Consensus classification of human prion disease histotypes allows reliable identification of molecular subtypes: an inter-rater study among surveillance centres in Europe and USA

Regional pattern of microgliosis in sporadic Creutzfeldt-Jakob disease in relation to phenotypic variants and disease progression

AIMS

The aim of this study was to describe the regional profiles of microglial activation in sporadic Creutzfeldt-Jakob disease (sCJD) subtypes and analyse the influence of prion strain, disease duration and codon 129 genotype.

METHODS

We studied the amount/severity and distribution of activated microglia, protease-resistant prion protein (PrP^Sc ) spongiform change, and astrogliosis in eight regions of 57 brains, representative of the entire spectrum of sCJD subtypes.

RESULTS

In each individual subtype, the regional extent and distribution of microgliosis significantly correlated with PrP^Sc deposition and spongiform change, leading to subtype-specific 'lesion profiles'. However, large differences in the ratio between PrP^Sc load or the score of spongiform change and microglial activation were seen among disease subtypes. Most significantly, atypical sCJD subtypes such as VV1 and MM2T showed a degree of microglial activation comparable to other disease variants despite the relatively low PrP^Sc deposition and the less severe spongiform change. Moreover, the mean microglial total load was significantly higher in subtype MM1 than in MM2C, whereas the opposite was true for the PrP^Sc and spongiform change total loads. Finally, some sCJD subtypes showed distinctive regional cerebellar profiles of microgliosis characterized by a high granular/molecular layer ratio (MV2K) and/or a predominant involvement of white matter (MVK and MM2T).

CONCLUSIONS

Microglial activation is an early event in sCJD pathogenesis and is strongly influenced by prion strain, PRNP codon 129 genotype and disease duration. Microglial lesion profiling, by highlighting strain-specific properties of prions, contributes to prion strain characterization and classification of human prion diseases, and represents a valid support to molecular and histopathologic typing.

Diagnostic Accuracy of a Combined Analysis of Cerebrospinal Fluid t-PrP, t-tau, p-tau, and Aβ42 in the Differential Diagnosis of Creutzfeldt-Jakob Disease from Alzheimer's Disease with Emphasis on Atypical Disease Variants

According to recent studies, the determination of cerebrospinal fluid (CSF) total tau (t-tau)/phosphorylated tau (p-tau) ratio and total prion protein (t-PrP) levels significantly improves the accuracy of the diagnosis of Alzheimer’s disease (AD) in atypical cases with clinical or laboratory features mimicking Creutzfeldt-Jakob disease (CJD). However, this has neither been validated nor tested in series including atypical CJD variants. Furthermore, the added diagnostic value of amyloid-β (Aβ)₄₂ remains unclear. To address these issues, we measured t-PrP, 14-3-3, t-tau, p-tau, and Aβ₄₂ CSF levels in 45 typical and 44 atypical/rapidly progressive AD patients, 54 typical and 54 atypical CJD patients, and 33 controls. CJD patients showed significantly lower CSF t-PrP levels than controls and AD patients. Furthermore, atypical CJD was associated with lower t-PrP levels in comparison to typical CJD. T-tau, 14-3-3, or t-PrP alone yielded, respectively, 80.6, 63.0, and 73.0% sensitivity and 75.3, 92.1, and 75% specificity in distinguishing AD from CJD. On receiver operating characteristic (ROC) curve analyses of biomarker combinations, the (t-tau×Aβ₄₂)/(p-tau×t-PrP) ratio achieved the best accuracy, with 98.1% sensitivity and 97.7% specificity overall, and 96.2% sensitivity and 95.5% specificity for the “atypical” disease groups. Our results show that the combined analysis of CSF t-PrP, t-tau, p-tau, and Aβ₄₂ is clinically useful in the differential diagnosis between CJD and AD. Furthermore, the finding of reduced CSF t-PrP levels in CJD patients suggest that, likewise Aβ₄₂ in AD, CSF t-PrP levels reflect the extent of PrP^c conversion into abnormal PrP (PrP^Sc) and the burden of PrP^Sc deposition in CJD.

Quantitative Magnetic Resonance Abnormalities in Creutzfeldt-Jakob Disease and Fatal Insomnia

BACKGROUND

Quantitative neuroimaging might unveil abnormalities in prion diseases that are not perceivable at visual inspection. On the other hand, scarce studies have quantified volumetric changes in prion diseases.

OBJECTIVES

We aim to characterize volumetric and diffusion tensor imaging (DTI) changes in patients with prion diseases who presented with either Creutzfeldt-Jakob disease (CJD) or fatal insomnia (FI) phenotype.

METHODS

Twenty patients with prion diseases- 15 with CJD and 5 with fatal insomnia (FI)- and 40 healthy controls were examined with a 3-Tesla magnetic resonance imaging scanner. Images were segmented and normalized with SPM12. DTI maps were obtained with FMRIB Software Library. Whole-brain voxel-wise and region-of-interest analyses of volumetric and DTI changes were performed with SPM12. White matter (WM) changes were also analyzed with tract-based spatial statistics. Semiquantitive assessment of neuropathological parameters was compared with DTI metrics in thalamus from 11 patients.

RESULTS

Patients with CJD and FI presented significant atrophy in thalamus and cerebellum. In CJD, mean diffusivity (MD) was decreased in striatum and increased in subcortical WM, while both increased and decreased values were observed across different thalamic nuclei. In FI, MD was increased in thalamus and cerebellum. Spongiform change and PrPSc deposition were more intense in thalamus in CJD than in FI, although no significant correlations arose with MD values in the nuclei studied.

CONCLUSION

Volumetric and DTI abnormalities suggest a central common role of the thalamus in prion diseases. We report, for the first time, quantitative MRI changes in FI, and provide further evidence of WM involvement in prion diseases.

Cerebrospinal fluid neurofilament light levels in neurodegenerative dementia: Evaluation of diagnostic accuracy in the differential diagnosis of prion diseases

INTRODUCTION

Neurofilament light (NFL) levels in the cerebrospinal fluid are increased in several neurodegenerative dementias. However, their diagnostic accuracy in the differential diagnostic context is unknown.

METHODS

Cerebrospinal fluid NFL levels were quantified in nonprimarily neurodegenerative neurological and psychiatric diseases (n = 122), mild cognitive impairment (n = 48), Alzheimer's disease (n = 108), dementia with Lewy bodies/Parkinson's disease dementia (n = 53), vascular dementia (n = 46), frontotemporal dementia (n = 41), sporadic Creutzfeldt-Jakob disease (sCJD, n = 132), and genetic prion diseases (n = 182).

RESULTS

The highest NFL levels were detected in sCJD, followed by vascular dementia, frontotemporal dementia, dementia with Lewy bodies/Parkinson's disease dementia, Alzheimer's disease, and mild cognitive impairment. In sCJD, NFL levels correlated with cerebrospinal fluid tau and disease duration. NFL levels were able to differentiate sCJD from nonprimarily neurodegenerative neurological and psychiatric diseases (area under the curve = 0.99, 95% confidence interval: 0.99-1) and from the other diagnostic groups showing cognitive impairment/dementia of a non-CJD etiology (area under the curve = 0.90, 95% confidence interval: 0.87-0.92). Compared to nonprimarily neurodegenerative neurological and psychiatric diseases, NFL was also elevated in genetic prion diseases associated with the E200K, V210I, P102L, and D178N prion protein gene mutations.

DISCUSSION

Increased NFL levels are a common feature in neurodegenerative dementias.

Neuropathology of iatrogenic Creutzfeldt-Jakob disease and immunoassay of French cadaver-sourced growth hormone batches suggest possible transmission of tauopathy and long incubation periods for the transmission of Abeta pathology

Abeta deposits and tau pathology were investigated in 24 French patients that died from iatrogenic Creutzfeldt-Jakob disease after exposure to cadaver-derived human growth hormone (c-hGH) in the 1980s. Abeta deposits were found only in one case that had experienced one of the longest incubation periods. Three cases had also intracellular tau accumulation. The analysis of 24 batches of c-hGH, produced between 1974 and 1988, demonstrated for the first time the presence of Abeta and tau contaminants in c-hGH (in 17 and 6 batches, respectively). The incubation of prion disease was shorter in the French patients than the incubation times reported in two previously published British series. We interpreted the low incidence of Abeta in this French series as a consequence of the shorter incubation period observed in France, as compared to that observed in the United Kingdom. This concept suggested that a mean incubation period for the development of detectable Abeta deposits would be longer than 18 years after the first exposure. Moreover, we hypothesized that tau pathology might also be transmissible in humans.

A novel Gerstmann-Sträussler-Scheinker disease mutation defines a precursor for amyloidogenic 8 kDa PrP fragments and reveals N-terminal structural changes shared by other GSS alleles

To explore pathogenesis in a young Gerstmann-Sträussler-Scheinker Disease (GSS) patient, the corresponding mutation, an eight-residue duplication in the hydrophobic region (HR), was inserted into the wild type mouse PrP gene. Transgenic (Tg) mouse lines expressing this mutation (Tg.HRdup) developed spontaneous neurologic syndromes and brain extracts hastened disease in low-expressor Tg.HRdup mice, suggesting de novo formation of prions. While Tg.HRdup mice exhibited spongiform change, PrP aggregates and the anticipated GSS hallmark of a proteinase K (PK)-resistant 8 kDa fragment deriving from the center of PrP, the LGGLGGYV insertion also imparted alterations in PrP's unstructured N-terminus, resulting in a 16 kDa species following thermolysin exposure. This species comprises a plausible precursor to the 8 kDa PK-resistant fragment and its detection in adolescent Tg.HRdup mice suggests that an early start to accumulation could account for early disease of the index case. A 16 kDa thermolysin-resistant signature was also found in GSS patients with P102L, A117V, H187R and F198S alleles and has coordinates similar to GSS stop codon mutations. Our data suggest a novel shared pathway of GSS pathogenesis that is fundamentally distinct from that producing structural alterations in the C-terminus of PrP, as observed in other prion diseases such as Creutzfeldt-Jakob Disease and scrapie.

