initiative study: 466 mutation carriers (195 C9orf72, 76 MAPT, 195 GRN) and 267 non‐mutation carriers (healthy controls). All mutation carriers were stratified according to their CDR® plus NACC FTLD into three groups: asymptomatic (CDR=0), mildly symptomatic (CDR=0.5) and fully symptomatic (CDR=1+). CBI‐R total scores were compared between mutation carrier groups using a mixed effects model that adjusted for age, education, sex and family clustering, with 95% bootstrapped confidence intervals with 2000 repetitions to adjust for non‐normally distributed data. We used the same mixed effects model to run a within‐group analysis between the 10 CBI‐R domains in CDR 1+ groups. Spearman rank correlations were run to assess the relationship of the CDR® plus NACC FTLD SOB and FRS scale with the CBI‐R total in CDR 1+ mutation carrier groups.ResultCBI‐R total scores were significantly higher in all CDR 1+ mutation carrier groups compared to controls (C9orf72 mean 70.5 (standard deviation 27.8), GRN 56.2 (33.5), MAPT 62.1 (36.9)), as well as their respective CDR 0.5 groups (C9orf72 13.5 (14.4), GRN 13.3 (13.5), MAPT 9.4 (10.4)) and CDR 0 groups (C9orf72 6.0 (7.9), GRN 3.6 (6.0), MAPT 8.5 (13.3)). Both C9orf72 and GRN 0.5 groups scored significantly higher than controls and their respective CDR 0 groups. Motivation and Memory were the highest scoring domains in both C9orf72 and GRN CDR 1+ groups, and in the MAPT group it was Stereotypic Behaviour and Memory. There was a positive correlation between the CBI‐R scores and the CDR® plus NACC FTLD SOB scores in all mutation carrier groups (C9orf72: rho= 0.8, p<0.001, GRN: rho= 0.8, p<0.001, MAPT: rho= 0.6, p<0.001), and a negative correlation between CBI‐R scores and FTD Rating Scale (FRS) scores (C9orf72; rho= ‐0.9, p<0.001, GRN; rho= ‐0.9, p<0.001, MAPT; rho= ‐0.9, p<0.001).ConclusionThe CBI‐R detects early behavioural change in genetic FTD, particularly in those with C9orf72 and GRN mutations.

The Boston Naming Test identifies presymptomatic anomia in MAPT mutation carriers

AbstractBackgroundPrior studies of prodromal genetic frontotemporal dementia (FTD) have identified impaired executive function and social cognition in C9orf72 and GRN mutation carriers but few cognitive deficits have been found in MAPT mutation carriers.MethodWe investigated performance on the Boston Naming Test (BNT) in the GENetic Frontotemporal dementia Initiative (GENFI) cohort of 499 mutation carriers and 248 mutation negative controls divided across three genetic groups: C9orf72, MAPT and GRN. Mutation carriers were further divided into 3 groups according to their global CDR plus NACC FTLD score: 0 (asymptomatic), 0.5 (prodromal) and 1+ (fully symptomatic). Mutation carrier groups were compared to each other and to mutation‐negative controls using a bootstrapped linear regression model, adjusting for age and education.ResultWe found that all of the symptomatic (1+) groups performed significantly worse on the BNT than controls, and worse than the prodromal and asymptomatic mutation carriers within the same genetic group. The MAPT symptomatic group also performed significantly worse than the GRN and C9orf72 symptomatic groups. Furthermore, both the MAPT asymptomatic and prodromal groups performed significantly worse than controls which was not the case in the other genetic groups.ConclusionThese results suggest a specific deficit in naming in MAPT mutation carriers consistent with previous literature, likely to be due to impaired semantic knowledge. Notably, this study shows that the BNT can be used to detect very early deficits in the disease course, allowing dissociation of MAPT mutation carriers from controls and from other genetic groups. Clinical trials focused on the prodromal period within individuals with MAPT mutations should use language tasks such as the BNT for patient stratification and as outcome measures.

