Prion protein mutation in family first reported by Gerstmann, Sträussler, and Scheinker

[Gerstmann-Sträussler disease: a familial case with common PRNP mutation and atypical features]

Gerstmann-Sträussler disease (GSD) is a very rare autosomal dominant late-onset neurodegenerative disorder related to prion protein gene PRNP. Mutation p.Pro102Leu produces about 80% of cases, which are often named GSD-102. DNA testing provides exact diagnosis. In the presented Russian family there were 3 patients: a female index case, age 32 years, her brother, age 37 years (age of onset in both is 27 years) and their deceased father (onset in 35 years, death in 44 years). GSD was not suspected until whole exome sequencing in the female detected PRNP mutation p.Pro102Leu confirmed in her and in the brother by Sanger sequencing. Atypical features of the case are: early onset in siblings, absence of mental and behavioral problems in the female and in the father and mild disturbances in the brother; epilepsy in the brother; atypical onset with transient signs in the brother. Other intrafamilial differences are prevailing spastic paraparesis in the female in contrast to predominant ataxia in the brother and dysarthria absence in the female. The case illustrates GSD-102 variability, complicating clinical diagnostics.

Shortening heparan sulfate chains prolongs survival and reduces parenchymal plaques in prion disease caused by mobile, ADAM10-cleaved prions

Cofactors are essential for driving recombinant prion protein into pathogenic conformers. Polyanions promote prion aggregation in vitro, yet the cofactors that modulate prion assembly in vivo remain largely unknown. Here we report that the endogenous glycosaminoglycan, heparan sulfate (HS), impacts prion propagation kinetics and deposition sites in the brain. Exostosin-1 haploinsufficient (Ext1^+/-) mice, which produce short HS chains, show a prolonged survival and a redistribution of plaques from the parenchyma to vessels when infected with fibrillar prions, and a modest delay when infected with subfibrillar prions. Notably, the fibrillar, plaque-forming prions are composed of ADAM10-cleaved prion protein lacking a glycosylphosphatidylinositol anchor, indicating that these prions are mobile and assemble extracellularly. By analyzing the prion-bound HS using liquid chromatography-mass spectrometry (LC-MS), we identified the disaccharide signature of HS differentially bound to fibrillar compared to subfibrillar prions, and found approximately 20-fold more HS bound to the fibrils. Finally, LC-MS of prion-bound HS from human patients with familial and sporadic prion disease also showed distinct HS signatures and higher HS levels associated with fibrillar prions. This study provides the first in vivo evidence of an endogenous cofactor that accelerates prion disease progression and enhances parenchymal deposition of ADAM10-cleaved, mobile prions.

Gerstmann-Sträussler-Scheinker disease: A case report

BACKGROUND

Gerstmann-Sträussler-Scheinker (GSS) disease is an inherited prion disease that is clinically characterized by the early onset of progressive cerebellar ataxia. The incidence of GSS is extremely low and it is particularly rare in China. Therefore, clinicians may easily confuse this disease with other diseases that also cause ataxia, resulting in its under-diagnosis or misdiagnosis.

CASE SUMMARY

Here, we report the first case of genetically diagnosed GSS disease in Northeast China. The patient exhibited typical ataxia and dysarthria 2.5 years after symptom onset. However, magnetic resonance imaging of the brain and spinal cord revealed a normal anatomy. Screening results for the spinocerebellar ataxia gene were also negative. We thus proposed to expand the scope of genetic screening to include over 200 mutations that can cause ataxia. A final diagnosis of GSS was presented and the patient was followed for more than 3.5 years, during which we noted imaging abnormalities. The patient gradually exhibited decorticate posturing and convulsions. We recommended administration of oral sodium valproate, which resolved the convulsions.

CONCLUSION

Patients with inherited ataxia should be considered for a diagnosis of GSS via genetic testing at an early disease stage.

