The genetics of prion diseases

A systemic analysis of Creutzfeldt Jakob disease cases in Asia

Creutzfeldt Jakob Disease (CJD) is a rapidly progressive, fatal neurodegenerative disorder, also known as a subacute spongiform encephalopathy. There are three major subtypes of CJD i.e. Sporadic CJD, which occurs for reasons unbeknown to science (85% of known cases), Genetic or Familial CJD which is characterized by the presence of mutations in the human prion protein (PRNP) gene (10-15% cases) and Iatrogenic CJD that occurs via accidental transmission through medical and surgical procedures (1-2% cases). CJD cases occur globally with 1 case per one million population/year. Considerable data is available related to the incidence and prevalence of CJD in Europe and America. However, the global surveillance database is yet to include Asia even though several Asian countries have their own CJD monitoring units. sCJD is the highest among all CJD cases in Asia. China (1957) and Japan (1705) have reported more cases of sCJD than any Asian country and Hong Kong (1) has reported the least. On the other hand, gCJD is highest in Japan (370) and least in India (2). Our analysis establishes the presence of all variants of CJD across Asia. However, in most Asian countries in general and Southeast Asian countries in particular, CJD cases are misdiagnosed and often underreported. Since Asia is the most populated continent in the world, the actual global prevalence of CJD cannot be estimated until and unless these countries are accounted for. Concrete and reliable surveillance networks are needed across Asia to evaluate the prevalence and incidence of CJD in the region. [Figure: see text]The graphical abstract demonstrates the prevalence of CJD cases in the world and systematically analyses the incidence of CJD in Asian countries between the year 1986-2022. Highest number of cases were reported in Japan followed by China. The study emphasizes the need for assimilation of Asian data in global prevalence.

Lung endothelium, tau, and amyloids in health and disease

Lung endothelia in the arteries, capillaries, and veins are heterogeneous in structure and function. Lung capillaries in particular represent a unique vascular niche, with a thin yet highly restrictive alveolar-capillary barrier that optimizes gas exchange. Capillary endothelium surveys the blood while simultaneously interpreting cues initiated within the alveolus and communicated via immediately adjacent type I and type II epithelial cells, fibroblasts, and pericytes. This cell-cell communication is necessary to coordinate the immune response to lower respiratory tract infection. Recent discoveries identify an important role for the microtubule-associated protein tau that is expressed in lung capillary endothelia in the host-pathogen interaction. This endothelial tau stabilizes microtubules necessary for barrier integrity, yet infection drives production of cytotoxic tau variants that are released into the airways and circulation, where they contribute to end-organ dysfunction. Similarly, beta-amyloid is produced during infection. Beta-amyloid has antimicrobial activity, but during infection it can acquire cytotoxic activity that is deleterious to the host. The production and function of these cytotoxic tau and amyloid variants are the subject of this review. Lung-derived cytotoxic tau and amyloid variants are a recently discovered mechanism of end-organ dysfunction, including neurocognitive dysfunction, during and in the aftermath of infection.

Elevated E200K Somatic Mutation of the Prion Protein Gene (PRNP) in the Brain Tissues of Patients with Sporadic Creutzfeldt-Jakob Disease (CJD)

Sporadic Creutzfeldt-Jakob disease (CJD) is a major human prion disease worldwide. CJD is a fatal neurodegenerative disease caused by an abnormal prion protein (PrPSc). To date, the exact etiology of sporadic CJD has not been fully elucidated. We investigated the E200K and V203I somatic mutations of the prion protein gene (PRNP) in sporadic CJD patients and matched healthy controls using pyrosequencing. In addition, we estimated the impact of somatic mutations on the human prion protein (PrP) using PolyPhen-2, PANTHER and PROVEAN. Furthermore, we evaluated the 3D structure and electrostatic potential of the human PrP according to somatic mutations using DeepView. The rates of PRNP K200 somatic mutation were significantly increased in the frontal cortex and hippocampus of sporadic CJD patients compared to the matched controls. In addition, the electrostatic potential of the human PrP was significantly changed by the K200 somatic mutation of the PRNP gene. To the best of our knowledge, this is the first report on an association of the PRNP K200 somatic mutation with sporadic CJD.

The epidemiological and clinical characteristics of patients with young-onset genetic Creutzfeldt-Jakob disease

OBJECTIVES

The onset of Creutzfeldt-Jakob disease (CJD) is usually around the age of 60, but younger patients have been described as well. Our study characterizes the demographic and clinical features of young-onset CJD patients.

METHODS

The CJD Israeli National Database was reviewed, and the patients were divided into groups of young (<40-year-old) (Y|) and older disease onset (>40-year-old) (O). Each group was further divided into sporadic (sCJD) and genetic (gCJD) patients. Clinical and demographic parameters were compared between the groups.

RESULTS

The study included 731 patients (Y- 18 patients, O- 713 patients). MRI showed classical features more often in the older population (O-76.9%, Y-36%, p = 0.006). Rapidly progressive dementia as a presenting feature was more common in the older group (O = 58%, Y = 27.7%, p = 0.019) whereas cerebellar onset (gait instability, dysarthria) was more common in the younger group (O = 6.7%, Y = 27.7%, p = 0.036)). Among gCJD patients, rapidly progressive dementia was commonly seen in older patients (O = 54%, Y = 21% p = 0.008) whereas cerebellar symptoms were seen in young patients (O = 7%, Y = 30% p = 0.01) Typical MRI findings were seen in 37% of young people compared to 87% of older patients (p = 0.002). No significant differences were between young and older patients in the sCJD group.

CONCLUSION

Young-onset gCJD patients have unique disease features including less typical brain MRI changes, a lower prevalence of dementia, and a higher prevalence of cerebellar signs at disease onset.

Mutant α-synuclein propagates via the lymphatic system of the brain in the monomeric state

Prion-like protein propagation is considered a common pathogenic mechanism in neurodegenerative diseases. Here we investigate the in vivo propagation pattern and aggregation state of mutant α-synuclein by injecting adeno-associated viral (AAV)-α-synuclein-A53T-EGFP into the mouse olfactory cortex. Comparison of aggregation states in various brain regions at multiple time points after injection using western blot analyses shows that the monomeric state of the mutant/misfolded protein propagates to remote brain regions by 2 weeks and that the propagated proteins aggregate in situ after being incorporated into neurons. Moreover, injection of Alexa 488-labeled α-synuclein-A53T confirms the monomeric propagation at 2 weeks. Super-resolution microscopy shows that both α-synuclein-A53T proteins propagate via the lymphatic system, penetrate perineuronal nets, and reach the surface of neurons. Electron microscopy shows that the propagated mutant/misfolded monomer forms fibrils characteristic of Parkinson's disease after its incorporation into neurons. These findings suggest a mode of propagation different from that of aggregate-dependent propagation.