Brain MRI signatures of atrophy in genetic frontotemporal lobar degeneration

AbstractBackgroundGenetic heterogeneity underlying different clinical presentations of the frontotemporal lobar degeneration (FTLD) spectrum hampers the identification of useful biomarkers that may be able to monitor disease progression and/or facilitate the enrolment in clinical trials. The aim of this study was to assess cortical, subcortical and cerebellar grey matter (GM) atrophy using magnetic resonance imaging (MRI) in patients affected by disorders of the FTLD spectrum with known genetic mutations.MethodSixty‐six patients carrying FTLD‐related mutations were enrolled, including 44 with pure motor neuron disease (MND) and 22 with frontotemporal dementia (FTD). Sixty‐one patients with sporadic FTLD (sFTLD) matched for age, sex and disease severity with genetic FTLD (gFTLD) were also included, as well as 52 healthy controls (HC). A whole‐brain voxel‐based morphometry (VBM) analysis was performed. GM volumes of subcortical and cerebellar structures were also obtained.ResultCompared with HC, GM volume loss on VBM was generally greater and more diffuse in genetic FTD (gFTD) cases, followed by sporadic FTD (sFTD) cases and genetic MND (gMND) cases, whereas sporadic MND (sMND) showed very focal atrophy of the motor cortex. Patients carrying GRN and C9ORF72 mutations showed the most widespread cortical volume loss, whereas SOD1 and TARDBP patients were the least atrophic. Greater atrophy of the parietal cortices and thalami was found, globally, in genetic FTLD patients compared with sporadic FTLD and, particularly, in C9‐MND patients compared with sMND. When assessing deep GM volumes, genetic FTLD patients showed significant volume loss compared with sporadic FTLD in the caudate nuclei and thalami. In particular, greater atrophy of the left caudate and right thalamus was found in C9MND compared with sMND. At the cerebellar level, greater atrophy of the right lobule VIIb could discriminate genetic FTLD from sporadic FTLD patients.ConclusionOur data suggest that measures of deep GM and cerebellar involvement might be useful markers of genetic FTLD, particularly C9ORF72‐related disorders, regardless of the clinical presentation within the FTLD spectrum.Supported by: Italian Ministry of Health (RF‐2011‐02351193; GR‐2011‐02351217) and European Research Council (StG‐2016_714388_NeuroTRACK).

Progression of neuropsychiatric symptoms in pre‐dementia GRN and C9orf72 mutation carriers

AbstractBackgroundNeuropsychiatric symptoms (NPS) are common in frontotemporal dementia (FTD) patients and may precede the clinical diagnosis of dementia. We hypothesized that GRN and C9orf72 mutation carriers have increased baseline burden and rates of progression of NPS compared to non‐carriers prior to the onset of dementia. To investigate, we examined a longitudinal cohort of FTD mutation carriers and non‐carrier family members.MethodWe analyzed data from 80 participants (21 C9orf72+ mutation carriers, 10 GRN+ mutation carriers, and 49 non‐carrier family members (NCs); mean±SD age in years: 47±13, 51±9, and 54±13 respectively) recruited through the University of British Columbia FTD Study. NPS were assessed annually with Neuropsychiatric Inventory (NPI), Frontal Behavioural Inventory (FBI) and Iowa Scale of Personality Change (ISPC) with a mean follow‐up of 5.8 years. For ISPC, we used both the “Change” (“Now” minus “Before”) and the “Now” measures. If a participant developed FTD during the follow‐up (N=2), we only analyzed observations collected before the conversion. We initially compared the baseline burden of NPI, FBI and ISPC adjusted for age and sex, among C9orf72+ carriers, GRN+ carriers and NCs. We then used random‐intercept mixed models to compare the rates of progression of NPS among genetic groups using total NPI, FBI, ISPC change and ISPC now scores as outcome measures and genetic status, sex, respective baseline scores, expected years to onset (EYO) and genetic group*EYO interaction term as dependent variables.ResultThere were no significant group differences in baseline demographic features or neuropsychiatric measures. In longitudinal assessments, NCs demonstrated minimal change in NPS measures. GRN+ carriers had significantly higher progression rates of NPI (p<0.0001) and ISPC “Now” (p=0.0004) compared to NCs. However, there were no significant differences in the NPS progression rates between C9orf72+ carriers and NCs.ConclusionAlthough there was no baseline difference in the burden of NPS among the genetic groups, GRN+ carriers had a faster progression of NPS compared to NCs prior to the onset of dementia. Future work is warranted to investigate the potential association between the NPS trajectories and structural/functional brain changes in FTD mutation carriers.

