Selective Breeding for Disease-Resistant PRNP Variants to Manage Chronic Wasting Disease in Farmed Whitetail Deer.

Chronic wasting disease (CWD) is a fatal transmissible spongiform encephalopathy (TSE) of cervids caused by a misfolded variant of the normal cellular prion protein, and it is closely related to sheep scrapie. Variations in a host's prion gene, PRNP, and its primary protein structure dramatically affect susceptibility to specific prion disorders, and breeding for PRNP variants that prevent scrapie infection has led to steep declines in the disease in North American and European sheep. While resistant alleles have been identified in cervids, a PRNP variant that completely prevents CWD has not yet been identified. Thus, control of the disease in farmed herds traditionally relies on quarantine and depopulation. In CWD-endemic areas, depopulation of private herds becomes challenging to justify, leading to opportunities to manage the disease in situ. We developed a selective breeding program for farmed white-tailed deer in a high-prevalence CWD-endemic area which focused on reducing frequencies of highly susceptible PRNP variants and introducing animals with less susceptible variants. With the use of newly developed primers, we found that breeding followed predictable Mendelian inheritance, and early data support our project's utility in reducing CWD prevalence. This project represents a novel approach to CWD management, with future efforts building on these findings.

Variably Protease-sensitive Prionopathy in a Middle-aged Man With Rapidly Progressive Dementia.

Variably protease-sensitive prionopathy (VPSPr) is a recently described sporadic prion disease with distinctive clinical and histopathological features. We report the clinical, imaging, and neuropathological features of VPSPr in a 46-year-old right-handed man who presented with progressive cognitive decline, behavior disturbances, and a 50-pound weight loss over 6 months. The initial evaluation revealed severe cognitive impairment with no focal neurologic deficits. His cognitive, psychiatric, and behavior symptoms progressed rapidly, and he died 12 months after the initial visit. Throughout his disease course, workup for rapid progressive dementia was unremarkable except that brain MRI diffusion-weighted imaging showed persistent diffuse cortical and thalamic signal abnormalities. Sporadic Creutzfeldt-Jakob disease was highly suspected; however, two EEGs (8 months apart) demonstrated only nonspecific cerebral dysfunction. The patient's CSF 14-3-3 protein was negative at the initial visit and again 8 months later. His CSF real-time quaking-induced conversion and total tau level were normal. An autopsy of his brain was performed, and the neuropathological findings confirmed VPSPr. Our case underlines the importance of considering VPSPr in the spectrum of prion disease phenotypes when evaluating individuals with rapidly progressive dementia.

Clinical Use of Improved Diagnostic Testing for Detection of Prion Disease.

Prion diseases are difficult to recognize as many symptoms are shared among other neurologic pathologies and the full spectra of symptoms usually do not appear until late in the disease course. Additionally, many commonly used laboratory markers are non-specific to prion disease. The recent introduction of second-generation real time quaking induced conversion (RT-QuIC) has revolutionized pre-mortem diagnosis of prion disease due to its extremely high sensitivity and specificity. However, RT-QuIC does not provide prognostic data and has decreased diagnostic accuracy in some rarer, atypical prion diseases. The objective of this review is to provide an overview of the current clinical utility of fluid-based biomarkers, neurodiagnostic testing, and brain imaging in the diagnosis of prion disease and to suggest guidelines for their clinical use, with a focus on rarer prion diseases with atypical features. Recent advancements in laboratory-based testing and imaging criteria have shown improved diagnostic accuracy and prognostic potential in prion disease, but because these diagnostic tests are not sensitive in some prion disease subtypes and diagnostic test sensitivities are unknown in the event that CWD transmits to humans, it is important to continue investigations into the clinical utility of various testing modalities.

Cognitive decline heralds onset of symptomatic inherited prion disease.

