Diagnostic accuracy of cerebrospinal fluid biomarkers in genetic prion diseases

Unmet needs of biochemical biomarkers for human prion diseases

Although the development of aggregation assays has noticeably improved the accuracy of the clinical diagnosis of prion diseases, research on biomarkers remains vital. The major challenges to overcome are non-invasive sampling and the exploration of new biomarkers that may predict the onset or reflect disease progression. This will become extremely important in the near future, when new therapeutics are clinically evaluated and eventually become available for treatment. This article aims to provide an overview of the achievements of biomarker research in human prion diseases, addresses unmet needs in the field, and points out future perspectives.

Fluid Biomarkers in Individuals at Risk for Genetic Prion Disease up to Disease Conversion

OBJECTIVES

To longitudinally characterize disease-relevant CSF and plasma biomarkers in individuals at risk for genetic prion disease up to disease conversion.

METHODS

This single-center longitudinal cohort study has followed known carriers of PRNP pathogenic variants at risk for prion disease, individuals with a close relative who died of genetic prion disease but who have not undergone predictive genetic testing, and controls. All participants were asymptomatic at first visit and returned roughly annually. We determined PRNP genotypes, measured NfL and GFAP in plasma, and RT-QuIC, total PrP, NfL, T-tau, and beta-synuclein in CSF.

RESULTS

Among 41 carriers and 21 controls enrolled, 28 (68%) and 15 (71%) were female, and mean ages were 47.5 and 46.1. At baseline, all individuals were asymptomatic. We observed RT-QuIC seeding activity in the CSF of 3 asymptomatic E200K carriers who subsequently converted to symptomatic and died of prion disease. 1 P102L carrier remained RT-QuIC negative through symptom conversion. No other individuals developed symptoms. The prodromal window from detection of RT-QuIC positivity to disease onset was 1 year long in an E200K individual homozygous (V/V) at PRNP codon 129 and 2.5 and 3.1 years in 2 codon 129 heterozygotes (M/V). Changes in neurodegenerative and neuroinflammatory markers were variably observed prior to onset, with increases observed for plasma NfL in 4/4 converters, and plasma GFAP, CSF NfL, CSF T-tau, and CSF beta-synuclein each in 2/4 converters, although values relative to age and fold changes relative to individual baseline were not remarkable for any of these markers. CSF PrP was longitudinally stable with mean coefficient of variation 9.0% across all individuals over up to 6 years, including data from converting individuals at RT-QuIC-positive timepoints.

DISCUSSION

CSF prion seeding activity may represent the earliest detectable prodromal sign in E200K carriers. Neuronal damage and neuroinflammation markers show limited sensitivity in the prodromal phase. CSF PrP levels remain stable even in the presence of RT-QuIC seeding activity.

CLINICAL TRIALS REGISTRATION

ClinicalTrials.gov NCT05124392 posted 2017-12-01, updated 2023-01-27.

Tau Aggregation-Dependent Lipid Peroxide Accumulation Driven by the hsa_circ_0001546/14-3-3/CAMK2D/Tau Complex Inhibits Epithelial Ovarian Cancer Peritoneal Metastasis

Intraperitoneal dissemination is the main method of epithelial ovarian cancer (EOC) metastasis, which is related to poor prognosis and a high recurrence rate. Circular RNAs (circRNAs) are a novel class of endogenous RNAs with covalently closed loop structures that are implicated in the regulation of tumor development. In this study, hsa_circ_0001546 is downregulated in EOC primary and metastatic tissues vs. control tissues and this phenotype has a favorable effect on EOC OS and DFS. hsa_circ_0001546 can directly bind with 14-3-3 proteins to act as a chaperone molecule and has a limited positive effect on 14-3-3 protein stability. This complex recruits CAMK2D to induce the Ser324 phosphorylation of Tau proteins, changing the phosphorylation status of Tau bound to 14-3-3 and ultimately forming the hsa_circ_0001546/14-3-3/CAMK2D/Tau complex. The existence of this complex stimulates the production of Tau aggregation, which then induces the accumulation of lipid peroxides (LPOs) and causes LPO-dependent ferroptosis. In vivo, treatment with ferrostatin-1 and TRx0237 rescued the inhibitory effect of hsa_circ_0001546 on EOC cell spreading. Therefore, based on this results, ferroptosis caused by Tau aggregation occurs in EOC cells, which is not only in Alzheimer's disease- or Parkinson's disease-related cells and this kind of ferroptosis driven by the hsa_circ_0001546/14-3-3/CAMK2D/Tau complex is LPO-dependent rather than GPX4-dependent is hypothesized.

