Comparative neuropathology of Kuru with the new variant of Creutzfeldt-Jakob disease: evidence for strain of agent predominating over genotype of host

Kuru Disease: Bridging the Gap Between Prion Biology and Human Health

This article explores the intriguing case of Kuru disease, a rare and fatal prion disease that once afflicted the Fore people of Papua New Guinea. Scientists are still perplexed as to the origins of Kuru because efforts to discover infectious agents like viruses have been ineffective. Initial research revealed similarities between Kuru and scrapie, a neurological disorder that affects sheep, suggesting potential similarities between the two diseases. In further research, experiments in which chimpanzee brain tissue from Kuru patients was implanted led to the development of Kuru-like symptoms in the animals, suggesting a transmissible component to the condition. Furthermore, data collected from epidemiological studies highlights a drop in Kuru transmission, especially after the Fore people stopped engaging in cannibalism, and the disease showed different incubation times that affected persons within particular age groups. Neuropathological tests in the infected brain tissue have found typical intracellular vacuoles, spongiform alterations, and amyloid plaques. According to studies, Kuru susceptibility has been linked genetically to particular PRNP gene variations. Kuru and other prion disorders have few effective treatments currently, underlining the vital need for early identification. Scientists have created sensitive detection techniques to stop the spread of prion diseases and looked into possible inhibitors. Hypochlorous acid, in particular, has shown potential in cleaning processes. Besides making great progress in understanding Kuru, there are still many unresolved issues surrounding its causes, transmission, and management. The terms "kuru disease," "human prion disease," "transmissible spongiform encephalopathies," and "Creutzfeldt-Jakob syndrome" were used to search the studies; papers unrelated to the review article were removed. Eighty-four articles are included in the review text to fully understand the complexities of this puzzling disease and its consequences for prion biology and human health; additional study is essential.

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.

Kuru, the First Human Prion Disease

Kuru, the first human prion disease was transmitted to chimpanzees by D. Carleton Gajdusek (1923–2008). In this review, we summarize the history of this seminal discovery, its anthropological background, epidemiology, clinical picture, neuropathology, and molecular genetics. We provide descriptions of electron microscopy and confocal microscopy of kuru amyloid plaques retrieved from a paraffin-embedded block of an old kuru case, named Kupenota. The discovery of kuru opened new vistas of human medicine and was pivotal in the subsequent transmission of Creutzfeldt–Jakob disease, as well as the relevance that bovine spongiform encephalopathy had for transmission to humans. The transmission of kuru was one of the greatest contributions to biomedical sciences of the 20th century.

Infectious prion diseases in humans: cannibalism, iatrogenicity and zoonoses

In contrast with other neurodegenerative disorders associated to protein misfolding, human prion diseases include infectious forms (also called transmitted forms) such as kuru, iatrogenic Creutzfeldt-Jakob disease and variant Creutzfeldt-Jakob disease. The transmissible agent is thought to be solely composed of the abnormal isoform (PrP(Sc)) of the host-encoded prion protein that accumulated in the central nervous system of affected individuals. Compared to its normal counterpart, PrP(Sc) is β-sheet enriched and aggregated and its propagation is based on an autocatalytic conversion process. Increasing evidence supports the view that conformational variations of PrP(Sc) encoded the biological properties of the various prion strains that have been isolated by transmission studies in experimental models. Infectious forms of human prion diseases played a pivotal role in the emergence of the prion concept and in the characterization of the very unconventional properties of prions. They provide a unique model to understand how prion strains are selected and propagate in humans. Here, we review and discuss how genetic factors interplay with strain properties and route of transmission to influence disease susceptibility, incubation period and phenotypic expression in the light of the kuru epidemics due to ritual endocannibalism, the various series iatrogenic diseases secondary to extractive growth hormone treatment or dura mater graft and the epidemics of variant Creutzfeldt-Jakob disease linked to dietary exposure to the agent of bovine spongiform encephalopathy.

Kuru: a journey back in time from papua new Guinea to the neanderthals' extinction

Kuru, the first human transmissible spongiform encephalopathy was transmitted to chimpanzees by D. Carleton Gajdusek (1923-2008). In this review, I briefly summarize the history of this seminal discovery along its epidemiology, clinical picture, neuropathology and molecular genetics. The discovery of kuru opened new windows into the realms of human medicine and was instrumental in the later transmission of Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheinker disease as well as the relevance that bovine spongiform encephalopathy had for transmission to humans. The transmission of kuru was one of the greatest contributions to biomedical sciences of the 20th century.