Dominantly inherited prion protein cerebral amyloidoses - a modern view of Gerstmann-Sträussler-Scheinker

Among genetically determined neurodegenerative diseases, the dominantly inherited prion protein cerebral amyloidoses are characterized by deposition of amyloid in cerebral parenchyma or blood vessels. Among them, Gerstmann-Sträussler-Scheinker disease has been the first to be described. Their clinical, neuropathologic, and molecular phenotypes are distinct from those observed in Creutzfeldt-Jakob disease (CJD) and related spongiform encephalopathies. It is not understood why specific mutations in the prion protein gene (PRNP) cause cerebral amyloidosis and others cause CJD. A significant neurobiologic event in these amyloidoses is the frequent coexistence of prion amyloid with tau neurofibrillary pathology, a phenomenon suggesting that similar pathogenetic mechanisms may be shared among different diseases in the sequence of events occurring in the cascade from amyloid formation to tau aggregation. This chapter describes the clinical, neuropathologic, and biochemical phenotypes associated with each of the PRNP mutations causing an inherited cerebral amyloidosis and emphasizes the variability of phenotypes.

High phenotypic variability in Gerstmann-Sträussler-Scheinker disease

Gerstmann-Sträussler-Scheinker is a genetic prion disease and the most common mutation is p.Pro102Leu. We report clinical, molecular and neuropathological data of seven individuals, belonging to two unrelated Brazilian kindreds, carrying the p.Pro102Leu. Marked differences among patients were observed regarding age at onset, disease duration and clinical presentation. In the first kindred, two patients had rapidly progressive dementia and three exhibited predominantly ataxic phenotypes with variable ages of onset and disease duration. In this family, age at disease onset in the mother and daughter differed by 39 years. In the second kindred, different phenotypes were also reported and earlier ages of onset were associated with 129 heterozygosis. No differences were associated with apoE genotype. In these kindreds, the codon 129 polymorphism could not explain the clinical variability and 129 heterozygosis was associated with earlier disease onset. Neuropathological examination in two patients confirmed the presence of typical plaques and PrPsc immunopositivity.

Thalamic involvement determined using VSRAD advance on MRI and easy Z-score analysis of 99mTc-ECD-SPECT in Gerstmann-Sträussler-Scheinker syndrome with P102L mutation

Gerstmann-Sträussler-Scheinker syndrome caused by the P102L mutation in the prion protein gene (GSS102) is usually characterized by the onset of slowly progressive cerebellar ataxia, with dementia occurring much later. Because of the relatively long disease course and the prominence of progressive cerebellar ataxia in the early stage, GSS102 is often misdiagnosed as other neurodegenerative disorders. We present two cases of genetically proven GSS102L, both of which present with atrophy and decreased blood flow of the thalamus as determined by voxel-based specific regional analysis system for Alzheimer's disease (VSRAD) advance software and easy Z-score analysis for ^99mTc-ethyl cysteinate dimer-SPECT, respectively. These thalamic abnormalities have not been fully evaluated to date, and detecting them might be useful for differentiating GSS102 from other neurodegenerative disorders.

Prion protein scrapie and the normal cellular prion protein

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

Transmission Properties of Human PrP 102L Prions Challenge the Relevance of Mouse Models of GSS

Inherited prion disease (IPD) is caused by autosomal-dominant pathogenic mutations in the human prion protein (PrP) gene (PRNP). A proline to leucine substitution at PrP residue 102 (P102L) is classically associated with Gerstmann-Sträussler-Scheinker (GSS) disease but shows marked clinical and neuropathological variability within kindreds that may be caused by variable propagation of distinct prion strains generated from either PrP 102L or wild type PrP. To-date the transmission properties of prions propagated in P102L patients remain ill-defined. Multiple mouse models of GSS have focused on mutating the corresponding residue of murine PrP (P101L), however murine PrP 101L, a novel PrP primary structure, may not have the repertoire of pathogenic prion conformations necessary to accurately model the human disease. Here we describe the transmission properties of prions generated in human PrP 102L expressing transgenic mice that were generated after primary challenge with ex vivo human GSS P102L or classical CJD prions. We show that distinct strains of prions were generated in these mice dependent upon source of the inoculum (either GSS P102L or CJD brain) and have designated these GSS-102L and CJD-102L prions, respectively. GSS-102L prions have transmission properties distinct from all prion strains seen in sporadic and acquired human prion disease. Significantly, GSS-102L prions appear incapable of transmitting disease to conventional mice expressing wild type mouse PrP, which contrasts strikingly with the reported transmission properties of prions generated in GSS P102L-challenged mice expressing mouse PrP 101L. We conclude that future transgenic modeling of IPDs should focus exclusively on expression of mutant human PrP, as other approaches may generate novel experimental prion strains that are unrelated to human disease.

