Background Frontotemporal dementia is a heterogenous neurodegenerative disorder, with about a third of cases being genetic. Most of this genetic component is accounted for by mutations in GRN, MAPT, and C9orf72. In this study, we aimed to complement previous phenotypic studies by doing an international study of age at symptom onset, age at death, and disease duration in individuals with mutations in GRN, MAPT, and C9orf72. Methods In this international, retrospective cohort study, we collected data on age at symptom onset, age at death, and disease duration for patients with pathogenic mutations in the GRN and MAPT genes and pathological expansions in the C9orf72 gene through the Frontotemporal Dementia Prevention Initiative and from published papers. We used mixed effects models to explore differences in age at onset, age at death, and disease duration between genetic groups and individual mutations. We also assessed correlations between the age at onset and at death of each individual and the age at onset and at death of their parents and the mean age at onset and at death of their family members. Lastly, we used mixed effects models to investigate the extent to which variability in age at onset and at death could be accounted for by family membership and the specific mutation carried. Findings Data were available from 3403 individuals from 1492 families: 1433 with C9orf72 expansions (755 families), 1179 with GRN mutations (483 families, 130 different mutations), and 791 with MAPT mutations (254 families, 67 different mutations). Mean age at symptom onset and at death was 49•5 years (SD 10•0; onset) and 58•5 years (11•3; death) in the MAPT group, 58•2 years (9•8; onset) and 65•3 years (10•9; death) in the C9orf72 group, and 61•3 years (8•8; onset) and 68•8 years (9•7; death) in the GRN group. Mean disease duration was 6•4 years (SD 4•9) in the C9orf72 group, 7•1 years (3•9) in the GRN group, and 9•3 years (6•4) in the MAPT group. Individual age at onset and at death was significantly correlated with both parental age at onset and at death and with mean family age at onset and at death in all three groups, with a stronger correlation observed in the MAPT group (r=0•45 between individual and parental age at onset, r=0•63 between individual and mean family age at onset, r=0•58 between individual and parental age at death, and r=0•69 between individual and mean family age at death) than in either the C9orf72 group (r=0•32 individual and parental age at onset, r=0•36 individual and mean family age at onset, r=0•38 individual and parental age at death, and r=0•40 individual and mean family age at death) or the GRN group (r=0•22 individual and parental age at onset, r=0•18 individual and mean family age at onset, r=0•22 individual and parental age at death, and r=0•32 individual and mean family age at death). Modelling showed that the variability in age at onset and at death in the MAPT group was explained partly by the specific mutation (48%, 95% CI 35-62, for age at onset; 61%, 47-73, for age at death), and even mor...

Background: Frontotemporal dementia (FTD) is frequently caused by genetic mutations in GRN, C9orf72 and MAPT. Neurofilament light chain (NfL) is a promising blood biomarker in genetic FTD, with elevated levels in symptomatic mutation carriers. A better understanding of NfL dynamics is essential for its use in upcoming therapeutic trials. We investigated longitudinal serum NfL trajectories in presymptomatic and symptomatic genetic FTD. over time was associated with atrophy rate in several grey matter regions, but not with rate of change in clinical parameters. Interpretation: This study confirms the value of blood NfL as a disease progression biomarker in genetic FTD and indicates that longitudinal NfL measurements could help identify mutation carriers approaching symptom onset and capture the rate of brain atrophy. The stable levels in C9orf72-and MAPT-associated FTD offer potential for NfL as a marker of treatment effect in therapeutic trials.

BackgroundThere are few validated fluid biomarkers in frontotemporal dementia (FTD). Glial fibrillary acidic protein (GFAP) is a measure of astrogliosis, a known pathological process of FTD, but has yet to be explored as potential biomarker.MethodsPlasma GFAP and neurofilament light chain (NfL) concentration were measured in 469 individuals enrolled in the Genetic FTD Initiative: 114 C9orf72 expansion carriers (74 presymptomatic, 40 symptomatic), 119 GRN mutation carriers (88 presymptomatic, 31 symptomatic), 53 MAPT mutation carriers (34 presymptomatic, 19 symptomatic) and 183 non-carrier controls. Biomarker measures were compared between groups using linear regression models adjusted for age and sex with family membership included as random effect. Participants underwent standardised clinical assessments including the Mini-Mental State Examination (MMSE), Frontotemporal Lobar Degeneration-Clinical Dementia Rating scale and MRI. Spearman’s correlation coefficient was used to investigate the relationship of plasma GFAP to clinical and imaging measures.ResultsPlasma GFAP concentration was significantly increased in symptomatic GRN mutation carriers (adjusted mean difference from controls 192.3 pg/mL, 95% CI 126.5 to 445.6), but not in those with C9orf72 expansions (9.0, –61.3 to 54.6), MAPT mutations (12.7, –33.3 to 90.4) or the presymptomatic groups. GFAP concentration was significantly positively correlated with age in both controls and the majority of the disease groups, as well as with NfL concentration. In the presymptomatic period, higher GFAP concentrations were correlated with a lower cognitive score (MMSE) and lower brain volume, while in the symptomatic period, higher concentrations were associated with faster rates of atrophy in the temporal lobe.ConclusionsRaised GFAP concentrations appear to be unique to GRN-related FTD, with levels potentially increasing just prior to symptom onset, suggesting that GFAP may be an important marker of proximity to onset, and helpful for forthcoming therapeutic prevention trials.