Prion disease: a tale of folds and strains

Research on prions, the infectious agents of devastating neurological diseases in humans and animals, has been in the forefront of developing the concept of protein aggregation diseases. Prion diseases are distinguished from other neurodegenerative diseases by three peculiarities. First, prion diseases, in addition to being sporadic or genetic like all other neurodegenerative diseases, are infectious diseases. Animal models were developed early on (a long time before the advent of transgenic technology), and this has made possible the discovery of the prion protein as the infectious agent. Second, human prion diseases have true equivalents in animals, such as scrapie, which has been the subject of experimental research for many years. Variant Creutzfeldt-Jakob disease (vCJD) is a zoonosis caused by bovine spongiform encephalopathy (BSE) prions. Third, they show a wide variety of phenotypes in humans and animals, much wider than the variants of any other sporadic or genetic neurodegenerative disease. It has now become firmly established that particular PrP(Sc) isoforms are closely related to specific human prion strains. The variety of human prion diseases, still an enigma in its own right, is a focus of this article. Recently, a series of experiments has shown that the concept of aberrant protein folding and templating, first developed for prions, may apply to a variety of neurodegenerative diseases. In the wake of these discoveries, the term prion has come to be used for Aβ, α-synuclein, tau and possibly others. The self-propagation of alternative conformations seems to be the common denominator of these "prions," which in future, in order to avoid confusion, may have to be specified either as "neurodegenerative prions" or "infectious prions."

Kuru: genes, cannibals and neuropathology

Kuru was the first human transmissible spongiform encephalopathy (TSE) or prion disease identified, occurring in the Fore linguistic group of Papua New Guinea. Kuru was a uniformly fatal cerebellar ataxic syndrome, usually followed by choreiform and athetoid movements. Kuru imposed a strong balancing selection on the Fore population, with individuals homozygous for the 129 Met allele of the gene (PRNP) encoding for prion protein (PrP) being the most susceptible. The decline in the incidence of kuru in the Fore has been attributed to the exhaustion of the susceptible genotype and ultimately by discontinuation of exposure via cannibalism. Neuropathologically, kuru-affected brains were characterized by widespread degeneration of neurons, astroglial and microglial proliferation, and the presence of amyloid plaques. These early findings have been confirmed and extended by recent immunohistochemical studies for the detection of the TSE-specific PrP (PrP). Confocal laser microscopy also showed the concentration of glial fibrillary acidic protein-positive astrocytic processes at the plaque periphery. The fine structure of plaques corresponds to that described earlier by light microscopy. The successful experimental transmission of kuru led to the awareness of its similarity to Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheinker disease and formed a background against which the recent epidemics of iatrogenic and variant Creutzfeldt-Jakob disease could be studied.

Atypical prion diseases in humans and animals

Although prion diseases, such as Creutzfeldt-Jakob disease (CJD) in humans and scrapie in sheep, have long been recognized, our understanding of their epidemiology and pathogenesis is still in its early stages. Progress is hampered by the lengthy incubation periods and the lack of effective ways of monitoring and characterizing these agents. Protease-resistant conformers of the prion protein (PrP), known as the "scrapie form" (PrP(Sc)), are used as disease markers, and for taxonomic purposes, in correlation with clinical, pathological, and genetic data. In humans, prion diseases can arise sporadically (sCJD) or genetically (gCJD and others), caused by mutations in the PrP-gene (PRNP), or as a foodborne infection, with the agent of bovine spongiform encephalopathy (BSE) causing variant CJD (vCJD). Person-to-person spread of human prion disease has only been known to occur following cannibalism (kuru disease in Papua New Guinea) or through medical or surgical treatment (iatrogenic CJD, iCJD). In contrast, scrapie in small ruminants and chronic wasting disease (CWD) in cervids behave as infectious diseases within these species. Recently, however, so-called atypical forms of prion diseases have been discovered in sheep (atypical/Nor98 scrapie) and in cattle, BSE-H and BSE-L. These maladies resemble sporadic or genetic human prion diseases and might be their animal equivalents. This hypothesis also raises the significant public health question of possible epidemiological links between these diseases and their counterparts in humans.

