A Novel Combination of Prion Strain Co-Occurrence in Patients with Sporadic Creutzfeldt-Jakob Disease

A case report of an individual with Creutzfeldt-Jakob disease characterized by prolonged isolated thalamic lesions and rare MM2-cortical-type pathology

BACKGROUND

Diffusion-weighted magnetic resonance imaging (DWI) is essential for diagnosing Creutzfeldt-Jakob disease (CJD). Thalamic lesions are rarely detected by DWI in sporadic CJD (sCJD) cases with methionine homozygosity at polymorphic codon 129 (129MM) of the prion protein (PrP) gene. Here, we describe an unusual sCJD case, characterized by prolonged isolated thalamic diffusion hyperintensities and atypical brain pathology, in combination with the 129MM genotype.

CASE PRESENTATION

A 72-year-old Japanese man developed a mild unsteady gait that had persisted for 1 year. DWI revealed isolated thalamic diffusion hyperintensities. Over the following 4 years, his condition progressed to include ataxia and cognitive decline. Repeated cerebrospinal fluid tests were negative for 14-3-3 protein, total tau protein, and real-time quaking-induced conversion assay. Electroencephalography did not show periodic sharp wave complexes or generalized periodic discharges. Despite these findings, thalamic DWI abnormalities persisted and evolved to include cortical lesions in the later stage of the disease. Genetic testing confirmed a 129MM genotype with no pathogenic PrP gene variants. Brain autopsy identified type 2 pathogenic PrP and the absence of the M2-thalamic prion strain, suggesting an MM2-cortical (MM2C)-subtype of sCJD. Histopathology revealed small vacuoles (sv) and patchy-perivacuolar PrP deposits without large vacuoles (lv). Patchy-perivacuolar deposits are a characteristic feature of the MM2C (lv) subtype and indicate MM2C (lv) pathology. Thus, this case was classified as a rare MM2C (sv + lv) subtype. No PrP protein staining was observed in the thalamus, despite spongiform changes with small vacuoles.

CONCLUSIONS

This case underscores the diagnostic challenges of atypical CJD with isolated thalamic abnormalities on DWI. Despite negative cerebrospinal fluid findings and clinical diagnostic criteria, persistent DWI abnormalities and evolving clinical symptoms continued to raise suspicion of CJD. A definitive diagnosis, being the MM2C (sv + lv) subtype of sCJD, was confirmed upon pathological examination. Even when atypical findings, such as isolated thalamic abnormalities, are observed and various tests are negative, if suspicion of CJD cannot be ruled out, it is important to confirm the diagnosis and pathological subtypes via postmortem analysis.

Enhanced Creutzfeldt-Jakob disease surveillance in the older population: Assessment of a protocol for screening brain tissue donations for prion disease

Human prion diseases, including Creutzfeldt-Jakob disease (CJD), occur in sporadic, genetic, and acquired forms. Variant Creutzfeldt-Jakob disease (vCJD) first reported in 1996 in the United Kingdom (UK), resulted from contamination of food with bovine spongiform encephalopathy. There is a concern that UK national surveillance mechanisms might miss some CJD cases (including vCJD), particularly in the older population where other neurodegenerative disorders are more prevalent. We developed a highly sensitive protocol for analysing autopsy brain tissue for the misfolded prion protein (PrPSc ) associated with prion disease, which could be used to screen for prion disease in the elderly. Brain tissue samples from 331 donors to the Edinburgh Brain and Tissue Bank (EBTB), from 2005 to 2022, were analysed, using immunohistochemical analysis on fixed tissue, and five biochemical tests on frozen specimens from six brain regions, based on different principles for detecting PrPSc . An algorithm was established for classifying the biochemical results. To test the effectiveness of the protocol, several neuropathologically confirmed prion disease controls, including vCJD, were included and blinded in the study cohort. On unblinding, all the positive control cases had been correctly identified. No other cases tested positive; our analysis uncovered no overlooked prion disease cases. Our algorithm for classifying cases was effective for handling anomalous biochemical results. An overall analysis suggested that a reduced biochemical protocol employing only three of the five tests on only two brain tissue regions gave sufficient sensitivity and specificity. We conclude that this protocol may be useful as a UK-wide screening programme for human prion disease in selected brains from autopsies in the elderly. Further improvements to the protocol were suggested by enhancements of the in vitro conversion assays made during the course of this study.