Reproductive choices and intrafamilial communication in neurogenetic diseases with different self-estimated severities

BACKGROUND

Low uptake of presymptomatic testing and medically assisted reproduction in families impacted by neurogenetic diseases prompted us to investigate how reproductive options are considered and whether there is a relationship with perceived severity of the disease. We hypothesised that self-estimated severity would influence opinion on reproductive options and that prenatal/preimplantation diagnosis would be a motivation to inform relatives about their risk.

METHODS

We invited people impacted by neurogenetic diseases to evaluate the severity of their familial disease using analogic visual scales and to answer questionnaires about reproductive choices and intrafamilial communication. We compared answers between diseases and with the perceived severity of each disease.

RESULTS

We analysed 562 questionnaires. Participants were impacted by Huntington disease (n=307), spinocerebellar ataxias (n=114), Steinert myotonic dystrophy (n=82) and amyotrophic lateral sclerosis/frontotemporal dementia (n=59). Self-estimated severity differed between pathologies (p<0.0001). Overall, participants considered prenatal diagnosis (78.0±34.4 out of 100) and preimplantation diagnosis (75.2±36.1 out of 100) justified more than termination of pregnancy (68.6±38.5 out of 100). They were less in favour of gamete donation (48.3±39.8 out of 100) or pregnancy abstention (43.3±40.3 out of 100). The greater the perceived severity of the disease, the more reproductive options were considered justified, except for gamete donation. Prenatal/preimplantation diagnosis was a motivation to inform relatives for only 55.3% of participants (p=0.01).

CONCLUSION

Self-estimated severity minimally impacts opinions towards reproductive options. Medically assisted reproduction procedures are rarely sought and do not motivate familial communication.

Measuring prion propagation in single bacteria elucidates mechanism of loss

Prions are self-propagating protein aggregates formed by specific proteins that can adopt alternative folds. Prions were discovered as the cause of the fatal transmissible spongiform encephalopathies in mammals, but prions can also constitute non-toxic protein-based elements of inheritance in fungi and other species. Prion propagation has recently been shown to occur in bacteria for more than a hundred cell divisions, yet a fraction of cells in these lineages lost the prion through an unknown mechanism. Here, we investigate prion propagation in single bacterial cells as they divide using microfluidics and fluorescence microscopy. We show that the propagation occurs in two distinct modes with distinct stability and inheritance characteristics. We find that the prion is lost through random partitioning of aggregates to one of the two daughter cells at division. Extending our findings to prion domains from two orthologous proteins, we observe similar propagation and loss properties. Our findings also provide support for the suggestion that bacterial prions can form more than one self-propagating state. We implement a stochastic version of the molecular model of prion propagation from yeast and mammals that recapitulates all the observed single-cell properties. This model highlights challenges for prion propagation that are unique to prokaryotes and illustrates the conservation of fundamental characteristics of prion propagation across domains of life.

The Effect of Curcuma phaeocaulis Valeton (Zingiberaceae) Extract on Prion Propagation in Cell-Based and Animal Models

Prion diseases are neurodegenerative disorders in humans and animals for which no therapies are currently available. Here, we report that Curcuma phaeocaulis Valeton (Zingiberaceae) (CpV) extract was partly effective in decreasing prion aggregation and propagation in both in vitro and in vivo models. CpV extract inhibited self-aggregation of recombinant prion protein (PrP) in a test tube assay and decreased the accumulation of scrapie PrP (PrP^Sc) in ScN2a cells, a cultured neuroblastoma cell line with chronic prion infection, in a concentration-dependent manner. CpV extract also modified the course of the disease in mice inoculated with mouse-adapted scrapie prions, completely preventing the onset of prion disease in three of eight mice. Biochemical and neuropathological analyses revealed a statistically significant reduction in PrP^Sc accumulation, spongiosis, astrogliosis, and microglia activation in the brains of mice that avoided disease onset. Furthermore, PrP^Sc accumulation in the spleen of mice was also reduced. CpV extract precluded prion infection in cultured cells as demonstrated by the modified standard scrapie cell assay. This study suggests that CpV extract could contribute to investigating the modulation of prion propagation.

No association of prion protein gene (PRNP) polymorphisms with susceptibility to the pandemic 2009 swine flu

Background

The pandemic 2009 swine flu is a highly infectious respiratory disorder caused by H1N1 influenza A viruses. A recent study reported that knockout of the prion protein gene (PRNP) induced susceptibility and lethality in influenza A virus-infected mice.

Objective

Thus, we examined the association between genetic variations of the PRNP gene and susceptibility to pandemic 2009 swine flu.

Results

We did not find an association between PRNP polymorphisms and susceptibility to pandemic 2009 swine flu.

Conclusions

To the best of our knowledge, this was the first evaluation of the association between PRNP polymorphisms and vulnerability to pandemic 2009 swine flu.

Creutzfeldt-Jakob Disease Incidence, South Korea, 2001-2019

We found increasing trends of Creutzfeldt-Jakob disease (CJD) cases and annual incidence in South Korea during 2001-2019. We noted relatively low (5.7%) distribution of familial CJD. An unusually high percentage (≈1%) of patients were in the 30-39 age group, which should prompt a preemptive CJD control system.

A longitudinal 18F-FDG PET/MRI study in asymptomatic stage of genetic Creutzfeldt-Jakob disease linked to G114V mutation

BACKGROUND

Pathogenic prion protein may start to deposit in some brain regions and cause functional alterations in the asymptomatic stage in Creutzfeldt-Jakob disease. The study aims to determine the trajectory of the brain metabolic changes for prion protein diseases at the preclinical stage.

METHODS

At baseline, we enrolled five asymptomatic PRNP G114V mutation carriers, six affected genetic PRNP E200K CJD patients and 23 normal controls. All participants completed clinical, diffusion-weighted imaging (DWI) and ¹⁸F fluorodeoxyglucose-positron emission tomography (¹⁸F-FDG-PET) examinations. Longitudinal follow-up was completed in five asymptomatic mutation carriers. We set three-time points to identify the changing trajectory in the asymptomatic carriers group including baseline, 2-year and 4-year follow-up.

RESULTS

At baseline, DWI signals, the cerebral glucose standardized uptake value rate ratio (SUVR) and clinical status in 5 asymptomatic cases were normal. At the follow-up period, mild hypometabolism on PET images was found in asymptomatic carriers without any DWI abnormal signal. Further group quantitatively analysis showed hypometabolic brain regions in the asymptomatic genetic CJD group were in the insula, frontal, parietal, and temporal lobes in 4-year follow-up. The SUVR changing trajectories of all asymptomatic cases were within the range between the normal controls and affected patients. Notably, the SUVR of one asymptomatic individual whose baseline age was older showed a rapid decline at the last follow-up.

CONCLUSIONS

Our study illustrates that the neurodegenerative process associated with genetic CJD may initiate before the clinical presentation of the disease.