Laminar distribution of the pathological changes in sporadic and variant creutzfeldt-jakob disease

The laminar distributions of the pathological changes in the cerebral cortex were compared in the prion diseases sporadic Creutzfeldt-Jakob disease (sCJD) and variant CJD (vCJD). First, in some cortical regions, the vacuolation (“spongiform change”) was more generally distributed across the cortex in sCJD. Second, there was greater neuronal loss in the upper cortex in vCJD and in the lower cortex in sCJD. Third, the “diffuse” and “florid” prion protein (PrP^sc) deposits were more frequently distributed in the upper cortex in vCJD and the “synaptic” deposits in the lower cortex in sCJD. Fourth, there was a significant gliosis mainly affecting the lower cortex of both disorders. The data suggest that the pattern of cortical degeneration is different in sCJD and vCJD which may reflect differences in aetiology and the subsequent spread of prion pathology within the brain.

Agent strain variation in human prion disease: insights from a molecular and pathological review of the National Institutes of Health series of experimentally transmitted disease

Six clinico-pathological phenotypes of sporadic Creutzfeldt-Jakob disease have been characterized which correlate at the molecular level with the type (1 or 2) of the abnormal prion protein, PrP(TSE), present in the brain and with the genotype of polymorphic (methionine or valine) codon 129 of the prion protein gene. However, to what extent these phenotypes with their corresponding molecular combinations (i.e. MM1, MM2, VV1 etc.) encipher distinct prion strains upon transmission remains uncertain. We studied the PrP(TSE) type and the prion protein gene in archival brain tissues from the National Institutes of Health series of transmitted Creutzfeldt-Jakob disease and kuru cases, and characterized the molecular and pathological phenotype in the affected non-human primates, including squirrel, spider, capuchin and African green monkeys. We found that the transmission properties of prions from the common sporadic Creutzfeldt-Jakob disease MM1 phenotype are homogeneous and significantly differ from those of sporadic Creutzfeldt-Jakob disease VV2 or MV2 prions. Animals injected with iatrogenic Creutzfeldt-Jakob disease MM1 and genetic Creutzfeldt-Jakob disease MM1 linked to the E200K mutation showed the same phenotypic features as those infected with sporadic Creutzfeldt-Jakob disease MM1 prions, whereas kuru most closely resembled the sporadic Creutzfeldt-Jakob disease VV2 or MV2 prion signature and neuropathology. The findings indicate that two distinct prion strains are linked to the three most common Creutzfeldt-Jakob disease clinico-pathological and molecular subtypes and kuru, and suggest that kuru may have originated from cannibalistic transmission of a sporadic Creutzfeldt-Jakob disease of the VV2 or MV2 subtype.

Variant Creutzfeldt-Jakob disease in France and the United Kingdom: Evidence for the same agent strain

OBJECTIVE

Variant Creutzfeldt-Jakob disease (vCJD) was first reported in the United Kingdom in 1996. Since then, the majority of cases have been observed in the United Kingdom where there was a major epidemic of bovine spongiform encephalopathy. France was the second country affected. To address the hypothesis of the involvement of a common strain of agent, we have compared clinical, neuropathological, and biochemical data on vCJD patients from both countries.

METHODS

In France and the United Kingdom, epidemiological and clinical data were obtained from analysis of medical records and direct interview of the family of the patients using the same standardized questionnaire in both countries. When brain material was available, we performed with similar methods a comparative study of brain lesions and PrP(res) glycoform ratios in both vCJD populations.

RESULTS

Clinical data, genetic background, neuropathological finding, and biochemical findings in the 185 patients observed in France (n = 23) and the United Kingdom (n = 162) were similar except for age at death. Currently, blood transfusion is a risk factor identified only in the United Kingdom.

INTERPRETATION

The close similarity between the cases of vCJD in France and the United Kingdom supports the hypothesis that a common strain of infectious agent is involved in both countries. The 5-year delay in the peak that we observed in France compared with the United Kingdom fits well with the increase in the importation of beef products to France from the United Kingdom between 1985 and 1995.

A quantitative study of the pathological changes in the cerebellum in 15 cases of variant Creutzfeldt-Jakob disease (vCJD)

AIMS

To determine in the cerebellum in variant Creutzfeldt-Jakob disease (vCJD): (i) whether the pathology affected all laminae; (ii) the spatial topography of the pathology along the folia; (iii) spatial correlations between the pathological changes; and (iv) whether the pathology was similar to that of the common methionine/methionine Type 1 subtype of sporadic CJD.

METHODS

Sequential cerebellar sections of 15 cases of vCJD were stained with haematoxylin and eosin, or immunolabelled with monoclonal antibody 12F10 against prion protein (PrP) and studied using spatial pattern analysis.