Inherited prion disease (IPD) is caused by pathogenic mutations in the human prion protein (PrP) gene leading to the formation of lethal prions in the brain. To-date the properties of prions causing IPD and their similarities to prions causing other forms of human prion disease remain ill-defined. In the present study we have investigated the properties of prions seen in patients with Gerstmann-Sträussler-Scheinker (GSS) disease associated with the substitution of leucine for proline at amino acid position 102 (GSS P102L). We examined the ability of these prions to infect transgenic mice expressing human mutant 102L PrP, human wild-type PrP or wild-type mice. We found that GSS-102L prions have properties distinct from other types of human prions by showing that they can only infect transgenic mice expressing human PrP carrying the same mutation. Mice expressing wild-type human PrP or wild-type mouse PrP were entirely resistant to infection with GSS-102L prions. We conclude that accurate modeling of inherited prion disease requires the expression of authentic mutant human PrP in transgenic models, as other approaches may generate results that do not mirror the human disease.

Gerstmann-Sträussler-Scheinker syndrome with the P102L pathogenic mutation presenting as familial Creutzfeldt-Jakob disease: a case report and review of the literature

Gerstmann-Sträussler-Scheinker syndrome is a rare autosomal dominant disease caused by a mutation in the prion gene, usually manifesting as progressive ataxia with late cognitive decline. A 44-year-old woman with a positive family history developed early personality and behavior changes, followed by paresthesias and ataxia, later associated with memory problems, pyramidal signs, anosognosia and very late myoclonus, spasticity, and severe dysexecutive impairment. Magnetic resonance showed caudate, mesio-frontal, and insular hyper-intensities, electroencephalography revealed generalized triphasic periodic complexes. A pathogenic P102L mutation in the prion gene was detected. Our case differed from classical Gerstmann-Sträussler-Scheinker syndrome by rapid progression, severe dementia, abnormal electroencephalography and magnetic resonance findings, which were highly suggestive of familial Creutzfeldt-Jakob disease.

Gerstmann-Sträussler-Scheinker disease

Gerstmann-Sträussler-Scheinker (GSS) is a slowly progressive hereditary autosomal dominant disease (OMIM: 137440) and the first human transmissible spongiform encephalopathy (TSE) in which a mutation in a gene encoding for prion protein (PrP) was discovered. The first "H" family had been known by the Viennese neuropsychiatrists since the XXth century and was reported by Gerstmann, Sträussler and Scheinker in 1936. In this chapter we present the clinical, neuropathological and molecular data on GSS with the mutations in the PRNP gene: at codons 102, 105, 117, 131, 145, 187, 198, 202, 212, 217 and 232. In several families with GSS the responsible mutations are unknown.

Human prion diseases: from Kuru to variant Creutzfeldt-Jakob disease

Transmissible spongiform encephalopathies (TSEs) or prion diseases are the names given to the group of fatal neurodegenerative disorders that includes kuru, Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker disease (GSS), fatal and sporadic familial insomnia and the novel prion disease variable protease-sensitive prionopathy (PSPr) in humans. Kuru was restricted to natives of the Foré linguistic group in Papua New Guinea and spread by ritualistic endocannibalism. CJD appears as sporadic, familial (genetic or hereditary) and infectious (iatrogenic) forms. Variant CJD is a zoonotic CJD type and of major public health importance, which resulted from transmission from bovine spongiform encephalopathy (BSE) through ingestion of contaminated meat products. GSS is a slowly progressive hereditary autosomal dominant disease and the first human TSE in which a mutation in a gene encoding for prion protein (PrP) was discovered. The rarest human prion disease is fatal insomnia, which may occur, in genetic and sporadic form. More recently a novel prion disease variable protease-sensitive prionopathy (PSPr) was described in humans.TSEs are caused by a still incompletely defined infectious agent known as a "prion" which is widely regarded to be an aggregate of a misfolded isoform (PrP(Sc)) of a normal cellular glycoprotein (PrP(c)). The conversion mechanism of PrP(c) into PrP(Sc) is still not certain.