2.2 Å Cryo-EM Tetra-Protofilament Structure of the Hamster Prion 108-144 Fibril Reveals an Ordered Water Channel in the Center

Fibrils of the hamster prion peptide (sHaPrP, sequence 108-144) were prepared in an acidic solution, and their structure was solved by cryogenic electron microscopy with a resolution of 2.23 Å based on the gold-standard Fourier shell correlation (FSC) curve. The fibril has a novel architecture that has never been found in other amyloid fibrils. Each fibril is assembled by four protofilaments (PFs) and has an ordered water channel in the center. Each protofilament contains three β-strands (125-130, 133-135, and 138-141) arranged in an "R"-shaped construct. The structural data indicate that these three β-strand segments are the most amyloidogenic region of the prion peptide/protein and might be the site of nucleation during fibrillization under conditions without denaturants.

Methionine homozygosity for PRNP polymorphism and susceptibility to human prion diseases

BACKGROUND

No studies have assessed the independent association of methionine homozygosity at codon 129 with the susceptibility to prion diseases, controlling for the effects of the codon 219 polymorphisms and other potential confounders, using a large-scale population-based dataset.

METHODS

We conducted a case-control study using a Japanese nationwide surveillance database for prion diseases. The main exposure was methionine homozygosity at codon 129, and the outcome was development of prion diseases. Multivariable logistic regression models were employed for specific disease subtypes (sporadic Creutzfeldt-Jakob disease (CJD), genetic CJD and Gerstmann-Sträussler-Scheinker disease (GSS)).

RESULTS

Of 5461 patients registered in the database, 2440 cases and 796 controls remained for the analysis. The cases comprised 1676 patients with sporadic CJD (69%), 649 with genetic CJD (27%) and 115 with GSS (5%). For patients with methionine homozygosity, potential risk for occurring prion diseases: adjusted OR (95% CI) was 2.21 (1.46 to 3.34) in sporadic CJD, 0.47 (0.32 to 0.68) in genetic CJD and 0.3 (0.17 to 0.55) in GSS. Among patients with specific prion protein abnormalities, the potential risk was 0.27 (0.17 to 0.41) in genetic CJD with 180 Val/Ile, 1.66 (0.65 to 5.58) in genetic CJD with 200 Glu/Lys, 3.97 (1.2 to 24.62) in genetic CJD with 232 Met/Arg and 0.71 (0.34 to 1.67) in GSS with 102 Pro/Leu.

CONCLUSIONS

Methionine homozygosity at codon 129 was predisposing to sporadic CJD, but protective against genetic CJD and GSS, after adjustment for codon 219 polymorphism effect. However, the impacts differed completely among patients with specific prion protein abnormalities.

Using Catchment Population to Estimate Sporadic Creutzfeldt-Jakob Disease Incidence

INTRODUCTION

Catchment populations have several uses. A method using catchment population to estimate the incidence of sporadic Creutzfeldt-Jakob disease (sCJD) is described.

MATERIALS AND METHODS

A cohort of nine consecutive patients diagnosed with sCJD, symptom onset spanning 26 months, were observed at a rural tertiary university medical center that has approximately 40,000 hospital discharges annually. An effective catchment population was determined using surrounding county utilization frequency that captured all nine sCJD patients and accounted for over 87% of discharges.

RESULTS

The effective sCJD hospital catchment population was 1.266 million, implying an annual sCJD incidence rate of 3.39 per million (95% CIs, 1.55-6.43), assuming a Poisson distribution for sCJD occurrence.

CONCLUSIONS

This annual incidence rate suggests that many sCJD patients are unrecognized and unreported. An advantage of this catchment population method is independence from death certificate accuracy, important in rare diseases that are both rapidly and invariably fatal. The relative absence of significant healthcare systems competition in this rural population enhances the reliability of this finding. The most likely explanation for the high sCJD incidence rate suggested by this study is enhanced clinical suspicion and improved diagnostic accuracy.

Novel quaternary structures of the human prion protein globular domain

Prion disease is caused by the misfolding of the cellular prion protein, PrP^C, into a self-templating conformer, PrP^Sc. Nuclear magnetic resonance (NMR) and X-ray crystallography revealed the 3D structure of the globular domain of PrP^C and the possibility of its dimerization via an interchain disulfide bridge that forms due to domain swap or by non-covalent association of two monomers. On the contrary, PrP^Sc is composed by a complex and heterogeneous ensemble of poorly defined conformations and quaternary arrangements that are related to different patterns of neurotoxicity. Targeting PrP^C with molecules that stabilize the native conformation of its globular domain emerged as a promising approach to develop anti-prion therapies. One of the advantages of this approach is employing structure-based drug discovery methods to PrP^C. Thus, it is essential to expand our structural knowledge about PrP^C as much as possible to aid such drug discovery efforts. In this work, we report a crystallographic structure of the globular domain of human PrP^C that shows a novel dimeric form and a novel oligomeric arrangement. We use molecular dynamics simulations to explore its structural dynamics and stability and discuss potential implications of these new quaternary structures to the conversion process.

Metabolic Changes Detected by 18F-FDG PET in the Preclinical Stage of Familial Creutzfeldt-Jakob Disease

BACKGROUND

Pathologic processes in Creutzfeldt-Jakob disease (CJD) are not fully understood. Familial CJD (fCJD) gives opportunities to discover pathologic changes in the preclinical stage.

OBJECTIVE

To investigate cerebral glucose metabolism in the preclinical stage via 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) in fCJD.

METHODS

Seven asymptomatic carriers of G114V mutation and six family members without PRNP mutation from the same fCJD kindred were included, and were followed for 2 years. Ten symptomatic CJD patients were also recruited. All subjects underwent standardized clinical examinations and 18F-FDG PET scans. Results were compared in three groups: baseline carriers against non-carriers (baseline analysis), changes after 2 years in carriers (follow-up analysis), and differences between symptomatic CJD patients and healthy controls (CJD patients analysis).

RESULTS

No carriers developed any neurological symptoms during 2-year follow-up. Baseline analysis: carriers demonstrates decreased metabolism (p < 0.001) in left and right postcentral, left fusiform, left superior temporal, left lingual, left superior parietal, and left Heschl gyrus. Follow-up analysis shows metabolic decline (p < 0.001) in right inferior temporal, left supra-marginal and left postcentral lobe, and increased metabolism (p < 0.001) in left fusiform, left angular, left thalamus, left Heschl's, right Rolandic operculum, and left superior parietal gyrus. CJD patients demonstrates decreased metabolism in right inferior triangularis frontal gyrus, right middle occipital gyrus, right putamen, right thalamus, and right middle temporal gyrus.

CONCLUSION

Hypo-metabolism of parietal and temporal lobe can be detected by 18F-FDG PET in the preclinical stage of CJD. Subcortical area might compensate in the preclinical stage and decompensate in the symptomatic stage.