RESULTS

Loss of Purkinje cells was evident compared with control cases. Densities of the vacuolation and the protease-resistant form of prion protein (PrP(Sc)) (diffuse and florid plaques) were greater in the granule cell layer (GL) than the molecular layer (ML). In the ML, vacuoles and PrP(Sc) plaques occurred in clusters regularly distributed along the folia with larger clusters of vacuoles and diffuse plaques in the GL. There was a negative spatial correlation between the vacuoles and the surviving Purkinje cells in the ML. There was a positive spatial correlation between the vacuoles and diffuse PrP(Sc) plaques in the ML and GL.

CONCLUSIONS

(i) all laminae were affected by the pathology, the GL more severely than the ML; (ii) the pathology was topographically distributed along the folia especially in the Purkinje cell layer and ML; (iii) pathological spread may occur in relation to the loop of anatomical connections involving the cerebellum, thalamus, cerebral cortex and pons; and (iv) there were pathological differences compared with methionine/methionine Type 1 sporadic CJD.

Review. The neuropathology of kuru and variant Creutzfeldt-Jakob disease

A comparison of the pathological profiles of two spongiform encephalopathies with a similar presumptive route of infection was performed. Archival kuru and recent variant Creutzfeldt–Jakob disease (vCJD) cases reveal distinct lesional differences, particularly with respect to prion protein, suggesting that the strain of agent is important in determining the phenotype. Genotype analysis of the polymorphism on codon 129 reveals (in conjunction with updated information from more kuru cases) that all three genotypes (VV, MV and MM (where M is methionine and V is valine)) are detected in kuru with some preference for MM homozygosity. The presence of valine does not therefore appear to determine peripheral selection of PrP^CJD. vCJD remains restricted to date to MM homozygosity on codon 129. It remains to be determined whether this genotype is dictating a shorter incubation period.

Review. The origin of the prion agent of kuru: molecular and biological strain typing

Kuru is an acquired human prion disease that primarily affected the Fore linguistic group of the Eastern Highlands of Papua New Guinea. The central clinical feature of kuru is progressive cerebellar ataxia and, in sharp contrast to most cases of sporadic Creutzfeldt–Jakob disease (CJD), dementia is a less prominent and usually late clinical feature. In this regard, kuru is more similar to variant CJD, which also has similar prodromal symptoms of sensory disturbance and joint pains in the legs and psychiatric and behavioural changes. Since a significant part of the clinicopathological diversity seen in human prion disease is likely to relate to the propagation of distinct human prion strains, we have compared the transmission properties of kuru prions with those isolated from patients with sporadic, iatrogenic and variant CJD in both transgenic and wild-type mice. These data have established that kuru prions have prion strain properties equivalent to those of classical (sporadic and iatrogenic) CJD prions but distinct from variant CJD prions. Here, we review these findings and discuss how peripheral routes of infection and other factors may be critical modifiers of the kuru phenotype.

Central and peripheral pathology of kuru: pathological analysis of a recent case and comparison with other forms of human prion disease

While the neuropathology of kuru is well defined, there are few data concerning the distribution of disease-related prion protein in peripheral tissues. Here we report the investigation of brain and peripheral tissues from a kuru patient who died in 2003. Neuropathological findings were compared with those seen in classical (sporadic and iatrogenic) Creutzfeldt–Jakob disease (CJD) and variant CJD (vCJD). The neuropathological findings of the kuru patient showed all the stereotypical changes that define kuru, with the occurrence of prominent PrP plaques throughout the brain. Lymphoreticular tissue showed no evidence of prion colonization, suggesting that the peripheral pathogenesis of kuru is similar to that seen in classical CJD rather than vCJD. These findings now strongly suggest that the characteristic peripheral pathogenesis of vCJD is determined by prion strain type alone rather than route of infection.

Ultrastructural study of florid plaques in variant Creutzfeldt-Jakob disease: a comparison with amyloid plaques in kuru, sporadic Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheinker disease

BACKGROUND

Although the histological features of the amyloid plaques in variant Creutzfeldt-Jakob disease (vCJD) are distinct from those in other forms of prion disease [kuru, sporadic Creutzfeldt-Jakob disease (sCJD) and Gerstmann-Sträussler-Scheinker disease (GSS)], their ultrastructural features have only been described in a single case report.

AIMS

To study vCJD plaques systematically and compare them with plaques in kuru, sCJD, GSS and Alzheimer disease (AD).

METHODS

Amyloid plaques were studied by transmission electron microscopy and image analysis in five cases of vCJD, three cases of GSS, two cases of sCJD, one case of kuru and five cases of AD. Immunohistochemistry was performed on paraffin sections from one case of vCJD, two cases of GSS, one case of kuru and two cases of sCJD.