The clinical effectiveness of any disease-modifying treatment for prion disease, as for other neurodegenerative disorders, will depend on early treatment before damage to neural tissue is irrevocable. Thus, there is a need to identify markers that predict disease onset in healthy at-risk individuals. Whilst imaging and neurophysiological biomarkers have shown limited use in this regard, we recently reported progressive neurophysiological changes in individuals with the inherited prion disease mutation P102L. We have also previously demonstrated a signature pattern of fronto-parietal dysfunction in mild prion disease. Here we address whether these cognitive features anticipate the onset of symptoms in a unique sample of patients with inherited prion disease. In the cross-sectional analysis, we analysed the performance of patients at three time points in the course of disease onset: prior to symptoms (n = 27), onset of subjective symptoms without positive clinical findings (n = 8) and symptomatic with positive clinical findings (n = 24). In the longitudinal analysis, we analysed data from 24 patients who were presymptomatic at the time of recruitment and were followed up over a period of up to 17 years, of whom 16 remained healthy and eight converted to become symptomatic. In the cross-sectional analysis, the key finding was that, relative to a group of 25 healthy non-gene carrier controls, patients with subjective symptoms but without positive clinical findings were impaired on a smaller but similar set of tests (Trail Making Test part A, Stroop test, Performance IQ, gesture repetition, figure recall) to those previously found to be impaired in mild prion disease. In the longitudinal analysis, Trail Making Test parts A and B, Stroop test and Performance IQ scores significantly discriminated between patients who remained presymptomatic and those who converted, even before the converters reached criteria for formal diagnosis. Notably, performance on the Stroop test significantly discriminated between presymptomatic patients and converters before the onset of clinical symptoms [area under the curve = 0.83 (95% confidence interval, 0.62-1.00), P = 0.009]. Thus, we report here, for the first time, neuropsychological abnormalities in healthy patients prior to either symptom onset or clinical diagnosis of inherited prion disease. This constitutes an important component of an evolving profile of clinical and biomarker abnormalities in this crucial group for preventive medicine.

Epilepsy and prion diseases: A narrative review.

Epileptic seizures have been described as one feature of prion diseases, but are an unusual clinical presentation. The aim of this narrative Review was to summarize current knowledge of epileptic seizures in the various forms of prion diseases, from a clinical perspective. Examination of the published literature identified no systematic studies; the evidence base is largely anecdotal, consisting mainly of case studies and small case series. Hence, uncertainty prevails as to seizure frequency, semiology, treatment, and pathogenesis in prion diseases. Seizures probably occur in around 10% of sporadic cases but less frequently in iatrogenic and familial forms, with the possible exception of the E200K mutation. The literature suggests a predominance of focal motor and nonconvulsive status epilepticus. Electroencephalographic accompaniments include periodic lateralized or generalized periodic epileptiform discharges (PLEDs, GPEDs), sometimes predating the more typical periodic sharp wave complexes. There are no convincing accounts of successful antiepileptic drug therapy. The underlying mechanisms of epileptogenesis in prion diseases may include loss of cellular prion protein function (PrPc) and aggregation of abnormally folded prion protein (PrPSc). The need for systematic studies and clinical trials to expand the evidence base surrounding epilepsy and prion diseases is evident.

Heidenhain variant of Creutzfeldt-Jakob disease in Brazil: a case report / Variante Heidenhain da Doença de Creutzfeldt-Jakob no Brasil: um relato de caso

Creutzfeldt-Jakob disease (CJD) is a rare spongiform encephalopathy characterized by a rapid neurodegenerative progress, caused by a misfolded variant of the cellular prion protein (PrP) known as PrPSc. The clinical presentation of sCJD includes a wide range of neurological signs of cortical, subcortical, or cerebellar origin, either isolated or in various combinations. Due to this protean clinical presentation form, sCJD must be distinguished from other dementias. In this case report, we discuss the Heidenhain variant of Creutzfeldt-Jakob disease (HvCJD), a rare variant characterized by early visual symptoms and typical findings in imaging scans. Our patient presented rapidly progressive dementia and a history of visual hallucinations. As for other prion diseases, only symptomatic treatment is available for HvCJD. Thirty years of clinical investigation of patients with prion disease have resulted in little progress in either defining or evaluating potential treatments.