Prion diseases can be sporadic, infectious or genetic. The central event of all prion diseases is the structural conversion of the cellular prion protein (PrP^C) to its disease associated conformer, PrP^Sc. Gerstmann-Sträussler-Scheinker Disease (GSS) is a genetic prion disease presenting as a multi-systemic neurological syndrome. A novel mutation, an eight amino acid insertion, was discovered in a young GSS patient. We created transgenic mice expressing this mutation and found that they recapitulate key features of the disease; namely PrP deposition in the brain and a low molecular weight proteinase K (PK) resistant internal PrP fragment. While structural investigations did not reveal a gross alteration in the conformation of this mutant PrP, the insertion lying at the boundary of the globular domain causes alterations in the unstructured amino terminal portion of the protein such that it becomes resistant to digestion by the enzyme thermolysin. We demonstrate by kinetic analysis and sequential digestion that this novel thermolysin resistant species is a precursor to the pathognomonic PK resistant fragment. Analysis of samples from other GSS patients revealed this same signature, suggesting a common molecular pathway.

The CSF neurofilament light signature in rapidly progressive neurodegenerative dementias

Background

Neurofilament light chain protein (NfL) is a surrogate biomarker of neurodegeneration that has never been systematically tested, either alone or in combination with other biomarkers, in atypical/rapidly progressive neurodegenerative dementias (NDs).

Methods

Using validated, commercially available enzyme-linked immunosorbent assay kits, we measured cerebrospinal fluid (CSF) NfL, total tau (t-tau), phosphorylated tau, and β-amyloid 42 in subjects with a neuropathological or clinical diagnosis of prion disease (n = 141), Alzheimer’s disease (AD) (n = 73), dementia with Lewy bodies (DLB) (n = 35), or frontotemporal lobar degeneration (FTLD) (n = 44). Several cases with an atypical/rapidly progressive course were included in each group. We evaluated the diagnostic accuracy of every CSF biomarker and their combinations by ROC curve analyses.

Results

In each patient group CSF NfL showed higher levels than in control subjects, reaching the highest values in those with Creutzfeldt-Jakob disease (CJD). In the latter, NfL showed a divergent, subtype-specific correlation with t-tau, depending on the degree of subcortical involvement and disease duration. Most significantly, patients with classic sporadic CJD (sCJD) MM1 showed a significantly lower concentration of CSF NfL than those with sCJD MV2, despite the much higher t-tau levels and the more rapid clinical course. High NfL levels were also detected in most atypical CJD cases, showing a disease duration longer than 2 years and/or borderline/negative results in other CSF assays (e.g., 14-3-3, t-tau, and prion real-time quaking-induced conversion). Rapidly progressive/atypical cases showed higher NfL levels than typical patients in FTLD, but not in AD or DLB. NfL showed accuracy similar to that of t-tau in discriminating CJD from other NDs, but it had higher efficacy in differentiating atypical forms, especially in regard to Alzheimer’s disease.

Conclusions

The present data indicate that CSF NfL and t-tau levels reflect distinct pathophysiological mechanisms of neurodegeneration and support the clinical use of NfL as a fast screening biomarker for the differential diagnosis of atypical/rapidly progressive NDs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0331-1) contains supplementary material, which is available to authorized users.

Concluding remarks

This is the first volume of the Handbook of Clinical Neurology totally devoted to prion diseases. The reason for this choice is to inform neurologists and neuroscientists about the remarkable advances that this field has made in the diagnosis of human and animal prion diseases, understanding the pathogenesis of disease, and in the development of novel in vivo and in vitro models. In recent years, the knowledge of prion replication and mechanisms of prion spreading within the brain and peripheral organs of infected people has also become important for understanding other protein misfolded diseases of the brain, such as Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis. Researchers in these diseases have recognized that the process within an individual leading to the deposition of misfolded proteins within the central nervous system shares remarkable common mechanisms with prion diseases, leading to the terminology of "prion-like diseases."

Sisyphus in Neverland

The study of life and living organisms and the way in which these interact and organize to form social communities have been central to my career. I have been fascinated by biology, neurology, and neuropathology, but also by history, sociology, and art. Certain current historical, political, and social events, some occurring proximally but others affecting people in apparently distant places, have had an impact on me. Epicurus, Seneca, and Camus shared their philosophical positions which I learned from. Many scientists from various disciplines have been exciting sources of knowledge as well. I have created a world of hypothesis and experiments but I have also got carried away by serendipity following unexpected observations. It has not been an easy path; errors and wanderings are not uncommon, and opponents close to home much more abundant than one might imagine. Ambition, imagination, resilience, and endurance have been useful in moving ahead in response to setbacks. In the end, I have enjoyed my dedication to science and I am grateful to have glimpsed beauty in it. These are brief memories of a Spanish neuropathologist born and raised in Barcelona, EU.

Regional and subtype-dependent miRNA signatures in sporadic Creutzfeldt-Jakob disease are accompanied by alterations in miRNA silencing machinery and biogenesis

Increasing evidence indicates that microRNAs (miRNAs) are contributing factors to neurodegeneration. Alterations in miRNA signatures have been reported in several neurodegenerative dementias, but data in prion diseases are restricted to ex vivo and animal models. The present study identified significant miRNA expression pattern alterations in the frontal cortex and cerebellum of sporadic Creutzfeldt-Jakob disease (sCJD) patients. These changes display a highly regional and disease subtype-dependent regulation that correlates with brain pathology. We demonstrate that selected miRNAs are enriched in sCJD isolated Argonaute(Ago)-binding complexes in disease, indicating their incorporation into RNA-induced silencing complexes, and further suggesting their contribution to disease-associated gene expression changes. Alterations in the miRNA-mRNA regulatory machinery and perturbed levels of miRNA biogenesis key components in sCJD brain samples reported here further implicate miRNAs in sCJD gene expression (de)regulation. We also show that a subset of sCJD-altered miRNAs are commonly changed in Alzheimer's disease, dementia with Lewy bodies and fatal familial insomnia, suggesting potential common mechanisms underlying these neurodegenerative processes. Additionally, we report no correlation between brain and cerebrospinal fluid (CSF) miRNA-profiles in sCJD, indicating that CSF-miRNA profiles do not faithfully mirror miRNA alterations detected in brain tissue of human prion diseases. Finally, utilizing a sCJD MM1 mouse model, we analyzed the miRNA deregulation patterns observed in sCJD in a temporal manner. While fourteen sCJD-related miRNAs were validated at clinical stages, only two of those were changed at early symptomatic phase, suggesting that the miRNAs altered in sCJD may contribute to later pathogenic processes. Altogether, the present work identifies alterations in the miRNA network, biogenesis and miRNA-mRNA silencing machinery in sCJD, whereby contributions to disease mechanisms deserve further investigation.

Atypical Creutzfeldt-Jakob disease with PrP-amyloid plaques in white matter: molecular characterization and transmission to bank voles show the M1 strain signature

Amyloid plaques formed by abnormal prion protein (PrP^Sc) aggregates occur with low frequency in Creutzfeldt-Jakob disease, but represent a pathological hallmark of three relatively rare disease histotypes, namely variant CJD, sporadic CJDMV2K (methionine/valine at PRNP codon 129, PrP^Sc type 2 and kuru-type amyloid plaques) and iatrogenic CJDMMiK (MM at codon 129, PrP^Sc of intermediate type and kuru plaques). According to recent studies, however, PrP-amyloid plaques involving the subcortical and deep nuclei white matter may also rarely occur in CJDMM1 (MM at codon 129 and PrP^Sc type 1), the most common CJD histotype.To further characterize the phenotype of atypical CJDMM1 with white matter plaques (p-CJDMM1) and unravel the basis of amyloid plaque formation in such cases, we compared clinical and histopathological features and PrP^Sc physico-chemical properties between 5 p-CJDMM1 and 8 typical CJDMM1 brains lacking plaques. Furthermore, transmission properties after bioassay in two genetic lines of bank voles were also explored in the two groups.All 5 p-CJDMM1 cases had a disease duration longer than one year. Three cases were classified as sporadic CJDMM1, one as sporadic CJDMM1 + 2C and one as genetic CJDE200K-MM1. Molecular mass, protease sensitivity and thermo-solubilization of PrP^Sc aggregates did not differ between p-CJDMM1 and classical CJDMM1 cases. Likewise, transmission properties such as incubation time, lesion profile and PrP^Sc properties in bank voles also matched in the two groups.The present data further define the clinical-pathologic phenotype of p-CJDMM1, definitely establish it as a distinctive CJD histotype and demonstrate that PrP-plaque formation in this histotype is not a strain-specific feature. Since cases lacking amyloid plaques may also manifest a prolonged (i.e. > than one year) disease course, unidentified, host-specific factors likely play a significant role, in addition to disease duration, in generating white matter PrP-amyloid plaques in p-CJDMM1.

