UK Iatrogenic Creutzfeldt-Jakob disease: investigating human prion transmission across genotypic barriers using human tissue-based and molecular approaches

In Vivo Seeding of Amyloid-β Protein and Implications in Modeling Alzheimer's Disease Pathology

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by extracellular plaques containing amyloid β-protein (Aβ) and intracellular neurofibrillary tangles formed by tau. Cerebral Aβ accumulation initiates a noxious cascade that leads to irreversible neuronal degeneration and memory impairment in older adults. Recent advances in Aβ seeding studies offer a promising avenue for exploring the mechanisms underlying amyloid deposition and the complex pathological features of AD. However, the extent to which inoculated Aβ seeds can induce reproducible and reliable pathological manifestations remains unclear due to significant variability across studies. In this review, we will discuss several factors that contribute to the induction or acceleration of amyloid deposition and consequent pathologies. Specifically, we focus on the diversity of host animals, sources and recipe of Aβ seeds, and inoculating strategies. By integrating these key aspects, this review aims to offer a comprehensive perspective on Aβ seeding in AD and provide guidance for modeling AD pathogenesis through the exogenous introduction of Aβ seeds.

Pathological spectrum of sporadic Creutzfeldt-Jakob disease

Human prion diseases are a rare group of transmissible neurodegenerative conditions which are classified according to their aetiology as sporadic, genetic or acquired forms. Creutzfeldt-Jakob disease (CJD) is the most common form of human prion disease, with the sporadic form accounting for ∼85% of all reported cases. While advances have been made in the development of clinical tools and biomarkers in the diagnosis of prion disease, allowing greater diagnostic certainty for surveillance purposes, definitive diagnosis requires neuropathological examination of the brain at postmortem. Since the 1990s, efforts have been made to develop a classification system for sporadic CJD (sCJD) based on observed differences in the clinical features and the pathological phenotype (the nature and degree of spongiform vacuolation, neuronal loss, astrogliosis and misfolded prion protein accumulation in the brain), also referred to as the 'histotype'. Six major clinicopathological subtypes of sCJD are internationally recognised, largely correlating with the combination of the two distinct types of the protease-resistant prion protein (PrPres type 1 or 2) and the methionine (M)/valine (V) polymorphism at codon 129 of the prion protein gene (PRNP): MM1/MV1, MM2-cortical, MM2-thalamic, MV2, VV1 and VV2. This classification system has been extended to recognise sCJD cases demonstrating both mixed PrPres types or mixed histotypes in the brain of the same individual, as well as including atypical or novel pathological phenotypes. In this review, we will provide an up-to-date overview of the current classification of sCJD based on the prominent neuropathological features. In addition, with levels of infectivity at their highest in the brain, we will also discuss the additional precautions that are recommended when handling and examining postmortem tissues from patients with suspected prion disease.

The importance of prion research

Over the past four decades, prion diseases have received considerable research attention owing to their potential to be transmitted within and across species as well as their consequences for human and animal health. The unprecedented nature of prions has led to the discovery of a paradigm of templated protein misfolding that underlies a diverse range of both disease-related and normal biological processes. Indeed, the "prion-like" misfolding and propagation of protein aggregates is now recognized as a common underlying disease mechanism in human neurodegenerative disorders such as Alzheimer's and Parkinson's disease, and the prion principle has led to the development of novel diagnostic and therapeutic strategies for these illnesses. Despite these advances, research into the fundamental biology of prion diseases has declined, likely due to their rarity and the absence of an acute human health crisis. Given the past translational influence, continued research on the etiology, pathogenesis, and transmission of prion disease should remain a priority. In this review, we highlight several important "unsolved mysteries" in the prion disease research field and how solving them may be crucial for the development of effective therapeutics, preventing future outbreaks of prion disease, and understanding the pathobiology of more common human neurodegenerative disorders.

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

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

A novel subtype of sporadic Creutzfeldt-Jakob disease with PRNP codon 129MM genotype and PrP plaques

The presence of amyloid kuru plaques is a pathological hallmark of sporadic Creutzfeldt-Jakob disease (sCJD) of the MV2K subtype. Recently, PrP plaques (p) have been described in the white matter of a small group of CJD (p-CJD) cases with the 129MM genotype and carrying resPrPD type 1 (T1). Despite the different histopathological phenotype, the gel mobility and molecular features of p-CJD resPrPD T1 mimic those of sCJDMM1, the most common human prion disease. Here, we describe the clinical features, histopathology, and molecular properties of two distinct PrP plaque phenotypes affecting the gray matter (pGM) or the white matter (pWM) of sCJD cases with the PrP 129MM genotype (sCJDMM). Prevalence of pGM- and pWM-CJD proved comparable and was estimated to be ~ 0.6% among sporadic prion diseases and ~ 1.1% among the sCJDMM group. Mean age at onset (61 and 68 years) and disease duration (~ 7 months) of pWM- and pGM-CJD did not differ significantly. PrP plaques were mostly confined to the cerebellar cortex in pGM-CJD, but were ubiquitous in pWM-CJD. Typing of resPrPD T1 showed an unglycosylated fragment of ~ 20 kDa (T120) in pGM-CJD and sCJDMM1 patients, while a doublet of ~ 21-20 kDa (T121-20) was a molecular signature of pWM-CJD in subcortical regions. In addition, conformational characteristics of pWM-CJD resPrPD T1 differed from those of pGM-CJD and sCJDMM1. Inoculation of pWM-CJD and sCJDMM1 brain extracts to transgenic mice expressing human PrP reproduced the histotype with PrP plaques only in mice challenged with pWM-CJD. Furthermore, T120 of pWM-CJD, but not T121, was propagated in mice. These data suggest that T121 and T120 of pWM-CJD, and T120 of sCJDMM1 are distinct prion strains. Further studies are required to shed light on the etiology of p-CJD cases, particularly those of T120 of the novel pGM-CJD subtype.