IntroductionSynapse dysfunction is emerging as an early pathological event in frontotemporal dementia (FTD), however biomarkers are lacking. We aimed to investigate the value of cerebrospinal fluid (CSF) neuronal pentraxins (NPTXs), a family of proteins involved in homeostatic synapse plasticity, as novel biomarkers in genetic FTD.MethodsWe included 106 presymptomatic and 54 symptomatic carriers of a pathogenic mutation in GRN, C9orf72 or MAPT, and 70 healthy non-carriers participating in the Genetic Frontotemporal dementia Initiative (GENFI), all of whom had at least one CSF sample. We measured CSF concentrations of NPTX2 using an in-house ELISA, and NPTX1 and NPTX receptor (NPTXR) by Western blot. We correlated NPTX2 with corresponding clinical and neuroimaging datasets as well as with CSF neurofilament light chain (NfL) using linear regression analyses.ResultsSymptomatic mutation carriers had lower NPTX2 concentrations (median 643 pg/mL, IQR (301–872)) than presymptomatic carriers (1003 pg/mL (624–1358), p<0.001) and non-carriers (990 pg/mL (597–1373), p<0.001) (corrected for age). Similar results were found for NPTX1 and NPTXR. Among mutation carriers, NPTX2 concentration correlated with several clinical disease severity measures, NfL and grey matter volume of the frontal, temporal and parietal lobes, insula and whole brain. NPTX2 predicted subsequent decline in phonemic verbal fluency and Clinical Dementia Rating scale plus FTD modules. In longitudinal CSF samples, available in 13 subjects, NPTX2 decreased around symptom onset and in the symptomatic stage.DiscussionWe conclude that NPTX2 is a promising synapse-derived disease progression biomarker in genetic FTD.

Objective:We tested the hypothesis that plasma neurofilament light chain (NfL) identifies asymptomatic carriers of familial frontotemporal lobar degeneration (FTLD)-causing mutations at risk of disease progression.Methods:Baseline plasma NfL concentrations were measured with Simoa in original (n = 277) and validation (n = 297) cohorts. C9orf72, GRN and MAPT mutation carriers and non-carriers from the same families were classified by disease severity [asymptomatic, prodromal and full phenotype] using the CDR® Dementia Staging Instrument plus behavior and language domains from the National Alzheimer’s Disease Coordinating Center FTLD module (CDR®+NACC-FTLD). Linear mixed effect models related NfL to clinical variables.Results:In both cohorts, baseline NfL was higher in asymptomatic mutation carriers who showed phenoconversion or disease progression compared to non-progressors (original: 11.4 ± 7 pg/mL vs. 6.7 ± 5 pg/mL, p = 0.002; validation: 14.1 ± 12 pg/mL vs. 8.7 ± 6 pg/mL, p = 0.035). Plasma NfL discriminated symptomatic from asymptomatic mutation carriers or prodromal disease (original cutoff: 13.6 pg/mL, 87.5% sensitivity, 82.7% specificity; validation cutoff: 19.8 pg/mL, 87.4% sensitivity, 84.3% specificity). Higher baseline NfL correlated with worse longitudinal CDR®+NACC-FTLD sum of boxes scores, neuropsychological function and atrophy, regardless of genotype or disease severity, including asymptomatic mutation carriers.Conclusions:Plasma NfL identifies asymptomatic carriers of FTLD-causing mutations at short-term risk of disease progression, and is a potential tool to select participants for prevention clinical trials.Classification of evidence:This study provides Class I evidence that in carriers of FTLD-causing mutations, elevation of plasma NfL predicts short-term risk of clinical progression.

Highlights Progressive and differential atrophy patterns are seen at presymptomatic stages across genetic groups. Very early presymptomatic brain changes are detectable only by looking at small regions. C9orf72 expansion carriers show the earliest and most widespread changes (cortex, pulvinar, cerebellum). MAPT mutation carriers show early differences in the dorsolateral temporal cortex, amygdala, and hippocampus. Late presymptomatic changes occur in GRN mutation carriers in dorsolateral prefrontal cortex, insula, and presubiculum.

The presymptomatic phase of neurodegenerative diseases are characterized by structural brain changes without significant clinical features. We set out to investigate the contribution of functional network resilience to preserved cognition in presymptomatic genetic frontotemporal dementia. We studied 172 people from families carrying genetic abnormalities in C9orf72, MAPT, or PGRN. Networks were extracted from functional MRI data and assessed using graph theoretical analysis. We found that despite loss of both brain volume and functional connections, there is maintenance of an efficient topological organization of the brain's functional network in the years leading up to the estimated age of frontotemporal dementia symptom onset. After this point, functional network efficiency declines markedly. Reduction in connectedness was most marked in highly connected hub regions. Measures of topological efficiency of the brain's functional network and organization predicted cognitive dysfunction in domains related to symptomatic frontotemporal dementia and connectivity correlated with brain volume loss in frontotemporal dementia. We propose that maintaining the efficient organization of the brain's functional network supports cognitive health even as atrophy and connectivity decline presymptomatically.

IMPORTANCE Behavioral disturbances are core features of frontotemporal dementia (FTD); however, symptom progression across the course of disease is not well characterized in genetic FTD.OBJECTIVE To investigate behavioral symptom frequency and severity and their evolution and progression in different forms of genetic FTD.