Brains with sporadic Creutzfeldt-Jakob disease and copathology showed a prolonged end-stage of disease

AIMS

To investigate the expression of major proteins related to primary neurodegenerative diseases and their prognostic significance in brains with Creutzfeldt-Jakob disease (CJD).

MATERIALS AND METHODS

Thirty consecutive cases of confirmed CJD during the period 2010-2015 at Basque Brain bank were retrospectively reviewed. Moreover, major neurodegenerative-associated proteins (phosphorylated Tau, 4R tau, 3R tau, alpha-synuclein, TDP43, amyloid beta) were tested. Clinical data were reviewed. Cases were divided according to the presence or absence of copathology. Survival curves were also determined.

RESULTS

Copathology was significantly associated with survival in brains with CJD (4.2±1.2 vs 9.2±1.9; P=0.019) and in brains with MM1/MV1 CJD (2.1±1.0 vs 6.7±2.8; P=0.012). Besides, the presence of more than one major neurodegenerative-associated protein was significantly associated with survival (4.2±1.2 vs 10.7±2.6; P=0.017). Thus, univariate analyses further pointed out variables significantly associated with better survival: copathology in CJD (HR=0.430; P=0.033); more than one neurodegenerative-associated protein in CJD (HR=0.369; P=0.036) and copathology in MM1/MV1 CJD (HR=0.525; P=0.032).

CONCLUSION

The existence of copathology significantly prolongs survival in patients with rapidly progressive dementia due to CJD. The study of major neurodegenerative-associated proteins in brains with CJD could allow us to further understand the molecular mechanisms behind prion diseases.

High diagnostic value of second generation CSF RT-QuIC across the wide spectrum of CJD prions

An early and accurate in vivo diagnosis of rapidly progressive dementia remains challenging, despite its critical importance for the outcome of treatable forms, and the formulation of prognosis. Real-Time Quaking-Induced Conversion (RT-QuIC) is an in vitro assay that, for the first time, specifically discriminates patients with prion disease. Here, using cerebrospinal fluid (CSF) samples from 239 patients with definite or probable prion disease and 100 patients with a definite alternative diagnosis, we compared the performance of the first (PQ-CSF) and second generation (IQ-CSF) RT-QuIC assays, and investigated the diagnostic value of IQ-CSF across the broad spectrum of human prions. Our results confirm the high sensitivity of IQ-CSF for detecting human prions with a sub-optimal sensitivity for the sporadic CJD subtypes MM2C and MM2T, and a low sensitivity limited to variant CJD, Gerstmann-Sträussler-Scheinker syndrome and fatal familial insomnia. While we found no difference in specificity between PQ-CSF and IQ-CSF, the latter showed a significant improvement in sensitivity, allowing prion detection in about 80% of PQ-CSF negative CJD samples. Our results strongly support the implementation of IQ-CSF in clinical practice. By rapidly confirming or excluding CJD with high accuracy the assay is expected to improve the outcome for patients and their enrollment in therapeutic trials.

Plasma and cerebrospinal fluid tau and neurofilament concentrations in rapidly progressive neurological syndromes: a neuropathology-based cohort

BACKGROUND AND PURPOSE

Cerebrospinal fluid (CSF) tau and neurofilament light chain (NF-L) proteins have proved to be reliable biomarkers for neuronal damage; however, there is a strong need for blood-based tests.

METHODS

The present study included 132 autopsy cases with rapidly progressive neurological syndromes, including Alzheimer disease (AD) (21), sporadic (65) and genetic (21) Creutzfeldt-Jakob disease (CJD), 25 cases with vascular, neoplastic and inflammatory alterations, and additionally 18 healthy control individuals. CSF tau and NF-L concentrations were measured by enzyme-linked immunosorbent assay. Plasma tau and NF-L concentrations were measured using ultra-sensitive single molecule array technology.

RESULTS

Plasma and CSF tau (R = 0.59, P < 0.001) and NF-L (R = 0.69, P < 0.001) levels correlated significantly (Spearman test). Plasma tau and NF-L levels were significantly higher in all disease groups compared to healthy controls (P < 0.001). Receiver operating characteristic curves were used and area under the curve values for comparisons with controls were 0.82 (AD), 0.94 (sporadic CJD), 0.92 (genetic CJD) and 0.83 (other neurological disorders) for plasma tau and 0.99, 0.99, 1.00 and 0.96 for plasma NF-L, respectively. Molecular subtyping of sporadic CJD showed a strong effect (linear logistic regression) on plasma tau (P < 0.001) but not NF-L levels (P = 0.19).

CONCLUSION

Plasma tau and NF-L concentrations are strongly increased in CJD and show similar diagnostic performance to the corresponding CSF measure. Molecular subtypes of sporadic CJD show different levels of plasma tau. Although not disease-specific, these findings support the use of plasma tau and NF-L as tools to identify, or to rule out, neurodegeneration.

Amyloid-β accumulation in the CNS in human growth hormone recipients in the UK

Human-to-human transmission of Creutzfeldt-Jakob disease (CJD) has occurred through medical procedures resulting in iatrogenic CJD (iCJD). One of the commonest causes of iCJD was the use of human pituitary-derived growth hormone (hGH) to treat primary or secondary growth hormone deficiency. As part of a comprehensive tissue-based analysis of the largest cohort yet collected (35 cases) of UK hGH-iCJD cases, we describe the clinicopathological phenotype of hGH-iCJD in the UK. In the 33/35 hGH-iCJD cases with sufficient paraffin-embedded tissue for full pathological examination, we report the accumulation of the amyloid beta (Aβ) protein associated with Alzheimer's disease (AD) in the brains and cerebral blood vessels in 18/33 hGH-iCJD patients and for the first time in 5/12 hGH recipients who died from causes other than CJD. Aβ accumulation was markedly less prevalent in age-matched patients who died from sporadic CJD and variant CJD. These results are consistent with the hypothesis that Aβ, which can accumulate in the pituitary gland, was present in the inoculated hGH preparations and had a seeding effect in the brains of around 50% of all hGH recipients, producing an AD-like neuropathology and cerebral amyloid angiopathy (CAA), regardless of whether CJD neuropathology had occurred. These findings indicate that Aβ seeding can occur independently and in the absence of the abnormal prion protein in the human brain. Our findings provide further evidence for the prion-like seeding properties of Aβ and give insights into the possibility of iatrogenic transmission of AD and CAA.

Altered Ca2+ homeostasis induces Calpain-Cathepsin axis activation in sporadic Creutzfeldt-Jakob disease

Sporadic Creutzfeldt-Jakob disease (sCJD) is the most prevalent form of human prion disease and it is characterized by the presence of neuronal loss, spongiform degeneration, chronic inflammation and the accumulation of misfolded and pathogenic prion protein (PrP^Sc). The molecular mechanisms underlying these alterations are largely unknown, but the presence of intracellular neuronal calcium (Ca²⁺) overload, a general feature in models of prion diseases, is suggested to play a key role in prion pathogenesis.

Here we describe the presence of massive regulation of Ca²⁺ responsive genes in sCJD brain tissue, accompanied by two Ca²⁺-dependent processes: endoplasmic reticulum stress and the activation of the cysteine proteases Calpains 1/2. Pathogenic Calpain proteins activation in sCJD is linked to the cleavage of their cellular substrates, impaired autophagy and lysosomal damage, which is partially reversed by Calpain inhibition in a cellular prion model. Additionally, Calpain 1 treatment enhances seeding activity of PrP^Sc in a prion conversion assay. Neuronal lysosomal impairment caused by Calpain over activation leads to the release of the lysosomal protease Cathepsin S that in sCJD mainly localises in axons, although massive Cathepsin S overexpression is detected in microglial cells. Alterations in Ca²⁺ homeostasis and activation of Calpain-Cathepsin axis already occur at pre-clinical stages of the disease as detected in a humanized sCJD mouse model.

Altogether our work indicates that unbalanced Calpain-Cathepsin activation is a relevant contributor to the pathogenesis of sCJD at multiple molecular levels and a potential target for therapeutic intervention.

UK Iatrogenic Creutzfeldt-Jakob disease: investigating human prion transmission across genotypic barriers using human tissue-based and molecular approaches

Creutzfeldt–Jakob disease (CJD) is the prototypic human prion disease that occurs most commonly in sporadic and genetic forms, but it is also transmissible and can be acquired through medical procedures, resulting in iatrogenic CJD (iCJD). The largest numbers of iCJD cases that have occurred worldwide have resulted from contaminated cadaveric pituitary-derived human growth hormone (hGH) and its use to treat primary and secondary growth hormone deficiency. We report a comprehensive, tissue-based and molecular genetic analysis of the largest series of UK hGH-iCJD cases reported to date, including in vitro kinetic molecular modelling of genotypic factors influencing prion transmission. The results show the interplay of prion strain and host genotype in governing the molecular, pathological and temporal characteristics of the UK hGH-iCJD epidemic and provide insights into the adaptive mechanisms involved when prions cross genotypic barriers. We conclude that all of the available evidence is consistent with the hypothesis that the UK hGH-iCJD epidemic resulted from transmission of the V2 human prion strain, which is associated with the second most common form of sporadic CJD.