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

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

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

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

Prion strains associated with iatrogenic CJD in French and UK human growth hormone recipients

Treatment with human pituitary-derived growth hormone (hGH) was responsible for a significant proportion of iatrogenic Creutzfeldt–Jakob disease (iCJD) cases. France and the UK experienced the largest case numbers of hGH-iCJD, with 122 and 81 cases respectively. Differences in the frequency of the three PRNP codon 129 polymorphisms (MM, MV and VV) and the estimated incubation periods associated with each of these genotypes in the French and the UK hGH-iCJD cohorts led to the suggestion that the prion strains responsible for these two hGH-iCJD cohorts were different. In this study, we characterized the prion strains responsible for hGH-iCJD cases originating from UK (n = 11) and France (n = 11) using human PrP expressing mouse models. The cases included PRNP MM, MV and VV genotypes from both countries. UK and French sporadic CJD (sCJD) cases were included as controls. The prion strains identified following inoculation with hGH-iCJD homogenates corresponded to the two most frequently observed sCJD prion strains (M1^CJD and V2^CJD). However, in clear contradiction to the initial hypothesis, the prion strains that were identified in the UK and the French hGH-iCJD cases were not radically different. In the vast majority of the cases originating from both countries, the V2^CJD strain or a mixture of M1^CJD + V2^CJD strains were identified. These data strongly support the contention that the differences in the epidemiological and genetic profiles observed in the UK and France hGH-iCJD cohorts cannot be attributed only to the transmission of different prion strains.

Understanding Intra-Species and Inter-Species Prion Conversion and Zoonotic Potential Using Protein Misfolding Cyclic Amplification

Prion diseases are fatal neurodegenerative disorders that affect humans and animals, and can also be transmitted from animals to humans. A fundamental event in prion disease pathogenesis is the conversion of normal host prion protein (PrP^C) to a disease-associated misfolded form (PrP^Sc). Whether or not an animal prion disease can infect humans cannot be determined a priori. There is a consensus that classical bovine spongiform encephalopathy (C-type BSE) in cattle transmits to humans, and that classical sheep scrapie is of little or no risk to human health. However, the zoonotic potential of more recently identified animal prion diseases, such as atypical scrapie, H-type and L-type BSE and chronic wasting disease (CWD) in cervids, remains an open question. Important components of the zoonotic barrier are (i) physiological differences between humans and the animal in question, (ii) amino acid sequence differences of the animal and human PrP^C, and (iii) the animal prion strain, enciphered in the conformation of PrP^Sc. Historically, the direct inoculation of experimental animals has provided essential information on the transmissibility and compatibility of prion strains. More recently, cell-free molecular conversion assays have been used to examine the molecular compatibility on prion replication and zoonotic potential. One such assay is Protein Misfolding Cyclic Amplification (PMCA), in which a small amount of infected tissue homogenate, containing PrP^Sc, is added as a seed to an excess of normal tissue homogenate containing PrP^C, and prion conversion is accelerated by cycles of incubation and ultrasonication. PMCA has been used to measure the molecular feasibility of prion transmission in a range of scenarios using genotypically homologous and heterologous combinations of PrP^Sc seed and PrP^C substrate. Furthermore, this method can be used to speculate on the molecular profile of PrP^Sc that might arise from a zoonotic transmission. We discuss the experimental approaches that have been used to model both the intra- and inter-species molecular compatibility of prions, and the factors affecting PrP^c to PrP^Sc conversion and zoonotic potential. We conclude that cell-free prion protein conversion assays, especially PMCA, are useful, rapid and low-cost approaches for elucidating the mechanisms of prion propagation and assessing the risk of animal prions to humans.

Characterization of Sporadic Creutzfeldt-Jakob Disease and History of Neurosurgery to Identify Potential Iatrogenic Cases

We previously reported a phenotype of Creutzfeldt-Jakob disease (CJD), CJD-MMiK, that could help identify iatrogenic CJD. To find cases mimicking CJD-MMiK, we investigated clinical features and pathology of 1,155 patients with diagnosed sporadic CJD or unclassified CJD with and without history of neurosurgery. Patients with history of neurosurgery more frequently had an absence of periodic sharp-wave complexes on electroencephalogram than patients without a history of neurosurgery. Among 27 patients with history of neurosurgery, 5 had no periodic sharp-wave complexes on electroencephalogram. We confirmed 1 case of CJD-MMiK and suspected another. Both had methionine homozygosity at codon 129 of the prion protein gene and hyperintensity lesions in the thalamus on magnetic resonance images of the brain, which might be a clinical marker of CJD-MMiK. A subgroup with a history of neurosurgery and clinical features mimicking dura mater graft-associated CJD might have been infected during neurosurgery and had symptoms develop after many years.

Creutzfeldt-Jakob disease: a systematic review of global incidence, prevalence, infectivity, and incubation

Creutzfeldt-Jakob disease (CJD) is a fatal disease presenting with rapidly progressive dementia, and most patients die within a year of clinical onset. CJD poses a potential risk of iatrogenic transmission, as it can incubate asymptomatically in humans for decades before becoming clinically apparent. In this Review, we sought evidence to understand the current iatrogenic risk of CJD to public health by examining global evidence on all forms of CJD, including clinical incidence and prevalence of subclinical disease. We found that although CJD, particularly iatrogenic CJD, is rare, the incidence of sporadic CJD is increasing. Incubation periods as long as 40 years have been observed, and all genotypes have now been shown to be susceptible to CJD. Clinicians and surveillance programmes should maintain awareness of CJD to mitigate future incidences of its transmission. Awareness is particularly relevant for sporadic CJD, which occurs in older people in whom clinical presentation could resemble rapidly developing dementia.