RESULTS

The florid plaques in vCJD were either compact or more diffuse; in both forms, the radiating fibrils were organized into thick 'tongues', in contrast to kuru plaques. Dystrophic neurites (DNs) containing lysosomal electron-dense bodies or vesicles surrounded florid plaques. Microglial cells were found within florid plaques; occasional amyloid fibrils were identified in membrane-bound pockets of microglial cells. In vCJD, there was significant tau immunoreactivity in DNs around florid plaques while, in sCJD, GSS and kuru, minimal tau immunoreactivity was observed around plaques.

CONCLUSIONS

The ultrastructure of the florid plaques and DNs in vCJD is more reminiscent of neuritic plaques in AD than kuru or multicentric plaques. These findings may reflect differences both in the strains of the transmissible agents responsible for these disorders and in host factors.

Kuru prions and sporadic Creutzfeldt-Jakob disease prions have equivalent transmission properties in transgenic and wild-type mice

Kuru provides our principal experience of an epidemic human prion disease and primarily affected the Fore linguistic group of the Eastern Highlands of Papua New Guinea. Kuru was transmitted by the practice of consuming dead relatives as a mark of respect and mourning (transumption). To date, detailed information of the prion strain type propagated in kuru has been lacking. Here, we directly compare the transmission properties of kuru prions with sporadic, iatrogenic, and variant Creutzfeldt-Jakob disease (CJD) prions in Prnp-null transgenic mice expressing human prion protein and in wild-type mice. Molecular and neuropathological data from these transmissions show that kuru prions are distinct from variant CJD and have transmission properties equivalent to those of classical (sporadic) CJD prions. These findings are consistent with the hypothesis that kuru originated from chance consumption of an individual with sporadic CJD.

Variant Creutzfeldt-Jakob disease: prion protein genotype analysis of positive appendix tissue samples from a retrospective prevalence study

OBJECTIVE

To perform prion protein gene (PRNP) codon 129 analysis in DNA extracted from appendix tissue samples that had tested positive for disease associated prion protein.

DESIGN

Reanalysis of positive cases identified in a retrospective anonymised unlinked prevalence study of variant Creutzfeldt-Jakob disease (vCJD) in the United Kingdom.

STUDY SAMPLES

Three positive appendix tissue samples out of 12,674 samples of appendix and tonsil tested for disease associated prion protein. The patients from whom these samples were obtained were aged 20-29 years at the time of surgery, which took place in 1996-9.

SETTING

Pathology departments in two tertiary centres in England and Scotland.

RESULTS

Adequate DNA was available for analysis in two of the three specimens, both of which were homozygous for valine at codon 129 in the PRNP.

CONCLUSIONS

This is the first indication that the valine homozygous subgroup at codon 129 in the PRNP is susceptible to vCJD infection. All tested clinical cases of vCJD have so far occurred in the methionine homozygous subgroup, and a single case of probable iatrogenic vCJD infection has been identified in one patient who was a methionine/valine heterozygote at this genetic locus. People infected with vCJD with a valine homozygous codon 129 PRNP genotype may have a prolonged incubation period, during which horizontal spread of the infection could occur either from blood donations or from contaminated surgical instruments used on these individuals during the asymptomatic phase of the illness.

Size frequency distribution of prion protein (PrP) aggregates in variant Creutzfeldt-Jakob disease (vCJD)

The frequency distribution of aggregate size of the diffuse and florid-type prion protein (PrP) plaques was studied in various brain regions in cases of variant Creutzfeldt-Jakob disease (vCJD). The size distributions were unimodal and positively skewed and resembled those of beta-amyloid (A beta) deposits in Alzheimer's disease (AD) and Down's syndrome (DS). The frequency distributions of the PrP aggregates were log-normal in shape, but there were deviations from the expected number of plaques in specific size classes. More diffuse plaques were observed in the modal size class and fewer in the larger size classes than expected and more florid plaques were present in the larger size classes compared with the log-normal model. It was concluded that the growth of the PrP aggregates in vCJD does not strictly follow a log-normal model, diffuse plaques growing to within a more restricted size range and florid plaques to larger sizes than predicted.