A doença de Creutzfeldt-Jakob (DCJ) é uma encefalopatia rara caracterizada por rápida progressão neurodegenerativa, causada pelo enovelamento incorreto da proteína priônica celular (PrP), conhecido como PrPSc. O quadro clínico da DCJ esporádica inclui um amplo espectro de sinais neurológicos de origens cortical, subcortical ou cerebelar, seja de forma isolada, seja combinada. Por causa da sua apresentação clínica variável, a DCJ esporádica deve ser distinguida de outras demências. Neste relato de caso, discutimos a variante Heidenhain da DCJ (vHDCJ), uma variante rara caracterizada por sintomas visuais precoces e características específicas no exame de imagem. Nossa paciente apresentou demência rapidamente progressiva e histórico de alucinações visuais. Assim como para as demais doenças priônicas, apenas o tratamento sintomático está disponível para a vHDCJ. Trinta anos de investigação clínica de pacientes com doença priônica têm resultado em pouco progresso, seja definindo os potenciais tratamentos, seja avaliando-os.

Movement Disorders in Prionopathies: A Systematic Review.

Background: Movement disorders are frequent features of prionopathies. However, their prevalence and onset remain poorly described. Methods: We performed a systematic review of case reports and case series of pathologically- and genetically confirmed prionopathies. Timing of symptom and movement disorder onset were documented. Continuous variables were compared between two groups using the Wilcoxon rank sum test and between multiple groups using Kruskal-Wallis test. Categorical variables were compared using Fisher's exact test. Results: A total of 324 cases were included in this analysis. Movement disorders were a common feature at the onset of symptoms in most prionopathies. Gait ataxia was present in more than half of cases in all types of prionopathies. The prevalence of limb ataxia (20%) and myoclonus (24%) was lower in Gerstmann-Sträussler-Scheinker disease compared to other prionopathies (p ≤ 0.004). Myoclonus was common but often a later feature in sporadic Creutzfeldt-Jakob disease (2 months before death). Chorea was uncommon but disproportionately prevalent in variant Creutzfeldt-Jakob disease (30% of cases; p < 0.001). In genetic Creutzfeldt-Jakob disease, E200K PRNP carriers exhibited gait and limb ataxia more often when compared to other mutation carriers. Discussion: Movement disorders are differentially present in the course of the various prionopathies. The movement phenomenology and appearance are associated with the type of prion disease and the PRNP genotype and likely reflect the underlying pattern of neurodegeneration. Reliance on myoclonus as a diagnostic feature of sporadic Creutzfeldt-Jakob disease may delay its recognition given its relatively late appearance in the disease course.

Could it be that neurodegenerative diseases are infectious?

The cell-to-cell transmission of the major pathogenic proteins of Parkinson's disease and Alzheimer's disease is reminiscent of the prion protein, which is defined as a proteinaceous infectious particle that causes human and animal transmissible spongiform encephalopathies. The possibility has raised that the pathogenic proteins of Parkinson's and Alzheimer's disease are infectious, i.e. that they can transmit disease from human to human. In this review, we address this question by comparing the similarities and differences between Alzheimer's disease/Parkinson's disease pathological proteins and prions and by discussing the possible consequences for disease transmission risk.

Co-occurrence of chronic traumatic encephalopathy and prion disease.