Stratifying the Presymptomatic Phase of Genetic Frontotemporal Dementia by Serum NfL and pNfH: A Longitudinal Multicentre Study.

Although the presymptomatic stages of frontotemporal dementia (FTD) provide a unique chance to delay or even prevent neurodegeneration by early intervention, they remain poorly defined. Leveraging a large multicenter cohort of genetic FTD mutation carriers, we provide a biomarker-based stratification and biomarker cascade of the likely most treatment-relevant stage within the presymptomatic phase: the conversion stage. We longitudinally assessed serum levels of neurofilament light (NfL) and phosphorylated neurofilament heavy (pNfH) in the Genetic FTD Initiative (GENFI) cohort (n=444), using single-molecule array technique. Subjects comprised 91 symptomatic and 179 presymptomatic subjects with mutations in the FTD genes C9orf72, GRN, or MAPT, and 174 mutation-negative within-family controls. In a biomarker cascade, NfL increase preceded the hypothetical clinical onset by 15 years and concurred with brain atrophy onset, whereas pNfH increase started close to clinical onset. The conversion stage was marked by increased NfL, but still normal pNfH levels, while both were increased at the symptomatic stage. Intra-individual change rates were increased for NfL at the conversion stage and for pNfH at the symptomatic stage, highlighting their respective potential as stage-dependent dynamic biomarkers within the biomarker cascade. Increased NfL levels and NfL change rates allowed identification of presymptomatic subjects converting to symptomatic disease and capture of proximity-to-onset. We estimate stage-dependent sample sizes for trials aiming to decrease neurofilament levels or change rates. Blood NfL and pNfH provide dynamic stage-dependent stratification and, potentially, treatment response biomarkers in presymptomatic FTD, allowing demarcation of the conversion stage. The proposed biomarker cascade might pave the way towards a biomarker-based precision medicine approach to genetic FTD. ANN NEUROL 2022;91:33-47.

A panel of CSF proteins separates genetic frontotemporal dementia from presymptomatic mutation carriers: a GENFI study

BackgroundA detailed understanding of the pathological processes involved in genetic frontotemporal dementia is critical in order to provide the patients with an optimal future treatment. Protein levels in CSF have the potential to reflect different pathophysiological processes in the brain. We aimed to identify and evaluate panels of CSF proteins with potential to separate symptomatic individuals from individuals without clinical symptoms (unaffected), as well as presymptomatic individuals from mutation non-carriers.MethodsA multiplexed antibody-based suspension bead array was used to analyse levels of 111 proteins in CSF samples from 221 individuals from families with genetic frontotemporal dementia. The data was explored using LASSO and Random forest.ResultsWhen comparing affected individuals with unaffected individuals, 14 proteins were identified as potentially important for the separation. Among these, four were identified as most important, namely neurofilament medium polypeptide (NEFM), neuronal pentraxin 2 (NPTX2), neurosecretory protein VGF (VGF) and aquaporin 4 (AQP4). The combined profile of these four proteins successfully separated the two groups, with higher levels of NEFM and AQP4 and lower levels of NPTX2 in affected compared to unaffected individuals. VGF contributed to the models, but the levels were not significantly lower in affected individuals. Next, when comparing presymptomatic GRN and C9orf72 mutation carriers in proximity to symptom onset with mutation non-carriers, six proteins were identified with a potential to contribute to a separation, including progranulin (GRN).ConclusionIn conclusion, we have identified several proteins with the combined potential to separate affected individuals from unaffected individuals, as well as proteins with potential to contribute to the separation between presymptomatic individuals and mutation non-carriers. Further studies are needed to continue the investigation of these proteins and their potential association to the pathophysiological mechanisms in genetic FTD.

Proteostasis deregulation as a driver of C9ORF72 pathogenesis.