Prion-specific and surrogate CSF biomarkers in Creutzfeldt-Jakob disease: diagnostic accuracy in relation to molecular subtypes and analysis of neuropathological correlates of p-tau and Aβ42 levels

The differential diagnosis of Creutzfeldt-Jakob disease (CJD) from other, sometimes treatable, neurological disorders is challenging, owing to the wide phenotypic heterogeneity of the disease. Real-time quaking-induced prion conversion (RT-QuIC) is a novel ultrasensitive in vitro assay, which, at variance with surrogate neurodegenerative biomarker assays, specifically targets the pathological prion protein (PrP^Sc). In the studies conducted to date in CJD, cerebrospinal fluid (CSF) RT-QuIC showed good diagnostic sensitivity (82–96%) and virtually full specificity. In the present study, we investigated the diagnostic value of both prion RT-QuIC and surrogate protein markers in a large patient population with suspected CJD and then evaluated the influence on CSF findings of the CJD type, and the associated amyloid-β (Aβ) and tau neuropathology. RT-QuIC showed an overall diagnostic sensitivity of 82.1% and a specificity of 99.4%. However, sensitivity was lower in CJD types linked to abnormal prion protein (PrP^Sc) type 2 (VV2, MV2K and MM2C) than in typical CJD (MM1). Among surrogate proteins markers (14-3-3, total (t)-tau, and t-tau/phosphorylated (p)-tau ratio) t-tau performed best in terms of both specificity and sensitivity for all sCJD types. Sporadic CJD VV2 and MV2K types demonstrated higher CSF levels of p-tau when compared to other sCJD types and this positively correlated with the amount of tiny tau deposits in brain areas showing spongiform change. CJD patients showed moderately reduced median Aβ42 CSF levels, with 38% of cases having significantly decreased protein levels in the absence of Aβ brain deposits. Our results: (1) support the use of both RT-QuIC and t-tau assays as first line laboratory investigations for the clinical diagnosis of CJD; (2) demonstrate a secondary tauopathy in CJD subtypes VV2 and MV2K, correlating with increased p-tau levels in the CSF and (3) provide novel insight into the issue of the accuracy of CSF p-tau and Aβ42 as markers of brain tauopathy and β-amyloidosis.

Validation of α-Synuclein as a CSF Biomarker for Sporadic Creutzfeldt-Jakob Disease

The analysis of cerebrospinal fluid (CSF) biomarkers gains importance in the differential diagnosis of prion diseases. However, no single diagnostic tool or combination of them can unequivocally confirm prion disease diagnosis. Electrochemiluminescence (ECL)-based immunoassays have demonstrated to achieve high diagnostic accuracy in a variety of sample types due to their high sensitivity and dynamic range. Quantification of CSF α-synuclein (a-syn) by an in-house ECL-based ELISA assay has been recently reported as an excellent approach for the diagnosis of sporadic Creutzfeldt-Jakob disease (sCJD), the most prevalent form of human prion disease. In the present study, we validated a commercially available ECL-based a-syn ELISA platform as a diagnostic test for correct classification of sCJD cases. CSF a-syn was analysed in 203 sCJD cases with definite diagnosis and in 445 non-CJD cases. We investigated reproducibility and stability of CSF a-syn and made recommendations for its analysis in the sCJD diagnostic workup. A sensitivity of 98% and a specificity of 97% were achieved when using an optimal cut-off of 820 pg/mL a-syn. Moreover, we were able to show a negative correlation between a-syn levels and disease duration suggesting that CSF a-syn may be a good prognostic marker for sCJD patients. The present study validates the use of a-syn as a CSF biomarker of sCJD and establishes the clinical and pre-analytical parameters for its use in differential diagnosis in clinical routine. Additionally, the current test presents some advantages compared to other diagnostic approaches: it is fast, economic, requires minimal amount of CSF and a-syn levels are stable along disease progression.

Cystatin F is a biomarker of prion pathogenesis in mice

Misfolding of the cellular prion protein (PrP^C) into the scrapie prion protein (PrP^Sc) results in progressive, fatal, transmissible neurodegenerative conditions termed prion diseases. Experimental and epidemiological evidence point toward a protracted, clinically silent phase in prion diseases, yet there is no diagnostic test capable of identifying asymptomatic individuals incubating prions. In an effort to identify early biomarkers of prion diseases, we have compared global transcriptional profiles in brains from pre-symptomatic prion-infected mice and controls. We identified Cst7, which encodes cystatin F, as the most strongly upregulated transcript in this model. Early and robust upregulation of Cst7 mRNA levels and of its cognate protein was validated in additional mouse models of prion disease. Surprisingly, we found no significant increase in cystatin F levels in both cerebrospinal fluid or brain parenchyma of patients with Creutzfeldt-Jakob disease compared to Alzheimer’s disease or non-demented controls. Our results validate cystatin F as a useful biomarker of early pathogenesis in experimental models of prion disease, and point to unexpected species-specific differences in the transcriptional responses to prion infections.

Neuroradiology of human prion diseases, diagnosis and differential diagnosis

Human transmissible spongiform encephalopathies (TSEs), or prion diseases, are invariably fatal conditions associated with a range of clinical presentations. TSEs are classified as sporadic [e.g. sporadic Creutzfeldt-Jakob disease (sCJD), which is the most frequent form], genetic (e.g. Gerstmann-Straussler-Scheinker disease, fatal familial insomnia, and inherited CJD), and acquired or infectious (e.g. Kuru, iatrogenic CJD, and variant CJD). In the past, brain imaging played a supporting role in the diagnosis of TSEs, whereas nowadays magnetic resonance imaging (MRI) plays such a prominent role that MRI findings have been included in the diagnostic criteria for sCJD. Currently, MRI is required for all patients with a clinical suspicion of TSEs. Thus, MRI semeiotics of TSEs should become part of the cultural baggage of any radiologist. The purposes of this update on the neuroradiology of CJD are to (i) review the pathophysiology and clinical presentation of TSEs, (ii) describe both typical and atypical MRI findings of CJD, and (iii) illustrate diseases mimicking CJD, underlining the MRI key findings useful in the differential diagnosis.

Diagnostic and prognostic value of human prion detection in cerebrospinal fluid

OBJECTIVE

Several prion amplification systems have been proposed for detection of prions in cerebrospinal fluid (CSF), most recently, the measurements of prion seeding activity with second-generation real-time quaking-induced conversion (RT-QuIC). The objective of this study was to investigate the diagnostic performance of the RT-QuIC prion test in the broad phenotypic spectrum of prion diseases.

METHODS

We performed CSF RT-QuIC testing in 2,141 patients who had rapidly progressive neurological disorders, determined diagnostic sensitivity and specificity in 272 cases that were autopsied, and evaluated the impact of mutations and polymorphisms in the PRNP gene, and type 1 or type 2 human prions on diagnostic performance.

RESULTS

The 98.5% diagnostic specificity and 92% sensitivity of CSF RT-QuIC in a blinded retrospective analysis matched the 100% specificity and 95% sensitivity of a blind prospective study. The CSF RT-QuIC differentiated 94% of cases of sporadic Creutzfeldt-Jakob disease (sCJD) MM1 from the sCJD MM2 phenotype, and 80% of sCJD VV2 from sCJD VV1. The mixed prion type 1-2 and cases heterozygous for codon 129 generated intermediate CSF RT-QuIC patterns, whereas genetic prion diseases revealed distinct profiles for each PRNP gene mutation.

INTERPRETATION

The diagnostic performance of the improved CSF RT-QuIC is superior to surrogate marker tests for prion diseases such as 14-3-3 and tau proteins, and together with PRNP gene sequencing the test allows the major prion subtypes to be differentiated in vivo. This differentiation facilitates prediction of the clinicopathological phenotype and duration of the disease-two important considerations for envisioned therapeutic interventions. ANN NEUROL 2017;81:79-92.

Revisiting the Heidenhain Variant of Creutzfeldt-Jakob Disease: Evidence for Prion Type Variability Influencing Clinical Course and Laboratory Findings

The Heidenhain variant defines a peculiar clinical presentation of sporadic Creutzfeldt-Jakob disease (sCJD) characterized by isolated visual disturbances at disease onset and reflecting the early targeting of prions to the occipital cortex. Molecular and histopathological typing, thus far performed in 23 cases, has linked the Heidenhain variant to the MM1 sCJD type. To contribute a comprehensive characterization of cases with the Heidenhain variant, we reviewed a series of 370 definite sCJD cases. Eighteen patients (4.9%) fulfilled the selection criteria. Fourteen of them belonging to sCJD types MM1 or MM1+2C had a short duration of isolated visual symptoms and overall clinical disease, a high prevalence of periodic sharp-wave complexes in EEG, and a marked increase of cerebrospinal fluid proteins t-tau and 14-3-3 levels. In contrast, three cases of the MM 2C or MM 2+1C types showed a longer duration of isolated visual symptoms and overall clinical disease, non-specific EEG findings, and cerebrospinal fluid concentration below threshold for the diagnosis of "probable" CJD of both 14-3-3 and t-tau. However, a brain DWI-MRI disclosed an occipital cortical hyperintensity in the majority of examined cases of both groups. While confirming the strong linkage with the methionine genotype at the polymorphic codon 129 of the prion protein gene, our results definitely establish that the Heidenhain variant can also be associated with the MM 2C sCJD type in addition to the more common MM1 type. Likewise, our results highlight the significant differences in clinical evolution and laboratory findings between cases according to the dominant PrPSc type (type 1 versus type 2).

