Evaluation of plasma tau and neurofilament light chain biomarkers in a 12-year clinical cohort of human prion diseases.

Prion diseases are fatal neurodegenerative conditions with highly accurate CSF and imaging diagnostic tests, but major unmet needs for blood biomarkers. Using ultrasensitive immuno-assays, we measured tau and neurofilament light chain (NfL) protein concentrations in 709 plasma samples taken from 377 individuals with prion disease during a 12 year prospective clinical study, alongside healthy and neurological control groups. This provides an unprecedented opportunity to evaluate their potential as biomarkers. Plasma tau and NfL were increased across all prion disease types. For distinguishing sCJD from control groups including clinically-relevant "CJD mimics", both show considerable diagnostic value. In sCJD, NfL was substantially elevated in every sample tested, including during early disease with minimal functional impairment and in all follow-up samples. Plasma tau was independently associated with rate of clinical progression in sCJD, while plasma NfL showed independent association with severity of functional impairment. In asymptomatic PRNP mutation carriers, plasma NfL was higher on average in samples taken within 2 years of symptom onset than in samples taken earlier. We present biomarker trajectories for nine mutation carriers healthy at enrolment who developed symptoms during follow-up. NfL started to rise as early as 2 years before onset in those with mutations typically associated with more slowly progressive clinical disease. This shows potential for plasma NfL as a "proximity marker", but further work is needed to establish predictive value on an individual basis, and how this varies across different PRNP mutations. We conclude that plasma tau and NfL have potential to fill key unmet needs for biomarkers in prion disease: as a secondary outcome for clinical trials (NfL and tau); for predicting onset in at-risk individuals (NfL); and as an accessible test for earlier identification of patients that may have CJD and require more definitive tests (NfL). Further studies should evaluate their performance directly in these specific roles.

Variants of PLCXD3 are not associated with variant or sporadic Creutzfeldt-Jakob disease in a large international study.

BACKGROUND: Human prion diseases are relentlessly progressive neurodegenerative disorders which include sporadic Creutzfeldt-Jakob disease (sCJD) and variant CJD (vCJD). Aside from variants of the prion protein gene (PRNP) replicated association at genome-wide levels of significance has proven elusive. A recent association study identified variants in or near to the PLCXD3 gene locus as strong disease risk factors in multiple human prion diseases. This study claimed the first non-PRNP locus to be highly significantly associated with prion disease in genomic studies. METHODS: A sub-study of a genome-wide association study with imputation aiming to replicate the finding at PLCXD3 including 129 vCJD and 2500 sCJD samples. Whole exome sequencing to identify rare coding variants of PLCXD3. RESULTS: Imputation of relevant polymorphisms was accurate based on wet genotyping of a sample. We found no supportive evidence that PLCXD3 variants are associated with disease. CONCLUSION: The marked discordance in vCJD genotype frequencies between studies, despite extensive overlap in vCJD cases, and the finding of Hardy-Weinberg disequilibrium in the original study, suggests possible reasons for the discrepancies between studies.

ApoE4 lowers age at onset in patients with frontotemporal dementia and tauopathy independent of amyloid-ß copathology.

INTRODUCTION: Apolipoprotein E (ApoE) is the most important genetic risk factor for Alzheimer's disease (AD), with ApoE4 thought to enhance and accelerate amyloid-ß (Aß) pathology. ApoE4 has recently been described to increase neurodegeneration in a mouse model of frontotemporal dementia (FTD), in vitro, and in patients, demonstrating that ApoE4 modifies tauopathy independently of Aß. This raises the question whether ApoE genotype also modifies the clinical phenotype in patients with FTD with tau pathology. METHODS: We analyzed 704 patients with FTD, including a genetically and neuropathologically confirmed subset, and 452 healthy elderly controls. We compared ApoE4 genotype frequency and age at onset in tau+ or TDP43+ FTD patients with or without Aß copathology. RESULTS: The ApoE4 genotype lowered age at onset in patients with FTD and tau pathology, particularly once accounting for confounding effects of Aß pathology. DISCUSSION: We conclude that ApoE4 accelerates neurodegeneration in FTD patients with MAPT mutations or FTLD-tau pathology, independent of Aß.

Longitudinal measurement of serum neurofilament light in presymptomatic familial Alzheimer's disease.