Prions from Sporadic Creutzfeldt-Jakob Disease Patients Propagate as Strain Mixtures

Sporadic Creutzfeldt-Jakob disease (sCJD) cases are currently classified according to the methionine/valine polymorphism at codon 129 of the PRNP gene and the proteinase K-digested abnormal prion protein (PrP^res) isoform identified by Western blotting (type 1 or type 2). Converging evidence led to the view that MM/MV1, VV/MV2, and VV1 and MM2 sCJD cases are caused by distinct prion strains. However, in a significant proportion of sCJD patients, both type 1 and type 2 PrP^res were reported to accumulate in the brain, which raised questions about the diversity of sCJD prion strains and the coexistence of two prion strains in the same patient. In this study, a panel of sCJD brain isolates (n = 29) that displayed either a single or mixed type 1/type 2 PrP^res were transmitted into human-PrP-expressing mice (tgHu). These bioassays demonstrated that two distinct prion strains (M1^CJD and V2^CJD) were associated with the development of sCJD in MM1/MV1 and VV2/MV2 patients. However, in about 35% of the investigated VV and MV cases, transmission results were consistent with the presence of both M1^CJD and V2^CJD strains, including in patients who displayed a "pure" type 1 or type 2 PrP^res The use of a highly sensitive prion in vitro amplification technique that specifically probes the V2^CJD strain revealed the presence of the V2^CJD prion in more than 80% of the investigated isolates, including isolates that propagated as a pure M1^CJD strain in tgHu. These results demonstrate that at least two sCJD prion strains can be present in a single patient.IMPORTANCE sCJD occurrence is currently assumed to result from spontaneous and stochastic formation of a misfolded PrP nucleus in the brains of affected patients. This original nucleus then recruits and converts nascent PrP^C into PrP^Sc, leading to the propagation of prions in the patient's brain. Our study demonstrates the coexistence of two prion strains in the brains of a majority of the 23 sCJD patients investigated. The relative proportion of these sCJD strains varied both between patients and between brain areas in a single patient. These findings strongly support the view that the replication of an sCJD prion strain in the brain of a patient can result in the propagation of different prion strain subpopulations. Beyond its conceptual importance for our understanding of prion strain properties and evolution, the sCJD strain mixture phenomenon and its frequency among patients have important implications for the development of therapeutic strategies for prion diseases.

Transmission characteristics of heterozygous cases of Creutzfeldt-Jakob disease with variable abnormal prion protein allotypes

In the human prion disease Creutzfeldt-Jakob disease (CJD), different CJD neuropathological subtypes are defined by the presence in normal prion protein (PrP^C) of a methionine or valine at residue 129, by the molecular mass of the infectious prion protein PrP^Sc, by the pattern of PrP^Sc deposition, and by the distribution of spongiform change in the brain. Heterozygous cases of CJD potentially add another layer of complexity to defining CJD subtypes since PrP^Sc can have either a methionine (PrP^Sc-M129) or valine (PrP^Sc-V129) at residue 129. We have recently demonstrated that the relative amount of PrP^Sc-M129 versus PrP^Sc-V129, i.e. the PrP^Sc allotype ratio, varies between heterozygous CJD cases. In order to determine if differences in PrP^Sc allotype correlated with different disease phenotypes, we have inoculated 10 cases of heterozygous CJD (7 sporadic and 3 iatrogenic) into two transgenic mouse lines overexpressing PrP^C with a methionine at codon 129. In one case, brain-region specific differences in PrP^Sc allotype appeared to correlate with differences in prion disease transmission and phenotype. In the other 9 cases inoculated, the presence of PrP^Sc-V129 was associated with plaque formation but differences in PrP^Sc allotype did not consistently correlate with disease incubation time or neuropathology. Thus, while the PrP^Sc allotype ratio may contribute to diverse prion phenotypes within a single brain, it does not appear to be a primary determinative factor of disease phenotype.

Interventions to reduce the risk of surgically transmitted Creutzfeldt-Jakob disease: a cost-effective modelling review

BACKGROUND

Creutzfeldt-Jakob disease is a fatal neurological disease caused by abnormal infectious proteins called prions. Prions that are present on surgical instruments cannot be completely deactivated; therefore, patients who are subsequently operated on using these instruments may become infected. This can result in surgically transmitted Creutzfeldt-Jakob disease.

OBJECTIVE

To update literature reviews, consultation with experts and economic modelling published in 2006, and to provide the cost-effectiveness of strategies to reduce the risk of surgically transmitted Creutzfeldt-Jakob disease.

METHODS

Eight systematic reviews were undertaken for clinical parameters. One review of cost-effectiveness was undertaken. Electronic databases including MEDLINE and EMBASE were searched from 2005 to 2017. Expert elicitation sessions were undertaken. An advisory committee, convened by the National Institute for Health and Care Excellence to produce guidance, provided an additional source of information. A mathematical model was updated focusing on brain and posterior eye surgery and neuroendoscopy. The model simulated both patients and instrument sets. Assuming that there were potentially 15 cases of surgically transmitted Creutzfeldt-Jakob disease between 2005 and 2018, approximate Bayesian computation was used to obtain samples from the posterior distribution of the model parameters to generate results. Heuristics were used to improve computational efficiency. The modelling conformed to the National Institute for Health and Care Excellence reference case. The strategies evaluated included neither keeping instruments moist nor prohibiting set migration; ensuring that instruments were kept moist; prohibiting instrument migration between sets; and employing single-use instruments. Threshold analyses were undertaken to establish prices at which single-use sets or completely effective decontamination solutions would be cost-effective.