Immunohistochemical comparison of anti-prion protein (PrP) antibodies in the CNS of mice infected with scrapie

One of the pathological changes characteristic of the transmissible spongiform encephalopathies (TSEs) is the accumulation of disease-specific PrP (PrP(sc)). Immunolabeling of PrP(sc) was compared using a panel of monoclonal and polyclonal antibodies. To determine the effects of tissue fixation on immunostaining, we performed a supplementary investigation reviewing the fixatives formol saline and periodate-lysine-paraformaldehyde (PLP). The main target sites of the antibodies were similar. However the monoclonal antibodies (MAbs) 6H4, 7A12 and 8H4 revealed targeted PrP(sc) labeling with no background labeling. Although 7A12 and 8H4 did not detect early PrP deposition, we propose that during the later stages of disease 7A12 and 8H4 can be used with equal effectiveness in place of 6H4. Tissues taken during the early stages of disease that had been fixed in PLP displayed more PrP immunolabeling than tissues that had undergone formol fixation. PLP fixation on 6H4-immunostained tissue revealed interweaving granular linear PrP deposits in the hippocampus. This labeling was not observed in tissue that had undergone formol fixation, suggesting that PLP fixation might enhance the sensitivity of the immunohistochemical (IHC) detection of PrP. In the two scrapie mouse models studied here, PLP fixation and immunolabeling with the anti-PrP antibody 6H4 gave superior results.

Synaptic pathology and cell death in the cerebellum in Creutzfeldt-Jakob disease

Prion protein (PrP(c)) is a cell membrane glycoprotein particularly abundant in the synapses. Prion diseases are characterized by the replacement of the normal PrPc by a protease-resistant, sheet-containing isoform (PrP(CJD), PrP(Sc), PrP(BSE)) that is pathogenic. Creutzfeldt-Jakob disease (CJD) in humans, scrapie (Sc) in sheep and goats, and bovine spongiform encephalopathy (BSE) in cattle are typical prion diseases. Classical CJD can be presented as sporadic, infectious or familial, whereas the new variant of CJD (nvCJD) is considered a BSE-derived human disease. Spongiform degeneration, glial proliferation, involving astrocytes and microglia, neuron loss and abnormal PrP deposition are the main neuopathological findings in most human and animal prion diseases. Yet recent data point to synapses as principal targets of abnormal PrP deposition. Loss of synapses is an early abnormality in experimental scrapie. Decreased expression of crucial proteins linked to exocytosis and neurotransmission, covering synaptophysin, synaptosomal-associated protein of 25,000 mol wt (SNAP-25), synapsins, syntaxins and Rab3a occurs in the cerebral cortex and cerebellum in sporadic CJD. Moreover, impairment of glomerular synapses and attenuation of parallel fiber pre-synaptic terminals on Purkinje cell dendrites is a cardinal consequence of abnormal PrP metabolism in CJD. Accumulation of synaptic proteins in the soma and axonal torpedoes of Purkinje cells suggests additional impairment of axonal transport. Increase in nuclear DNA vulnerability leading to augmented numbers of cells bearing nuclear DNA fragments is a common feature in the brains of humans affected by prion diseases examined at post-mortem, but also in archival biopsy samples processed with the method of in situ end-labeling of nuclear DNA fragmentation. This form of cell death is reminiscent of apoptosis found in experimental scrapie in rodents. It is not clear that all forms of cell death in human and animal prion diseases are due to apoptosis. Yet new observations have shown cleaved (active) caspase-3 (17 kDa), a main executioner of apoptosis, expressed in scattered cells in the brains of mice with experimental scrapie and in the cerebellum of patients with sporadic CJD. Together, these data suggest activation of the caspase pathway of apoptosis in human and animal prion diseases.

Kuru: the old epidemic in a new mirror

The kuru epidemic lasted almost a century; it started in 1901-1902, reached epidemic proportions in the mid-1950s, and disappeared in the 1990s. Kuru is the prototype member of a group of disorders known as transmissible spongiform encephalopathies (TSEs) or prion diseases. Recent data on the genetics and pathogenesis of TSEs contribute to a better understanding of the documented kuru phenomena, and vice versa, observations made during the kuru epidemic are immensely helpful in understanding the epidemic of variant Creutzfeldt-Jakob disease that is currently developing in Europe. The major goal of this review is to identify and illustrate these points.