BACKGROUND: To investigate how serum neurofilament light (NfL) concentration changes through the course of disease in familial Alzheimer's disease (FAD) and to assess when NfL concentration first increases. METHODS: NfL was measured using an ultrasensitive immunoassay in 117 serum samples from 61 individuals from families with PSEN1 or APP mutations in a longitudinal study (mean ± SD = 1.9 ± 1.1 visits/patient; inter-visit interval = 1.8 ± 1.1 years). The relationship between NfL concentration and estimated years to/from symptom onset (EYO) was modelled using linear regression, including all time points and robust standard errors to allow for repeated measurements, adjusting for age at visit and sex. Also, for the 27 participants who became symptomatic (during or before the study), NfL concentration was also modelled against known actual years to/from onset (AYO). RESULTS: There were 15 non-carriers and 46 mutation carriers (21 symptomatic; 25 presymptomatic). NfL concentration was increased (p = 0.045) in mutation carriers compared with non-carriers 15 years prior to expected symptom onset, increasing progressively thereafter. There was a significant inter- and intra-individual variability in the longitudinal pattern of change. Modelling NfL for the 27 mutation carriers with known AYO also showed a progressive increase over time. CONCLUSIONS: There is evidence that serum NfL is increased more than a decade before the onset of clinical symptoms in FAD and rises thereafter. While there is variability in change over time, both within and between individuals, and more work is needed to understand the sources of this variability, serum NfL remains a promising, accessible biomarker of early neurodegeneration in presymptomatic Alzheimer's disease.

Serum neurofilament light in familial Alzheimer disease: A marker of early neurodegeneration.

OBJECTIVES: To investigate whether serum neurofilament light (NfL) concentration is increased in familial Alzheimer disease (FAD), both pre and post symptom onset, and whether it is associated with markers of disease stage and severity. METHODS: We recruited 48 individuals from families with PSEN1 or APP mutations to a cross-sectional study: 18 had symptomatic Alzheimer disease (AD) and 30 were asymptomatic but at 50% risk of carrying a mutation. Serum NfL was measured using an ultrasensitive immunoassay on the single molecule array (Simoa) platform. Cognitive testing and MRI were performed; 33 participants had serial MRI, allowing calculation of atrophy rates. Genetic testing established mutation status. A generalized least squares regression model was used to compare serum NfL among symptomatic mutation carriers, presymptomatic carriers, and noncarriers, adjusting for age and sex. Spearman coefficients assessed associations between serum NfL and (1) estimated years to/from symptom onset (EYO), (2) cognitive measures, and (3) MRI measures of atrophy. RESULTS: Nineteen of the asymptomatic participants were mutation carriers (mean EYO -9.6); 11 were noncarriers. Compared with noncarriers, serum NfL concentration was higher in both symptomatic (p < 0.0001) and presymptomatic mutation carriers (p = 0.007). Across all mutation carriers, serum NfL correlated with EYO (ρ = 0.81, p < 0.0001) and multiple cognitive and imaging measures, including Mini-Mental State Examination (ρ = -0.62, p = 0.0001), Clinical Dementia Rating Scale sum of boxes (ρ = 0.79, p < 0.0001), baseline brain volume (ρ = -0.62, p = 0.0002), and whole-brain atrophy rate (ρ = 0.53, p = 0.01). CONCLUSIONS: Serum NfL concentration is increased in FAD prior to symptom onset and correlates with measures of disease stage and severity. Serum NfL may thus be a feasible biomarker of early AD-related neurodegeneration.

Clinical Trial Simulations Based on Genetic Stratification and the Natural History of a Functional Outcome Measure in Creutzfeldt-Jakob Disease.

IMPORTANCE: A major challenge for drug development in neurodegenerative diseases is that adequately powered efficacy studies with meaningful end points typically require several hundred participants and long durations. Prion diseases represent the archetype of brain diseases caused by protein misfolding, the most common subtype being sporadic Creutzfeldt-Jakob disease (sCJD), a rapidly progressive dementia. There is no well-established trial method in prion disease. OBJECTIVE: To establish a more powerful and meaningful clinical trial method in sCJD. DESIGN, SETTING, AND PARTICIPANTS: A stratified medicine and simulation approach based on a prospective interval-cohort study conducted from October 2008 to June 2014. This study involved 598 participants with probable or definite sCJD followed up over 470 patient-years at a specialist national referral service in the United Kingdom with domiciliary, care home, and hospital patient visits. We fitted linear mixed models to the outcome measurements, and simulated clinical trials involving 10 to 120 patients (no dropouts) with early to moderately advanced prion disease using model parameters to compare the power of various designs. MAIN OUTCOMES AND MEASURES: A total of 2681 assessments were done using a functionally orientated composite end point (Medical Research Council Scale) and associated with clinical investigations (brain magnetic resonance imaging, electroencephalography, and cerebrospinal fluid analysis) and molecular data (prion protein [PrP] gene sequencing, PrPSc type). RESULTS: Of the 598 participants, 273 were men. The PrP gene sequence was significantly associated with decline relative to any other demographic or investigation factors. Patients with sCJD and polymorphic codon 129 genotypes MM, VV, and MV lost 10% of their function in 5.3 (95% CI, 4.2-6.9), 13.2 (95% CI, 10.9-16.6), and 27.8 (95% CI, 21.9-37.8) days, respectively (P < .001). Simulations indicate that an adequately powered (80%; 2-sided α = .05) open-label randomized trial using 50% reduction in Medical Research Council Scale decline as the primary outcome could be conducted with only 120 participants assessed every 10 days and only 90 participants assessed daily, providing considerably more power than using survival as the primary outcome. Restricting to VV or MV codon 129 genotypes increased power even further. Alternatively, single-arm intervention studies (half the total sample size) could provide similar power in comparison to the natural history cohort. CONCLUSIONS AND RELEVANCE: Functional end points in neurodegeneration need not require long and very large clinical studies to be adequately powered for efficacy. Patients with sCJD may be an efficient and cost-effective group for testing disease-modifying therapeutics. Stratified medicine and natural history cohort approaches may transform the feasibility of clinical trials in orphan diseases.

