Iatrogenic Creutzfeldt-Jakob disease, final assessment

Extended and direct evaluation of RT-QuIC assays for Creutzfeldt-Jakob disease diagnosis

Real-Time Quaking-Induced Conversion (RT-QuIC) testing of human cerebrospinal fluid (CSF) is highly sensitive and specific in discriminating sporadic CJD patients from those without prion disease. Here, using CSF samples from 113 CJD and 64 non-prion disease patients, we provide the first direct and concurrent comparison of our improved RT-QuIC assay to our previous assay, which is similar to those commonly used internationally for CJD diagnosis. This extended comparison demonstrated a ~21% increase in diagnostic sensitivity, a 2-day reduction in average detection time, and 100% specificity.

Dura mater graft-associated Creutzfeldt-Jakob disease with 30-year incubation period

Over 60% of all patients with dura mater graft-associated Creutzfeldt-Jakob disease (dCJD) have been diagnosed in Japan. The incubation period has ranged from 1 to 30 years and the age at onset from 15 to 80 years. Here, we report a 77-year-old male Japanese autopsied dCJD case with the longest incubation period so far in Japan. He received a cadaveric dural graft at the right cranial convexity following a craniotomy for meningioma at the age of 46. At 30 years post-dural graft placement, disorientation was observed as an initial symptom of dCJD. He rapidly began to present with inconsistent speech, cognitive impairment and tremor of the left upper extremity. Occasional myoclonic jerks were predominantly observed on the left side. Brain MRI presented hyperintense signals on diffusion-weighted and T2-weighted images, at the right cerebral cortex. The most hyperintense lesion was located at the right parietal lobe, where the dura mater graft had been transplanted. Single-photon emission CT scan showed markedly decreased cerebral blood flow at the right parietal lobe. EEG revealed diffuse and slow activities with periodic sharp-wave complex discharges seen in the right parietal, temporal and occipital lobes. He died of pneumonia 9 months after onset. Brain pathology revealed non-plaque-type dCJD. Laterality of neuropathological changes, including spongiform change, neuronal loss, gliosis or PrP deposits, was not evident. Western blot analysis showed type 1 PrP^CJD . Alzheimer-type pathology and PSP-like pathology were also observed.

Inactivation of Prions and Amyloid Seeds with Hypochlorous Acid

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

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

Neuroinvasion of α-Synuclein Prionoids after Intraperitoneal and Intraglossal Inoculation

α-Synuclein is a soluble, cellular protein that in a number of neurodegenerative diseases, including Parkinson's disease and multiple system atrophy, forms pathological deposits of protein aggregates. Because misfolded α-synuclein has some characteristics that resemble those of prions, we investigated its potential to induce disease after intraperitoneal or intraglossal challenge injection into bigenic Tg(M83^+/−:Gfap-luc^+/−) mice, which express the A53T mutant of human α-synuclein and firefly luciferase. After a single intraperitoneal injection with α-synuclein fibrils, four of five mice developed paralysis and α-synuclein pathology in the central nervous system, with a median incubation time of 229 ± 17 days. Diseased mice accumulated aggregates of Sarkosyl-insoluble and phosphorylated α-synuclein in the brain and spinal cord, which colocalized with ubiquitin and p62 and were accompanied by gliosis. In contrast, only one of five mice developed α-synuclein pathology in the central nervous system after intraglossal injection with α-synuclein fibrils, after 285 days. These findings are novel and important because they show that, similar to prions, α-synuclein prionoids can neuroinvade the central nervous system after intraperitoneal or intraglossal injection and can cause neuropathology and disease.

IMPORTANCE Synucleinopathies are neurodegenerative diseases that are characterized by the pathological presence of aggregated α-synuclein in cells of the nervous system. Previous studies have shown that α-synuclein aggregates made of recombinant protein or derived from brains of patients can spread in the central nervous system in a spatiotemporal manner when inoculated into the brains of animals and can induce pathology and neurologic disease, suggesting that misfolded α-synuclein can behave similarly to prions. Here we show that α-synuclein inoculation into the peritoneal cavity or the tongue in mice overexpressing α-synuclein causes neurodegeneration after neuroinvasion from the periphery, which further corroborates the prionoid character of misfolded α-synuclein.

Like prions: the propagation of aggregated tau and α-synuclein in neurodegeneration

The abnormal aggregation of a small number of known proteins underlies the most common human neurodegenerative diseases. In tauopathies and synucleinopathies, the normally soluble intracellular proteins tau and α-synuclein become insoluble and filamentous. In recent years, non-cell autonomous mechanisms of aggregate formation have come to the fore, suggesting that nucleation-dependent aggregation may occur in a localized fashion in human tauopathies and synucleinopathies, followed by seed-dependent propagation. There is a long prodromal phase between the formation of protein aggregates and the appearance of the first clinical symptoms, which manifest only after extensive propagation, opening novel therapeutic avenues.

Prion diseases: New considerations

The transmissible spongiform encephalopathies, which include Creutzfeldt-Jakob disease, are fatal neurodegenerative disorders caused by the pathological accumulation of abnormal prion protein. The diagnosis of Creutzfeldt-Jakob disease is complex. The electroencephalogram, magnetic resonance imaging, lumbar puncture and genetic testing findings can help in the differential diagnosis of rapidly progressive dementia. There has recently been considerable debate as to whether proteins involved in the development of neurodegenerative diseases should be regarded as prions or only share prion-like mechanisms. Two recent reports described the detection of abnormal prion protein in the nasal mucosa and urine of patients with Creutzfeldt-Jakob disease. These findings raise major health concerns regarding the transmissibility of human prion diseases. We set out to address this neurological hot topic and to draw conclusions on the basis of what is known in the literature thus far.

