Two distinct prions in fatal familial insomnia and its sporadic form

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.

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.

A point mutation in GPI-attachment signal peptide accelerates the development of prion disease

A missense variant from methionine to arginine at codon 232 (M232R) of the prion protein gene accounts for ~ 15% of Japanese patients with genetic prion diseases. However, pathogenic roles of the M232R substitution for the induction of prion disease have remained elusive because family history is usually absent in patients with M232R. In addition, the clinicopathologic phenotypes of patients with M232R are indistinguishable from those of sporadic Creutzfeldt-Jakob disease patients. Furthermore, the M232R substitution is located in the glycosylphosphatidylinositol (GPI)-attachment signal peptide that is cleaved off during the maturation of prion proteins. Therefore, there has been an argument that the M232R substitution might be an uncommon polymorphism rather than a pathogenic mutation. To unveil the role of the M232R substitution in the GPI-attachment signal peptide of prion protein in the pathogenesis of prion disease, here we generated a mouse model expressing human prion proteins with M232R and investigated the susceptibility to prion disease. The M232R substitution accelerates the development of prion disease in a prion strain-dependent manner, without affecting prion strain-specific histopathologic and biochemical features. The M232R substitution did not alter the attachment of GPI nor GPI-attachment site. Instead, the substitution altered endoplasmic reticulum translocation pathway of prion proteins by reducing the hydrophobicity of the GPI-attachment signal peptide, resulting in the reduction of N-linked glycosylation and GPI glycosylation of prion proteins. To the best of our knowledge, this is the first time to show a direct relationship between a point mutation in the GPI-attachment signal peptide and the development of disease.

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

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

Establishment and Phenotypic Analysis of the Novel Gaucher Disease Mouse Model With the Partially Humanized Gba1 Gene and F213I Mutation

Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder caused by mutations in the GBA1 gene, which produces the glucocerebrosidase (GCase) protein. There are more than 500 mutations reported in GBA1, among which L444P (p.Leu444Pro) and F213I (p.Phe213Ile) are the most common in the Chinese population, while the function of F213I mutation remains elusive. This study aims to establish the GD mouse model of partially humanized Gba1 gene with F213I mutation. In vitro GCase activity assays showed that the product of partially humanized Gba1 gene, in which the mouse exons 5-7 were replace by the corresponding human exons, displayed similar activity with the wild-type mouse Gba1, while the F213I mutation in the humanized Gba1 led to significant decrease in enzyme activity. ES cell targeting was used to establish the mice expressing the partially humanized Gba1-F213I. Gba1^F213I/+ mice did not show obviously abnormal phenotypes, but homozygous Gba1^F213I/F213I mice died within 24 h after birth, whose epidermal stratum corneum were abnormal from the wild-type. The GCase activity in Gba1^F213I/F213I mice greatly decreased. In conclusion, our results showed that the partially humanized GD mouse model with the F213I mutation was developed and homozygous F213I mutation is lethal for newborn mice.

A fatal familial insomnia patient newly diagnosed as having depression: A case report

INTRODUCTION

Fatal familial insomnia (FFI) is a rare clinical case. The study was mainly to report the clinical symptoms and imaging and genetic characteristics of a FFI case with depression, with relevant literature summarized.

PATIENT CONCERNS

A male, aged 57 years old, with mental disorders and progressive memory decline one year before admission.

DIAGNOSIS

Clinical manifestations: he had obvious abnormal mental behavior, rapidly progressing dementia symptoms, stubborn insomnia, abnormal movements and laryngeal stridor after falling asleep at night. Imaging and genetic test results: the cranial magnetic resonance imaging showed frontal temporal lobe atrophy; the polysomnography results showed no effective sleep; the 14-3-3 test result of cerebrospinal fluid was negative; the prion protein (PRNP) test showed that the D178N gene locus had mutations. And the patient was finally diagnosed as FFI.

INTERVENTIONS

There were no obvious effects in the treatment using medicines such as Risperidone, Olanzapine, Alprazolam, Clonazepam, and Deanxit.

OUTCOMES

Mobility dysfunction of the patient was further aggravated. He was no longer able to move around on his own, and there were serious mental disorders.

CONCLUSION

PRNP examination is of guiding significance for the diagnosis of the FFI of depression. Hence, it is very necessary to perform PRNP examination in clinical diagnosis of FFI of depression.

Defining the Prion Type of Fatal Familial Insomnia

Fatal familial insomnia (FFI) belongs to the genetic human transmissible spongiform encephalopathies (TSE), such as genetic Creutzfeldt-Jakob disease (CJD) or Gerstmann-Straeussler-Scheinker syndrome (GSS). Here, we analyzed the properties of the pathological prion protein in six FFI cases by Western blot analysis, a protein aggregate stability assay, and aggregate deposition characteristics visualized with the paraffin-embedded tissue blot. While in all cases the unglycosylated fragment in Western blot analysis shared the same size with sporadic CJD prion type 2, the reticular/synaptic deposition pattern of the prion aggregates resembled the ones found in sporadic CJD type 1 (CJD types according to the Parchi classification from 1999). Regarding the conformational stability against denaturation with GdnHCl, FFI prion aggregates resembled CJD type 1 more than type 2. Our results suggest that the size of the proteinase-K-resistant fragments is not a valid criterion on its own. Additional criteria supplying information about conformational differences or similarities need to be taken into account. FFI may resemble a prion type with its own conformation sharing properties partly with type 1 and type 2 prions.