Inactivation of Prions and Amyloid Seeds with Hypochlorous Acid

Hypochlorous acid (HOCl) is produced naturally by neutrophils and other cells to kill conventional microbes in vivo. Synthetic preparations containing HOCl can also be effective as microbial disinfectants. Here we have tested whether HOCl can also inactivate prions and other self-propagating protein amyloid seeds. Prions are deadly pathogens that are notoriously difficult to inactivate, and standard microbial disinfection protocols are often inadequate. Recommended treatments for prion decontamination include strongly basic (pH ≥~12) sodium hypochlorite bleach, ≥1 N sodium hydroxide, and/or prolonged autoclaving. These treatments are damaging and/or unsuitable for many clinical, agricultural and environmental applications. We have tested the anti-prion activity of a weakly acidic aqueous formulation of HOCl (BrioHOCl) that poses no apparent hazard to either users or many surfaces. For example, BrioHOCl can be applied directly to skin and mucous membranes and has been aerosolized to treat entire rooms without apparent deleterious effects. Here, we demonstrate that immersion in BrioHOCl can inactivate not only a range of target microbes, including spores of Bacillus subtilis, but also prions in tissue suspensions and on stainless steel. Real-time quaking-induced conversion (RT-QuIC) assays showed that BrioHOCl treatments eliminated all detectable prion seeding activity of human Creutzfeldt-Jakob disease, bovine spongiform encephalopathy, cervine chronic wasting disease, sheep scrapie and hamster scrapie; these findings indicated reductions of ≥10³- to 10⁶-fold. Transgenic mouse bioassays showed that all detectable hamster-adapted scrapie infectivity in brain homogenates or on steel wires was eliminated, representing reductions of ≥~10^5.75-fold and >10⁴-fold, respectively. Inactivation of RT-QuIC seeding activity correlated with free chlorine concentration and higher order aggregation or destruction of proteins generally, including prion protein. BrioHOCl treatments had similar effects on amyloids composed of human α-synuclein and a fragment of human tau. These results indicate that HOCl can block the self-propagating activity of prions and other amyloids.

Many serious diseases have been linked to pathogenic states of various proteins. These naturally occurring proteins can be corrupted to form aggregates such as prions and amyloids that propagate in and between tissues by acting as seeds that convert the normal form of the protein into more of the pathological form. For example, corrupted prion protein can cause fatal transmissible neurodegenerative diseases such as Creutzfeldt-Jakob disease in humans, chronic wasting disease in cervids and bovine spongiform encephalopathy. Other amyloid-forming protein aggregates are pathogenic in Parkinson’s, Alzheimer’s, and other diseases. The fact that prions and amyloids are composed predominantly of tough, tightly packed proteins makes them unusually resistant to conventional microbial disinfection procedures. Infectious prions can persist indefinitely in, or on, a variety of materials such as tissues, fluids, tools, instruments, and environmental surfaces, making it important to identify decontaminants that are effective without being dangerous or damaging. Here we show that hypochlorous acid, a disinfectant that is produced naturally by certain cells within the body, has strong anti-prion and anti-amyloid activity. We find that a non-irritating and broadly applicable hypochlorous acid preparation can disinfect prions in tissue homogenates and on stainless steel wires serving as surrogates for surgical instruments.

Iatrogenic and sporadic Creutzfeldt-Jakob disease in 2 sisters without mutation in the prion protein gene

Human genetic prion diseases have invariably been linked to alterations of the prion protein (PrP) gene PRNP. Two sisters died from probable Creutzfeldt-Jakob disease (CJD) in Switzerland within 14 y. At autopsy, both patients had typical spongiform change in their brains accompanied by punctuate deposits of PrP. Biochemical analyses demonstrated proteinase K-resistant PrP. Sequencing of PRNP showed 2 wild-type alleles in both siblings. Retrospectively, clinical data revealed a history of dural transplantation in the initially deceased sister, compatible with a diagnosis of iatrogenic CJD. Clinical and familial histories provided no evidence for potential horizontal transmission. This observation of 2 siblings suffering from CJD without mutations in the PRNP gene suggests potential involvement of non-PRNP genes in prion disease etiology.

Tau pathology in Creutzfeldt-Jakob disease revisited

Creutzfeldt-Jakob disease (CJD) is a human prion disease with different etiologies. To determine the spectrum of tau pathologies in CJD, we assessed phospho-Tau (pTau) immunoreactivities in 75 sporadic CJD cases including an evaluation of the entorhinal cortex and six hippocampal subregions. Twelve cases (16%) showed only small tau-immunoreactive neuritic profiles. Fifty-two (69.3%) showed additional tau pathology in the medial temporal lobe compatible with primary age related tauopathy (PART). In 22/52 cases the lower pTau immunoreactivity load in the entorhinal cortex as compared to subiculum, dentate gyrus or CA4 region of the hippocampus was significantly different from the typical distribution of the Braak staging. A further 11 cases (14.7%) showed widespread tau pathologies compatible with features of primary tauopathies or the gray matter type of ageing-related tau astrogliopathy (ARTAG). Prominent gray matter ARTAG was also observed in two out of three additionally examined V203I genetic CJD cases. Analysis of cerebrospinal fluid revealed prominent increase of total tau protein in cases with widespread tau pathology, while pTau (T181) level was increased only in four. This correlated with immunohistochemical observations showing less pathology with anti-pTau T181 antibody when compared to anti-pTau S202/T205, T212/S214 and T231. The frequency of tau pathologies is not unusually high in sporadic CJD and does not precisely relate to PrP deposition. However, the pattern of hippocampal tau pathology often deviates from the stages of Braak. Currently applied examination of cerebrospinal fluid pTau (T181) level does not reliably reflect primary tauopathies, PART and ARTAG seen in CJD brains.

An autopsied case of MM1 + MM2-cortical with thalamic-type sporadic Creutzfeldt-Jakob disease presenting with hyperintensities on diffusion-weighted MRI before clinical onset

A 78-year-old Japanese man presented with rapidly progressive dementia and gait disturbances. Eight months before the onset of clinical symptoms, diffusion-weighted magnetic resonance imaging (DWI) demonstrated hyperintensities in the right temporal, right parietal and left medial occipital cortices. Two weeks after symptom onset, DWI showed extensive hyperintensity in the bilateral cerebral cortex, with regions of higher brightness that existed prior to symptom onset still present. Four weeks after clinical onset, periodic sharp wave complexes were identified on an electroencephalogram. Myoclonus was observed 8 weeks after clinical onset. The patient reached an akinetic mutism state and died 5 months after onset. Neuropathological examination showed widespread cerebral neocortical involvement of fine vacuole-type spongiform changes with large confluent vacuole-type spongiform changes. Spongiform degeneration with neuron loss and hypertrophic astrocytosis was also observed in the striatum and medial thalamus. The inferior olivary nucleus showed severe neuron loss with hypertrophic astrocytosis. Prion protein (PrP) immunostaining showed widespread synaptic-type PrP deposition with perivacuolar-type PrP deposition in the cerebral neocortex. Mild to moderate PrP deposition was also observed extensively in the basal ganglia, thalamus, cerebellum and brainstem, but it was not apparent in the inferior olivary nucleus. PrP gene analysis showed no mutations, and polymorphic codon 129 showed methionine homozygosity. Western blot analysis of protease-resistant PrP showed both type 1 scrapie type PrP (PrP^Sc ) and type 2 PrP^Sc . Based on the relationship between the neuroimaging and pathological findings, we speculated that cerebral cortical lesions with large confluent vacuoles and type 2 PrP^Sc would show higher brightness and continuous hyperintensity on DWI than those with fine vacuoles and type 1 PrP^Sc . We believe the present patient had a combined form of MM1 + MM2-cortical with thalamic-type sporadic Creutzfeldt-Jakob disease (sCJD), which suggests a broader spectrum of sCJD clinicopathological findings.

Altered Mitochondria, Protein Synthesis Machinery, and Purine Metabolism Are Molecular Contributors to the Pathogenesis of Creutzfeldt-Jakob Disease

Neuron loss, synaptic decline, and spongiform change are the hallmarks of sporadic Creutzfeldt-Jakob disease (sCJD), and may be related to deficiencies in mitochondria, energy metabolism, and protein synthesis. To investigate these relationships, we determined the expression levels of genes encoding subunits of the 5 protein complexes of the electron transport chain, proteins involved in energy metabolism, nucleolar and ribosomal proteins, and enzymes of purine metabolism in frontal cortex samples from 15 cases of sCJD MM1 and age-matched controls. We also assessed the protein expression levels of subunits of the respiratory chain, initiation and elongation translation factors of protein synthesis, and localization of selected mitochondrial components. We identified marked, generalized alterations of mRNA and protein expression of most subunits of all 5 mitochondrial respiratory chain complexes in sCJD cases. Expression of molecules involved in protein synthesis and purine metabolism were also altered in sCJD. These findings point to altered mRNA and protein expression of components of mitochondria, protein synthesis machinery, and purine metabolism as components of the pathogenesis of CJD.