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive traumatic brain injury (TBI). CTE is generally found in athletes participating in contact sports and military personnel exposed to explosive blasts but can also affect civilians. Clinically and pathologically, CTE overlaps with post-traumatic stress disorder (PTSD), a term mostly used in a clinical context. The histopathology of CTE is defined by the deposition of hyperphosphorylated tau protein in neurons and astrocytes preferentially with perivascular distribution and at the depths of the cortical sulci. In addition to hyperphosphorylated tau, other pathologic proteins are deposited in CTE, including amyloid ß (Aß), transactive response (TAR) DNA-binding protein 43 kDa (TDP-43) and α-synuclein. However, the coexistence of prion disease in CTE has not been observed. We report three cases of histopathologically validated CTE with co-existing sporadic prion disease. Two were identified in a cohort of 55 pathologically verified cases of CTE submitted to the CTE Center of Boston University. One was identified among brain tissues submitted to the National Prion Disease Pathology Surveillance Center of Case Western Reserve University. The histopathological phenotype and properties of the abnormal, disease-related prion protein (PrPD) of the three CTE cases were examined using lesion profile, immunohistochemistry, electrophoresis and conformational tests. Subjects with sporadic Creutzfeldt-Jakob disease (sCJD) matched for age, PrP genotype and PrPD type were used as controls. The histopathology phenotype and PrPD properties of the three CTE subjects showed no significant differences from their respective sCJD controls suggesting that recurring neurotrauma or coexisting CTE pathology did not detectably impact the prion disease phenotype and PrPD conformational characteristics. Based on the reported incidence of sporadic prion disease, the detection of two cases with sCJD in the CTE Center series of 55 CTE cases by chance alone would be highly unlikely (p = 8.93*10- 6). Nevertheless, examination of a larger cohort of CTE is required to conclusively determine whether the risk of CJD is significantly increased in patients with CTE.

Alpha-synuclein and the prion hypothesis in Parkinson's disease.

Protein intracellular inclusions within the central nervous system are hallmarks of several progressive neurodegenerative disorders in man. The protein constituents of those deposits and the affected regions within the brain differ from one neurodegenerative disorder to another. Until recently, the vicious circle consisting of spread, seeded assembly and accumulation over time within the central nervous system of misfolded proteins aggregates was thought to be restricted to the prion protein PrP. Recent reports suggest that other protein aggregates spread and amplify within the central nervous system leading to distinct diseases. How alpha-synuclein protein assemblies traffic between cells, amplify by recruiting endogenous monomeric alpha-synuclein and cause distinct synucleinopathies is unclear. I review here the experimental evidence supporting the propagation of alpha-synuclein mega-dalton assemblies in a manner similar to prion protein aggregates. I also describe how alpha-synuclein aggregates. I also explain why the aggregation of alpha-synuclein may lead to distinct synucleinopathies.

Mammalian prion propagation in PrP transgenic Drosophila.

Mammalian prions propagate by template-directed misfolding and aggregation of normal cellular prion related protein PrPC as it converts into disease-associated conformers collectively referred to as PrPSc. Mammalian species may be permissive for prion disease because these hosts have co-evolved specific co-factors that assist PrPC conformational change and prion propagation. We have tested this hypothesis by examining whether faithful prion propagation occurs in the normally PrPC-null invertebrate host Drosophila melanogaster. Ovine PrP transgenic Drosophila exposed at the larval stage to ovine scrapie showed a progressive accumulation of transmissible prions in adult flies. Strikingly, the biological properties of distinct ovine prion strains were maintained during their propagation in Drosophila. Our observations show that the co-factors necessary for strain-specific prion propagation are not unique to mammalian species. Our studies establish Drosophila as a novel host for the study of transmissible mammalian prions.

Variably protease-sensitive prionopathy.

Variably protease-sensitive prionopathy (VPSPr), originally identified in 2008, was further characterized and renamed in 2010. Thirty-seven cases of VPSPr have been reported to date, consistent with estimated prevalence of 0.7-1.7% of all sporadic prion diseases. The lack of gene mutations establishes VPSPr as a sporadic form of human prion diseases, along with sporadic Creutzfeldt-Jakob disease (sCJD) and sporadic fatal insomnia. Like sCJD, VPSPr affects patients harboring any of the three genotypes, MM, MV, and VV at the prion protein (PrP) gene polymorphic codon 129, with VPSPr VV accounting for 65% of all VPSPr cases. Distinguishing clinical features include a median 2-year duration and presentation with psychiatric signs, speech/language impairment, or cognitive decline. Neuropathology comprises moderate spongiform degeneration, PrP amyloid miniplaques, and a target-like or plaque-like PrP deposition. The abnormal PrP associated with VPSPr typically forms an electrophoretic profile of five to seven bands (according to the antibody) presenting variable protease resistance depending on the 129 genotype. The familial prion disease associated with the V180I PrP gene mutation which harbors an abnormal PrP with similar electrophoretic profile might serve as a model for VPSPr. Transmission to animals has definitively established VPSPr as a prion disease. Because of its recent identification, rarity, and the elusiveness of its abnormal PrP, VPSPr remains largely understudied.