Potential for transmission of sporadic Creutzfeldt-Jakob disease through peripheral routes

Five sporadic Creutzfeldt-Jakob disease (CJD) strains have been identified to date, based on differences in clinicopathological features of the patients, the biochemical properties of abnormal prion proteins, and transmission properties. Recent advances in our knowledge about iatrogenic transmission of sporadic CJD have raised the possibility that the infectivity of sporadic CJD strains through peripheral routes is different from that of intracranial infection. To test this possibility, here we assessed systematically the infectivity of sporadic CJD strains through the peripheral route for the first time using a mouse model expressing human prion protein. Although the infectivity of the V2 and M1 sporadic CJD strains is almost the same in intracerebral transmission studies, the V2 strain infected more efficiently than the M1 strain through the peripheral route. The other sporadic CJD strains examined lacked infectivity. Of note, both the V2 and M1 strains showed preference for mice with the valine homozygosity at the PRNP polymorphic codon. These results indicate that the V2 strain is the most infectious sporadic CJD strain for infection through peripheral routes. In addition, these findings raise the possibility that individuals with the valine homozygosity at the PRNP polymorphic codon might have higher risks of infection through peripheral routes compared with the methionine homozygotes. Thus, preventive measures against the transmission of the V2 sporadic CJD strain will be important for the eradication of iatrogenic CJD transmission through peripheral routes.

Phenotypic diversity of genetic Creutzfeldt-Jakob disease: a histo-molecular-based classification

The current classification of sporadic Creutzfeldt–Jakob disease (sCJD) includes six major clinicopathological subtypes defined by the physicochemical properties of the protease-resistant core of the pathologic prion protein (PrP^Sc), defining two major PrP^Sc types (i.e., 1 and 2), and the methionine (M)/valine (V) polymorphic codon 129 of the prion protein gene (PRNP). How these sCJD subtypes relate to the well-documented phenotypic heterogeneity of genetic CJD (gCJD) is not fully understood. We analyzed molecular and phenotypic features in 208 individuals affected by gCJD, carrying 17 different mutations, and compared them with those of a large series of sCJD cases. We identified six major groups of gCJD based on the combination PrP^Sc type and codon 129 genotype on PRNP mutated allele, each showing distinctive histopathological characteristics, irrespectively of the PRNP associated mutation. Five gCJD groups, named M1, M2C, M2T, V1, and V2, largely reproduced those previously described in sCJD subtypes. The sixth group shared phenotypic traits with the V2 group and was only detected in patients carrying the E200K-129M haplotype in association with a PrP^Sc type of intermediate size (“i”) between type 1 and type 2. Additional mutation-specific effects involved the pattern of PrP deposition (e.g., a “thickened” synaptic pattern in E200K carriers, cerebellar “stripe-like linear granular deposits” in those with insertion mutations, and intraneuronal globular dots in E200K-V2 or -M”i”). A few isolated cases linked to rare PRNP haplotypes (e.g., T183A-129M), showed atypical phenotypic features, which prevented their classification into the six major groups. The phenotypic variability of gCJD is mostly consistent with that previously found in sCJD. As in sCJD, the codon 129 genotype and physicochemical properties of PrP^Sc significantly correlated with the phenotypic variability of gCJD. The most common mutations linked to CJD appear to have a variable and overall less significant effect on the disease phenotype, but they significantly influence disease susceptibility often in a strain-specific manner. The criteria currently used for sCJD subtypes can be expanded and adapted to gCJD to provide an updated classification of the disease with a molecular basis.

PMCA-generated prions from the olfactory mucosa of patients with Fatal Familial Insomnia cause prion disease in mice

Background:

Fatal Familial Insomnia (FFI) is a genetic prion disease caused by the D178N mutation in the prion protein gene (PRNP) in coupling phase with methionine at PRNP 129. In 2017, we have shown that the olfactory mucosa (OM) collected from FFI patients contained traces of PrPSc detectable by Protein Misfolding Cyclic Amplification (PMCA).

Methods:

In this work, we have challenged PMCA-generated products obtained from OM and brain homogenate of FFI patients in BvPrP-Tg407 transgenic mice expressing the bank vole prion protein to test their ability to induce prion pathology.

Results:

All inoculated mice developed mild spongiform changes, astroglial activation, and PrPSc deposition mainly affecting the thalamus. However, their neuropathological alterations were different from those found in the brain of BvPrP-Tg407 mice injected with raw FFI brain homogenate.

Conclusions:

Although with some experimental constraints, we show that PrPSc present in OM of FFI patients is potentially infectious.

Funding:

This work was supported in part by the Italian Ministry of Health (GR-2013-02355724 and Ricerca Corrente), MJFF, ALZ, Alzheimer’s Research UK and the Weston Brain Institute (BAND2015), and Euronanomed III (SPEEDY) to FM; by the Spanish Ministerio de Economía y Competitividad (grant AGL2016-78054-R [AEI/FEDER, UE]) to JMT and JCE; AM-M was supported by a fellowship from the INIA (FPI-SGIT-2015-02).

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.

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.