RESULTS

A total of 169 papers were identified for the clinical review. The evidence from published literature was not deemed sufficiently strong to take precedence over the distributions obtained from expert elicitation. Forty-eight papers were identified in the review of cost-effectiveness. The previous modelling structure was revised to add the possibility of misclassifying surgically transmitted Creutzfeldt-Jakob disease as another neurodegenerative disease, and assuming that all patients were susceptible to infection. Keeping instruments moist was estimated to reduce the risk of surgically transmitted Creutzfeldt-Jakob disease cases and associated costs. Based on probabilistic sensitivity analyses, keeping instruments moist was estimated to on average result in 2.36 (range 0-47) surgically transmitted Creutzfeldt-Jakob disease cases (across England) caused by infection occurring between 2019 and 2023. Prohibiting set migration or employing single-use instruments reduced the estimated risk of surgically transmitted Creutzfeldt-Jakob disease cases further, but at considerable cost. The estimated costs per quality-adjusted life-year gained of these strategies in addition to keeping instruments moist were in excess of £1M. It was estimated that single-use instrument sets (currently £350-500) or completely effective cleaning solutions would need to cost approximately £12 per patient to be cost-effective using a £30,000 per quality-adjusted life-year gained value.

LIMITATIONS

As no direct published evidence to implicate surgery as a cause of Creutzfeldt-Jakob disease has been found since 2005, the estimations of potential cases from elicitation are still speculative. A particular source of uncertainty was in the number of potential surgically transmitted Creutzfeldt-Jakob disease cases that may have occurred between 2005 and 2018.

CONCLUSIONS

Keeping instruments moist is estimated to reduce the risk of surgically transmitted Creutzfeldt-Jakob disease cases and associated costs. Further surgical management strategies can reduce the risks of surgically transmitted Creutzfeldt-Jakob disease but have considerable associated costs.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42017071807.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 24, No. 11. See the NIHR Journals Library website for further project information.

Core transcriptional regulatory circuits in prion diseases

Complex diseases involve dynamic perturbations of pathophysiological processes during disease progression. Transcriptional programs underlying such perturbations are unknown in many diseases. Here, we present core transcriptional regulatory circuits underlying early and late perturbations in prion disease. We first identified cellular processes perturbed early and late using time-course gene expression data from three prion-infected mouse strains. We then built a transcriptional regulatory network (TRN) describing regulation of early and late processes. We found over-represented feed-forward loops (FFLs) comprising transcription factor (TF) pairs and target genes in the TRN. Using gene expression data of brain cell types, we further selected active FFLs where TF pairs and target genes were expressed in the same cell type and showed correlated temporal expression changes in the brain. We finally determined core transcriptional regulatory circuits by combining these active FFLs. These circuits provide insights into transcriptional programs for early and late pathophysiological processes in prion disease.

Study protocol for enhanced CJD surveillance in the 65+ years population group in Scotland: an observational neuropathological screening study of banked brain tissue donations for evidence of prion disease

INTRODUCTION

Creutzfeldt-Jakob disease (CJD) is a human prion disease that occurs in sporadic, genetic and acquired forms. Variant CJD (vCJD) is an acquired form first identified in 1996 in the UK. To date, 178 cases of vCJD have been reported in the UK, most of which have been associated with dietary exposure to the bovine spongiform encephalopathy agent. Most vCJD cases have a young age of onset, with a median age at death of 28 years. In the UK, suspected cases of vCJD are reported to the UK National Creutzfeldt-Jakob Disease Research & Surveillance Unit (NCJDRSU). There is, however, a concern that the national surveillance system might be missing some cases of vCJD or other forms of human prion disease, particularly in the older population, perhaps because of atypical clinical presentation. This study aims to establish whether there is unrecognised prion disease in people aged 65 years and above in the Scottish population by screening banked brain tissue donated to the Edinburgh Brain Bank (EBB).

METHODS

Neuropathological screening of prospective and retrospective brain tissue samples is performed. This involves histopathological and immunohistochemical analysis and prion protein biochemical analysis. During the study, descriptive statistics are used to describe the study population, including the demographics and clinical, pathological and referral characteristics. Controlling for confounders, univariate and multivariate analyses will be used to compare select characteristics of newly identified suspect cases with previously confirmed cases referred to the NCJDRSU.

ETHICS AND DISSEMINATION

Brain tissue donations to EBB are made voluntarily by the relatives of patients, with consent for use in research. The EBB has ethical approval to provide tissue samples to research projects (REC reference 16/ES/0084). The findings of this study will be disseminated in meetings, conferences, workshops and as peer-reviewed publications.

TRIAL REGISTRATION NUMBERS

10/S1402/69 and 10/S1402/70.