Tau Protein Phosphorylated at Threonine-231 is Expressed Abundantly in the Cerebellum in Prion Encephalopathies

Background:

Transmissible spongiform encephalopathies (TSEs) are rare neurodegenerative disorders that affect animals and humans. Bovine spongiform encephalopathy (BSE) in cattle, and Creutzfeld-Jakob Disease (CJD) in humans belong to this group. The causative agent of TSEs is called “prion”, which corresponds to a pathological form (PrP^Sc) of a normal cellular protein (PrP^C) expressed in nerve cells. PrP^Sc is resistant to degradation and can induce abnormal folding of PrP^C, and TSEs are characterized by extensive spongiosis and gliosis and the presence of PrP^Sc amyloid plaques. CJD presents initially with clinical symptoms similar to Alzheimer’s disease (AD). In AD, tau aggregates and amyloid-β protein plaques are associated with memory loss and cognitive impairment in patients.

Objective:

In this work, we study the role of tau and its relationship with PrP^Sc plaques in CJD.

Methods:

Multiple immunostainings with specific antibodies were carried out and analyzed by confocal microscopy.

Results:

We found increased expression of the glial fibrillary acidic protein (GFAP) and matrix metalloproteinase (MMP-9), and an exacerbated apoptosis in the granular layer in cases with prion disease. In these cases, tau protein phosphorylated at Thr-231 was overexpressed in the axons and dendrites of Purkinje cells and the extensions of parallel fibers in the cerebellum.

Conclusion:

We conclude that phosphorylation of tau may be a response to a toxic and inflammatory environment generated by the pathological form of prion.

Epidemiological verification of the mechanism of occurrence of atypical L-type bovine spongiform encephalopathy

Since 2004, a novel bovine spongiform encephalopathy (BSE), distinct from the conventional 'classical BSE' (C-BSE), has been reported as an atypical BSE. Atypical BSE is detected mostly in aged cattle, and it is suggested that atypical BSE may occur spontaneously. Relaxation of the relevant countermeasures such as feed ban, which prevents the use of bovine meat-and-bone meal as feed, has been discussed in recent years owing to the decrease in C-BSE cases. If atypical BSE occurs spontaneously without exposure to an agent called abnormal prion protein (PrP^Sc ), complete removal of these measures will be difficult. In this study, we verified the possibility that L-BSE, which is a subtype of atypical BSE, occurs spontaneously. We first hypothesized that L-BSE occurs only through the process of infection via oral exposure. If the hypothesis was true, the infection of L-BSE would be mostly limited to calves under 1 year of age due to their high susceptibility, and the feed ban would effectively reduce the number of infected calves by birth cohort. Thus, we created a mathematical model to estimate the number of infected calves by birth cohort and compared the effectiveness of the feed ban on C-BSE and L-BSE. The number of tested animals and detected cases in nine European countries were used for this analysis. Our results showed that the estimated number of infected calves in the birth cohort indicated that feed ban was less effective on L-BSE. This result supports the alternative hypothesis that at least a part of the L-BSE can occur without infection via oral exposure. Our results suggest that the complete abolition of countermeasures, such as feed ban, should be discussed carefully. As for the occurrence mechanism, although there remains uncertainty to reach conclusions, it is reasonable to assume that L-BSE can occur spontaneously at present.

Parkinson's Disease: A Prionopathy?

The principal pathogenic event in Parkinson's disease is characterized by the conformational change of α-synuclein, which form pathological aggregates of misfolded proteins, and then accumulate in intraneuronal inclusions causing dopaminergic neuronal loss in specific brain regions. Over the last few years, a revolutionary theory has correlated Parkinson's disease and other neurological disorders with a shared mechanism, which determines α-synuclein aggregates and progresses in the host in a prion-like manner. In this review, the main characteristics shared between α-synuclein and prion protein are compared and the cofactors that influence the remodeling of native protein structures and pathogenetic mechanisms underlying neurodegeneration are discussed.

Condition-dependent structural collapse in the intrinsically disordered N-terminal domain of prion protein

Prion protein is composed of a structure-unsolved N-terminal domain and a globular C-terminal domain. Under limited trypsin digestion, mouse recombinant prion protein can be cleaved into two parts at residue Lys105. Here, we termed these two fragments as the N-domain (sequence 23-105) and the C-domain (sequence 106-230). In this study, the structural properties of the N-domain, the C-domain, and the full-length protein were explored using small-angle X-ray scattering, analytical ultracentrifugation, circular dichroism spectroscopy, and the 8-anilino-1-naphthalenesulfonic acid binding assay. The conformation and size of the prion protein were found to change sensitively under the solvent conditions. The positive residues in the sequence 23-99 of the N-domain were found to be responsible for the enhanced flexibility with the salt concentration reduced below 5 mM. The C-domain containing a hydrophobic patch tends to unfold and aggregate during a salt-induced structural collapse. The N-domain collapsed together with the C-domain at pH 5.2, whereas it collapsed independently at pH 4.2. The positively charged cluster (sequence 100-105) in the N-domain contributed to protecting the exposed hydrophobic surface of the C-domain.

[Inherited Creutzfeldt-Jakob disease with four-octapeptide repeat insertional mutation in the prion gene]

We report a case of a 60-year-old man who presented with symptoms of memory loss, gait disorder, and sluggish movement. We considered both Parkinson's disease and multiple system atrophy as possible diagnoses and consequently hospitalized the patient owing to the worsening symptoms and the development of consciousness disorder. During the course of the disease, dementia, loss of consciousness, and movement disorders worsened rapidly within one year after admission, and the patient eventually developed mutism. The significant clinical characteristics of our case included no myoclonus and involuntary tremors in the extremities. There was no periodic synchronous discharge on electro-encephalography and cranial MRI with diffusion-weighted images showed no high-intensity findings in cortex. Prion protein genetic analysis identified four repeated insertional mutations in the octapeptide repeat (OPR) region, and the patient was diagnosed with inherited Creutzfeldt-Jakob disease. Cases of OPR insertional mutations are a few in Japan and occur in about 10% of population in Europe. Creutzfeldt-Jakob disease with OPR insertional mutation shows various clinical manifestations and atypical findings on electroencephalography and cranial MRI. Diagnosing for Creutzfeldt-Jakob disease with OPR insertional mutation is important in Prion protein genetic analysis.

Stress Response Is the Main Trigger of Sporadic Amyloidoses

Amyloidoses are a group of diseases associated with the formation of pathological protein fibrils with cross-β structures. Approximately 5-10% of the cases of these diseases are determined by amyloidogenic mutations, as well as by transmission of infectious amyloids (prions) between organisms. The most common group of so-called sporadic amyloidoses is associated with abnormal aggregation of wild-type proteins. Some sporadic amyloidoses are known to be induced only against the background of certain pathologies, but in some cases the cause of amyloidosis is unclear. It is assumed that these diseases often occur by accident. Here we present facts and hypotheses about the association of sporadic amyloidoses with vascular pathologies, trauma, oxidative stress, cancer, metabolic diseases, chronic infections and COVID-19. Generalization of current data shows that all sporadic amyloidoses can be regarded as a secondary event occurring against the background of diseases provoking a cellular stress response. Various factors causing the stress response provoke protein overproduction, a local increase in the concentration or modifications, which contributes to amyloidogenesis. Progress in the treatment of vascular, metabolic and infectious diseases, as well as cancers, should lead to a significant reduction in the risk of sporadic amyloidoses.