Prions

The discovery of infectious proteins, denoted prions, was unexpected. After much debate over the chemical basis of heredity, resolution of this issue began with the discovery that DNA, not protein, from pneumococcus was capable of genetically transforming bacteria (Avery et al. 1944). Four decades later, the discovery that a protein could mimic viral and bacterial pathogens with respect to the transmission of some nervous system diseases (Prusiner 1982) met with great resistance. Overwhelming evidence now shows that Creutzfeldt-Jakob disease (CJD) and related disorders are caused by prions. The prion diseases are characterized by neurodegeneration and lethality. In mammals, prions reproduce by recruiting the normal, cellular isoform of the prion protein (PrP(C)) and stimulating its conversion into the disease-causing isoform (PrP(Sc)). PrP(C) and PrP(Sc) have distinct conformations: PrP(C) is rich in α-helical content and has little β-sheet structure, whereas PrP(Sc) has less α-helical content and is rich in β-sheet structure (Pan et al. 1993). The conformational conversion of PrP(C) to PrP(Sc) is the fundamental event underlying prion diseases. In this article, we provide an introduction to prions and the diseases they cause.

The prion diseases

The prion diseases are a family of rare neurodegenerative disorders that result from the accumulation of a misfolded isoform of the prion protein (PrP), a normal constituent of the neuronal membrane. Five subtypes constitute the known human prion diseases; kuru, Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome (GSS), fatal insomnia (FI), and variant CJD (vCJD). These subtypes are distinguished, in part, by their clinical phenotype, but primarily by their associated brain histopathology. Evidence suggests these phenotypes are defined by differences in the pathogenic conformation of misfolded PrP. Although the vast majority of cases are sporadic, 10% to 15% result from an autosomal dominant mutation of the PrP gene (PRNP). General phenotype-genotype correlations can be made for the major subtypes of CJD, GSS, and FI. This paper will review some of the general background related to prion biology and detail the clinical and pathologic features of the major prion diseases, with a particular focus on the genetic aspects that result in prion disease or modification of its risk or phenotype.

A Drosophila model of GSS syndrome suggests defects in active zones are responsible for pathogenesis of GSS syndrome

We have established a Drosophila model of Gerstmann-Sträussler-Scheinker (GSS) syndrome by expressing mouse prion protein (PrP) having leucine substitution at residue 101 (MoPrP(P101L)). Flies expressing MoPrP(P101L), but not wild-type MoPrP (MoPrP(3F4)), showed severe defects in climbing ability and early death. Expressed MoPrP(P101L) in Drosophila was differentially glycosylated, localized at the synaptic terminals and mainly present as deposits in adult brains. We found that behavioral defects and early death of MoPrP(P101L) flies were not due to Caspase 3-dependent programmed cell death signaling. In addition, we found that Type 1 glutamatergic synaptic boutons in larval neuromuscular junctions of MoPrP(P101L) flies showed significantly increased numbers of satellite synaptic boutons. Furthermore, the amount of Bruchpilot and Discs large in MoPrP(P101L) flies was significantly reduced. Brains from scrapie-infected mice showed significantly decreased ELKS, an active zone matrix marker compared with those of age-matched control mice. Thus, altered active zone structures at the molecular level may be involved in the pathogenesis of GSS syndrome in Drosophila and scrapie-infected mice.

Absence of spontaneous disease and comparative prion susceptibility of transgenic mice expressing mutant human prion proteins

Approximately 15 % of human prion disease is associated with autosomal-dominant pathogenic mutations in the prion protein (PrP) gene. Previous attempts to model these diseases in mice have expressed human PrP mutations in murine PrP, but this may have different structural consequences. Here, we describe transgenic mice expressing human PrP with P102L or E200K mutations and methionine (M) at the polymorphic residue 129. Although no spontaneous disease developed in aged animals, these mice were readily susceptible to prion infection from patients with the homotypic pathogenic mutation. However, while variant Creutzfeldt–Jakob disease (CJD) prions transmitted infection efficiently to both lines of mice, markedly different susceptibilities to classical (sporadic and iatrogenic) CJD prions were observed. Prions from E200K and classical CJD M129 homozygous patients, transmitted disease with equivalent efficiencies and short incubation periods in human PrP 200K, 129M transgenic mice. However, mismatch at residue 129 between inoculum and host dramatically increased the incubation period. In human PrP 102L, 129M transgenic mice, short disease incubation periods were only observed with transmissions of prions from P102L patients, whereas classical CJD prions showed prolonged and variable incubation periods irrespective of the codon 129 genotype. Analysis of disease-related PrP (PrP^Sc) showed marked alteration in the PrP^Sc glycoform ratio propagated after transmission of classical CJD prions, consistent with the PrP point mutations directly influencing PrP^Sc assembly. These data indicate that P102L or E200K mutations of human PrP have differing effects on prion propagation that depend upon prion strain type and can be significantly influenced by mismatch at the polymorphic residue 129.