Sporadic Creutzfeldt-Jakob Disease in a Woman Married Into a Gerstmann-Sträussler-Scheinker Family: An Investigation of Prions Transmission via Microchimerism

This is the first report of presumed sporadic Creutzfeldt-Jakob disease (sCJD) and Gerstmann-Sträussler-Scheinker disease (GSS) with the prion protein gene c.305C>T mutation (p.P102L) occurring in one family. The father and son were affected with GSS and the mother had a rapidly progressive form of CJD. Diagnosis of genetic, variant, and iatrogenic CJD was ruled out based on the mother's clinical history, genetic tests, and biochemical investigations, all of which supported the diagnosis of sCJD. However, given the low incidence of sCJD and GSS, their co-occurrence in one family is extraordinary and challenging. Thus, a hypothesis for the transmission of infectious prion proteins (PrPSc) via microchimerism was proposed and investigated. DNA from 15 different brain regions and plasma samples of the CJD patient was subjected to PCR and shallow sequencing for detection of a male sex-determining chromosome Y (chr. Y). However, no trace of chr. Y was found. A long CJD incubation period or presumed small concentrations of chr. Y may explain the obtained results. Further studies of CJD and GSS animal models with controlled genetic and proteomic features are needed to determine whether maternal CJD triggered via microchimerism by a GSS fetus might present a new PrPSc transmission route.

Frequent Detection of Pituitary-Derived PrPres in Human Prion Diseases

Human prion diseases including sporadic Creutzfeldt-Jakob disease (sCJD), inherited prion diseases, and acquired human prion diseases are lethal neurodegenerative diseases. One of the major sources of iatrogenic Creutzfeldt-Jakob disease was human growth hormone (hGH-iCJD) derived from contaminated cadaveric pituitaries. The incidence of hGH-iCJD has decreased since changing from growth hormone extracted from human cadaveric pituitaries to recombinant pituitary hormones. However, extensive analysis on the localization and detecting of abnormal prion protein in the pituitary gland are limited. In this study, we examined 9 autopsied brains and pituitary glands from 6 patients with prion disease (3 Gerstmann-Sträussler-Scheinker disease, 2 sCJD, and 1 dura mater graft-associated CJD) and 3 individuals with nonprion diseases. Western blot analysis of pituitary samples demonstrated unique glycoforms of normal cellular prion protein with molecular weights of 30-40 kDa, which was higher than the typical 25-35 kDa prion protein in brains. Proteomic analysis also revealed prion protein approximately the molecular weight of 40 kDa in pituitary samples. Moreover, proteinase K-resistant Prion protein was frequently detected in pituitary samples of the prion diseases. Immunohistochemistry for Prion protein revealed mosaic cellular distribution preferentially in growth hormone- or prolactin-producing cells.

Epitope mapping of the protease resistant products of RT-QuIC does not allow the discrimination of sCJD subtypes

Sporadic Creutzfeldt-Jakob disease (sCJD) is a transmissible, rapidly progressive and fatal neurodegenerative disease. The transmissible agent linked to sCJD is composed of the misfolded form of the host-encoded prion protein. The combination of histopathological and biochemical analyses has allowed the identification and sub-classification of six sCJD subtypes. This classification depends on the polymorphic variability of codon 129 of the prion protein gene and the PrPres isotype, and appears to be associated with neuropathological and clinical features. Currently, sCJD subtyping is only fully achievable post mortem. However, a rapid and non-invasive method for discriminating sCJD subtypes in vita would be invaluable for the clinical management of affected individuals, and for the selection of participants for clinical trials. The CSF analysis by Real Time Quaking Induced Conversion (RT-QuIC) reaction is the most sensitive and specific ante mortem sCJD diagnostic test available to date, and it is used by a number of laboratories internationally. RT-QuIC takes advantage of the natural replication mechanisms of prions by template-induced misfolding, employing recombinant prion protein as reaction substrate. We asked whether epitope mapping, of the RT-QuIC reaction products obtained from seeding RT-QuIC with brain and CSF samples from each of the six molecular subtypes of sCJD could be employed to distinguish them and therefore achieve in vita sCJD molecular subtyping. We found that it is possible to distinguish the RT-QuIC products generated by sCJD biological samples from the ones generated by spontaneous conversion in the negative controls, but that different sCJD subtypes generate very similar, if not identical RT-QuIC reaction products. We concluded that whilst RT-QuIC has demonstrable diagnostic value it has limited prognostic value at this point in time.

The characterization of AD/PART co-pathology in CJD suggests independent pathogenic mechanisms and no cross-seeding between misfolded Aβ and prion proteins

Current evidence indicating a role of the human prion protein (PrP) in amyloid-beta (Aβ) formation or a synergistic effect between Aβ and prion pathology remains controversial. Conflicting results also concern the frequency of the association between the two protein misfolding disorders and the issue of whether the apolipoprotein E gene (APOE) and the prion protein gene (PRNP), the major modifiers of Aβ- and PrP-related pathologies, also have a pathogenic role in other proteinopathies, including tau neurofibrillary degeneration. Here, we thoroughly characterized the Alzheimer's disease/primary age-related tauopathy (AD/PART) spectrum in a series of 450 cases with definite sporadic or genetic Creutzfeldt-Jakob disease (CJD). Moreover, we analyzed: (i) the effect of variables known to affect CJD pathogenesis and the co-occurring Aβ- and tau-related pathologies; (II) the influence of APOE genotype on CJD pathology, and (III) the effect of AD/PART co-pathology on the clinical CJD phenotype. AD/PART characterized 74% of CJD brains, with 53.3% and 8.2% showing low or intermediate-high levels of AD pathology, and 12.4 and 11.8% definite or possible PART. There was no significant correlation between variables affecting CJD (i.e., disease subtype, prion strain, PRNP genotype) and those defining the AD/PART spectrum (i.e., ABC score, Thal phase, prevalence of CAA and Braak stage), and no difference in the distribution of APOE ε4 and ε2 genotypes among CJD subtypes. Moreover, AD/PART co-pathology did not significantly affect the clinical presentation of typical CJD, except for a tendency to increase the frequency of cognitive symptoms. Altogether, the present results seem to exclude an increased prevalence AD/PART co-pathology in sporadic and genetic CJD, and indicate that largely independent pathogenic mechanisms drive AD/PART and CJD pathology even when they coexist in the same brain.