The cellular and pathologic prion protein.

The cellular prion protein, PrPC, is a small, cell surface glycoprotein with a function that is currently somewhat ill defined. It is also the key molecule involved in the family of neurodegenerative disorders called transmissible spongiform encephalopathies, which are also known as prion diseases. The misfolding of PrPC to a conformationally altered isoform, designated PrPTSE, is the main molecular process involved in pathogenesis and appears to precede many other pathologic and clinical manifestations of disease, including neuronal loss, astrogliosis, and cognitive loss. PrPTSE is also believed to be the major component of the infectious "prion," the agent responsible for disease transmission, and preparations of this protein can cause prion disease when inoculated into a naïve host. Thus, understanding the biochemical and biophysical properties of both PrPC and PrPTSE, and ultimately the mechanisms of their interconversion, is critical if we are to understand prion disease biology. Although entire books could be devoted to research pertaining to the protein, herein we briefly review the state of knowledge of prion biochemistry, including consideration of prion protein structure, function, misfolding, and dysfunction.

Fatal familial insomnia and sporadic fatal insomnia.

Fatal familial insomnia (FFI) and sporadic fatal insomnia (sFI), or thalamic form of sporadic Creutzfeldt-Jakob disease MM2 (sCJDMM2T), are prion diseases originally named and characterized in 1992 and 1999, respectively. FFI is genetically determined and linked to a D178N mutation coupled with the M129 genotype in the prion protein gene (PRNP) at chromosome 20. sFI is a phenocopy of FFI and likely its sporadic form. Both diseases are primarily characterized by progressive sleep impairment, disturbances of autonomic nervous system, and motor signs associated with severe loss of nerve cells in medial thalamic nuclei. Both diseases harbor an abnormal disease-associated prion protein isoform, resistant to proteases with relative mass of 19 kDa identified as resPrPTSE type 2. To date at least 70 kindreds affected by FFI with 198 members and 18 unrelated carriers along with 25 typical cases of sFI have been published. The D178N-129M mutation is thought to cause FFI by destabilizing the mutated prion protein and facilitating its conversion to PrPTSE. The thalamus is the brain region first affected. A similar mechanism triggered spontaneously may underlie sFI.

Differential diagnosis with other rapid progressive dementias in human prion diseases.

Prion diseases are unique in medicine as in humans they occur in sporadic, genetic, and acquired forms. The most common human prion disease is sporadic Creutzfeldt-Jakob disease (CJD), which commonly presents as a rapidly progressive dementia (RPD) with behavioral, cerebellar, extrapyramidal, and some pyramidal features, with the median survival from symptom onset to death of just a few months. Because human prion diseases, as well as other RPDs, are relatively rare, they can be difficult to diagnose, as most clinicians have seen few, if any, cases. Not only can prion diseases mimic many other conditions that present as RPD, but some of those conditions can present similarly to prion disease. In this article, the authors discuss the different etiologic categories of conditions that often present as RPD and also present RPDs that had been misdiagnosed clinically as CJD. Etiologic categories of conditions are presented in order of the mnemonic used for remembering the various categories of RPDs: VITAMINS-D, for vascular, infectious, toxic-metabolic, autoimmune, mitochondrial/metastases, iatrogenic, neurodegenerative, system/seizures/sarcoid, and demyelinating. When relevant, clinical, imaging, or other features of an RPD that overlap with those of CJD are presented.

The language disorder of prion disease is characteristic of a dynamic aphasia and is rarely an isolated clinical feature.