Patient with rapidly evolving neurological disease with neuropathological lesions of Creutzfeldt-Jakob disease, Lewy body dementia, chronic subcortical vascular encephalopathy and meningothelial meningioma

We report a case of rapidly evolving neurological disease in a patient with neuropathological lesions of Creutzfeldt-Jakob disease (CJD), Lewy body dementia (LBD), chronic subcortical vascular encephalopathy and meningothelial meningioma. The coexistence of severe multiple pathologies in a single patient strengthens the need to perform accurate clinical differential diagnoses in rapidly progressive dementias.

Pathogenic mechanisms of prion protein, amyloid-β and α-synuclein misfolding: the prion concept and neurotoxicity of protein oligomers

Proteinopathies represent a group of diseases characterized by the unregulated misfolding and aggregation of proteins. Accumulation of misfolded protein in the central nervous system (CNS) is associated with neurodegenerative diseases, such as the transmissible spongiform encephalopathies (or prion diseases), Alzheimer's disease, and the synucleinopathies (the most common of which is Parkinson's disease). Of these, the pathogenic mechanisms of prion diseases are particularly striking where the transmissible, causative agent of disease is the prion, or proteinaceous infectious particle. Prions are composed almost exclusively of PrP^Sc ; a misfolded isoform of the normal cellular protein, PrP^C , which is found accumulated in the CNS in disease. Today, mounting evidence suggests other aggregating proteins, such as amyloid-β (Aβ) and α-synuclein (α-syn), proteins associated with Alzheimer's disease and synucleinopathies, respectively, share similar biophysical and biochemical properties with PrP^Sc that influences how they misfold, aggregate, and propagate in disease. In this regard, the definition of a 'prion' may ultimately expand to include other pathogenic proteins. Unifying knowledge of folded proteins may also reveal common mechanisms associated with other features of disease that are less understood, such as neurotoxicity. This review discusses the common features Aβ and α-syn share with PrP and neurotoxic mechanisms associated with these misfolded proteins. Several proteins are known to misfold and accumulate in the central nervous system causing a range of neurodegenerative diseases, such as Alzheimer's, Parkinson's, and the prion diseases. Prions are transmissible misfolded conformers of the prion protein, PrP, which seed further generation of infectious proteins. Similar effects have recently been observed in proteins associated with Alzheimer's disease and the synucleinopathies, leading to the proposition that the definition of a 'prion' may ultimately expand to include other pathogenic proteins. Unifying knowledge of misfolded proteins may also reveal common mechanisms associated with other features of disease that are less understood, such as neurotoxicity.

Prion Diseases

PURPOSE OF REVIEW

This article presents an update on the clinical aspects of human prion disease, including the wide spectrum of their presentations.

RECENT FINDINGS

Prion diseases, a group of disorders caused by abnormally shaped proteins called prions, occur in sporadic (Jakob-Creutzfeldt disease), genetic (genetic Jakob-Creutzfeldt disease, Gerstmann-Sträussler-Scheinker syndrome, and fatal familial insomnia), and acquired (kuru, variant Jakob-Creutzfeldt disease, and iatrogenic Jakob-Creutzfeldt disease) forms. This article presents updated information on the clinical features and diagnostic methods for human prion diseases. New antemortem potential diagnostic tests based on amplifying prions in order to detect them are showing very high specificity. Understanding of the diversity of possible presentations of human prion diseases continues to evolve, with some genetic forms progressing slowly over decades, beginning with dysautonomia and neuropathy and progressing to a frontal-executive dementia with pathology of combined prionopathy and tauopathy. Unfortunately, to date, all human prion disease clinical trials have failed to show survival benefit. A very rare polymorphism in the prion protein gene recently has been identified that appears to protect against prion disease; this finding, in addition to providing greater understanding of the prionlike mechanisms of neurodegenerative disorders, might lead to potential treatments.

SUMMARY

Sporadic Jakob-Creutzfeldt disease is the most common form of human prion disease. Genetic prion diseases, resulting from mutations in the prion-related protein gene (PRNP), are classified based on the mutation, clinical phenotype, and neuropathologic features and can be difficult to diagnose because of their varied presentations. Perhaps most relevant to this Continuum issue on neuroinfectious diseases, acquired prion diseases are caused by accidental transmission to humans, but fortunately, they are the least common form and are becoming rarer as awareness of transmission risk has led to implementation of measures to prevent such occurrences.

Prion-like disorders and Transmissible Spongiform Encephalopathies: An overview of the mechanistic features that are shared by the various disease-related misfolded proteins

Prion diseases or Transmissible Spongiform Encephalopathies (TSEs) are a group of fatal neurodegenerative disorders affecting several mammalian species. Its causative agent, disease-associated prion protein (PrP^d), is a self-propagating β-sheet rich aberrant conformation of the cellular prion protein (PrP^C) with neurotoxic and aggregation-prone properties, capable of inducing misfolding of PrP^C molecules. PrP^d is the major constituent of prions and, most importantly, is the first known example of a protein with infectious attributes. It has been suggested that similar molecular mechanisms could be shared by other proteins implicated in diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis or systemic amyloidoses. Accordingly, several terms have been proposed to collectively group all these disorders. Through the stringent evaluation of those aspects that characterise TSE-causing prions, in particular propagation and spread, strain variability or transmissibility, we will discuss whether terms such as "prion", "prion-like", "prionoid" or "propagon" can be used when referring to the aetiological agents of the above other disorders. Moreover, it will also be discussed whether the term "infectious", which defines a prion essential trait, is currently misused when referring to the other misfolded proteins.