Dura mater is a potential source of Aβ seeds

Deposition of amyloid-β (Aβ) in the brain parenchyma and vessels is one of the hallmarks of Alzheimer disease (AD). Recent observations of Aβ deposition in iatrogenic Creutzfeldt-Jakob disease (iCJD) after dural grafting or treatment with pituitary extracts raised concerns whether Aβ is capable of transmitting disease as seen in prion diseases by the disease-associated prion protein. To address this issue, we re-sampled and re-evaluated archival material, including the grafted dura mater of two cases with iCJD (28 and 33-years-old) without mutations in the AβPP, PSEN1 and PSEN2 genes, and carrying ε3/ε3 alleles of the APOE gene. In addition, we evaluated 84 dura mater samples obtained at autopsy (mean age 84.9 ± 0.3) in the community-based VITA study for the presence of Aβ deposition. We show that the dura mater may harbor Aβ deposits (13 %) in the form of cerebral amyloid angiopathy or amorphous aggregates. In both iCJD cases, the grafted dura mater had accumulated Aβ. The morphology and distribution pattern of cerebral Aβ deposition together with the lack of tau pathology distinguishes the Aβ proteinopathy in iCJD from AD, from that seen in young individuals without cognitive decline carrying one or two APOE4 alleles, and from that related to traumatic brain injury. Our novel findings of Aβ deposits in the dura mater, including the grafted dura, and the distinct cerebral Aβ distribution in iCJD support the seeding properties of Aβ. However, in contrast to prion diseases, our study suggests that such Aβ seeding is unable to reproduce the full clinicopathological phenotype of AD.

Advanced tests for early and accurate diagnosis of Creutzfeldt-Jakob disease

Early and accurate diagnosis of Creutzfeldt-Jakob disease (CJD) is a necessary to distinguish this untreatable disease from treatable rapidly progressive dementias, and to prevent iatrogenic transmission. Currently, definitive diagnosis of CJD requires detection of the abnormally folded, CJD-specific form of protease-resistant prion protein (PrP(CJD)) in brain tissue obtained postmortem or via biopsy; therefore, diagnosis of sporadic CJD in clinical practice is often challenging. Supporting investigations, including MRI, EEG and conventional analyses of cerebrospinal fluid (CSF) biomarkers, are helpful in the diagnostic work-up, but do not allow definitive diagnosis. Recently, novel ultrasensitive seeding assays, based on the amplified detection of PrP(CJD), have improved the diagnostic process; for example, real-time quaking-induced conversion (RT-QuIC) is a sensitive method to detect prion-seeding activity in brain homogenate from humans with any subtype of sporadic CJD. RT-QuIC can also be used for in vivo diagnosis of CJD: its diagnostic sensitivity in detecting PrP(CJD) in CSF samples is 96%, and its specificity is 100%. Recently, we provided evidence that RT-QuIC of olfactory mucosa brushings is a 97% sensitive and 100% specific for sporadic CJD. These assays provide a basis for definitive antemortem diagnosis of prion diseases and, in doing so, improve prospects for reducing the risk of prion transmission. Moreover, they can be used to evaluate outcome measures in therapeutic trials for these as yet untreatable infections.

The Priority position paper: Protecting Europe's food chain from prions

Bovine spongiform encephalopathy (BSE) created a global European crisis in the 1980s and 90s, with very serious health and economic implications. Classical BSE now appears to be under control, to a great extent as a result of a global research effort that identified the sources of prions in meat and bone meal (MBM) and developed new animal-testing tools that guided policy. Priority ( www.prionpriority.eu ) was a European Union (EU) Framework Program 7 (FP7)-funded project through which 21 European research institutions and small and medium enterprises (SMEs) joined efforts between 2009 and 2014, to conduct coordinated basic and applied research on prions and prion diseases. At the end of the project, the Priority consortium drafted a position paper ( www.prionpriority.eu/Priority position paper) with its main conclusions. In the present opinion paper, we summarize these conclusions. With respect to the issue of re-introducing ruminant protein into the feed-chain, our opinion is that sustaining an absolute ban on feeding ruminant protein to ruminants is essential. In particular, the spread and impact of non-classical forms of scrapie and BSE in ruminants is not fully understood and the risks cannot be estimated. Atypical prion agents will probably continue to represent the dominant form of prion diseases in the near future in Europe. Atypical L-type BSE has clear zoonotic potential, as demonstrated in experimental models. Similarly, there are now data indicating that the atypical scrapie agent can cross various species barriers. More epidemiological data from large cohorts are necessary to reach any conclusion on the impact of its transmissibility on public health. Re-evaluations of safety precautions may become necessary depending on the outcome of these studies. Intensified searching for molecular determinants of the species barrier is recommended, since this barrier is key for important policy areas and risk assessment. Understanding the structural basis for strains and the basis for adaptation of a strain to a new host will require continued fundamental research, also needed to understand mechanisms of prion transmission, replication and how they cause nervous system dysfunction and death. Early detection of prion infection, ideally at a preclinical stage, also remains crucial for development of effective treatment strategies.

Cerebrospinal fluid markers in the differentiation of molecular subtypes of sporadic Creutzfeldt-Jakob disease

BACKGROUND AND PURPOSE

Cerebrospinal fluid (CSF) analysis supports the clinical diagnosis of sporadic Creutzfeldt-Jakob disease (sCJD) when applied within an adequate clinical context. A diagnostic potential has been attributed to CSF proteins such as 14-3-3, but also tau protein, phosphorylated tau (181P) (p-tau) protein, amyloid β1-42 , S100B and neuron-specific enolase (NSE). There has been only limited information available about the contribution of CSF analysis in the differentiation of various molecular sCJD subtypes.

METHODS

The CSF levels of the aforementioned proteins from 73 sCJD patients with distinct molecular subtypes were determined.

RESULTS

Differences in tau values were significant amongst the homozygous patients (MM and VV genotype) compared to the heterozygous group (P = 0.07 and P = 0.02 respectively). Significantly higher CSF tau levels (P = 0.003) and NSE (P = 0.02) but lower p-tau/tau ratio (P = 0.01) were observed in MM1 compared to MM2 patients. The p-tau/tau ratio enabled the differentiation of MV genotype with higher levels in PrP(sc) type 2 (P = 0.04). Elevation of S100B (P < 0.001) and NSE (P = 0.03) was observed in VV2 compared to VV1 subtype. PRNP codon 129 genotype, PrP(sc) isotype, disease duration and clinical stage influenced the test sensitivity in all proteins.

CONCLUSIONS

Cerebrospinal fluid protein levels might be useful in the pre-mortem differentiation of molecular sCJD subtypes when the codon 129 genotype is known.

The Distribution of Prion Protein Allotypes Differs Between Sporadic and Iatrogenic Creutzfeldt-Jakob Disease Patients

Sporadic Creutzfeldt-Jakob disease (sCJD) is the most prevalent of the human prion diseases, which are fatal and transmissible neurodegenerative diseases caused by the infectious prion protein (PrP^Sc). The origin of sCJD is unknown, although the initiating event is thought to be the stochastic misfolding of endogenous prion protein (PrP^C) into infectious PrP^Sc. By contrast, human growth hormone-associated cases of iatrogenic CJD (iCJD) in the United Kingdom (UK) are associated with exposure to an exogenous source of PrP^Sc. In both forms of CJD, heterozygosity at residue 129 for methionine (M) or valine (V) in the prion protein gene may affect disease phenotype, onset and progression. However, the relative contribution of each PrP^C allotype to PrP^Sc in heterozygous cases of CJD is unknown. Using mass spectrometry, we determined that the relative abundance of PrP^Sc with M or V at residue 129 in brain specimens from MV cases of sCJD was highly variable. This result is consistent with PrP^C containing an M or V at residue 129 having a similar propensity to misfold into PrP^Sc thus causing sCJD. By contrast, PrP^Sc with V at residue 129 predominated in the majority of the UK human growth hormone associated iCJD cases, consistent with exposure to infectious PrP^Sc containing V at residue 129. In both types of CJD, the PrP^Sc allotype ratio had no correlation with CJD type, age at clinical onset, or disease duration. Therefore, factors other than PrP^Sc allotype abundance must influence the clinical progression and phenotype of heterozygous cases of CJD.

In Creutzfeldt-Jakob disease (CJD), heterozygosity at residue 129 for methionine or valine in normal prion protein may affect disease phenotype, onset and progression. However, the relative contribution of each prion protein allotype to the infectious, disease associated form of prion protein (PrP^Sc) is unknown. Here we report the novel observation that in heterozygous cases of sporadic CJD the PrP^Sc allotype ratio is highly variable. This case-by-case variability is consistent with the origin of sporadic CJD being the spontaneous, but random, misfolding of either host prion protein allotype into infectious PrP^Sc. By contrast, in heterozygous cases of iatrogenic CJD in the United Kingdom resulting from exposure to contaminated human growth hormone, the PrP^Sc allotype ratio is much more homogeneous and consistent with exposure to infectious PrP^Sc containing valine at residue 129. Surprisingly, the PrP^Sc allotype ratio did not correlate with disease onset or duration in either disease type. Thus, factors other than PrP^Sc allotype ratio likely influence the clinical progression of heterozygous cases of CJD. Moreover, our results suggest that the ratio of methionine to valine in PrP^Sc may be a means of determining the origin of prion infection.