BACKGROUND: Akinetic mutism is a key diagnostic feature of prion diseases, however, their rapidly progressive nature makes detailed investigation of the language disorder in a large cohort extremely challenging. This study aims to position prion diseases in the nosology of language disorders and improve early clinical recognition. METHODS: A systematic, prospective investigation of language disorders in a large cohort of patients diagnosed with prion diseases. 568 patients were included as a sub-study of the National Prion Monitoring Cohort. All patients had at least one assessment with the MRC Scale, a milestone-based functional scale with language and non-language components. Forty patients, with early symptoms and able to travel to the study site, were also administered a comprehensive battery of language tests (spontaneous speech, semantics, syntax, repetition, naming, comprehension and lexical retrieval under different conditions). RESULTS: 5/568 (0.9%) patients presented with leading language symptoms. Those with repeated measurements deteriorated at a slower rate in language compared to non-language milestones. Amongst the subgroup of 40 patients who underwent detailed language testing, only three tasks-semantic and phonemic fluency and sentence comprehension-were particularly vulnerable early in the disease. These tasks were highly correlated with performance on non-verbal executive tests. Patients were also impaired on a test of dynamic aphasia. CONCLUSION: These results provide evidence that the language disorder in prion disease is rarely an isolated clinical or cognitive feature. The language abnormality is indicative of a dynamic aphasia in the context of a prominent dysexecutive syndrome, similar to that seen in patients with the degenerative movement disorder progressive supranuclear palsy (PSP).

α-Synuclein: Multiple System Atrophy Prions.

Multiple system atrophy (MSA) is a rapidly progressive neurodegenerative disease arising from the misfolding and accumulation of the protein α-synuclein in oligodendrocytes, where it forms glial cytoplasmic inclusions (GCIs). Several years of studying synthetic α-synuclein fibrils has provided critical insight into the ability of α-synuclein to template endogenous protein misfolding, giving rise to fibrillar structures capable of propagating from cell to cell. However, more recent studies with MSA-derived α-synuclein aggregates have shown that they have a similar ability to undergo template-directed propagation, like PrP prions. Almost 20 years after α-synuclein was discovered as the primary component of GCIs, α-synuclein aggregates isolated from MSA patient samples were shown to infect cultured mammalian cells and also to transmit neurological disease to transgenic mice. These findings argue that α-synuclein becomes a prion in MSA patients. In this review, we discuss the in vitro and in vivo data supporting the recent classification of MSA as a prion disease.

Parkinson's Disease Is Not Simply a Prion Disorder.

The notion that prion-like spreading of misfolded α-synuclein (α-SYN) causes Parkinson's disease (PD) has received a great deal of attention. Although attractive in its simplicity, the hypothesis is difficult to reconcile with postmortem analysis of human brains and connectome-mapping studies. An alternative hypothesis is that PD pathology is governed by regional or cell-autonomous factors. Although these factors provide an explanation for the pattern of neuronal loss in PD, they do not readily explain the apparently staged distribution of Lewy pathology in many PD brains, the feature of the disease that initially motivated the spreading hypothesis by Braak and colleagues. While each hypothesis alone has its shortcomings, a synthesis of the two can explain much of what we know about the etiopathology of PD.Dual Perspectives Companion Paper: Prying into the Prion Hypothesis for Parkinson's Disease, by Patrik Brundin and Ronald Melki.

Prying into the Prion Hypothesis for Parkinson's Disease.

In Parkinson's disease, intracellular α-synuclein inclusions form in neurons. We suggest that prion-like behavior of α-synuclein is a key component in Parkinson's disease pathogenesis. Although multiple molecular changes are involved in the triggering of the disease process, we propose that neuron-to-neuron transfer is a crucial event that is essential for Lewy pathology to spread from one brain region to another. In this review, we describe key findings in human postmortem brains, cultured cells, and animal models of disease that support the idea that α-synuclein can act as a prion. We consider potential triggers of the α-synuclein misfolding and why the aggregates escape cellular degradation under disease conditions. We also discuss whether different strains of α-synuclein fibrils can underlie differences in cellular and regional distribution of aggregates in different synucleinopathies. Our conclusion is that α-synuclein probably acts as a prion in human diseases, and a deeper understanding of this step in the pathogenesis of Parkinson's disease can facilitate the development of disease-modifying therapies in the future.Dual Perspectives Companion Paper: Parkinson's Disease Is Not Simply a Prion Disorder, by D. James Surmeier, José A. Obeso, and Glenda M. Halliday.