How strong is the evidence that Parkinson's disease is a prion disorder?

PURPOSE OF REVIEW

We describe evidence supporting the hypothesis that α-synuclein has a prion-like role in Parkinson's disease and related α-synucleinopathies, and discuss how this novel thinking impacts the development of diagnostics and disease-modifying therapies.

RECENT FINDINGS

Observations that immature dopamine neurons grafted to Parkinson's disease patients can develop Lewy bodies triggered a surge of interest in the putative prion-like properties of α-synuclein. We recount results from experiments which confirm that misfolded α-synuclein can exhibit disease-propagating properties, and describe how they relate to the spreading of α-synuclein aggregates in α-synucleinopathies. We share insights into the underlying molecular mechanisms and their relevance to novel therapeutic targets. Finally, we discuss what the initial triggers of α-synuclein misfolding might be, where in the body the misfolding events might take place, and how this can instruct development of novel diagnostic tools. We speculate that differences in anatomical trigger sites and variability in α-synuclein fibril structure can contribute to clinical differences between α-synucleinopathies.

SUMMARY

The realization that α-synuclein pathology can propagate between brain regions in neurodegenerative diseases has deepened and expanded our understanding of potential pathogenic processes which can lead to the development of novel diagnostic tools as well as the identification of new therapeutic targets.

The Prion-Like Properties of Amyloid-β Assemblies: Implications for Alzheimer's Disease

Since the discovery that prion diseases can be transmitted to experimental animals by inoculation with afflicted brain matter, researchers have speculated that the brains of patients suffering from other neurodegenerative diseases might also harbor causative agents with transmissible properties. Foremost among these disorders is Alzheimer's disease (AD), the most common cause of dementia in the elderly. A growing body of research supports the concept that the pathogenesis of AD is initiated and sustained by the endogenous, seeded misfolding and aggregation of the protein fragment amyloid-β (Aβ). At the molecular level, this mechanism of nucleated protein self-assembly is virtually identical to that of prions consisting of the prion protein (PrP). The formation, propagation, and spread of Aβ seeds within the brain can thus be considered a fundamental feature of AD pathogenesis.

A novel equine-derived pericardium membrane for dural repair: A preliminary, short-term investigation

Background:

A large variety of biological and artificial materials are employed in dural repair, each of them with major limitations. Autologous grafts have limited availability and require an additional incision and surgical time. Cadaveric preparations and heterologous materials entail the risk of iatrogenic transmission of prions, whereas synthetic substitutes have been reported to cause inflammatory reactions and graft rejection. An equine-derived pericardium membrane has been developed (Heart^®, Bioteck, Vicenza, Italy) with mechanical and safety-related features that could make it suitable for neurosurgical application.

Aims:

This preliminary study aimed to evaluate the short-term safety and efficacy of the Heart^® membrane in dural repair procedures following meningioma surgeries.

Subjects and Methods:

Medical records of patients who were surgically treated for an intracranial meningioma and underwent duraplasty with the Heart^® membrane were reviewed retrospectively. The occurrence of any graft-related complications such as cerebrospinal fluid (CSF) leakage, postoperative hematoma, wound infection, meningitis, and neurological symptoms was analyzed.

Results:

Eight patients were identified as meeting the inclusion criteria. A watertight closure was achieved in all of them. Postoperatively, no patients exhibited CSF leak, cerebral contusion, hemorrhage, or wound infection. The 1-month radiological follow-up revealed no evidence of pseudomeningocele, wound breakdown, or meningitis. Neurologic complications were observed in three patients but not directly imputable to the dural substitute or its application.

Conclusions:

In all the patients, the pericardium membrane enabled achievement of a watertight dural closure without graft-related adverse events. Further investigations should be performed to assess medium- and long-term clinical outcomes in a larger set of patients.

Epidemiological characteristics of human prion diseases

Human prion diseases are a group of transmissible, progressive, and invariably fatal neurodegenerative disorders, which include Kuru, Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome, and fatal familial insomnia. Human prion diseases affect approximately 1–2 persons per million worldwide annually, occurring in sporadic, inherited, and acquired forms. These diseases have attracted both scientific and public attention not only because of their mysterious pathogen, but also due to their considerable threat to public health since the emergence of the variant CJD.

There are still no specific therapeutic and prophylactic interventions available for prion diseases, thus active surveillance of human prion diseases is critical for disease control and prevention. Since 1993, CJD surveillance systems have been established in many countries and regions, and several long-term multinational cooperative projects have been conducted.

In this paper, the epidemiological characteristics of various human prion diseases and the active surveillance systems pertaining to them in different countries and regions are summarized and reviewed.