Understanding Prion Strains: Evidence from Studies of the Disease Forms Affecting Humans

Prion diseases are a unique group of rare neurodegenerative disorders characterized by tissue deposition of heterogeneous aggregates of abnormally folded protease-resistant prion protein (PrPSc), a broad spectrum of disease phenotypes and a variable efficiency of disease propagation in vivo. The dominant clinicopathological phenotypes of human prion disease include Creutzfeldt⁻Jakob disease, fatal insomnia, variably protease-sensitive prionopathy, and Gerstmann⁻Sträussler⁻Scheinker disease. Prion disease propagation into susceptible hosts led to the isolation and characterization of prion strains, initially operatively defined as "isolates" causing diseases with distinctive characteristics, such as the incubation period, the pattern of PrPSc distribution, and the regional severity of neuropathological changes after injection into syngeneic hosts. More recently, the structural basis of prion strains has been linked to amyloid polymorphs (i.e., variant amyloid protein conformations) and the concept extended to all protein amyloids showing polymorphic structures and some evidence of in vivo or in vitro propagation by seeding. Despite the significant advances, however, the link between amyloid structure and disease is not understood in many instances. Here we reviewed the most significant contributions of human prion disease studies to current knowledge of the molecular basis of phenotypic variability and the prion strain phenomenon and underlined the unsolved issues from the human disease perspective.

Recent advances in the histo-molecular pathology of human prion disease

Prion diseases are progressive neurodegenerative disorders affecting humans and other mammalian species. The term prion, originally put forward to propose the concept that a protein could be infectious, refers to PrP^Sc , a misfolded isoform of the cellular prion protein (PrP^C ) that represents the pathogenetic hallmark of these disorders. The discovery that other proteins characterized by misfolding and seeded aggregation can spread from cell to cell, similarly to PrP^Sc , has increased interest in prion diseases. Among neurodegenerative disorders, however, prion diseases distinguish themselves for the broader phenotypic spectrum, the fastest disease progression and the existence of infectious forms that can be transmitted through the exposure to diseased tissues via ingestion, injection or transplantation. The main clinicopathological phenotypes of human prion disease include Creutzfeldt-Jakob disease, by far the most common, fatal insomnia, variably protease-sensitive prionopathy, and Gerstmann-Sträussler-Scheinker disease. However, clinicopathological manifestations extend even beyond those predicted by this classification. Because of their transmissibility, the phenotypic diversity of prion diseases can also be propagated into syngenic hosts as prion strains with distinct characteristics, such as incubation period, pattern of PrP^Sc distribution and regional severity of histopathological changes in the brain. Increasing evidence indicates that different PrP^Sc conformers, forming distinct ordered aggregates, encipher the phenotypic variants related to prion strains. In this review, we summarize the most recent advances concerning the histo-molecular pathology of human prion disease focusing on the phenotypic spectrum of the disease including co-pathologies, the characterization of prion strains by experimental transmission and their correlation with the physicochemical properties of PrP^Sc aggregates.

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 β (Aβ), 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.

Sporadic Creutzfeldt-Jakob disease

Sporadic Creutzfeldt-Jakob disease (CJD), the most common human prion disease, is generally regarded as a spontaneous neurodegenerative illness, arising either from a spontaneous PRNP somatic mutation or a stochastic PrP structural change. Alternatively, the possibility of an infection from animals or other source remains to be completely ruled out. Sporadic CJD is clinically characterized by rapidly progressive dementia with ataxia, myoclonus, or other neurologic signs and, neuropathologically, by the presence of aggregates of abnormal prion protein, spongiform change, neuronal loss, and gliosis. Despite these common features the disease shows a wide phenotypic variability which was recognized since its early descriptions. In the late 1990s the identification of key molecular determinants of phenotypic expression and the availability of a large series of neuropathologically verified cases led to the characterization of definite clinicopathologic and molecular disease subtypes and to an internationally recognized disease classification. By showing that these disease subtypes correspond to specific agent strain-host genotype combinations, recent transmission studies have confirmed the biologic basis of this classification. The introduction of brain magnetic resonance imaging techniques such as fluid-attenuated inversion recovery and diffusion-weighted imaging sequences and cerebrospinal fluid biomarker assays for the detection of brain-derived proteins as well as real-time quaking-induced conversion assay, allowing the specific detection of prions in accessible biologic fluids and tissues, has significantly contributed to the improved accuracy of the clinical diagnosis of sporadic CJD in recent years.

Brains with sporadic Creutzfeldt-Jakob disease and copathology showed a prolonged end-stage of disease

AIMS

To investigate the expression of major proteins related to primary neurodegenerative diseases and their prognostic significance in brains with Creutzfeldt-Jakob disease (CJD).

MATERIALS AND METHODS

Thirty consecutive cases of confirmed CJD during the period 2010-2015 at Basque Brain bank were retrospectively reviewed. Moreover, major neurodegenerative-associated proteins (phosphorylated Tau, 4R tau, 3R tau, alpha-synuclein, TDP43, amyloid beta) were tested. Clinical data were reviewed. Cases were divided according to the presence or absence of copathology. Survival curves were also determined.