From Cell Culture to Organoids-Model Systems for Investigating Prion Strain Characteristics

Prion diseases are the hallmark protein folding neurodegenerative disease. Their transmissible nature has allowed for the development of many different cellular models of disease where prion propagation and sometimes pathology can be induced. This review examines the range of simple cell cultures to more complex neurospheres, organoid, and organotypic slice cultures that have been used to study prion disease pathogenesis and to test therapeutics. We highlight the advantages and disadvantages of each system, giving special consideration to the importance of strains when choosing a model and when interpreting results, as not all systems propagate all strains, and in some cases, the technique used, or treatment applied, can alter the very strain properties being studied.

The importance of ongoing international surveillance for Creutzfeldt-Jakob disease

Creutzfeldt-Jakob disease (CJD) is a rapidly progressive, fatal and transmissible neurodegenerative disease associated with the accumulation of misfolded prion protein in the CNS. International CJD surveillance programmes have been active since the emergence, in the mid-1990s, of variant CJD (vCJD), a disease linked to bovine spongiform encephalopathy. Control measures have now successfully contained bovine spongiform encephalopathy and the incidence of vCJD has declined, leading to questions about the requirement for ongoing surveillance. However, several lines of evidence have raised concerns that further cases of vCJD could emerge as a result of prolonged incubation and/or secondary transmission. Emerging evidence from peripheral tissue distribution studies employing high-sensitivity assays suggests that all forms of human prion disease carry a theoretical risk of iatrogenic transmission. Finally, emerging diseases, such as chronic wasting disease and camel prion disease, pose further risks to public health. In this Review, we provide an up-to-date overview of the transmission of prion diseases in human populations and argue that CJD surveillance remains vital both from a public health perspective and to support essential research into disease pathophysiology, enhanced diagnostic tests and much-needed treatments.

Methionine oxidation within the prion protein

Prion diseases are characterized by the self-templated misfolding of the cellular prion protein (PrPC) into infectious aggregates (PrPSc). The detailed molecular basis of the misfolding and aggregation of PrPC remains incompletely understood. It is believed that the transient misfolding of PrPC into partially structured intermediates precedes the formation of insoluble protein aggregates and is a critical component of the prion misfolding pathway. A number of environmental factors have been shown to induce the destabilization of PrPC and promote its initial misfolding. Recently, oxidative stress and reactive oxygen species (ROS) have emerged as one possible mechanism by which the destabilization of PrPC can be induced under physiological conditions. Methionine residues are uniquely vulnerable to oxidation by ROS and the formation of methionine sulfoxides leads to the misfolding and subsequent aggregation of PrPC. Here, we provide a review of the evidence for the oxidation of methionine residues in PrPC and its potential role in the formation of pathogenic prion aggregates.

A case report of genetic prion disease with two different PRNP variants

Background

Prion diseases are a group of lethal neurodegenerative conditions that occur when the normal, cellular form of the prion protein (PrP^C) is converted into an abnormal, scrapie, form of the protein (PrP^Sc). Disease may be caused by genetic, infectious, or sporadic etiologies. The genetic form of prion disease comprises~10%–15% of all cases. Prion disease is typically inherited in an autosomal dominant manner. The low incidence of disease makes it highly unlikely that a patient would have two different pathogenic variants. However, we recently identified a case in which the patient did have two pathogenic PRNP variants and presented with an atypical phenotype.

Methods

The patient was evaluated at the Washington Hospital Healthcare System in Fremont, CA. The clinical information for this case report was obtained retrospectively. Variants in the PRNP were identified by polymerase chain reaction (PCR) amplification of exon two of the gene followed by bi‐directional sequence analysis. To determine the phase of the identified variants, a restriction enzyme digestion was utilized, followed by sequence analysis of the products. Cerebral spinal fluid (CSF) was analyzed for surrogate markers of prion disease, 14–3–3 and Tau proteins. CSF real‐time quaking‐induced conversion (RT‐QuIC) assays were also performed.

Results

The patient was a compound heterozygote for the well‐characterized c.628G>A (p.Val210Ile) variant and the rare octapeptide deletion of two repeats [c.202_249del48 (p.P68_Q83del)]. Clinically, the patient presented with an early onset demyelinating peripheral neuropathy, followed by later onset cognitive symptoms.

Conclusion

This presentation is reminiscent of prion protein knockout mice whose predominate symptom, due to complete loss of PrP, was late‐onset peripheral neuropathy. To our knowledge this is the first case reported of a patient with prion disease who had two different pathogenic variants in PRNP.

Evaluation of Human Cerebrospinal Fluid Malate Dehydrogenase 1 as a Marker in Genetic Prion Disease Patients

The exploration of accurate diagnostic markers for differential diagnosis of neurodegenerative diseases is an ongoing topic. A previous study on cerebrospinal fluid (CSF)-mitochondrial malate dehydrogenase 1 (MDH1) in sporadic Creutzfeldt–Jakob disease (sCJD) patients revealed a highly significant upregulation of MDH1. Here, we measured the CSF levels of MDH1 via enzyme-linked immunosorbent assay in a cohort of rare genetic prion disease cases, such as genetic CJD (gCJD) cases, exhibiting the E200K, V210I, P102L (Gerstmann–Sträussler–Scheinker syndrome (GSS)), or D178N (fatal familial insomnia (FFI)) mutations in the PRNP. Interestingly, we observed enhanced levels of CSF-MDH1 in all genetic prion disease patients compared to neurological controls (without neurodegeneration). While E200K and V210I carriers showed highest levels of MDH1 with diagnostic discrimination from controls of 0.87 and 0.85 area under the curve (AUC), FFI and GSS patients exhibited only moderately higher CSF-MDH1 levels than controls. An impact of the PRNP codon 129 methionine/valine (MV) genotype on the amount of MDH1 could be excluded. A correlation study of MDH1 levels with other neurodegenerative marker proteins revealed a significant positive correlation between CSF-MDH1 concentration with total tau (tau) but not with 14-3-3 in E200K, as well as in V210I patients. In conclusion, our study indicated the potential use of MDH1 as marker for gCJD patients which may complement the current panel of diagnostic biomarkers.