V180I genetic Creutzfeldt-Jakob disease: Severe degeneration of the inferior olivary nucleus in an autopsied patient with identification of the M2T prion strain

Genetic Creutzfeldt-Jakob disease (gCJD) with a V180I mutation (V180I gCJD) is the most common type of gCJD in Japan, characterized by an older age at onset, slower progression, and moderate to severe cortical degeneration with spongiform changes and sparing of the brainstem and cerebellum. Degeneration of the inferior olivary nucleus (IO) is rarely observed in patients with CJD but is known to occur in fatal familial insomnia (FFI) and MM2-thalamic-type sporadic CJD (sCJD-MM2T) involving type 2 prion protein (M2T prion). Here we report on an 81-year-old Japanese woman who initially developed depressive symptoms followed by progressive cognitive impairment, myoclonus, and hallucinations and died after a clinical course of 23 months. Insomnia was not evident. Genetic analysis of the prion protein (PrP) identified a V180I mutation with methionine/valine heterozygosity at codon 129. Pathologic analysis demonstrated extensive spongiform degeneration, neuronal loss in the cortices, and weak synaptic-type PrP deposition. Except for IO degeneration, the clinicopathologic features and Western blotting PrP band pattern were compatible with those of previously reported V180I gCJD cases. Quantitative analysis revealed that the neuronal density of the IO, especially in the dorsal area, was considerably reduced to the same extent as that of a patient with sCJD-MM2T but preserved in other patients with V180I gCJD and sCJD-MM1 (this patient, 2.3 ± 0.53/mm2 ; a patient with sCJD-MM2T, 4.2 ± 2; a patient with V180I gCJD, 60.5 ± 9.3; and a patient with sCJD-MM1, 84.5 ± 17.9). Use of the protein misfolding cyclic amplification (PMCA) method confirmed the presence of the M2T prion strain, suggesting that the latter might be associated with IO degeneration in V180I gCJD. Autopsy studies are necessary to better understand the nature of CJD, since even if patients present with the common clinical picture, pathologic analysis might provide new insights, as was the case here.

Understanding the key features of the spontaneous formation of bona fide prions through a novel methodology that enables their swift and consistent generation

Among transmissible spongiform encephalopathies or prion diseases affecting humans, sporadic forms such as sporadic Creutzfeldt-Jakob disease are the vast majority. Unlike genetic or acquired forms of the disease, these idiopathic forms occur seemingly due to a random event of spontaneous misfolding of the cellular PrP (PrPC) into the pathogenic isoform (PrPSc). Currently, the molecular mechanisms that trigger and drive this event, which occurs in approximately one individual per million each year, remain completely unknown. Modelling this phenomenon in experimental settings is highly challenging due to its sporadic and rare occurrence. Previous attempts to model spontaneous prion misfolding in vitro have not been fully successful, as the spontaneous formation of prions is infrequent and stochastic, hindering the systematic study of the phenomenon. In this study, we present the first method that consistently induces spontaneous misfolding of recombinant PrP into bona fide prions within hours, providing unprecedented possibilities to investigate the mechanisms underlying sporadic prionopathies. By fine-tuning the Protein Misfolding Shaking Amplification method, which was initially developed to propagate recombinant prions, we have created a methodology that consistently produces spontaneously misfolded recombinant prions in 100% of the cases. Furthermore, this method gives rise to distinct strains and reveals the critical influence of charged surfaces in this process.