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

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

Distinctive properties of plaque-type dura mater graft-associated Creutzfeldt-Jakob disease in cell-protein misfolding cyclic amplification

There are two distinct subtypes of dura mater graft-associated Creutzfeldt-Jakob disease (dCJD) with methionine homozygosity at codon 129 of the PRNP gene. The majority of cases is represented by a non-plaque-type (np-dCJD) resembling sporadic CJD (sCJD)-MM1 or -MV1, while the minority by a plaque-type (p-dCJD). p-dCJD shows distinctive phenotypic features, namely numerous kuru plaques and an abnormal isoform of prion protein (PrP(Sc)) intermediate in size between types 1 and 2. Transmission studies have shown that the unusual phenotypic features of p-dCJD are linked to the V2 prion strain that is associated with sCJD subtypes VV2 or -MV2. In this study, we applied protein misfolding cyclic amplification (PMCA) using recombinant human prion protein as a substrate and demonstrated that p-dCJD prions show amplification features that are distinct from those of np-dCJD. Although no amplification of np-dCJD prions was observed with either 129 M or 129 V substrate, p-dCJD prions were drastically amplified with the 129 V substrates, despite the PRNP codon 129 incompatibility between seed and substrate. Moreover, by using a type 2 PrP(Sc)-specific antibody not recognizing PrP(Sc) in p-dCJD, we found that type 2 products are generated de novo from p-dCJD prions during PMCA with the 129 V substrates. These findings suggest that our cell-PMCA is a useful tool for easily and rapidly identifying acquired CJD associated with the transmission of the V2 CJD strain to codon 129 methionine homozygotes, based on the preference for the 129 V substrate and the type of the amplified products.

Mechanisms of prion-induced neurodegeneration

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are fatal neurodegenerative disorders characterised by long incubation period, short clinical duration, and transmissibility to susceptible species. Neuronal loss, spongiform changes, gliosis and the accumulation in the brain of the misfolded version of a membrane-bound cellular prion protein (PrP(C)), termed PrP(TSE), are diagnostic markers of these diseases. Compelling evidence links protein misfolding and its accumulation with neurodegenerative changes. Accordingly, several mechanisms of prion-mediated neurotoxicity have been proposed. In this paper, we provide an overview of the recent knowledge on the mechanisms of neuropathogenesis, the neurotoxic PrP species and the possible therapeutic approaches to treat these devastating disorders.

Recent US Case of Variant Creutzfeldt-Jakob Disease-Global Implications

A recently diagnosed case highlights the need for continued global surveillance.

Variant Creutzfeldt-Jakob disease (vCJD) is a rare, fatal prion disease resulting from transmission to humans of the infectious agent of bovine spongiform encephalopathy. We describe the clinical presentation of a recent case of vCJD in the United States and provide an update on diagnostic testing. The location of this patient’s exposure is less clear than those in the 3 previously reported US cases, but strong evidence indicates that exposure to contaminated beef occurred outside the United States more than a decade before illness onset. This case exemplifies the persistent risk for vCJD acquired in unsuspected geographic locations and highlights the need for continued global surveillance and awareness to prevent further dissemination of vCJD.

Prion protein scrapie and the normal cellular prion protein

Prions are infectious proteins and over the past few decades, some prions have become renowned for their causative role in several neurodegenerative diseases in animals and humans. Since their discovery, the mechanisms and mode of transmission and molecular structure of prions have begun to be established. There is, however, still much to be elucidated about prion diseases, including the development of potential therapeutic strategies for treatment. The significance of prion disease is discussed here, including the categories of human and animal prion diseases, disease transmission, disease progression and the development of symptoms and potential future strategies for treatment. Furthermore, the structure and function of the normal cellular prion protein (PrP(C)) and its importance in not only in prion disease development, but also in diseases such as cancer and Alzheimer's disease will also be discussed.

Neuropathological and biochemical criteria to identify acquired Creutzfeldt-Jakob disease among presumed sporadic cases

As an experimental model of acquired Creutzfeldt-Jakob disease (CJD), we performed transmission studies of sporadic CJD using knock-in mice expressing human prion protein (PrP). In this model, the inoculation of the sporadic CJD strain V2 into animals homozygous for methionine at polymorphic codon 129 (129 M/M) of the PRNP gene produced quite distinctive neuropathological and biochemical features, that is, widespread kuru plaques and intermediate type abnormal PrP (PrP(Sc) ). Interestingly, this distinctive combination of molecular and pathological features has been, to date, observed in acquired CJD but not in sporadic CJD. Assuming that these distinctive phenotypic traits are specific for acquired CJD, we revisited the literature and found two cases showing widespread kuru plaques despite the 129 M/M genotype, in a neurosurgeon and in a patient with a medical history of neurosurgery without dura mater grafting. By Western blot analysis of brain homogenates, we revealed the intermediate type of PrP(Sc) in both cases. Furthermore, transmission properties of brain extracts from these two cases were indistinguishable from those of a subgroup of dura mater graft-associated iatrogenic CJD caused by infection with the sporadic CJD strain V2. These data strongly suggest that the two atypical CJD cases, previously thought to represent sporadic CJD, very likely acquired the disease through exposure to prion-contaminated brain tissues. Thus, we propose that the distinctive combination of 129 M/M genotype, kuru plaques, and intermediate type PrP(Sc) , represents a reliable criterion for the identification of acquired CJD cases among presumed sporadic cases.