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two related neurodegenerative disorders that display overlapping features. The hexanucleotide repeat expansion GGGGCC (G4 C2 ) in C9ORF72gene has been causally linked to both ALS and FTD emergence, thus opening a novel potential therapeutic target for disease intervention. The main driver of C9ORF72 pathology is the disruption of distinct cellular processes involved in the function of the proteostasis network. Here we discuss main findings relating to the induction of neurodegeneration by C9ORF72mutation and proteostasis deregulation, highlighting the role of the endoplasmic reticulum stress, nuclear transport, and autophagy in the disease process. We further discuss possible points of intervention to target proteostasis mediators to treat C9ORF72-linked ALS/FTD.

Transcriptomic and Network Meta-Analysis of Frontotemporal Dementias.

Frontotemporal lobar degeneration (FTLD), also known as frontotemporal dementia (FTD), results in a progressive decline in executive function, leading to behavioral changes, speech problems, and movement disorders. FTD is the second most common cause of young-onset dementia affecting approximately 50–60,000 Americans. FTD exists in familial and sporadic forms, with GRN progranulin and C9orf72 mutations being the most common causes. In this study, we compared the sporadic and familial transcriptome within the cerebellum, frontal cortex, hippocampus, and Brodmann’s area 8 of patients with FTD to determine genes and pathways involved in the disease process. Most dysregulated genes expression occurred in the frontal cortex and Brodmann’s area 8 for genetic and sporadic forms of FTD, respectively. A meta-analysis revealed 50 genes and 95 genes are dysregulated in at least three brain regions in patients with familial mutations and sporadic FTD patients, respectively. Familial FTD genes centered on the Wnt signaling pathway, whereas genes associated with the sporadic form of FTD centered on MAPK signaling. The results reveal the similarities and differences between sporadic and familial FTD. In addition, valproic acid and additional therapeutic agents may be beneficial in treating patients with FTD.

A data-driven disease progression model of fluid biomarkers in genetic frontotemporal dementia.

Several CSF and blood biomarkers for genetic frontotemporal dementia have been proposed, including those reflecting neuroaxonal loss (neurofilament light chain and phosphorylated neurofilament heavy chain), synapse dysfunction [neuronal pentraxin 2 (NPTX2)], astrogliosis (glial fibrillary acidic protein) and complement activation (C1q, C3b). Determining the sequence in which biomarkers become abnormal over the course of disease could facilitate disease staging and help identify mutation carriers with prodromal or early-stage frontotemporal dementia, which is especially important as pharmaceutical trials emerge. We aimed to model the sequence of biomarker abnormalities in presymptomatic and symptomatic genetic frontotemporal dementia using cross-sectional data from the Genetic Frontotemporal dementia Initiative (GENFI), a longitudinal cohort study.Two-hundred and seventy-five presymptomatic and 127 symptomatic carriers of mutations in GRN, C9orf72 or MAPT, as well as 247 non-carriers, were selected from the GENFI cohort based on availability of one or more of the aforementioned biomarkers. Nine presymptomatic carriers developed symptoms within 18 months of sample collection (‘converters’). Sequences of biomarker abnormalities were modelled for the entire group using discriminative event-based modelling (DEBM) and for each genetic subgroup using co-initialized DEBM. These models estimate probabilistic biomarker abnormalities in a data-driven way and do not rely on previous diagnostic information or biomarker cut-off points. Using cross-validation, subjects were subsequently assigned a disease stage based on their position along the disease progression timeline.CSF NPTX2 was the first biomarker to become abnormal, followed by blood and CSF neurofilament light chain, blood phosphorylated neurofilament heavy chain, blood glial fibrillary acidic protein and finally CSF C3b and C1q. Biomarker orderings did not differ significantly between genetic subgroups, but more uncertainty was noted in the C9orf72 and MAPT groups than for GRN. Estimated disease stages could distinguish symptomatic from presymptomatic carriers and non-carriers with areas under the curve of 0.84 (95% confidence interval 0.80–0.89) and 0.90 (0.86–0.94) respectively. The areas under the curve to distinguish converters from non-converting presymptomatic carriers was 0.85 (0.75–0.95).Our data-driven model of genetic frontotemporal dementia revealed that NPTX2 and neurofilament light chain are the earliest to change among the selected biomarkers. Further research should investigate their utility as candidate selection tools for pharmaceutical trials. The model’s ability to accurately estimate individual disease stages could improve patient stratification and track the efficacy of therapeutic interventions.