Gerstmann-Sträussler-Scheinker Disease Presenting as Late-Onset Slowly Progressive Spinocerebellar Ataxia, and Comparative Case Series with Neuropathology

BACKGROUND

Genetic prion diseases, including Gerstmann-Sträussler-Scheinker disease (GSS), are extremely rare, fatal neurodegenerative disorders, often associated with progressive ataxia and cognitive/neuropsychiatric symptoms. GSS typically presents as a rapidly progressive cerebellar ataxia, associated with cognitive decline. Late-onset cases are rare.

OBJECTIVE

To compare a novel GSS phenotype with six other cases and present pathological findings from a single case.

METHODS

Case series of seven GSS patients, one proceeding to autopsy.

RESULTS

Case 1 developed slowly progressive gait difficulties at age 71, mimicking a spinocerebellar ataxia, with a family history of balance problems in old age. Genome sequencing revealed a heterozygous c.392G > A (p.G131E) pathogenic variant and a c.395A > G resulting in p.129 M/V polymorphism in the PRNP gene. Probability analyses considering family history, phenotype, and a similar previously reported point mutation (p.G131V) suggest p.G131E as a new pathogenic variant. Clinical features and imaging of this case are compared with those six additional cases harboring p.P102L mutations. Autopsy findings of a case are described and were consistent with the prion pathology of GSS.

CONCLUSIONS

We describe a patient with GSS with a novel p.G131E mutation in the PRNP gene, presenting with a late-onset, slowly progressive phenotype, mimicking a spinocerebellar ataxia, and six additional cases with the typical P102L mutation.

Creutzfeldt-Jakob disease and other prion diseases

Prion diseases share common clinical and pathological characteristics such as spongiform neuronal degeneration and deposition of an abnormal form of a host-derived protein, termed prion protein. The characteristic features of prion diseases are long incubation times, short clinical courses, extreme resistance of the transmissible agent to degradation and lack of nucleic acid involvement. Sporadic and genetic forms of prion diseases occur worldwide, of which genetic forms are associated with mutations in PRNP. Human to human transmission of these diseases has occurred due to iatrogenic exposure, and zoonotic forms of prion diseases are linked to bovine disease. Significant progress has been made in the diagnosis of these disorders. Clinical tools for diagnosis comprise brain imaging and cerebrospinal fluid tests. Aggregation assays for detection of the abnormally folded prion protein have a clear potential to diagnose the disease in peripherally accessible biofluids. After decades of therapeutic nihilism, new treatment strategies and clinical trials are on the horizon. Although prion diseases are relatively rare disorders, understanding their pathogenesis and mechanisms of prion protein misfolding has significantly enhanced the field in research of neurodegenerative diseases.

MoDAFold: a strategy for predicting the structure of missense mutant protein based on AlphaFold2 and molecular dynamics

Protein structure prediction is a longstanding issue crucial for identifying new drug targets and providing a mechanistic understanding of protein functions. To enhance the progress in this field, a spectrum of computational methodologies has been cultivated. AlphaFold2 has exhibited exceptional precision in predicting wild-type protein structures, with performance exceeding that of other methods. However, predicting the structures of missense mutant proteins using AlphaFold2 remains challenging due to the intricate and substantial structural alterations caused by minor sequence variations in the mutant proteins. Molecular dynamics (MD) has been validated for precisely capturing changes in amino acid interactions attributed to protein mutations. Therefore, for the first time, a strategy entitled 'MoDAFold' was proposed to improve the accuracy and reliability of missense mutant protein structure prediction by combining AlphaFold2 with MD. Multiple case studies have confirmed the superior performance of MoDAFold compared to other methods, particularly AlphaFold2.