Genetic Creutzfeldt-Jakob disease-M232R with the cooccurrence of multiple prion strains, M1 + M2C + M2T: Report of an autopsy case

Genetic Creutzfeldt-Jakob disease (gCJD) with a methionine to arginine substitution at codon 232 of the prion protein gene (gCJD-M232R) is rare and has only been reported in Japan. We report an autopsy case of gCJD-M232R showing alleles of codon 129 that were homozygous for methionine and the presence of multiple strains of the protease-resistant, abnormal isoform of prion protein (PrP^Sc ), M1 + M2C + M2T. The patient, a 54-year-old Japanese man, died after a clinical course of 21 months characterized by slowly progressive dementia and sleep disturbance. At autopsy, the neuropil of the cerebral neocortex showed a widespread and severe spongiform change. Grape-like clusters of large confluent vacuoles were admixed with fine vacuoles. Neuronal loss was moderate, but reactive astrocytosis was mild. The dorsomedial nucleus of the thalamus and the inferior olivary nucleus showed moderate and severe neuronal loss, respectively. Many amyloid plaques were present in the cerebellar molecular layer. PrP^Sc deposition pattern was predominantly the synaptic type in the cerebrum and corresponded to the plaques in the cerebellum. Perivacuolar deposition was also seen. Western blot analysis of PrP^Sc revealed the predominance of type 2. Moreover, by employing Western blot analysis in combination with the protein misfolding cyclic amplification (PMCA) method, which selectively amplifies the minor M2T prion strain, we demonstrated the presence of M2T, in addition to M1 and M2C strains, in the brain of the patient. PMCA was a powerful method for demonstrating the presence of the M2T strain, although the amount is often small and the transmission is difficult.

Feasibility studies of radioiodinated pyridyl benzofuran derivatives as potential SPECT imaging agents for prion deposits in the brain

INTRODUCTION

Prion diseases are fatal neurodegenerative disorders caused by the deposition of abnormal prion protein aggregates (PrPSc) in the central nervous system. This study aimed to evaluate the use of iodinated pyridyl benzofuran (IPBF) derivatives as single-photon emission computed tomography (SPECT) probes for the detection of cerebral PrPSc deposits.

METHODS

In vitro binding assays of IPBF derivatives were carried out in the recombinant mouse prion protein (rMoPrP) and brain sections of mouse-adapted bovine spongiform encephalopathy (mBSE)-infected mice. SPECT imaging of 5-(5-[123I]iodobenzofuran-2-yl)-N-methylpyridin-2-amine ([123I]IPBF-NHMe) was performed on mBSE-infected and mock-infected mice.

RESULTS

Fluorescence microscopy results showed that fluorescence signals of IPBF derivatives corresponded to the thioflavin-T positive amyloid deposits of PrPSc in the brain sections of mouse-adapted bovine spongiform encephalopathy (mBSE)-infected mice. Among the IPBF derivatives, 5-(5-iodobenzofuran-2-yl)-N-methylpyridin-2-amine (IPBF-NHMe) exhibited the highest binding affinity to the recombinant mouse prion protein (rMoPrP) aggregates with a Ki of 14.3 nM. SPECT/computed tomography (CT) imaging and ex vivo autoradiography demonstrated that the [123I]IPBF-NHMe distribution in brain tissues of mBSE-infected mice co-localized with PrPSc deposits.

CONCLUSION

[123I]IPBF-NHMe appears to be a prospective SPECT tracer for monitoring prion deposits in living brain tissues.

MM2-type sporadic Creutzfeldt-Jakob disease: new diagnostic criteria for MM2-cortical type

OBJECTIVE

To clinically diagnose MM2-cortical (MM2C) and MM2-thalamic (MM2T)-type sporadic Creutzfeldt-Jakob disease (sCJD) at early stage with high sensitivity and specificity.

METHODS

We reviewed the results of Creutzfeldt-Jakob disease Surveillance Study in Japan between April 1999 and September 2019, which included 254 patients with pathologically confirmed prion diseases, including 9 with MM2C-type sCJD (MM2C-sCJD) and 10 with MM2T-type sCJD (MM2T-sCJD), and 607 with non-prion diseases.