Clinical Laboratory Tests Used To Aid in Diagnosis of Human Prion Disease

Prion diseases are a group of rapidly progressive and always fatal neurodegenerative disorders caused by misfolded prion protein in the brain. Although autopsy remains the gold-standard diagnostic tool, antemortem laboratory testing can be performed to aid in the diagnosis of prion disease. This review is meant to help laboratory directors and physicians in their interpretation of test results. Laboratory assays to detect both nonspecific biomarkers of prion disease and prion-specific biomarkers can be used. The levels of nonspecific biomarkers in cerebrospinal fluid (CSF) are elevated when rapid neurodegeneration is occurring in the patient, and these markers include 14-3-3, tau, neuron-specific enolase, S100B, and alpha-synuclein. These markers have various sensitivities and specificities but are overall limited, as the levels of any of these analytes can be elevated in nonprion disease that is causing rapid damage of brain tissue. Prion-specific assays used in clinical laboratory testing are currently limited to two options. The first option is second-generation real-time quaking-induced conversion (RT-QuIC) performed on CSF, and the second option is Western blotting of a brain biopsy specimen used to detect protease-resistant prion protein. Although both tests have exquisite specificity, RT-QuIC has a sensitivity of 92 to 97.2% in symptomatic individuals, compared to the brain biopsy Western blot sensitivity of 20 to 60%. RT-QuIC was added to the Centers for Disease Control and Prevention's diagnostic criteria for prion disease in 2018. Other caveats of laboratory testing need to be considered, as sporadic, genetic, and acquired forms of prion disease have different clinical and laboratory presentations, and these caveats are discussed. Laboratory testing plays an important role in the diagnosis of prion disease, which is often challenging to diagnose.

Enhanced detection of prion infectivity from blood by preanalytical enrichment with peptoid-conjugated beads

Prions cause transmissible infectious diseases in humans and animals and have been found to be transmissible by blood transfusion even in the presymptomatic stage. However, the concentration of prions in body fluids such as blood and urine is extremely low; therefore, direct diagnostic tests on such specimens often yield false-negative results. Quantitative preanalytical prion enrichment may significantly improve the sensitivity of prion assays by concentrating trace amounts of prions from large volumes of body fluids. Here, we show that beads conjugated to positively charged peptoids not only captured PrP aggregates from plasma of prion-infected hamsters, but also adsorbed prion infectivity in both the symptomatic and preclinical stages of the disease. Bead absorbed prion infectivity efficiently transmitted disease to transgenic indicator mice. We found that the readout of the peptoid-based misfolded protein assay (MPA) correlates closely with prion infectivity in vivo, thereby validating the MPA as a simple, quantitative, and sensitive surrogate indicator of the presence of prions. The reliable and sensitive detection of prions in plasma will enable a wide variety of applications in basic prion research and diagnostics.

Profiles of 14-3-3 and Total Tau in CSF Samples of Chinese Patients of Different Genetic Prion Diseases

Background

The abnormal alterations of proteins 14-3-3 and tau in cerebrospinal fluid (CSF) are widely used for the diagnosis of sporadic Creutzfeldt-Jakob disease (sCJD), while the situations of CSF biomarkers in genetic prion diseases (gPrDs), particularly in Chinese gPrDs patients, have not been well documented.

Methods

Here, with the help of commercial 14-3-3 and total tau ELISA kits, we evaluated the levels of proteins 14-3-3 and tau in the CSF samples of 140 Chinese patients of 14 different types of gPrDs.

Results

We found that CSF 14-3-3 ELISA values in the patients with P102L GSS and D178N FFI were remarkably low, while those in the patients with T188K, E196A, and E200K gCJD were relatively high. Linear correlation assays identified a positive correlation between positive rate in Western blot (WB) and ELISA values of CSF 14-3-3. ELISA assays for total tau in CSF samples identified relatively high levels in the cases of T188K, E196A, and E200K gCJD (median: 133840.81, 159992.80, and 153342.92 AU/ml), but relatively low levels in those of P102L GSS and D178N FFI (median: 64397.77 and 43856.79 AU/ml).

Conclusion

These data illustrate heterogeneous profiles of CSF 14-3-3 and tau in various types of gPrDs, depending on the differences in the mutations in PRNP.

Gerstmann-Sträussler-Scheinker syndrome misdiagnosed as conversion disorder

Gerstmann-Sträussler-Scheinker syndrome (GSS) is a rare cause of genetic prion disease. Overlapping neurological, cognitive and psychiatric symptoms make GSS difficult to diagnose based on clinical features alone. We present a 40-year-old man without relevant medical or family history who developed progressive neurocognitive and behavioural symptoms over 3 years. Initial extensive diagnostic workup of his variable motor symptoms was unrevealing and he was diagnosed with conversion disorder. This diagnosis persisted for over 2 years, despite progressive neurocognitive symptoms. He eventually developed dementia and severe neurological impairment. Repeat brain MRI revealed generalised cortical volume loss, establishing the diagnosis of a rapidly progressive neurodegenerative process. He ultimately died from aspiration pneumonia at age 43. Postmortem neuropathological examination showed widespread multicentric prion protein amyloid plaques characteristic of GSS. Ultimately, genetic testing of brain tissue revealed a heterozygous A117V variant in the PNRP gene, confirming the diagnosis.

Novel prion mutation (p.Tyr225Cys) in a Korean patient with atypical Creutzfeldt-Jakob disease

Background: A novel prion variant, PRNP p.Tyr225Cys (c.674A>G; p.Y225C), was identified in an atypical Creutzfeldt–Jakob disease (CJD) patient. The patient had a 5-year history of progressive cognitive impairment with speech and gait disturbances. From the basic neurological examination at his first hospital visit, rigidity and myoclonic jerks in all limbs were observed without focal weakness. Electroencephalogram showed the diffuse slow continuous delta activity in the bilateral cerebral hemisphere. Magnetic resonance imaging revealed abnormalities in the brain, such as cortical signal changes and edema in the frontotemporoparietal lobes and the basal ganglia. Cerebrospinal fluid 14–3-3 protein analysis showed a weakly positive signal. Family history remained unclear, but the patient’s mother and sister were diagnosed with cognitive impairment but both refused genetic testing.

Methods: Targeted next generation sequencing (NGS) was performed on 50 genes, involved in different neurodegeneratives diseases, such as Alzheimer's, Parkinson's, frontotemporal dementia or prion diseases. In silico analyses and structure predictions were performed on the potential patohgenic mutations.

Results: NGS and standard sequencing revealed the novel PRNP p.Tyr225Cys mutation in the patient. Structure predictions revealed that this may make the helix more flexible. In addition, the extra cysteine residue in TM-III of prion protein may result in disturbances of natural disulfide bond.

Conclusion: Hence, the pathogenicity of PRNP p.Tyr225Cys was not fully confirmed at present, and its penetrance was suggested to be low. However, its possible pathogenic nature in prion diseases cannot be ignored, since Tyr/Cys exchange could disturb the helix dynamics and contribute to conformational alteration and disease progression.