A case report of fatal familial insomnia with cerebrospinal fluid leukocytosis during the COVID-19 epidemic and review of the literature

Fatal familial insomnia (FFI) is a rare autosomal dominant genetic neurodegenerative disease. Generally, FFI patients will develop rapidly progressive dementia, sleep disturbance, autonomic dysfunction, and so on. Cerebrospinal fluid examination of FFI patients normally shows no obvious abnormalities. Here, we report a young male patient who was diagnosed with FFI during the COVID-19 epidemic. Clinical symptoms include psychobehavioral abnormality, cognitive decline, sleep disturbance, and autonomic dysfunction. No abnormalities were found in routine examinations after admission. However, the number of white blood cells in the cerebrospinal fluid increased. Though the patient was treated with anti-infection and immunotherapy, the symptoms were not relieved. A lumbar puncture was performed again, and it was found that the total Tau protein in the cerebrospinal fluid was elevated, and PET results showed that brain metabolism decreased. Finally, a genetic test was used to confirm the diagnosis of FFI. This case suggests that patients with FFI may also have elevated white blood cells in cerebrospinal fluid and timely detection of Tau protein in cerebrospinal fluid is helpful for early identification of FFI. And precise diagnosis relies on genetic testing.

Biomarker changes preceding symptom onset in genetic prion disease

Importance

Genetic prion disease is a universally fatal and rapidly progressive neurodegenerative disease for which genetically targeted therapies are currently under development. Preclinical proofs of concept indicate that treatment before symptoms will offer outsize benefit. Though early treatment paradigms will be informed by the longitudinal biomarker trajectory of mutation carriers, to date limited cases have been molecularly tracked from the presymptomatic phase through symptomatic onset.

Objective

To longitudinally characterize disease-relevant cerebrospinal fluid (CSF) and plasma biomarkers in individuals at risk for genetic prion disease up to disease conversion, alongside non-converters and healthy controls.

Design setting and participants

This single-center longitudinal cohort study has followed 41 PRNP mutation carriers and 21 controls for up to 6 years. Participants spanned a range of known pathogenic PRNP variants; all subjects were asymptomatic at first visit and returned roughly annually. Four at-risk individuals experienced prion disease onset during the study.

Main outcomes and measures

RT-QuIC prion seeding activity, prion protein (PrP), neurofilament light chain (NfL) total tau (t-tau), and beta synuclein were measured in CSF. Glial fibrillary acidic protein (GFAP) and NfL were measured in plasma.

Results

We observed RT-QuIC seeding activity in the CSF of three E200K carriers prior to symptom onset and death, while the CSF of one P102L carrier remained RT-QuIC negative through symptom conversion. The prodromal window of RT-QuIC positivity was one year long in an E200K individual homozygous (V/V) at PRNP codon 129 and was longer than two years in two codon 129 heterozygotes (M/V). Other neurodegenerative and neuroinflammatory markers gave less consistent signal prior to symptom onset, whether analyzed relative to age or individual baseline. CSF PrP was longitudinally stable (mean CV 10%) across all individuals over up to 6 years, including at RT-QuIC positive timepoints.

Conclusion and relevance

In this study, we demonstrate that at least for the E200K mutation, CSF prion seeding activity may represent the earliest detectable prodromal sign, and that its prognostic value may be modified by codon 129 genotype. Neuronal damage and neuroinflammation markers show limited sensitivity in the prodromal phase. CSF PrP levels remain stable even in the presence of RT-QuIC seeding activity.

Real-time quaking-induced conversion assays for prions: Applying a sensitive but imperfect test in clinical practice

BACKGROUND AND PURPOSE

Real-time quaking-induced conversion (RT-QuIC) assays offer a sensitive and specific means for detection of prions, although false negative results are recognized in clinical practice. We profile the clinical, laboratory, and pathologic features associated with false negative RT-QuIC assays and extend these to frame the diagnostic approach to patients with suspected prion disease.

METHODS

A total of 113 patients with probable or definite prion disease were assessed at Mayo Clinic (Rochester, MN; Jacksonville, FL; Scottsdale, AZ) or Washington University School of Medicine (Saint Louis, MO) from 2013 to 2021. RT-QuIC testing for prions was performed in cerebrospinal fluid (CSF) at the National Prion Disease Pathology Surveillance Center (Cleveland, OH).