Transgenic and knockout mice in research on prion diseases

Since the discovery of the prion protein (PrP) gene more than a decade ago, transgenetic investigations on the PrP gene have shaped the field of prion biology in an unprecedented way. Many questions regarding the role of PrP in susceptibility of an organism exposed to prions have been elucidated. For example mice with a targeted disruption of the PrP gene have allowed the demonstration that an organism that lacks PrPc is resistant to infection by prions. Reconstitution of these mice with mutant PrP genes allowed investigations on the structure-activity relationship of the PrP gene with regard to scrapie susceptibility. Unexpectedly, transgenic mice expressing PrP with specific amino-proximal truncations spontaneously develop a neurologic syndrome presenting with ataxia and cerebellar lesions. A distinct spontaneous neurologic phenotype was observed in mice with internal deletions in PrP. Using ectopic expression of PrP in PrP knockout mice has turned out to be a valuable approach towards the identification of host cells that are capable of replicating prions. Transgenic mice have also contributed to our understanding of the molecular basis of the species barrier for prions. Finally, the availability of PrP knockout mice and transgenic mice overexpressing PrP allows selective reconstitution experiments aimed at expressing PrP in neurografts or in specific populations of hemato- and lymphopoietic cells. Such studies have shed new light onto the mechanisms of prion spread and disease pathogenesis.

Neuropathological features of a case with schizophrenia and prion protein gene P102L mutation before onset of Gerstmann-Sträussler-Scheinker disease

Gerstmann-Sträussler-Scheinker disease (GSS) is a hereditary transmissible spongiform encephalopathy associated with prion protein gene mutation P102L. The age of onset is roughly restricted to around the sixth decade; however, it is unclear whether the disease-specific pathology of GSS is already evident in the pre-clinical stage. We had a chance to examine an autopsy case with PRNP P102L mutation. The patient had died at 50 years of age before the clinical symptoms of GSS had appeared; neither neuronal loss, gliosis nor spongiform change was found anywhere in the brain. Immunohistochemistry failed to detect any deposition of prion protein. It is thus considered that amyloid plaque formation in GSS probably develops in a relatively rapid fashion compared with Alzheimer's disease. Although the patient suffered from schizophrenia, no significant pathological changes were detected except for astrocytic inclusion bodies in the cerebral cortex. The nature and significance of the inclusion bodies, which are not observed in patients with GSS, remain unclear.

Hereditary prion protein amyloidoses

Prion protein (PrP) amyloid accumulation is the pathologic hallmark of some inherited prion diseases such as Gerstmann-Sträussler-Scheinker disease (GSS) and PrP cerebral amyloid angiopathy (PrP-CAA). In GSS, parenchymal amyloidosis may coexist with spongiform degeneration or neurofibrillary tangles, whereas in PrP-CAA, vascular amyloid coexists with neurofibrillary tangles. In GSS, N-truncated and C-truncated proteinase K-resistant PrP isoforms are present in the brain.

Folding pathways of prion and doppel

The relevance of various residue positions for the stability and the folding characteristics of the prion protein in its normal cellular form are investigated by using molecular dynamics simulations of models exploiting the topology of the native state. These models allow for reproducing the experimentally validated two-state behavior of the normal prion isoform. Highly significant correlations are found between the most topologically relevant sites in our analysis and the single point mutations known to be associated with the arousal of the genetic forms of prion disease. Insight into the conformational change is provided by comparing the folding process of cellular prion and doppel that share a similar native state topology: the folding pathways of the former can be grouped in two main classes according to which tertiary structure contacts are formed first enroute to the native state. For the latter a single class of pathways leads to the native state again through a two-state process. Our results are consistent and supportive of the recent experimental findings that doppel lacks the scrapie isoform and that such remarkably different behavior involves residues in the region containing the two beta-strands and the intervening helix.

Disordered proteins in dementia

Aggregates of dysfunctional proteins and peptides in or between brain neurons are key neuropathological features of dementia and are believed to directly cause or substantially contribute to the development of these diseases. Fundamental parts of the mechanisms underlying the dysregulation of proteins in Alzheimer's disease, frontotemporal dementia, prion diseases and other dementing disorders are now well characterized, mainly due to the discovery of genes causing dominantly inherited disease forms (Table 1). As of today, no efficient pharmacotherapies are available, but new insights into the underlying molecular mechanisms are providing strategies to prevent or even cure these devastating disorders.