Novel screening approaches for human prion diseases drug discovery

Introduction: Human prion diseases are rare fatal neurodegenerative diseases caused by the misfolding and aggregation of the prion protein in the form of infectious prions. So far, these diseases are incurable. One of the major difficulties in identifying suitable drugs is the availability of robust preclinical screening methods. All molecules identified have been screened using cell-based assays and in vivo murine models. The existence of a continuum of prion strains has hampered the identification of efficacious molecules modulating the progression of different forms of the disease. Areas covered: The advent of new in vitro screening methodologies is allowing for novel strategies to develop new compounds that could interfere with a broad range of diseases. In particular, two innovative techniques named Real Time Quaking Induced Conversion (RT-QuIC) and Protein Misfolding Cyclic Amplification (PMCA) have opened new venues for testing compounds in a rapid a reproducible way. These are discussed within. Expert opinion: For human prion diseases, one major hurdle has been a well-defined screening methodology. In other animal species, cell-based assays have been employed that could replicate animal prions indefinitely. Such a tool for human prion diseases is still missing. Therefore, the advent of RT-QuIC and PMCA has proven instrumental to overcome this limitation.

Amyloid- and tau-PET imaging in a familial prion kindred

Objective

To study the in vivo binding properties of ¹⁸F-AV-1451 (tau-PET) and Pittsburgh compound B (PiB-PET) in a unique kindred with a familial prion disorder known to produce amyloid plaques composed of prion protein alongside Alzheimer disease (AD)–like tau tangles.

Methods

A case series of 4 symptomatic family members with the 12-octapeptide repeat insertion in the PRNP gene were imaged with 3T MRI, PiB-PET, and tau-PET in their fourth decade of life.

Results

There was significant neocortical uptake of the tau-PET tracer in all 4 familial prion cases. However, PiB-PET images did not demonstrate abnormally elevated signal in neocortical or cerebellar regions for any of the patients.

Conclusions

In vivo detection of molecular hallmarks of neurodegenerative diseases will be a prerequisite to well-conducted therapeutic trials. Understanding the in vivo behavior of these PET biomarkers in the setting of various neurodegenerative processes is imperative to their proper use in such trials and for research studies focused on the basic neurobiology of neurodegeneration. This study supports the high specificity of neocortical ¹⁸F-AV-1451 binding to AD-like tau and the lack of PiB binding to PrP plaques. It is uncertain how early in the disease course tau pathology appears in the brains of individuals who carry this PRNP gene mutation or how it evolves throughout the disease course, but future longitudinal ¹⁸F-AV-1451 imaging of symptomatic and asymptomatic individuals in this kindred will help address these uncertainties.

Altered Processing of β-Amyloid in SH-SY5Y Cells Induced by Model Senescent Microglia

The single greatest risk factor for neurodegenerative diseases is aging. Aging of cells such as microglia in the nervous system has an impact not only on the ability of those cells to function but also on cells they interact with. We have developed a model microglia system that recapitulates the dystrophic/senescent phenotype, and we have combined this with the study of β-amyloid processing. The model is based on the observation that aged microglia have increased iron content. By overloading a human microglial cell line with iron, we were able to change the secretory profile of the microglia. When combining these senescent microglia with SH-SY5Y cells, we noted an increase in extracellular β-amyloid. The increased levels of β-amyloid were due to a decrease in the release of insulin-degrading enzyme by the model senescent microglia. Further analysis revealed that the senescent microglia showed both decreased autophagy and increased ER stress. These studies demonstrate the potential impact of an aging microglial population in terms of β-amyloid produced by neurons, which could play a causal role in diseases like Alzheimer's disease. Our results also further develop the potential utility of an in vitro model of senescent microglia for the study of brain aging and neurodegenerative disease.

Cerebrospinal Fluid Total Prion Protein in the Spectrum of Prion Diseases

Cerebrospinal fluid (CSF) total prion protein (t-PrP) is decreased in sporadic Creutzfeldt-Jakob disease (sCJD). However, data on the comparative signatures of t-PrP across the spectrum of prion diseases, longitudinal changes during disease progression, and levels in pre-clinical cases are scarce. T-PrP was quantified in neurological diseases (ND, n = 147) and in prion diseases from different aetiologies including sporadic (sCJD, n = 193), iatrogenic (iCJD, n = 12) and genetic (n = 209) forms. T-PrP was also measured in serial lumbar punctures obtained from sCJD cases at different symptomatic disease stages, and in asymptomatic prion protein gene (PRNP) mutation carriers. Compared to ND, t-PrP concentrations were significantly decreased in sCJD, iCJD and in genetic prion diseases associated with the three most common mutations E200K, V210I (associated with genetic CJD) and D178N-129M (associated with fatal familial insomnia). In contrast, t-PrP concentrations in P102L mutants (associated with the Gerstmann-Sträussler-Scheinker syndrome) remained unaltered. In serial lumbar punctures obtained at different disease stages of sCJD patients, t-PrP concentrations inversely correlated with disease progression. Decreased mean t-PrP values were detected in asymptomatic D178-129M mutant carriers, but not in E200K and P102L carriers. The presence of low CSF t-PrP is common to all types of prion diseases regardless of their aetiology albeit with mutation-specific exceptions in a minority of genetic cases. In some genetic prion disease, decreased levels are already detected at pre-clinical stages and diminish in parallel with disease progression. Our data indicate that CSF t-PrP concentrations may have a role as a pre-clinical or early symptomatic diagnostic biomarker in prion diseases as well as in the evaluation of therapeutic interventions.

Case of fatal familial insomnia caused by a d178n mutation with phenotypic similarity to Hashimoto's encephalopathy

Fatal familial insomnia (FFI) is a rare prion disease commonly inherited in an autosomal dominant pattern from a mutation in the PRioN Protein (PRNP) gene. Hashimoto's encephalopathy (HE) is characterised by encephalopathy associated with antithyroid peroxidase (TPO) or antithyroglobulin (Tg) antibodies. These two conditions characteristically have differing clinical presentations with dramatically different clinical course and outcomes. Here, we present a case of FFI mimicking HE. A woman in her 50s presented with worsening confusion, hallucinations, tremor and leg jerks. Several maternal relatives had been diagnosed with FFI, but the patient had had negative genetic testing for PRNP. MRI of brain, cervical and thoracic spine were unremarkable except for evidence of prior cervical transverse myelitis. Cerebrospinal fluid analysis was normal. Anti-TPO and anti-Tg antibodies were elevated. She was started on steroids for possible HE and showed improvement in symptoms. Following discharge, the results of her PRNP gene test returned positive for variant p.Asp178Asn.

Familial Creutzfeldt-Jakob Disease Cluster Among an African American Family

Familial Creutzfeldt-Jakob disease (fCJD) results from inheritance of mutations in the prion protein gene. Confirming fCJD diagnosis is essential for informing persons of their potential hereditary risk and for genetic counseling to support personal decisions for genetic testing and family planning. We describe a case of fCJD that was linked to a large cluster of African Americans with fCJD identified through a public health investigation, including 8 confirmed cases and 13 suspected cases involving 7 generations in 1 family. Genetic counseling is an important component of fCJD management for families coping with genetic prion diseases.