RESULTS

Initial RT-QuIC testing was negative in 13 of 113 patients (sensitivity = 88.5%). RT-QuIC negative patients were younger (median = 52.0 years vs. 66.1 years, p < 0.001). Other demographic and presenting features, and CSF cell count, protein, and glucose levels were similar in RT-QuIC negative and positive patients. Frequency of 14-3-3 positivity (4/13 vs. 77/94, p < 0.001) and median CSF total tau levels were lower in RT-QuIC negative patients (2517 vs. 4001 pg/mL, p = 0.020), and time from symptom onset to first presentation (153 vs. 47 days, p = 0.001) and symptomatic duration (710 vs. 148 days, p = 0.001) were longer.

CONCLUSIONS

RT-QuIC is a sensitive yet imperfect measure necessitating incorporation of other test results when evaluating patients with suspected prion disease. Patients with negative RT-QuIC had lower markers of neuronal damage (CSF total tau and protein 14-3-3) and longer symptomatic duration of disease, suggesting that false negative RT-QuIC testing associates with a more indolent course.

Application of real-time quaking-induced conversion in Creutzfeldt-Jakob disease surveillance

BACKGROUND

Evaluation of the application of CSF real-time quaking-induced conversion in Creutzfeldt-Jakob disease surveillance to investigate test accuracy, influencing factors, and associations with disease incidence.

METHODS

In a prospective surveillance study, CSF real-time quaking-induced conversion was performed in patients with clinical suspicion of prion disease (2014-2022). Clinically or histochemically characterized patients with sporadic Creutzfeldt-Jakob disease (n = 888) and patients with final diagnosis of non-prion disease (n = 371) were included for accuracy and association studies.

RESULTS

The overall test sensitivity for sporadic Creutzfeldt-Jakob disease was 90% and the specificity 99%. Lower sensitivity was associated with early disease stage (p = 0.029) and longer survival (p < 0.001). The frequency of false positives was significantly higher in patients with inflammatory CNS diseases (3.7%) than in other diagnoses (0.4%, p = 0.027). The incidence increased from 1.7 per million person-years (2006-2017) to 2.0 after the test was added to diagnostic the criteria (2018-2021).

CONCLUSION

We validated high diagnostic accuracy of CSF real-time quaking-induced conversion but identified inflammatory brain disease as a potential source of (rare) false-positive results, indicating thorough consideration of this condition in the differential diagnosis of Creutzfeldt-Jakob disease. The surveillance improved after amendment of the diagnostic criteria, whereas the incidence showed no suggestive alterations during the COVID-19 pandemic.

Clinical profiles and ethnic heterogeneity of sporadic fatal insomnia

BACKGROUND AND PURPOSE

This study was undertaken to elucidate the clinical profile of sporadic fatal insomnia (sFI), assess the similarities and differences between sFI and fatal familial insomnia (FFI), and evaluate the influence of ethnicity on the phenotype of sFI patients.

METHODS

The data of sFI and FFI patients were retrieved from our case series and through literature review. The clinical and diagnostic features of sFI and FFI were compared, as were the phenotypes of Asian and Caucasian sFI patients.

RESULTS

We identified 44 sFI and 157 FFI cases. The prevalence of sleep-related, neuropsychiatric, and autonomic symptoms among the sFI patients were 65.9%, 100.0%, and 43.2%, respectively. Compared to FFI, sFI exhibited longer disease duration and a higher proportion of neuropsychiatric symptoms, whereas FFI was characterized by a higher incidence of sleep-related and autonomic symptoms in the early stages of the disease or throughout its course. In addition, a higher proportion of the sFI patients showed hyperintensity on magnetic resonance imaging (MRI) and periodic sharp wave complexes on electroencephalography compared to the FFI patients, especially those presenting with pathological changes associated with MM2-cortical type sporadic Creutzfeldt-Jakob disease. The Asian sFI patients had a higher proportion of males and positivity for cerebrospinal fluid 14-3-3 protein, and fewer sleep-related symptoms compared to Caucasian sFI patients. The age at onset and duration of sFI differed between ethnic groups, but the difference failed to reach statistical significance.

CONCLUSIONS

Despite its similarities to FFI, sFI is characterized by longer disease duration, higher proportion of neuropsychiatric symptoms, and hyperintensity on MRI, along with differences in the clinical characteristics based on ethnicity.