RESULTS

According to the conventional criteria of sCJD, 4 of 9 patients with MM2C- and 7 of 10 patients with MM2T-sCJD could not be diagnosed with probable sCJD until their death. Compared with other types of sCJD, patients with MM2C-sCJD showed slower progression of the disease and cortical distribution of hyperintensity lesions on diffusion-weighted images of brain MRI. Patients with MM2T-sCJD also showed relatively slow progression and negative results for most of currently established investigations for diagnosis of sCJD. To clinically diagnose MM2C-sCJD, we propose the new criteria; diagnostic sensitivity and specificity to distinguish 'probable' MM2C-sCJD from other subtypes of sCJD, genetic or acquired prion diseases and non-prion disease controls were 77.8% and 98.5%, respectively. As for MM2T-sCJD, clinical and laboratory features are not characterised enough to develop its diagnostic criteria.

CONCLUSIONS

MM2C-sCJD can be diagnosed at earlier stage using the new criteria with high sensitivity and specificity, although it is still difficult to diagnose MM2T-sCJD clinically.

Two distinct prions in fatal familial insomnia and its sporadic form

Fatal familial insomnia is a genetic prion disease, which is associated with the aspartic acid to asparagine substitution at codon 178 of the prion protein gene. Although the hallmark pathological feature is thalamic and olivary degeneration, there is a patient with an atypical fatal familial insomnia without the hallmark feature. The cause of the pathological variability is unclear. We analysed a Japanese fatal familial insomnia kindred and compared one atypical clinicopathological fatal familial insomnia phenotype case and typical fatal familial insomnia phenotype cases with transmission studies using multiple lines of knock-in mice and with protein misfolding cyclic amplification. We also analysed the transmissibility and the amplification properties of sporadic fatal insomnia. Transmission studies revealed that the typical fatal familial insomnia with thalamic and olivary degeneration showed successful transmission only using knock-in mice expressing human-mouse chimeric prion protein gene. The atypical fatal familial insomnia with spongiform changes showed successful transmission only using knock-in mice expressing bank vole prion protein gene. Two sporadic fatal insomnia cases with thalamic and olivary degeneration showed the same transmissibility as the typical fatal familial insomnia phenotype. Interestingly, one sporadic fatal insomnia case with thalamic/olivary degeneration and spongiform changes showed transmissibility of both the typical and atypical fatal familial insomnia phenotypes. Protein misfolding cyclic amplification could amplify both typical fatal familial insomnia cases and sporadic fatal insomnia cases but not the atypical fatal familial insomnia phenotype or other sporadic Creutzfeldt-Jakob disease subtypes. In addition to clinical findings and neuropathological features, the transmission properties and the amplification properties were different between the typical and atypical fatal familial insomnia phenotypes. It is suggested that two distinct prions were associated with the diversity in the fatal familial insomnia phenotype, and these two prions could also be detected in sporadic fatal insomnia.

Heterogeneity and Architecture of Pathological Prion Protein Assemblies: Time to Revisit the Molecular Basis of the Prion Replication Process?

Prions are proteinaceous infectious agents responsible for a range of neurodegenerative diseases in animals and humans. Prion particles are assemblies formed from a misfolded, β-sheet rich, aggregation-prone isoform (PrP^Sc) of the host-encoded cellular prion protein (PrP^C). Prions replicate by recruiting and converting PrP^C into PrP^Sc, by an autocatalytic process. PrP^Sc is a pleiomorphic protein as different conformations can dictate different disease phenotypes in the same host species. This is the basis of the strain phenomenon in prion diseases. Recent experimental evidence suggests further structural heterogeneity in PrP^Sc assemblies within specific prion populations and strains. Still, this diversity is rather seen as a size continuum of assemblies with the same core structure, while analysis of the available experimental data points to the existence of structurally distinct arrangements. The atomic structure of PrP^Sc has not been elucidated so far, making the prion replication process difficult to understand. All currently available models suggest that PrP^Sc assemblies exhibit a PrP^Sc subunit as core constituent, which was recently identified. This review summarizes our current knowledge on prion assembly heterogeneity down to the subunit level and will discuss its importance with regard to the current molecular principles of the prion replication process.