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.

Pathogenesis of prion diseases: a progress report

Almost 20 years have passed since Stanley Prusiner proposed that the agent causing transmissible spongiform encephalopathies consists exclusively of a protein and termed it prion. A mixed balance can be drawn from the enormous research efforts that have gone into prion research during this time. On the negative side, the protein-only hypothesis has not been conclusively proven yet. On the positive side, our understanding of spongiform encephalopathies has experienced tremendous advances, mostly through human genetics, mouse transgenetics, and biophysical methods. Perhaps the most astonishing development is the realization that many human neurodegenerative diseases for which transmissibility has been more or less stringently excluded, may follow pathogenetic principles similar to those of prion diseases. Also, the hypothesis that prion-like phenomena may underlie certain non-genetic traits observed in yeast has resulted in the surprising recognition that the instructional self-propagating changes in protein conformation may be much more prevalent in nature than previously thought. The latter developments have been astonishingly successful, and one could now argue that the prion principle is much more solidly established in yeast than in mammals.

Creutzfeldt-Jakob disease and the eye. I. Background and patient management

This article attempts to summarise our current understanding of TSEs as they affect man. Specific aspects relevant to ophthalmological practice, in particular the management of patients in day-to-day clinical practice and with respect to corneal transplantation, have been discussed. In the companion article we discuss the specific ophthalmic and neuro-ophthalmic features of these diseases.

Transmissible spongiform encephalopathies in humans

Creutzfeldt-Jakob disease (CJD), the first transmissible spongiform encephalopathy (TSE) to be described in humans, occurs in a sporadic, familial, or iatrogenic form. Other TSEs in humans, shown to be associated with specific prion protein gene mutations, have been reported in different parts of the world. These TSEs compose a heterogeneous group of familial diseases that traditionally have been classified as familial CJD, Gerstmann-Sträussler-Scheinker syndrome, or fatal familial insomnia. In 1996, a newly recognized variant form of CJD among young patients (median age, 28 years) with unusual clinical features and a unique neuropathologic profile was reported in the United Kingdom. In the absence of known CJD risk factors or prion protein gene abnormalities, the UK government concluded that the clustering of these cases may represent transmission to humans of the agent causing bovine spongiform encephalopathy. Additional epidemiologic and recent laboratory data strongly support the UK government's conclusion.

Creutzfeldt-Jakob disease, new variant creutzfeldt-jakob disease, and bovine spongiform encephalopathy

Creutzfeldt-Jakob disease (CJD) is a subacute spongiform encephalopathy (SSE) that is manifested by a variety of neurologic signs that usually include dementia, myoclonus, and an abnormal electroencephalogram (EEG). In 1996, a new variant of CJD (nvCJD) with a somewhat distinctive clinical presentation and neuropathology was reported in adolescents and young adults, a cohort of patients not normally affected with CJD. The appearance of nvCJD coincided temporally and geographically with the emergence of an SSE in cattle known as bovine spongiform encephalopathy (BSE), or mad cow disease. This article discusses the clinical syndrome, pathology, and pathogenesis of classical CJD, nvCJD, and other human SSEs, as well as the link between BSE and nvCJD.

The prion diseases: Creutzfeldt-Jakob, Gerstmann-Sträussler-Scheinker, and related disorders

The prion diseases are an interesting group of neurodegenerative disorders for a variety of reasons. The most obvious is their property of transmissibility, but beyond that they constitute a fascinating example of the diversity of disease expression possible from a common etiologic factor. Thought of as "strains" in animals and phenotypes in humans, these varied expressions of prion disease are most likely due to subtle conformational changes in the pathogenic form of the prion protein. These strain-like characteristics are best exemplified in the genetic varieties of human prion disease in which specific mutations are associated with specific phenotypic profiles. This review attempts to highlight the clinical and pathologic features of the prion diseases with a particular focus on the genetic determinants that define the various familial forms and that modify sporadic and iatrogenic forms of the disease.