RESULTS

Copathology was significantly associated with survival in brains with CJD (4.2±1.2 vs 9.2±1.9; P=0.019) and in brains with MM1/MV1 CJD (2.1±1.0 vs 6.7±2.8; P=0.012). Besides, the presence of more than one major neurodegenerative-associated protein was significantly associated with survival (4.2±1.2 vs 10.7±2.6; P=0.017). Thus, univariate analyses further pointed out variables significantly associated with better survival: copathology in CJD (HR=0.430; P=0.033); more than one neurodegenerative-associated protein in CJD (HR=0.369; P=0.036) and copathology in MM1/MV1 CJD (HR=0.525; P=0.032).

CONCLUSION

The existence of copathology significantly prolongs survival in patients with rapidly progressive dementia due to CJD. The study of major neurodegenerative-associated proteins in brains with CJD could allow us to further understand the molecular mechanisms behind prion diseases.

Creutzfeldt-Jakob disease and blood transfusion safety

Transmissible spongiform encephalopathies (TSEs) are untreatable, fatal neurologic diseases affecting mammals. Human disease forms include sporadic, familial and acquired Creutzfeldt-Jakob disease (CJD). While sporadic CJD (sCJD) has been recognized for near on 100 years, variant CJD (vCJD) was first reported in 1996 and is the result of food-borne transmission of the prion of bovine spongiform encephalopathy (BSE, 'mad cow disease'). Currently, 230 vCJD cases have been reported in 12 countries, the majority in the UK (178) and France (27). Animal studies demonstrated highly efficient transmission of natural scrapie and experimental BSE by blood transfusion and fuelled concern that sCJD was potentially transfusion transmissible. No such case has been recorded and case-control evaluations and lookback studies indicate that, if transfusion transmission occurs at all, it is very rare. In contrast, four cases of apparent transfusion transmission of vCJD infectivity have been identified in the UK. Risk minimization strategies in response to the threat of vCJD include leucodepletion, geographically based donor deferrals and deferral of transfusion recipients. A sensitive and specific, high-throughput screening test would provide a potential path to mitigation but despite substantial effort no such test has yet appeared. The initial outbreak of vCJD appears to be over, but concern remains about subsequent waves of disease among those already infected. There is considerable uncertainty about the size of the infected population, and there will be at least a perception of some continuing risk to blood safety. Accordingly, at least some precautionary measures will remain in place and continued surveillance is necessary.

Rapid amplification of prions from variant Creutzfeldt-Jakob disease cerebrospinal fluid

Human prion diseases constitute a group of infectious and invariably fatal neurodegenerative disorders associated with misfolding of the prion protein. Variant Creutzfeldt–Jakob disease (vCJD) is a zoonotic prion disease linked to oral exposure to the infectious agent that causes bovine spongiform encephalopathy (BSE) in cattle. The most recent case of definite vCJD was heterozygous (MV) at polymorphic codon 129 of the prion protein gene PRNP while all of the previous 177 definite or probable vCJD cases who underwent genetic analysis were methionine homozygous (MM). Retrospective prevalence studies conducted on lympho‐reticular tissue suggest that the number of asymptomatic vCJD carriers in the United Kingdom might be around 1 in 2000 people. In addition, there have been four known cases of the transmission of vCJD infection via blood transfusion. For these reasons, a sensitive, reliable, and fast diagnostic test is currently needed. We describe a rapid and highly sensitive seeding conversion assay that detects disease‐associated prion protein in the brain and cerebrospinal fluid in vCJD after 48–96 h of amplification, with 100% sensitivity and specificity. This method can amplify prions from definite, probable, and possible vCJD cases from patients who are either MM or MV at PRNP‐codon 129.

Prion diseases

The human prion diseases comprise Creutzfeldt-Jakob disease, variably protease-sensitive prionopathy, Gerstmann-Sträussler-Scheinker disease, fatal familial insomnia, and kuru. Each is a uniformly fatal rare neurodegenerative disease in which conformational changes in the prion protein are thought to be the central pathophysiologic event. The majority of cases of human prion diseases occur worldwide in the form of sporadic Creutzfeldt-Jakob disease and a minority of around 10-15% are associated with mutations of the prion protein gene, termed PRNP, in the forms of genetic Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker disease, and fatal familial insomnia. Prion diseases are also transmissible and occur in iatrogenic and zoonotic forms (iatrogenic Creutzfeldt-Jakob disease and variant Creutzfeldt-Jakob disease respectively), adding a public health dimension to their management. Despite having a high public profile, human prion diseases are both rare and heterogeneous in their clinicopathologic phenotype, sometimes making a diagnosis challenging. A combined clinical, genetic, neuropathologic, and biochemical approach to diagnosis is therefore essential. The intensive study of these diseases continues to inform on neurodegenerative mechanisms and the role of protein misfolding in more common neurodegenerative diseases such as Parkinson disease and Alzheimer disease.

Iatrogenic Creutzfeldt-Jakob disease with Amyloid-β pathology: an international study