Molecular Pathological Classification of Neurodegenerative Diseases: Turning towards Precision Medicine

Neurodegenerative diseases (NDDs) are characterized by selective dysfunction and loss of neurons associated with pathologically altered proteins that deposit in the human brain but also in peripheral organs. These proteins and their biochemical modifications can be potentially targeted for therapy or used as biomarkers. Despite a plethora of modifications demonstrated for different neurodegeneration-related proteins, such as amyloid-β, prion protein, tau, α-synuclein, TAR DNA-binding protein 43 (TDP-43), or fused in sarcoma protein (FUS), molecular classification of NDDs relies on detailed morphological evaluation of protein deposits, their distribution in the brain, and their correlation to clinical symptoms together with specific genetic alterations. A further facet of the neuropathology-based classification is the fact that many protein deposits show a hierarchical involvement of brain regions. This has been shown for Alzheimer and Parkinson disease and some forms of tauopathies and TDP-43 proteinopathies. The present paper aims to summarize current molecular classification of NDDs, focusing on the most relevant biochemical and morphological aspects. Since the combination of proteinopathies is frequent, definition of novel clusters of patients with NDDs needs to be considered in the era of precision medicine. Optimally, neuropathological categorizing of NDDs should be translated into in vivo detectable biomarkers to support better prediction of prognosis and stratification of patients for therapy trials.

Mitochondrial DNA differentiates Alzheimer's disease from Creutzfeldt-Jakob disease

INTRODUCTION

Low content of cell-free mitochondrial DNA (mtDNA) in cerebrospinal fluid (CSF) is a biomarker of early stage Alzheimer's disease (AD), but whether mtDNA is altered in a rapid neurodegenerative dementia such as Creutzfeldt-Jakob disease is unknown.

METHODS

CSF mtDNA was measured using digital polymerase chain reaction (dPCR) in two independent cohorts comprising a total of 112 patients diagnosed with sporadic Creutzfeldt-Jakob disease (sCJD), probable AD, or non-Alzheimer's type dementia.

RESULTS

Patients with AD exhibit low mtDNA content in CSF compared with patients diagnosed with sCJD or with non-Alzheimer's type dementias. The CSF concentration of mtDNA does not correlate with Aβ, t-tau, p-tau, and 14-3-3 protein levels in CSF.

DISCUSSION

Low-CSF mtDNA is not a consequence of brain damage and allows the differential diagnosis of AD from sCJD and other dementias. These results support the hypothesis that mtDNA in CSF is a pathophysiological biomarker of AD.

Detection of Atypical H-Type Bovine Spongiform Encephalopathy and Discrimination of Bovine Prion Strains by Real-Time Quaking-Induced Conversion

Prion diseases of cattle include the classical bovine spongiform encephalopathy (C-BSE) and the atypical H-type BSE (H-BSE) and L-type BSE (L-BSE) strains. Although the C- and L-BSE strains can be detected and discriminated by ultrasensitive real-time quaking-induced conversion (RT-QuIC) assays, no such test has yet been described for the detection of H-BSE or the discrimination of each of the major bovine prion strains. Here, we demonstrate an RT-QuIC assay for H-BSE that can detect as little as 10(-9) dilutions of brain tissue and neat cerebrospinal fluid samples from clinically affected cattle. Moreover, comparisons of the reactivities with different recombinant prion protein substrates and/or immunoblot band profiles of proteinase K-treated RT-QuIC reaction products indicated that H-, L-, and C-BSE have distinctive prion seeding activities and can be discriminated by RT-QuIC on this basis.

Clinicopathological Correlations and Concomitant Pathologies in Rapidly Progressive Dementia: A Brain Bank Series

BACKGROUND

Rapidly progressive dementia (RPD) is caused by a heterogeneous group of both neurodegenerative and non-neurodegenerative disorders. The presence of concomitant pathologies, mainly Alzheimer's disease (AD), may act as a confounding variable in the diagnostic process of this group of diseases.

OBJECTIVES

We aimed to describe clinicopathological features, including Alzheimer's co-pathology, and diagnostic accuracy in a postmortem series of RPD.

METHODS

Retrospective analysis of 160 brain donors with RPD (defined as 2 years of disease duration from the first symptom to death) registered at the Neurological Tissue Bank of the Biobanc-Hospital Clínic-IDIBAPS, from 2001 to 2011.

RESULTS

Prion diseases were the most frequent neuropathological diagnosis (67%), followed by non-prion neurodegenerative pathologies (17%), mostly AD and dementia with Lewy bodies, and non-neurodegenerative diseases (16%). We observed clinicopathological diagnostic agreement in 94% of the patients with prion RPD but only in 21% of those with non-prion RPD. Four patients with potentially treatable disorders were diagnosed, while still alive, as having Creutzfeldt-Jakob disease. Concomitant pathologies were detected in 117 (73%). Among all RPD cases, 51 presented moderate or frequent mature β-amyloid plaques (neuritic plaques), which are considered to be associated with positive amyloid biomarkers in vivo.

CONCLUSIONS

Prion diseases were accurately identified in our series. In contrast, non-prion RPD diagnosis was poor while the patients were still alive, supporting the need for better diagnostic tools and confirmatory neuropathological studies. The presence of concomitant AD pathology in RPD should be taken into account in the interpretation of amyloid biomarkers.

Evidence for human transmission of amyloid-β pathology and cerebral amyloid angiopathy

More than two hundred individuals developed Creutzfeldt-Jakob disease (CJD) worldwide as a result of treatment, typically in childhood, with human cadaveric pituitary-derived growth hormone contaminated with prions. Although such treatment ceased in 1985, iatrogenic CJD (iCJD) continues to emerge because of the prolonged incubation periods seen in human prion infections. Unexpectedly, in an autopsy study of eight individuals with iCJD, aged 36-51 years, in four we found moderate to severe grey matter and vascular amyloid-β (Aβ) pathology. The Aβ deposition in the grey matter was typical of that seen in Alzheimer's disease and Aβ in the blood vessel walls was characteristic of cerebral amyloid angiopathy and did not co-localize with prion protein deposition. None of these patients had pathogenic mutations, APOE ε4 or other high-risk alleles associated with early-onset Alzheimer's disease. Examination of a series of 116 patients with other prion diseases from a prospective observational cohort study showed minimal or no Aβ pathology in cases of similar age range, or a decade older, without APOE ε4 risk alleles. We also analysed pituitary glands from individuals with Aβ pathology and found marked Aβ deposition in multiple cases. Experimental seeding of Aβ pathology has been previously demonstrated in primates and transgenic mice by central nervous system or peripheral inoculation with Alzheimer's disease brain homogenate. The marked deposition of parenchymal and vascular Aβ in these relatively young patients with iCJD, in contrast with other prion disease patients and population controls, is consistent with iatrogenic transmission of Aβ pathology in addition to CJD and suggests that healthy exposed individuals may also be at risk of iatrogenic Alzheimer's disease and cerebral amyloid angiopathy. These findings should also prompt investigation of whether other known iatrogenic routes of prion transmission may also be relevant to Aβ and other proteopathic seeds associated with neurodegenerative and other human diseases.

Inconsistency in the analysis of morphological deformities in chironomidae (Insecta: Diptera) larvae

The incidence of morphological deformities of chironomid larvae as an indicator of sediment toxicity has been studied for decades. However, standards for deformity analysis are lacking. The authors evaluated whether 25 experts diagnosed larval deformities in a similar manner. Based on high-quality digital images, the experts rated 211 menta of Chironomus spp. larvae as normal or deformed. The larvae were from a site with polluted sediments or from a reference site. The authors revealed this to a random half of the experts, and the rest conducted the assessment blind. The authors quantified the interrater agreement by kappa coefficient, tested whether open and blind assessments differed in deformity incidence and in differentiation between the sites, and identified those deformity types rated most consistently or inconsistently. The total deformity incidence varied greatly, from 10.9% to 66.4% among experts. Kappa coefficient across rater pairs averaged 0.52, indicating insufficient agreement. The deformity types rated most consistently were those missing teeth or with extra teeth. The open and blind assessments did not differ, but differentiation between sites was clearest for raters who counted primarily absolute deformities such as missing and extra teeth and excluded apparent mechanical aberrations or deviations in tooth size or symmetry. The highly differing criteria in deformity assignment have likely led to inconsistent results in midge larval deformity studies and indicate an urgent need for standardization of the analysis.

Structural determinants of phenotypic diversity and replication rate of human prions

The infectious pathogen responsible for prion diseases is the misfolded, aggregated form of the prion protein, PrP^Sc. In contrast to recent progress in studies of laboratory rodent-adapted prions, current understanding of the molecular basis of human prion diseases and, especially, their vast phenotypic diversity is very limited. Here, we have purified proteinase resistant PrP^Sc aggregates from two major phenotypes of sporadic Creutzfeldt-Jakob disease (sCJD), determined their conformational stability and replication tempo in vitro, as well as characterized structural organization using recently emerged approaches based on hydrogen/deuterium (H/D) exchange coupled with mass spectrometry. Our data clearly demonstrate that these phenotypically distant prions differ in a major way with regard to their structural organization, both at the level of the polypeptide backbone (as indicated by backbone amide H/D exchange data) as well as the quaternary packing arrangements (as indicated by H/D exchange kinetics for histidine side chains). Furthermore, these data indicate that, in contrast to previous observations on yeast and some murine prion strains, the replication rate of sCJD prions is primarily determined not by conformational stability but by specific structural features that control the growth rate of prion protein aggregates.