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

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

Deer Prion Proteins Modulate the Emergence and Adaptation of Chronic Wasting Disease Strains

Transmission of chronic wasting disease (CWD) between cervids is influenced by the primary structure of the host cellular prion protein (PrP^C). In white-tailed deer, PRNP alleles encode the polymorphisms Q95 G96 (wild type [wt]), Q95 S96 (referred to as the S96 allele), and H95 G96 (referred to as the H95 allele), which differentially impact CWD progression. We hypothesize that the transmission of CWD prions between deer expressing different allotypes of PrP^C modifies the contagious agent affecting disease spread. To evaluate the transmission properties of CWD prions derived experimentally from deer of four PRNP genotypes (wt/wt, S96/wt, H95/wt, or H95/S96), transgenic (tg) mice expressing the wt allele (tg33) or S96 allele (tg60) were challenged with these prion agents. Passage of deer CWD prions into tg33 mice resulted in 100% attack rates, with the CWD H95/S96 prions having significantly longer incubation periods. The disease signs and neuropathological and protease-resistant prion protein (PrP-res) profiles in infected tg33 mice were similar between groups, indicating that a prion strain (Wisc-1) common to all CWD inocula was amplified. In contrast, tg60 mice developed prion disease only when inoculated with the H95/wt and H95/S96 CWD allotypes. Serial passage in tg60 mice resulted in adaptation of a novel CWD strain (H95⁺) with distinct biological properties. Transmission of first-passage tg60CWD-H95⁺ isolates into tg33 mice, however, elicited two prion disease presentations consistent with a mixture of strains associated with different PrP-res glycotypes. Our data indicate that H95-PRNP heterozygous deer accumulated two CWD strains whose emergence was dictated by the PrP^C primary structure of the recipient host. These findings suggest that CWD transmission between cervids expressing distinct PrP^C molecules results in the generation of novel CWD strains.

IMPORTANCE CWD prions are contagious among wild and captive cervids in North America and in South Korea. We present data linking the amino acid variant Q95H in white-tailed deer cellular prion protein (PrP^C) to the emergence of a novel CWD strain (H95⁺). We show that, upon infection, deer expressing H95-PrP^C molecules accumulated a mixture of CWD strains that selectively propagated depending on the PRNP genotype of the host in which they were passaged. Our study also demonstrates that mice expressing the deer S96-PRNP allele, previously shown to be resistant to various cervid prions, are susceptible to H95⁺ CWD prions. The potential for the generation of novel strains raises the possibility of an expanded host range for CWD.

Neurodegeneration: Amyloid-β pathology induced in humans

People who died of the neurodegenerative condition Creutzfeldt-Jakob disease after treatment with cadaver-derived human growth hormone also developed some of the pathological traits of Alzheimer's disease.

Iatrogenic CJD due to pituitary-derived growth hormone with genetically determined incubation times of up to 40 years

Cases of iatrogenic CJD still occur in the UK 30 years after administration of human pituitary-derived growth hormone ceased. Rudge et al. report a change over time in genotype profile at polymorphic codon 129 of the human prion protein gene in UK patients, distinct from that seen in other countries.

Patients with iatrogenic Creutzfeldt-Jakob disease due to administration of cadaver-sourced growth hormone during childhood are still being seen in the UK 30 years after cessation of this treatment. Of the 77 patients who have developed iatrogenic Creutzfeldt-Jakob disease, 56 have been genotyped. There has been a marked change in genotype profile at polymorphic codon 129 of the prion protein gene (PRNP) from predominantly valine homozygous to a mixed picture of methionine homozygous and methionine-valine heterozygous over time. The incubation period of iatrogenic Creutzfeldt-Jakob disease is significantly different between all three genotypes. This experience is a striking contrast with that in France and the USA, which may relate to contamination of different growth hormone batches with different strains of human prions. We describe the clinical, imaging, molecular and autopsy features in 22 of 24 patients who have developed iatrogenic Creutzfeldt-Jakob disease in the UK since 2003. Mean age at onset of symptoms was 42.7 years. Gait ataxia and lower limb dysaesthesiae were the most frequent presenting symptoms. All had cerebellar signs, and the majority had myoclonus and lower limb pyramidal signs, with relatively preserved cognitive function, when first seen. There was a progressive decline in neurological and cognitive function leading to death after 5–32 (mean 14) months. Despite incubation periods approaching 40 years, the clinical duration in methionine homozygote patients appeared to be shorter than that seen in heterozygote patients. MRI showed restricted diffusion in the basal ganglia, thalamus, hippocampus, frontal and the paracentral motor cortex and cerebellar vermis. The electroencephalogram was abnormal in 15 patients and cerebrospinal fluid 14-3-3 protein was positive in half the patients. Neuropathological examination was conducted in nine patients. All but one showed synaptic prion deposition with numerous kuru type plaques in the basal ganglia, anterior frontal and parietal cortex, thalamus, basal ganglia and cerebellum. The patient with the shortest clinical duration had an atypical synaptic deposition of abnormal prion protein and no kuru plaques. Taken together, these data provide a remarkable example of the interplay between the strain of the pathogen and host prion protein genotype. Based on extensive modelling of human prion transmission barriers in transgenic mice expressing human prion protein on a mouse prion protein null background, the temporal distribution of codon 129 genotypes within the cohort of patients with iatrogenic Creutzfeldt-Jakob disease in the UK suggests that there was a point source of infecting prion contamination of growth hormone derived from a patient with Creutzfeldt-Jakob disease expressing prion protein valine 129.

Creutzfeldt-Jakob disease mortality in Canada, 1998 to 2013

BACKGROUND

Human prion diseases, known collectively as Creutzfeldt-Jakob disease (CJD), are fatal, infectious neurodegenerative disorders that occur in all human populations.

OBJECTIVE

To summarize national surveillance data for CJD in Canada between January 1, 1998, and December 31, 2013.