Prions

Prions are unprecedented infectious pathogens that cause a group of invariably fatal neurodegenerative diseases by an entirely novel mechanism. Prion diseases may present as genetic, infectious, or sporadic disorders, all of which involve modification of the prion protein (PrP). Bovine spongiform encephalopathy (BSE), scrapie of sheep, and Creutzfeldt-Jakob disease (CJD) of humans are among the most notable prion diseases. Prions are transmissible particles that are devoid of nucleic acid and seem to be composed exclusively of a modified protein (PrPSc). The normal, cellular PrP (PrPC) is converted into PrPSc through a posttranslational process during which it acquires a high beta-sheet content. The species of a particular prion is encoded by the sequence of the chromosomal PrP gene of the mammals in which it last replicated. In contrast to pathogens carrying a nucleic acid genome, prions appear to encipher strain-specific properties in the tertiary structure of PrPSc. Transgenetic studies argue that PrPSc acts as a template upon which PrPC is refolded into a nascent PrPSc molecule through a process facilitated by another protein. Miniprions generated in transgenic mice expressing PrP, in which nearly half of the residues were deleted, exhibit unique biological properties and should facilitate structural studies of PrPSc. While knowledge about prions has profound implications for studies of the structural plasticity of proteins, investigations of prion diseases suggest that new strategies for the prevention and treatment of these disorders may also find application in the more common degenerative diseases.

The prion diseases

The human prion diseases are fatal neurodegenerative maladies that may present as sporadic, genetic, or infectious illnesses. The sporadic form is called Creutzfeldt-Jakob disease (CJD) while the inherited disorders are called familial (f) CJD, Gerstmann-Straussler-Scheinker (GSS) disease and fatal familial insomnia (FFI). Prions are transmissible particles that are devoid of nucleic acid and seem to be composed exclusively of a modified protein (PrPSc). The normal, cellular PrP (PrPC) is converted into PrPSc through a posttranslational process during which it acquires a high beta-sheet content. In fCJD, GSS, and FFI, mutations in the PrP gene located on the short arm of chromosome 20 are the cause of disease. Considerable evidence argues that the prion diseases are disorders of protein conformation.

Decade of the brain: neurological advances

In the last half century, neurological developments have been phenomenal and have escalated in this decade of the brain. Many infective disorders have been conquered, but AIDS has posed new challenges. Neuropharmacology has transformed the management of parkinsonism and epilepsy. New imaging techniques such as CT, NMR, PET and ultrasonic scanning have presented us with remarkable images of the nervous system in health and disease. Steroids control many autoimmune disorders; beta-interferon and other new drugs have begun to influence multiple sclerosis. Intensive care has saved many of those with head injury or acute neurological disorders, and we have greatly improved methods of rehabilitation. There are still many incurable neurological disorders but none are untreatable. Today's discovery in basic science brings tomorrow's improvement in patient care, as is clearly shown by molecular genetics. Some neurological and neuromuscular diseases in which the causal gene or genes have been located and characterised and in which the missing or abnormal gene product has been identified will be mentioned, as well as the prospects of carrier detection, antenatal diagnosis and gene therapy.

Genetics of prions

Prions are unprecedented infectious pathogens that cause a group of invariably fatal, neurodegenerative diseases by an entirely novel mechanism. Prion diseases may present as genetic, infectious, or sporadic disorders, all of which involve modification of the prion protein (PrP). The human prion disease Creutzfeldt-Jakob disease (CJD) generally presents as a progressive dementia, whereas scrapie of sheep and bovine spongiform encephalopathy (BSE) are manifest as ataxic illnesses. Prions are devoid of nucleic acid and seem to be composed exclusively of a modified isoform of PrP designated PrPSc. The normal, cellular PrP designated PrPC is converted into PrPSc through a process whereby some of its alpha-helical structure is converted into beta-sheet. The species of a particular prion is encoded by the sequence of the chromosomal PrP gene of the mammals in which it last replicated. In contrast to pathogens with a nucleic acid genome, prions encipher strain-specific properties in the tertiary structure of PrPSc. Transgenetic studies argue that PrPSc acts as a template upon which PrPC is refolded into a nascent PrPSc molecule through a process facilitated by another protein.

Prion diseases and the BSE crisis

Bovine spongiform encephalopathy (BSE) and human Creutzfeldt-Jakob disease (CJD) are among the most notable central nervous system degenerative disorders caused by prions. CJD may present as a sporadic, genetic, or infectious illness. Prions are transmissible particles that are devoid of nucleic acid and seem to be composed exclusively of a modified protein (PrPSc). The normal, cellular prion protein (PrPC) is converted into PrPSc through a posttranslational process during which it acquires a high beta-sheet content. It is thought that BSE is a result of cannibalism in which faulty industrial practices produced prion-contaminated feed for cattle. There is now considerable concern that bovine prions may have been passed to humans, resulting in a new form of CJD.