The presence of pathology related to the deposition of amyloid-β (Aβ) has been recently reported in iatrogenic Creutzfeldt-Jakob disease (iCJD) acquired from inoculation of growth hormone (GH) extracted from human cadaveric pituitary gland or use of cadaveric dura mater (DM) grafts.To investigate this phenomenon further, a cohort of 27 iCJD cases - 21 with adequate number of histopathological sections - originating from Australia, France, Italy, and the Unites States, were examined by immunohistochemistry, amyloid staining, and Western blot analysis of the scrapie prion protein (PrPSc), and compared with age-group matched cases of sporadic CJD (sCJD), Alzheimer disease (AD) or free of neurodegenerative diseases (non-ND).Cases of iCJD and sCJD shared similar profiles of proteinase K-resistant PrPSc with the exception of iCJD harboring the "MMi" phenotype. Cerebral amyloid angiopathy (CAA), either associated with, or free of, Thioflavin S-positive amyloid core plaques (CP), was observed in 52% of 21 cases of iCJD, which comprised 37.5% and 61.5% of the cases of GH- and DM-iCJD, respectively. If only cases younger than 54 years were considered, Aβ pathology affected 41%, 2% and 0% of iCJD, sCJD and non-ND, respectively. Despite the patients' younger age CAA was more severe in iCJD than sCJD, while Aβ diffuse plaques, in absence of Aβ CP, populated one third of sCJD. Aβ pathology was by far most severe in AD. Tau pathology was scanty in iCJD and sCJD.In conclusion, (i) despite the divergences in the use of cadaveric GH and DM products, our cases combined with previous studies showed remarkably similar iCJD and Aβ phenotypes indicating that the occurrence of Aβ pathology in iCJD is a widespread phenomenon, (ii) CAA emerges as the hallmark of the Aβ phenotype in iCJD since it is observed in nearly 90% of all iCJD with Aβ pathology reported to date including ours, and it is shared by GH- and DM-iCJD, (iii) although the contributions to Aβ pathology of other factors, including GH deficiency, cannot be discounted, our findings increase the mounting evidence that this pathology is acquired by a mechanism resembling that of prion diseases.

Iatrogenic Creutzfeldt-Jakob disease

Iatrogenic transmission of Creutzfeldt-Jakob disease (CJD) has occurred through particular medical procedures. Among them, dura mater grafts and pituitary-derived growth hormone obtained from human cadavers undiagnosed as CJD are the most frequent sources of infection. Recent advances in our knowledge about dura mater graft- and human pituitary-derived growth hormone-associated CJD patients have revealed that the combination of the infected CJD strain and the PRNP genotype of the patient determines their clinical, neuropathologic, and biochemical features. In this chapter, we summarize the clinical, neuropathologic, biochemical, and diagnostic features of dura mater graft- and human pituitary-derived growth hormone-associated CJD patients for the appropriate diagnosis of iatrogenic CJD.

Atypical Creutzfeldt-Jakob disease with PrP-amyloid plaques in white matter: molecular characterization and transmission to bank voles show the M1 strain signature

Amyloid plaques formed by abnormal prion protein (PrP^Sc) aggregates occur with low frequency in Creutzfeldt-Jakob disease, but represent a pathological hallmark of three relatively rare disease histotypes, namely variant CJD, sporadic CJDMV2K (methionine/valine at PRNP codon 129, PrP^Sc type 2 and kuru-type amyloid plaques) and iatrogenic CJDMMiK (MM at codon 129, PrP^Sc of intermediate type and kuru plaques). According to recent studies, however, PrP-amyloid plaques involving the subcortical and deep nuclei white matter may also rarely occur in CJDMM1 (MM at codon 129 and PrP^Sc type 1), the most common CJD histotype.To further characterize the phenotype of atypical CJDMM1 with white matter plaques (p-CJDMM1) and unravel the basis of amyloid plaque formation in such cases, we compared clinical and histopathological features and PrP^Sc physico-chemical properties between 5 p-CJDMM1 and 8 typical CJDMM1 brains lacking plaques. Furthermore, transmission properties after bioassay in two genetic lines of bank voles were also explored in the two groups.All 5 p-CJDMM1 cases had a disease duration longer than one year. Three cases were classified as sporadic CJDMM1, one as sporadic CJDMM1 + 2C and one as genetic CJDE200K-MM1. Molecular mass, protease sensitivity and thermo-solubilization of PrP^Sc aggregates did not differ between p-CJDMM1 and classical CJDMM1 cases. Likewise, transmission properties such as incubation time, lesion profile and PrP^Sc properties in bank voles also matched in the two groups.The present data further define the clinical-pathologic phenotype of p-CJDMM1, definitely establish it as a distinctive CJD histotype and demonstrate that PrP-plaque formation in this histotype is not a strain-specific feature. Since cases lacking amyloid plaques may also manifest a prolonged (i.e. > than one year) disease course, unidentified, host-specific factors likely play a significant role, in addition to disease duration, in generating white matter PrP-amyloid plaques in p-CJDMM1.

Amyloid-β accumulation in the CNS in human growth hormone recipients in the UK

Human-to-human transmission of Creutzfeldt-Jakob disease (CJD) has occurred through medical procedures resulting in iatrogenic CJD (iCJD). One of the commonest causes of iCJD was the use of human pituitary-derived growth hormone (hGH) to treat primary or secondary growth hormone deficiency. As part of a comprehensive tissue-based analysis of the largest cohort yet collected (35 cases) of UK hGH-iCJD cases, we describe the clinicopathological phenotype of hGH-iCJD in the UK. In the 33/35 hGH-iCJD cases with sufficient paraffin-embedded tissue for full pathological examination, we report the accumulation of the amyloid beta (Aβ) protein associated with Alzheimer's disease (AD) in the brains and cerebral blood vessels in 18/33 hGH-iCJD patients and for the first time in 5/12 hGH recipients who died from causes other than CJD. Aβ accumulation was markedly less prevalent in age-matched patients who died from sporadic CJD and variant CJD. These results are consistent with the hypothesis that Aβ, which can accumulate in the pituitary gland, was present in the inoculated hGH preparations and had a seeding effect in the brains of around 50% of all hGH recipients, producing an AD-like neuropathology and cerebral amyloid angiopathy (CAA), regardless of whether CJD neuropathology had occurred. These findings indicate that Aβ seeding can occur independently and in the absence of the abnormal prion protein in the human brain. Our findings provide further evidence for the prion-like seeding properties of Aβ and give insights into the possibility of iatrogenic transmission of AD and CAA.