METHODS

Detailed investigations were conducted of individual suspected CJD cases, with collaboration between Canadian health professionals and investigators affiliated with a central CJD surveillance registry operated by the Public Health Agency of Canada. Data were collected on the clinical profile, family history, and results of paraclinical and laboratory investigations, including post-mortem neuropathological examination.

RESULTS

A total of 662 deaths from definite and probable CJD were identified in Canadian residents during the study period, comprising 613 cases of sporadic CJD (92.6%), 43 cases of genetic prion disease (6.5%), 4 cases of iatrogenic CJD (0.6%), and 2 cases of variant CJD disease (0.3%). The overall crude mortality rate for sporadic CJD was 1.18 per million per year [95% confidence interval (CI): 1.08,1.27]. Age-specific rates ranged from 0.05 [95% CI: 0.03,0.08] in persons under 50 years of age to 7.11 [95% CI: 6.20,8.11] in those aged 70 to 79. A significant net upward trend in age-adjusted rates was observed over the study period. Standardized mortality ratios, calculated for 10 individual Canadian provinces with reference to national average mortality rates, did not differ significantly from 1.0.

CONCLUSION

Creutzfeldt-Jakob disease remains rare in Canada, although mortality rates vary by two orders of magnitude between older and younger age groups. The upward trend in age-standardized sporadic CJD mortality rate over the study period can be better accounted for by gradually improving case ascertainment than by a real increase in incidence.

The influence of PRNP polymorphisms on human prion disease susceptibility: an update

Two normally occurring polymorphisms of the human PRNP gene, methionine (M)/valine (V) at codon 129 and glutamic acid (E)/lysine (K) at codon 219, can affect the susceptibility to prion diseases. It has long been recognized that 129M/M homozygotes are overrepresented in sporadic Creutzfeldt-Jakob disease (CJD) patients and variant CJD patients, whereas 219E/K heterozygotes are absent in sporadic CJD patients. In addition to these pioneering findings, recent progress in experimental transmission studies and worldwide surveillance of prion diseases have identified novel relationships between the PRNP polymorphisms and the prion disease susceptibility. For example, although 219E/K heterozygosity confers resistance against the development of sporadic CJD, this genotype is not entirely protective against acquired forms (iatrogenic CJD and variant CJD) or genetic forms (genetic CJD and Gerstmann-Sträussler-Scheinker syndrome) of prion diseases. In addition, 129M/V heterozygotes predispose to genetic CJD caused by a pathogenic PRNP mutation at codon 180. These findings show that the effects of the PRNP polymorphisms may be more complicated than previously thought. This review aims to summarize recent advances in our knowledge about the influence of the PRNP polymorphisms on the prion disease susceptibility.

Transmission of scrapie prions to primate after an extended silent incubation period

Classical bovine spongiform encephalopathy (c-BSE) is the only animal prion disease reputed to be zoonotic, causing variant Creutzfeldt-Jakob disease (vCJD) in humans and having guided protective measures for animal and human health against animal prion diseases. Recently, partial transmissions to humanized mice showed that the zoonotic potential of scrapie might be similar to c-BSE. We here report the direct transmission of a natural classical scrapie isolate to cynomolgus macaque, a highly relevant model for human prion diseases, after a 10-year silent incubation period, with features similar to those reported for human cases of sporadic CJD. Scrapie is thus actually transmissible to primates with incubation periods compatible with their life expectancy, although fourfold longer than BSE. Long-term experimental transmission studies are necessary to better assess the zoonotic potential of other prion diseases with high prevalence, notably Chronic Wasting Disease of deer and elk and atypical/Nor98 scrapie.

Distinct pathological phenotypes of Creutzfeldt-Jakob disease in recipients of prion-contaminated growth hormone

Introduction

The present study compares the clinical, pathological and molecular features of a United States (US) case of growth hormone (GH)-associated Creutzfeldt-Jakob disease (GH-CJD) (index case) to those of two earlier referred US cases of GH-CJD and one case of dura mater (d)-associated CJD (dCJD). All iatrogenic CJD (iCJD) subjects were methionine (M) homozygous at codon 129 (129MM) of the prion protein (PrP) gene and had scrapie prion protein (PrP^Sc) type 1 (iCJDMM1).

Results

The index subject presented with ataxia, weight loss and changes in the sleep pattern about 38 years after the midpoint of GH treatment. Autopsy examination revealed a neuropathological phenotype reminiscent of both sCJDMV2-K (a sporadic CJD subtype in subjects methionine/valine heterozygous at codon 129 with PrP^Sc type 2 and the presence of kuru plaques) and variant CJD (vCJD). The two earlier cases of GH-CJDMM1 and the one of dCJDMM1 were associated with neuropathological phenotypes that differed from that of the index case mainly because they lacked PrP plaques. The phenotype of the earlier GH-CJDMM1 cases shared several, but not all, characteristics with sCJDMM1, whereas dCJDMM1 was phenotypically indistinguishable from sCJDMM1. Two distinct groups of dCJDMM1 have also been described in Japan based on clinical features, the presence or absence of PrP plaques and distinct PK-resistant PrP^Sc (resPrP^Sc) electrophoretic mobilities. The resPrP^Sc electrophoretic mobility was, however, identical in our GH-CJDMM1 and dCJDMM1 cases, and matched that of sCJDMM1.

Conclusions

Our study shows that receipt of prion-contaminated GH can lead to a prion disease with molecular features (129MM and PrP^Sc type 2) and phenotypic characteristics that differ from those of sporadic prion disease (sCJDMM1), a difference that may reflect adaptation of “heterologous” prion strains to the 129MM background.