From parasomnia to agrypnia excitata - An illustrative case on diagnostic approach

The diagnostic approach to sleep-related movements disorders is seldom discussed. We report a case of fatal familial insomnia who initially presented with persistent limb movements in sleep, which later progressed to a state of agrypnia excitata. Here, the evaluation of abnormal movements in sleep is discussed using a step-by-step diagnostic approach. Although no cure is available for fatal familial insomnia, prompt recognition of this condition is important to facilitate proper management, including the involvement of interdisciplinary neuropalliative care.

Differential proteomic profile of lumbar and ventricular cerebrospinal fluid

BACKGROUND

Pathological cerebral conditions may manifest in altered composition of the cerebrospinal fluid (CSF). Although diagnostic CSF analysis seeks to establish pathological disturbances in the brain proper, CSF is generally sampled from the lumbar compartment for reasons of technical ease and ethical considerations. We here aimed to compare the molecular composition of CSF obtained from the ventricular versus the lumbar CSF compartments to establish a relevance for employing lumbar CSF as a proxy for the CSF bathing the brain tissue.

METHODS

CSF was collected from 46 patients with idiopathic normal pressure hydrocephalus (iNPH) patients during their diagnostic workup (lumbar samples) and in connection with their subsequent CSF diversion shunt surgery (ventricular samples). The mass-spectrometry-based proteomic profile was determined in these samples and in addition, selected biomarkers were quantified with ELISA (S100B, neurofilament light (NfL), amyloid-β (Aβ₄₀, Aβ₄₂), and total tau (T-tau) and phosphorylated tau (P-tau) forms). The latter analysis was extended to include paired porcine samples obtained from the lumbar compartment and the cerebromedullary cistern closely related to the ventricles.

RESULTS

In total 1231 proteins were detected in the human CSF. Of these, 216 distributed equally in the two CSF compartments, whereas 22 were preferentially (or solely) present in the ventricular CSF and four in the lumbar CSF. The selected biomarkers of neurodegeneration and Alzheimer's disease displayed differential distribution, some with higher (S100B, T-tau, and P-tau) and some with lower (NfL, Aβ₄₀, Aβ₄₂) levels in the ventricular compartment. In the porcine samples, all biomarkers were most abundant in the lumbar CSF.

CONCLUSIONS

The overall proteomic profile differs between the ventricular and the lumbar CSF compartments, and so does the distribution of clinically employed biomarkers. However, for a range of CSF proteins and biomarkers, one can reliably employ lumbar CSF as a proxy for ventricular CSF if or a lumbar/cranial index for the particular molecule has been established. It is therefore important to verify the compartmental preference of the proteins or biomarkers of interest prior to extrapolating from lumbar CSF to that of the ventricular fluid bordering the brain.

Human prion diseases and the prion protein - what is the current state of knowledge?

Prion diseases and the prion protein are only partially understood so far in many aspects. This explains the continued research on this topic, calling for an overview on the current state of knowledge. The main objective of the present review article is to provide a comprehensive up-to-date presentation of all major features of human prion diseases bridging the gap between basic research and clinical aspects. Starting with the prion protein, current insights concerning its physiological functions and the process of pathological conversion will be highlighted. Diagnostic, molecular, and clinical aspects of all human prion diseases will be discussed, including information concerning rare diseases like prion-associated amyloidoses and Huntington disease-like 1, as well as the question about a potential human threat due to the transmission of prions from prion diseases of other species such as chronic wasting disease. Finally, recent attempts to develop future therapeutic strategies will be addressed.

Role of different recombinant PrP substrates in the diagnostic accuracy of the CSF RT-QuIC assay in Creutzfeldt-Jakob disease

The development of the real-time quaking-induced conversion (RT-QuIC), an in vitro protein misfolding amplification assay, was an innovation in the scientific field of protein misfolding diseases. In prion diseases, these types of assays imitate the pathological conversion of the cellular prion protein (PrPC) into a protease-resistant and/or amyloid form of PrP, called PrP resistant (PrPRes). The RT-QuIC is an automatic assay system based on real-time measuring of thioflavin-T (Th-T) incorporation into amyloid fibrils using shaking for disaggregation. It has already been applied in diagnostics, drug pre-screening, and to distinguish between different prion strains. The seeded conversion efficiency and the diagnostic accuracy of the RT-QuIC assay strongly depend on the kind of recombinant PrP (rec PrP) substrate. The DNA sequences of different substrates may originate from different species, such as human, bank vole, and hamster, or from a combination of two species, e.g., hamster-sheep chimera. In routine use, either full-length (FL) or truncated substrates are applied which can accelerate the conversion reaction, e.g., to a more sensitive version of RT-QuIC assay. In the present review, we provide an overview on the different types of PrP substrates (FL and truncated forms), recapitulate the production and purification process of different rec PrP substrates, and discuss the diagnostic value of CSF RT-QuIC in human prion disease diagnostics.