Gerstmann-Sträussler-Scheinker syndrome,fatal familial insomnia, and kuru: a review of these less common human transmissible spongiform encephalopathies

Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome (GSS), fatal familial insomnia (FFI) and kuru constitute major human prion disease phenotypes. Each has been successfully transmitted in animal models and all are invariably fatal neurodegenerative disorders, with the brains of affected individuals harbouring variable amounts of an abnormal, protease-resistant form of the prion protein (PrPres), which is inextricably linked to pathogenesis and transmissibility. Classical sporadic CJD is the most common human transmissible spongiform encephalopathy (TSE), but recently the variant form (vCJD), first described in the UK in 1996, has drawn considerable attention. In contrast to sporadic CJD, FFI and GSS are almost invariably genetically determined TSEs, caused by a range of mutations within the open reading frame of the prion protein gene (PRNP) on chromosome 20. By definition, the nosologic term FFI is reserved for patients manifesting prominent insomnia, generally in combination with dysautonomia, myoclonus, and eventual dementia, with the predominant pathologic changes lying within the thalami and a specific underlying mutation in PRNP. GSS, however, encompasses a more diverse clinical spectrum ranging from progressive cerebellar ataxia or spastic paraparesis (both usually in combination with dementia), to isolated cognitive impairment resembling Alzheimer's disease. Additional extra-pyramidal features, which may respond to dopaminergic therapy can also be seen. Neuropathological findings are also relatively diverse, partly overlapping with those found in Alzheimer's disease, especially the presence of neurofibrillary tangles (NFTs). Although GSS and FFI in their classical forms are differentiable clinical profiles, such divisions may have no intrinsic biological validity given the considerable intra-familial clinico-pathological diversity so commonly seen. Kuru constitutes a horizontally transmitted prion disease, which after a lengthy incubation period, presents clinically as a progressive cerebellar ataxia associated with tremors. It has now almost disappeared since the cessation of ritualistic endocannibalism in the late 1950s but was previously exclusively endemic amongst the Fore linguistic group and neighbouring tribes in the Eastern Highlands of New Guinea. Uniform topographical central nervous system histopathology includes spongiform change and neuronal loss, with amyloid (kuru) plaques in approximately 75% of cases.

Sporadic Creutzfeldt-Jakob disease in a young Dutch valine homozygote: atypical molecular phenotype

A case of sporadic Creutzfeldt-Jakob disease (sCJD) is described in a young Dutch protein prion gene (PRNP) codon 129 valine homozygote. Certain clinical and molecular features of this case overlap those of variant CJD. The case highlights possible difficulties in the differential diagnosis of vCJD and the more rare sCJD subtypes based on molecular features alone.

Variant Creutzfeldt-Jakob disease: immunocytochemical studies and image analysis

Variant Creutzfeldt-Jakob disease (vCJD) is a recently identified human prion disease that appears to arise from exposure to the bovine spongiform encephalopathy agent. The clinical features and neuropathology of vCJD are distinctive, particularly the patterns of PrP(sc) accumulation in the brain. PrP immunocytochemistry has also demonstrated the accumulation of PrP(sc) in tissues outside the central nervous system, including sensory ganglia and lymphoid tissues. These observations have allowed the use of tonsillar biopsy as an investigation to aid the diagnosis of vCJD, since accumulation of PrP(sc) in lymphoid tissues does not occur in other forms of human prion disease. The patterns of PrP(sc) accumulation in vCJD can be studied by image analysis techniques, using both quantitative and qualitative approaches. Preliminary results of textural analysis are presented, which indicate that this approach can be used to discriminate and study the unique features of PrP(sc) accumulation in the brain in vCJD. This technique has major potential as a research tool in human prion diseases, particularly for the characterisation of disease phenotype in large series of cases.

Intracerebral distribution of the abnormal isoform of the prion protein in sporadic Creutzfeldt-Jakob disease and fatal insomnia

Molecular genetics and protein chemistry have led to major advances in our understanding of the molecular basis of phenotypic variability of prion diseases. A large body of evidence indicates that a common methionine/valine polymorphism at codon 129 in the prion protein gene (PRNP), alone or in conjunction with PRNP mutations, modulates both disease susceptibility and phenotypic expression of human prion diseases. In addition, there are physicochemical properties of the abnormal isoform of the prion protein (PrP(sc)), such as relative molecular mass and glycosylation, that correlate with distinct phenotypes even in subjects carrying the same PRNP genotype. Different PrP(sc) "type"-PRNP genotype combinations are found associated with pathological phenotypes that differ in the relative severity of lesions among distinct brain regions, the presence and morphology of certain lesions such as amyloid plaques, and the pattern of intracerebral and tissue deposition of PrP(sc). This review summarizes the currently available data on the molecular pathology of sporadic Creutzfeldt-Jakob disease, the most common human prion disease, and fatal insomnia, a more recently defined entity that has rapidly become one of the best characterized of the human prion diseases.