Rapidly progressive young-onset dementias: neuropsychiatric aspects

Rapidly progressive dementia (RPD) is roughly defined as neurocognitive decline resulting in dementia or death within 2 years. Although RPDs affect all age groups, many occur in patients with young-onset dementia. Although prion disease (eg, Creutzfeldt-Jakob disease) is often thought to be the prototypic rapidly progressive young-onset dementia, the differential diagnosis is broad and some etiologies may be treatable. Hence, an appropriate workup to determine the etiology of RPD is crucial to planning the appropriate management. This article reviews the differential diagnosis, diagnostic workup, and management considerations for this unique patient population.

Animal models for prion-like diseases

Prion diseases or Transmissible Spongiform Encephalopathies (TSEs) are a group of fatal neurodegenerative disorders affecting several mammalian species being Creutzfeldt-Jacob Disease (CJD) the most representative in human beings, scrapie in ovine, Bovine Spongiform Encephalopathy (BSE) in bovine and Chronic Wasting Disease (CWD) in cervids. As stated by the "protein-only hypothesis", the causal agent of TSEs is a self-propagating aberrant form of the prion protein (PrP) that through a misfolding event acquires a β-sheet rich conformation known as PrP(Sc) (from scrapie). This isoform is neurotoxic, aggregation prone and induces misfolding of native cellular PrP. Compelling evidence indicates that disease-specific protein misfolding in amyloid deposits could be shared by other disorders showing aberrant protein aggregates such as Alzheimer's Disease (AD), Parkinson's Disease (PD), Amyotrophic lateral sclerosis (ALS) and systemic Amyloid A amyloidosis (AA amyloidosis). Evidences of shared mechanisms of the proteins related to each disease with prions will be reviewed through the available in vivo models. Taking prion research as reference, typical prion-like features such as seeding and propagation ability, neurotoxic species causing disease, infectivity, transmission barrier and strain evidences will be analyzed for other protein-related diseases. Thus, prion-like features of amyloid β peptide and tau present in AD, α-synuclein in PD, SOD-1, TDP-43 and others in ALS and serum α-amyloid (SAA) in systemic AA amyloidosis will be reviewed through models available for each disease.

Neurodegenerative diseases: expanding the prion concept

The prion paradigm has emerged as a unifying molecular principle for the pathogenesis of many age-related neurodegenerative diseases. This paradigm holds that a fundamental cause of specific disorders is the misfolding and seeded aggregation of certain proteins. The concept arose from the discovery that devastating brain diseases called spongiform encephalopathies are transmissible to new hosts by agents consisting solely of a misfolded protein, now known as the prion protein. Accordingly, "prion" was defined as a "proteinaceous infectious particle." As the concept has expanded to include other diseases, many of which are not infectious by any conventional definition, the designation of prions as infectious agents has become problematic. We propose to define prions as "proteinaceous nucleating particles" to highlight the molecular action of the agents, lessen unwarranted apprehension about the transmissibility of noninfectious proteopathies, and promote the wider acceptance of this revolutionary paradigm by the biomedical community.

Is the prevalent human prion protein 129M/V mutation a living fossil from a Paleolithic panzootic superprion pandemic?

Prion diseases are consistently associated with prion protein (PrP(C)) misfolding rendering a cascade of auto-catalytic self-perpetuation of misfolded PrP in an afflicted individual. The molecular process is intriguingly similar to all known amyloid diseases both local and systemic. The prion disease is also infectious by the transfer of misfolded PrP from one individual to the next. Transmissibility is surprisingly efficient in prion diseases and given the rapid disease progression following initial symptoms the prionoses stand out from other amyloidoses, which all may be transmissible under certain circumstances. The nature of the infectious prion as well as the genotype of the host is important for transmissibility. For hitherto unexplained reasons the majority of Europeans carry a missense mutation on one or both alleles of the PrP gene (PRNP), and hence express a variant of PrP with a substitution for valine (V) instead of methionine (M) in position 129. In fact the 129M/V variant is very common in all populations except for the Japanese. Sporadic Creutzfeldt-Jakob disease is a disease rarely striking people below the age of 60, where homozygosity especially 129MM is a very strong risk factor. Paradoxically, the 129M/V polymorphism suggestive of heterozygote advantage is one of the most clear cut disease associated traits of the human population, yet prion disease is extraordinarily rare. The genetic basis for how this trait spread with such prevalence within human populations is still target to investigations and deserves attention. This short essay represents a somewhat provocative hypothetical notion of a possible ancient significance of this polymorphism.

Blood reference materials from macaques infected with variant Creutzfeldt-Jakob disease agent

BACKGROUND

Variant Creutzfeldt-Jakob disease (vCJD) is a fatal neurodegenerative infection that can be transmitted by blood and blood products from donors in the latent phase of the disease. Currently, there is no validated antemortem vCJD blood screening test. Several blood tests are under development. Any useful test must be validated with disease-relevant blood reference panels.

STUDY DESIGN AND METHODS

To generate blood reference materials, we infected four cynomolgus macaques with macaque-adapted vCJD brain homogenates. Blood was collected throughout the preclinical and clinical phases of infection. In parallel, equivalent blood was collected from one uninfected macaque. For each blood collection, an aliquot was stored as whole blood and the remainder was separated into components. Aliquots of plasma from terminally ill macaques were assayed for the presence of PrP(TSE) with the protein misfolding cyclic amplification (PMCA) method. Infectivity of the macaque brain homogenate used to infect macaques was titrated in C57BL/6 and RIII J/S inbred wild-type mice.