Serum neurofilament light chain protein is a measure of disease intensity in frontotemporal dementia.

OBJECTIVE: To investigate serum neurofilament light chain (NfL) concentrations in frontotemporal dementia (FTD) and to see whether they are associated with the severity of disease. METHODS: Serum samples were collected from 74 participants (34 with behavioral variant FTD [bvFTD], 3 with FTD and motor neuron disease and 37 with primary progressive aphasia [PPA]) and 28 healthy controls. Twenty-four of the FTD participants carried a pathogenic mutation in C9orf72 (9), microtubule-associated protein tau (MAPT; 11), or progranulin (GRN; 4). Serum NfL concentrations were determined with the NF-Light kit transferred onto the single-molecule array platform and compared between FTD and healthy controls and between the FTD clinical and genetic subtypes. We also assessed the relationship between NfL concentrations and measures of cognition and brain volume. RESULTS: Serum NfL concentrations were higher in patients with FTD overall (mean 77.9 pg/mL [SD 51.3 pg/mL]) than controls (19.6 pg/mL [SD 8.2 pg/mL]; p < 0.001). Concentrations were also significantly higher in bvFTD (57.8 pg/mL [SD 33.1 pg/mL]) and both the semantic and nonfluent variants of PPA (95.9 and 82.5 pg/mL [SD 33.0 and 33.8 pg/mL], respectively) compared with controls and in semantic variant PPA compared with logopenic variant PPA. Concentrations were significantly higher than controls in both the C9orf72 and MAPT subgroups (79.2 and 40.5 pg/mL [SD 48.2 and 20.9 pg/mL], respectively) with a trend to a higher level in the GRN subgroup (138.5 pg/mL [SD 103.3 pg/mL). However, there was variability within all groups. Serum concentrations correlated particularly with frontal lobe atrophy rate (r = 0.53, p = 0.003). CONCLUSIONS: Increased serum NfL concentrations are seen in FTD but show wide variability within each clinical and genetic group. Higher concentrations may reflect the intensity of the disease in FTD and are associated with more rapid atrophy of the frontal lobes.

Small deletion in C9orf72 hides a proportion of expansion carriers in FTLD.

Frontotemporal lobar degeneration is a highly familial disease and the most common known genetic cause is the repeat expansion mutation in the gene C9orf72. We have identified 2 brothers with an expansion mutation in C9orf72 using Southern blotting that is undetectable using repeat-primed polymerase chain reaction. Sequencing using high concentrations of DNA denaturants of a bacterial artificial chromosome clone obtained from one of the brothers identified a 10-base pair deletion adjacent to the expansion that presumably confers strong secondary structure that interferes with the genotyping. Using an alternative method, we have identified missed expansion carriers in our cohort, and this number has increased by approximately 25%. This observation has important implications for patients undergoing genetic testing for C9orf72.

Filamentous white matter prion protein deposition is a distinctive feature of multiple inherited prion diseases.

BACKGROUND: Sporadic, inherited and acquired prion diseases show distinct histological patterns of abnormal prion protein (PrP) deposits. Many of the inherited prion diseases show striking histological patterns, which often associate with specific mutations. Most reports have focused on the pattern of PrP deposition in the cortical or cerebellar grey matter. RESULTS: We observed that the subcortical white matter in inherited prion diseases frequently contained filamentous depositions of abnormal PrP, and we have analysed by immunohistochemistry, immunofluorescence and electron microscopy 35 cases of inherited prion disease seen at the UK National Prion Clinic. We report here that filamentous PrP is abundantly deposited in myelinated fibres in inherited prion diseases, in particular in those with N-terminal mutations. CONCLUSIONS: It is possible that the presence of filamentous PrP is related to the pathogenesis of inherited forms, which is different from those sporadic and acquired forms.