Genetic PrP Prion Diseases

Genetic prion diseases (gPrDs) caused by mutations in the prion protein gene (PRNP) have been classified as genetic Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker disease, or fatal familial insomnia. Mutations in PRNP can be missense, nonsense, and/or octapeptide repeat insertions or, possibly, deletions. These mutations can produce diverse clinical features. They may also show varying ancillary testing results and neuropathological findings. Although the majority of gPrDs have a rapid progression with a short survival time of a few months, many also present as ataxic or parkinsonian disorders, which have a slower decline over a few to several years. A few very rare mutations manifest as neuropsychiatric disorders, with systemic symptoms that include gastrointestinal disorders and neuropathy; these forms can progress over years to decades. In this review, we classify gPrDs as rapid, slow, or mixed types based on their typical rate of progression and duration, and we review the broad spectrum of phenotypes manifested by these 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.

Rare case of atypical parkinsonism: why family history is important

We discuss the clinical presentation and assessment of a middle aged previously fit and well man who presented with two episodes of syncope to the cardiologists followed by the development of a rapidly progressive parkinsonian syndrome a couple of years later, which was not responsive to standard dopaminergic replacement therapies. Magnetic resonance imaging scan of the brain was normal and a DAT SPECT scan showed reduced dopamine uptake in the basal ganglia. On further enquiry, a family history of a similar presentation in his first cousin was elicited and that cousin had tested positive for a mutation in the PRNP gene. Subsequently, he also tested positive for A117V mutation in the PRNP gene, confirming familial Creutzfeld Jakob disease. Familial Creutzfeld Jakob disease presenting with parkinsonism is rare in clinical practice, but it is something that neurologists and geriatricians running movement disorder clinics should be aware of, as this is a rapidly progressive and uniformly fatal condition with inheritance risks to family members.

Extracellular Vesicles in Neurodegenerative Diseases: A Double-Edged Sword

Extracellular vesicles (EVs), a heterogenous group of membrane-bound particles, are virtually secreted by all cells and play important roles in cell-cell communication. Loaded with proteins, mRNAs, non-coding RNAs and membrane lipids from their donor cells, these vesicles participate in normal physiological and pathogenic processes. In addition, these sub-cellular vesicles are implicated in the progression of neurodegenerative disorders. Accumulating evidence suggests that intercellular communication via EVs is responsible for the propagation of key pathogenic proteins involved in the pathogenesis of amyotrophic lateral sclerosis, Parkinson's diseases, Alzheimer's diseases and other neurodegenerative disorders. For therapeutic perspective, EVs present advantage over other synthetic drug delivery systems or cell therapy; ability to cross biological barriers including blood brain barrier (BBB), ability to modulate inflammation and immune responses, stability and longer biodistribution with lack of tumorigenicity. In this review, we summarized the current state of EV research in central nervous system in terms of their values in diagnosis, disease pathology and therapeutic applications.

Transgenic mice recapitulate the phenotypic heterogeneity of genetic prion diseases without developing prion infectivity: Role of intracellular PrP retention in neurotoxicity

Genetic prion diseases are degenerative brain disorders caused by mutations in the gene encoding the prion protein (PrP). Different PrP mutations cause different diseases, including Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker (GSS) syndrome and fatal familial insomnia (FFI). The reason for this variability is not known. It has been suggested that prion strains with unique self-replicating and neurotoxic properties emerge spontaneously in individuals carrying PrP mutations, dictating the phenotypic expression of disease. We generated transgenic mice expressing the FFI mutation, and found that they developed a fatal neurological illness highly reminiscent of FFI, and different from those of similarly generated mice modeling genetic CJD and GSS. Thus transgenic mice recapitulate the phenotypic differences seen in humans. The mutant PrPs expressed in these mice are misfolded but unable to self-replicate. They accumulate in different compartments of the neuronal secretory pathway, impairing the membrane delivery of ion channels essential for neuronal function. Our results indicate that conversion of mutant PrP into an infectious isoform is not required for pathogenesis, and suggest that the phenotypic variability may be due to different effects of mutant PrP on intracellular transport.

Toward Therapy of Human Prion Diseases

Three decades after the discovery of prions as the cause of Creutzfeldt-Jakob disease and other transmissible spongiform encephalopathies, we are still nowhere close to finding an effective therapy. Numerous pharmacological interventions have attempted to target various stages of disease progression, yet none has significantly ameliorated the course of disease. We still lack a mechanistic understanding of how the prions damage the brain, and this situation results in a dearth of validated pharmacological targets. In this review, we discuss the attempts to interfere with the replication of prions and to enhance their clearance. We also trace some of the possibilities to identify novel targets that may arise with increasing insights into prion biology.

Genetic human prion disease modelled in PrP transgenic Drosophila

Inherited human prion diseases, such as fatal familial insomnia (FFI) and familial Creutzfeldt–Jakob disease (fCJD), are associated with autosomal dominant mutations in the human prion protein gene PRNP and accumulation of PrP^Sc, an abnormal isomer of the normal host protein PrP^C, in the brain of affected individuals. PrP^Sc is the principal component of the transmissible neurotoxic prion agent. It is important to identify molecular pathways and cellular processes that regulate prion formation and prion-induced neurotoxicity. This will allow identification of possible therapeutic interventions for individuals with, or at risk from, genetic human prion disease. Increasingly, Drosophila has been used to model human neurodegenerative disease. An important unanswered question is whether genetic prion disease with concomitant spontaneous prion formation can be modelled in Drosophila. We have used pUAST/PhiC31-mediated site-directed mutagenesis to generate Drosophila transgenic for murine or hamster PrP (prion protein) that carry single-codon mutations associated with genetic human prion disease. Mouse or hamster PrP harbouring an FFI (D178N) or fCJD (E200K) mutation showed mild Proteinase K resistance when expressed in Drosophila. Adult Drosophila transgenic for FFI or fCJD variants of mouse or hamster PrP displayed a spontaneous decline in locomotor ability that increased in severity as the flies aged. Significantly, this mutant PrP-mediated neurotoxic fly phenotype was transferable to recipient Drosophila that expressed the wild-type form of the transgene. Collectively, our novel data are indicative of the spontaneous formation of a PrP-dependent neurotoxic phenotype in FFI- or CJD-PrP transgenic Drosophila and show that inherited human prion disease can be modelled in this invertebrate host.

Biosafety of Prions

Prions are the infectious agents that cause devastating and untreatable disorders known as Transmissible Spongiform Encephalopathies (TSEs). The pathologic events and the infectious nature of these transmissible agents are not completely understood yet. Due to the difficulties in inactivating prions, working with them requires specific recommendations and precautions. Moreover, with the advent of innovative technologies, such as the Protein Misfolding Cyclic Amplification (PMCA) and the Real Time Quaking-Induced Conversion (RT-QuIC), prions could be amplified in vitro and the infectious features of the amplified products need to be carefully assessed.