RESULTS

We sampled blood 19 times from the inoculated monkeys at various stages of the disease over a period of 29 months, generating liters of vCJD-infected macaque blood. vCJD was confirmed in all inoculated macaques. After PMCA, PrP(TSE) was detected in plasma from infected monkeys, but not from uninfected animals. Both mouse models were more sensitive to infection with macaque-adapted vCJD agent than to primary human vCJD agent.

CONCLUSION

The macaque vCJD blood panels generated in this study provide a unique resource to support vCJD assay development and to characterize vCJD infectivity in blood.

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

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

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

Detection of the disease-associated form of the prion protein in biological samples

Transmissible spongiform encephalopathies (TSEs) are neurodegenerative diseases that occur in a variety of mammals. In TSEs, a chromosomally encoded protein (PrPC) undergoes a conformational change to the disease-associated form (PrPd). PrPd is capable of inducing a change in additional molecules of PrPC to the PrPd conformation. TSEs are inevitably fatal and cross-species transmission is known to occur, and there is potential for transmission via blood transfusion and organ transplantation in humans. Thus, there is interest in high-quality diagnostics for both humans and animals. This review summarizes methods of TSE detection currently in use in diagnostic settings and discusses recent advances in PrPd detection that afford substantial enhancements in sensitivity over currently approved methods for use in clinical settings.

Evidence for zoonotic potential of ovine scrapie prions

Although Bovine Spongiform Encephalopathy (BSE) is the cause of variant Creutzfeldt Jakob disease (vCJD) in humans, the zoonotic potential of scrapie prions remains unknown. Mice genetically engineered to overexpress the human prion protein (tgHu) have emerged as highly relevant models for gauging the capacity of prions to transmit to humans. These models can propagate human prions without any apparent transmission barrier and have been used used to confirm the zoonotic ability of BSE. Here we show that a panel of sheep scrapie prions transmit to several tgHu mice models with an efficiency comparable to that of cattle BSE. The serial transmission of different scrapie isolates in these mice led to the propagation of prions that are phenotypically identical to those causing sporadic CJD (sCJD) in humans. These results demonstrate that scrapie prions have a zoonotic potential and raise new questions about the possible link between animal and human prions.

Descriptive epidemiology of prion disease in Japan: 1999-2012

BACKGROUND

Epidemiologic features of prion diseases in Japan, in particular morbidity and mortality, have not been clarified.

METHODS

Since 1999, the Research Committee has been conducting surveillance of prion diseases, and the surveillance data were used to assess incident cases of prion diseases. For the observation of fatal cases, vital statistics were used.

RESULTS

Both incidence and mortality rates of prion diseases increased during the 2000s in Japan. However, this increase was observed only in relatively old age groups.

CONCLUSIONS

The increased number of patients among old age groups might be due to increased recognition of the diseases. If so, the number of cases should plateau in the near future.

Aβ seeds resist inactivation by formaldehyde

Cerebral β-amyloidosis can be exogenously induced by the intracerebral injection of brain extracts containing aggregated β-amyloid (Aβ) into young, pre-depositing Aβ precursor protein- (APP) transgenic mice. Previous work has shown that the induction involves a prion-like seeding mechanism in which the seeding agent is aggregated Aβ itself. Here we report that the β-amyloid-inducing activity of Alzheimer's disease (AD) brain tissue or aged APP-transgenic mouse brain tissue is preserved, albeit with reduced efficacy, after formaldehyde fixation. Moreover, spectral analysis with amyloid conformation-sensitive luminescent conjugated oligothiophene dyes reveals that the strain-like properties of aggregated Aβ are maintained in fixed tissues. The resistance of Aβ seeds to inactivation and structural modification by formaldehyde underscores their remarkable durability, which in turn may contribute to their persistence and spread within the body. The present findings can be exploited to establish the relationship between the molecular structure of Aβ aggregates and the variable clinical features and disease progression of AD even in archived, formalin-fixed autopsy material.

Is there a risk of prion-like disease transmission by Alzheimer- or Parkinson-associated protein particles?

The misfolding and aggregation of endogenous proteins in the central nervous system is a neuropathological hallmark of Alzheimer's disease (AD), Parkinson's disease (PD), as well as prion diseases. A molecular mechanism referred to as "nucleation-dependent aggregation" is thought to underlie this neuropathological phenomenon. According to this concept, disease-associated protein particles act as nuclei, or seeds, that recruit cellular proteins and incorporate them, in a misfolded form, into their growing aggregate structure. Experimental studies have shown that the aggregation of the AD-associated proteins amyloid-β (Aβ) and tau, and of the PD-associated protein α-synuclein, can be stimulated in laboratory animal models by intracerebral (i.c.) injection of inocula containing aggregated species of the respective proteins. This has raised the question of whether AD or PD can be transmitted, like certain human prion diseases, between individuals by self-propagating protein particles potentially present on medical instruments or in blood or blood products. While the i.c. injection of inocula containing AD- or PD-associated protein aggregates was found to cause neuronal damage and clinical abnormalities (e.g., motor impairments) in some animal models, none of the studies published so far provided evidence for a transmission of severe or even fatal disease. In addition, available epidemiological data do not indicate a transmissibility of AD or PD between humans. The findings published so far on the effects of experimentally transmitted AD- or PD-associated protein seeds do not suggest specific precautionary measures in the context of hemotherapy, but call for vigilance in transfusion medicine and other medical areas.