Immunohistochemical studies of the PrP(CJD) deposition in Creutzfeldt-Jakob disease

The PrP(CJD) deposition in eight brains of sporadic Creutzfeldt-Jakob disease (CJD) was examined immunohistochemically using both hydrolytic autoclaving and formic acid pretreatment in order to understand the pathogenesis of CJD. Synaptic-type PrP immunoreactivity was revealed in the gray matter in all cases and had a tendency to be weaker in devastated areas in cases with a longer duration of illness. However, in one particular case with numerous prion plaques, the degeneration was relatively mild while PrP(CJD) immunoreactivity was intense despite the longest duration of illness among the examined cases. Deep layer accentuation of PrP(CJD) immunoreactivity was observed in the cerebral cortices in most cases. This staining pattern, however, disappeared in a burnt-out lesion exhibiting status spongiosus. The granular layer was damaged mostly in the cerebellum of the advanced cases. PrP(CJD) and synaptophysin immunoreactivities decreased as the tissue degeneration progressed. Interestingly, the Purkinje cells had no positivity for PrP(CJD) in all cases, although the neurons in relatively preserved cerebellum showed apparent positivity for synaptophysin. In the Ammon's horn and subiculum the neurons were well preserved despite the marked immunoreactivity for PrP(CJD) in all cases, although some cases demonstrated severe spongiform change. Approximately half of the cases showed intracytoplasmic inclusion body-like immunoreactivity for PrP(CJD) in neurons of the dentate nucleus. These findings suggest that PrP(CJD) deposition may be an event that precedes neuronal degeneration evolving from deeper layers of the cerebral cortex. Although the Ammon's horn and subiculum showed striking PrP(CJD) deposition and spongiform change, neuronal loss did not take place, suggesting that deposited PrP(CJD) itself seems not to be directly harmful to the neurons. Some investigators have assumed that microglia activated by PrP(CJD) plays an important role in neuronal degeneration. Considering this, we speculate that microglia in the Ammon's horn and subiculum may have a unique characteristic of not responding to PrP(CJD).

A case of sporadic Creutzfeldt-Jakob disease with both plaque and synaptic-type deposition of prion protein

We report a Japanese case of sporadic Creutzfeldt-Jakob disease (CJD) with particular clinical course and neuropathological findings. A 74-year-old female exhibited parkinsonism and later, dementia, myoclonus as well as visual hallucinations, lacking periodic synchronous discharges in the electroencephalogram. The duration of her illness was 2 years, longer than typical CJD cases which average 8 months' duration. Gray matter was severely affected, the Ammon's horn and subicular cortex were well preserved and many kuru plaques were observed in the cerebellum using routine histological stainings. Immunohistochemistry for prion protein (PrP) using both formic acid and hydrolytic autoclaving pretreatment revealed numerous prion plaques throughout the brain together with intense synaptic-type deposition of PrPCJD (abnormal isoform of PrP) in all gray matter examined, particularly in the Ammon's horn and subicular cortex. The definite combination of these two types of stain has never been reported previously in Japan other than in Gerstmann-Sträussler-Scheinker syndrome. Relative resistance of the Ammon's horn and subicular cortex to the PrPCJD deposition is also discussed.

Phenotype-genotype studies in kuru: implications for new variant Creutzfeldt-Jakob disease

The PRNP polymorphic (methionine/valine) codon 129 genotype influences the phenotypic features of transmissible spongiform encephalopathy. All tested cases of new variant Creutzfeldt-Jakob disease (nvCJD) have been homozygous for methionine, and it is conjectural whether different genotypes, if they appear, might have distinctive phenotypes and implications for the future "epidemic curve" of nvCJD. Genotype-phenotype studies of kuru, the only other orally transmitted transmissible spongiform encephalopathy, might be instructive in predicting the answers to these questions. We therefore extracted DNA from blood clots or sera from 92 kuru patients, and analyzed their codon 129 PRNP genotypes with respect to the age at onset and duration of illness and, in nine cases, to detailed clinical and neuropathology data. Homozygosity at codon 129 (particularly for methionine) was associated with an earlier age at onset and a shorter duration of illness than was heterozygosity, but other clinical characteristics were similar for all genotypes. In the nine neuropathologically examined cases, the presence of histologically recognizable plaques was limited to cases carrying at least one methionine allele (three homozygotes and one heterozygote). If nvCJD behaves like kuru, future cases (with longer incubation periods) may begin to occur in older individuals with heterozygous codon 129 genotypes and signal a maturing evolution of the nvCJD "epidemic." The clinical phenotype of such cases should be similar to that of homozygous cases, but may have less (or at least less readily identified) amyloid plaque formation.