Sporadic Creutzfeldt-Jakob disease (sCJD) represents ~90% of all human prion diseases worldwide. This neurodegenerative disease, which is transmissible and invariably fatal, is characterized by variable progression rates and remarkable diversity of clinical and pathological traits. The infectious sCJD prions propagating the pathology mainly in the brain are assemblies of abnormally folded isoform (PrP^Sc) of a host-encoded prion protein (PrP^C). The structure and replication mechanisms of human prions are unknown, and whether the PrP^Sc subtypes identified by proteolytic fragmentation represent distinct strains of sCJD prions has been debated. Here, we isolated sCJD prions from patients with two very distant phenotypes of the disease, compared their structural organization using recently developed biophysical techniques, and investigated their replication in vitro. Our data indicate that these sCJD prions are characterized by different secondary structure organization and quaternary packing arrangements, and that these structural differences are responsible for distinct prion replication rates and unique phenotypic characteristics of the disease. Furthermore, our analysis reveals that, contrary to previous observations for yeast prions, the replication tempo of sCJD prions is determined not so much by their conformational stability but by specific structural features that control the growth speed of prion particles.

Atypical sporadic CJD-MM phenotype with white matter kuru plaques associated with intranuclear inclusion body and argyrophilic grain disease

We describe an atypical neuropathological phenotype of sporadic Creutzfeldt-Jakob disease in a 76-year-old man. The clinical symptoms were characterized by progressive dementia, gait ataxia, rigidity and urinary incontinence. The disease duration was 6 weeks. MRI did not show prominent atrophy or hyperintensities in cortical areas, striatum or thalamus. Biomarker examination of the cerebrospinal fluid deviated from that seen in pure Alzheimer's disease. Triphasic waves in the EEG were detected only later in the disease course, while 14-3-3 assay was positive. PRNP genotyping revealed methionine homozygosity (MM) at codon 129. Neuropathology showed classical CJD changes corresponding to the MM type 1 cases. However, a striking feature was the presence of abundant kuru-type plaques in the white matter. This rare morphology was associated with neuropathological signs of intranuclear inclusion body disease and advanced stage of argyrophilic grain disease. These alterations did not show correlation with each other, thus seemed to develop independently. This case further highlights the complexity of neuropathological alterations in the ageing brain.

Implications of prion adaptation and evolution paradigm for human neurodegenerative diseases

There is a growing body of evidence indicating that number of human neurodegenerative diseases, including Alzheimer disease, Parkinson disease, fronto-temporal dementias, and amyotrophic lateral sclerosis, propagate in the brain via prion-like intercellular induction of protein misfolding. Prions cause lethal neurodegenerative diseases in humans, the most prevalent being sporadic Creutzfeldt-Jakob disease (sCJD); they self-replicate and spread by converting the cellular form of prion protein (PrP^C) to a misfolded pathogenic conformer (PrP^Sc). The extensive phenotypic heterogeneity of human prion diseases is determined by polymorphisms in the prion protein gene, and by prion strain-specific conformation of PrP^Sc. Remarkably, even though informative nucleic acid is absent, prions may undergo rapid adaptation and evolution in cloned cells and upon crossing the species barrier. In the course of our investigation of this process, we isolated distinct populations of PrP^Sc particles that frequently co-exist in sCJD. The human prion particles replicate independently and undergo competitive selection of those with lower initial conformational stability. Exposed to mutant substrate, the winning PrP^Sc conformers are subject to further evolution by natural selection of the subpopulation with the highest replication rate due to the lowest stability. Thus, the evolution and adaptation of human prions is enabled by a dynamic collection of distinct populations of particles, whose evolution is governed by the selection of progressively less stable, faster replicating PrP^Sc conformers. This fundamental biological mechanism may explain the drug resistance that some prions gained after exposure to compounds targeting PrP^Sc. Whether the phenotypic heterogeneity of other neurodegenerative diseases caused by protein misfolding is determined by the spectrum of misfolded conformers (strains) remains to be established. However, the prospect that these conformers may evolve and adapt by a prion-like mechanism calls for the reevaluation of therapeutic strategies that target aggregates of misfolded proteins, and argues for new therapeutic approaches that will focus on prior pathogenetic steps.

Rapid and sensitive RT-QuIC detection of human Creutzfeldt-Jakob disease using cerebrospinal fluid

Fast, definitive diagnosis of Creutzfeldt-Jakob disease (CJD) is important in assessing patient care options and transmission risks. Real-time quaking-induced conversion (RT-QuIC) assays of cerebrospinal fluid (CSF) and nasal-brushing specimens are valuable in distinguishing CJD from non-CJD conditions but have required 2.5 to 5 days. Here, an improved RT-QuIC assay is described which identified positive CSF samples within 4 to 14 h with better analytical sensitivity. Moreover, analysis of 11 CJD patients demonstrated that while 7 were RT-QuIC positive using the previous conditions, 10 were positive using the new assay. In these and further analyses, a total of 46 of 48 CSF samples from sporadic CJD patients were positive, while all 39 non-CJD patients were negative, giving 95.8% diagnostic sensitivity and 100% specificity. This second-generation RT-QuIC assay markedly improved the speed and sensitivity of detecting prion seeds in CSF specimens from CJD patients. This should enhance prospects for rapid and accurate ante mortem CJD diagnosis.

A long-standing problem in dealing with various neurodegenerative protein misfolding diseases is early and accurate diagnosis. This issue is particularly important with human prion diseases, such as CJD, because prions are deadly, transmissible, and unusually resistant to decontamination. The recently developed RT-QuIC test allows for highly sensitive and specific detection of CJD in human cerebrospinal fluid and is being broadly implemented as a key diagnostic tool. However, as currently applied, RT-QuIC takes 2.5 to 5 days and misses 11 to 23% of CJD cases. Now, we have markedly improved RT-QuIC analysis of human CSF such that CJD and non-CJD patients can be discriminated in a matter of hours rather than days with enhanced sensitivity. These improvements should allow for much faster, more accurate, and practical testing for CJD. In broader terms, our study provides a prototype for tests for misfolded protein aggregates that cause many important amyloid diseases, such as Alzheimer’s, Parkinson’s, and tauopathies.

No reactivation of JCV and CMV infections in the temporal cortex and cerebellum of sporadic Creutzfeldt-Jakob disease patients

Sporadic Creutzfeldt-Jakob disease (sCJD) is characterized by great phenotypic variability regarding clinical course and neuropathology. The most prominent disease modifiers are a polymorphism in Codon 129 of the prion protein gene and conformational variations of the misfolded prion protein. The cellular form of the prion protein restricts replication of viruses and may be involved in viral host defense, and viral infections influence the presentation and neuropathology in prion diseased mice. We investigated the occurrence of reactivated persistent viral infections of the brain in brain tissue samples of 25 sCJD patients. No evidence of reactivated JCV and CMV infections could be detected. This suggests that JCV and CMV infections are not reactivated as consequence of prion disease and do not act as disease modifiers in sCJD.

Mathematical models for the diffusion magnetic resonance signal abnormality in patients with prion diseases

In clinical practice signal hyperintensity in the cortex and/or in the striatum on magnetic resonance (MR) diffusion-weighted images (DWIs) is a marker of sporadic Creutzfeldt–Jakob Disease (sCJD). MR diagnostic accuracy is greater than 90%, but the biophysical mechanisms underpinning the signal abnormality are unknown. The aim of this prospective study is to combine an advanced DWI protocol with new mathematical models of the microstructural changes occurring in prion disease patients to investigate the cause of MR signal alterations. This underpins the later development of more sensitive and specific image-based biomarkers. DWI data with a wide a range of echo times and diffusion weightings were acquired in 15 patients with suspected diagnosis of prion disease and in 4 healthy age-matched subjects. Clinical diagnosis of sCJD was made in nine patients, genetic CJD in one, rapidly progressive encephalopathy in three, and Gerstmann–Sträussler–Scheinker syndrome in two. Data were analysed with two bi-compartment models that represent different hypotheses about the histopathological alterations responsible for the DWI signal hyperintensity. A ROI-based analysis was performed in 13 grey matter areas located in affected and apparently unaffected regions from patients and healthy subjects. We provide for the first time non-invasive estimate of the restricted compartment radius, designed to reflect vacuole size, which is a key discriminator of sCJD subtypes. The estimated vacuole size in DWI hyperintense cortex was in the range between 3 and 10 µm that is compatible with neuropathology measurements. In DWI hyperintense grey matter of sCJD patients the two bi-compartment models outperform the classic mono-exponential ADC model. Both new models show that T₂ relaxation times significantly increase, fast and slow diffusivities reduce, and the fraction of the compartment with slow/restricted diffusion increases compared to unaffected grey matter of patients and healthy subjects. Analysis of the raw DWI signal allows us to suggest the following acquisition parameters for optimized detection of CJD lesions: b = 3000 s/mm² and TE = 103 ms. In conclusion, these results provide the first in vivo estimate of mean vacuole size, new insight on the mechanisms of DWI signal changes in prionopathies and open the way to designing an optimized acquisition protocol to improve early clinical diagnosis and subtyping of sCJD.

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An advanced DWI acquisition scheme was applied to 15 patients with suspected sCJD.

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Data fitting with two bi-compartment models outperformed the classic ADC model.

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In affected GM T₂ values were increased, diffusion was more hindered or restricted.

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For the first time an estimate of the restricted compartment radius was provided.

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The radius may reflect vacuole size, which is a key discriminator of sCJD subtypes.