Diagnostic Utility of Cerebrospinal Fluid α-Synuclein in Creutzfeldt-Jakob Disease: A Systematic Review and Meta-Analysis

BACKGROUND

Creutzfeldt-Jakob disease (CJD) can be difficult to distinguish clinically from some non-prion neurological diseases. Previous studies have reported markedly increased levels of α-synuclein in cerebrospinal fluid (CSF) of CJD patients, indicating that it is a potential diagnostic biomarker.

OBJECTIVE

The aim of this study was to assess the diagnostic power of CSF α-synuclein in discriminating CJD from non-prion disorders.

METHODS

The Ovid MEDLINE, Cochrane, and Embase databases were searched for articles published on or before February 25, 2022, using the search term (prion diseases OR Creutzfeldt-Jakob syndrome) AND (synuclein OR α-synuclein). The difference in CSF α-synuclein levels between CJD and non-prion diseases was calculated using random-effects models (I2 > 50%) or fixed-effects models (I2 < 50%) in terms of standardized mean difference (SMD) and 95% confidence interval (CI). The publication bias was estimated using funnel plots and the Egger's test.

RESULTS

Ten studies were included in this study. The concentrations of CSF α-synuclein were significantly higher in CJD patients compared to total non-prion controls (SMD = 1.98, 95% CI 1.60 to 2.36, p < 0.00001), tauopathies (SMD = 1.34, 95% CI 0.99 to 1.68, p < 0.00001), synucleinopathies (SMD = 1.78, 95% CI 1.11 to 2.44, p < 0.00001), or Alzheimer's (SMD = 1.14, 95% CI 0.95 to 1.33, p < 0.00001). CSF α-synuclein could distinguish CJD from non-prion diseases with overall sensitivity of 89% (95% CI 80-95%), specificity of 92% (95% CI 86-95%), and AUC of 0.96 (95% CI: 0.94-0.97).

CONCLUSION

CSF α-synuclein has excellent diagnostic value in discriminating CJD from non-prion neurological diseases. Given the high heterogeneity among the included studies, further studies are needed to confirm its clinical utility.

Plasma neurofilament light chain as a biomarker for Fatal Familial Insomnia

BACKGROUND

Fatal Familial Insomnia is a rare hereditary prion disease associated with the D178N-129M PRNP mutation. Early diagnosis is difficult because the clinical syndrome may overlap with affective disorders. In addition, most known cerebrospinal fluid biomarkers for prion diseases and magnetic resonance imaging do not show a good diagnostic accuracy for Fatal Familial Insomnia. In this context, data on plasma biomarkers are scarce.

METHODS

We analyzed levels of neurofilament light chain, glial fibrillary acidic protein, chitinase-3-like protein 1, calcium-binding protein B, and total Tau protein in six serial plasma samples from a patient with Fatal Familial Insomnia. Subsequently, plasma neurofilament light chain was analyzed in n=25 patients and n=19 controls. The diagnostic accuracy and associations with disease stage and duration were explored.

RESULTS

Among all biomarker candidates in the case study, only neurofilament light chain levels showed a constant evolution and increased over time. It discriminated Fatal Familial Insomnia from controls with an area under the curve of 0.992 (95%CI:0.974 to 1) in the case-control study. Higher concentrations were associated with methionine homozygosity at Codon 129 PRNP (p=0.006), shorter total disease duration (rho=-0.467, p=0.019, 95%CI:-0.790 to -0.015), and shorter time from sampling to death (rho=-0.467, p=0.019, 95%CI -0.773 to -0.019).

CONCLUSION

Plasma neurofilament light chain may be a valuable minimal-invasive diagnostic biomarker for Fatal Familial Insomnia after clinical onset. Most important, stage-related increase and association with disease duration indicate potential as a prognostic marker and as a surrogate marker in clinical trials.