A Japanese family with a variant of Gerstmann-Sträussler-Scheinker disease

OBJECTIVE

A new variant of Gerstmann-Sträussler-Scheinker disease (GSS) was reported, which had a substitution of glutamate to lysine at codon 219 (E219K) in addition to a P102L mutation on the same allele of the PrP gene. However, clinical features were not detailed and pathological studies were not done. Unusual clinical, neuroradiological, and pathological findings are reported for these patients.

METHODS AND RESULTS

Clinical presentations of the patients in the same family were variable; progressive dementia with minimal ataxia in some patients but ataxia without dementia in others. PET studies with 18F-2-fluoro-2-deoxyglucose (FDG) disclosed a relative decrease of FDG uptake in bilateral temporoparietal cortices of a patient with dementia, but in the cerebellar cortices in a patient with ataxia. At necropsy, a patient with dementia had multicentric and diffuse plaques stained with PrP antiserum, but not with haematoxylin and eosin or Congo red, in the cerebral and cerebellar cortices.

CONCLUSION

Neurological and neuropathological features in the patients were atypical of the classic form of GSS with P102L mutation. The absence of Congo red staining prion protein plaques is probably attributable to E219K polymorphism on the same allele of the PrP gene.

Prion protein amyloidosis

The prion protein (PrP) plays an essential role in the pathogenesis of a group of sporadic, genetically determined and infectious fatal degenerative diseases, referred to as "prion diseases", affecting the central nervous system of humans and other mammals. The cellular PrP is encoded by a single copy gene, highly conserved across mammalian species. In prion diseases, PrP undergoes conformational changes involving a shift from alpha-helix to beta-sheet structure. This conversion is important for PrP amyloidogenesis, which occurs to the highest degree in the genetically determined Gerstmann-Sträussler-Scheinker disease (GSS) and prion protein cerebral amyloid angiopathy (PrP-CAA), while it is less frequently seen in other prion diseases. GSS and PrP-CAA are associated with point mutations of the prion protein gene (PRNP); these conditions show a broad spectrum of clinical presentation, the main signs being ataxia, spastic paraparesis, extrapyramidal signs and dementia. In GSS, parenchymal amyloid may be associated with spongiform changes or neurofibrillary lesions; in PrP-CAA, vascular amyloid is associated with neurofibrillary lesions. A major component of the amyloid fibrils in the two diseases is a 7 kDa peptide, spanning residues 81-150 of PrP.

Neuropathological diagnostic criteria for Creutzfeldt-Jakob disease (CJD) and other human spongiform encephalopathies (prion diseases)

Neuropathological diagnostic criteria for Creutzfeldt-Jakob disease (CJD) and other human transmissible spongiform encephalopathies (prion diseases) are proposed for the following disease entities: CJD--sporadic, iatrogenic (recognised risk) or familial (same disease in 1st degree relative): spongiform encephalopathy in cerebral and/or cerebellar cortex and/or subcortical grey matter; or encephalopathy with prion protein (PrP) immunoreactivity (plaque and/or diffuse synaptic and/or patchy/perivacuolar types). Gerstmann-Sträussler-Scheinker disease (GSS) (in family with dominantly inherited progressive ataxia and/or dementia): encephalo(myelo)pathy with multicentric PrP plaques. Familial fatal insomnia (FFI) (in member of a family with PRNP178 mutation): thalamic degeneration, variable spongiform change in cerebrum. Kuru (in the Fore population). Without PrP data, the crucial feature is the spongiform change accompanied by neuronal loss and gliosis. This spongiform change is characterised by diffuse or focally clustered small round or oval vacuoles in the neuropil of the deep cortical layers, cerebellar cortex or subcortical grey matter, which might become confluent. Spongiform change should not be confused with non-specific spongiosis. This includes status spongiosus ("spongiform state"), comprising irregular cavities in gliotic neuropil following extensive neuronal loss (including also lesions of "burnt-out" CJD), "spongy" changes in brain oedema and metabolic encephalopathies, and artefacts such as superficial cortical, perineuronal, or perivascular vacuolation; focal changes indistinguishable from spongiform change may occur in some cases of Alzheimer's and diffuse Lewy body diseases. Very rare cases might not be diagnosed by these criteria. Then confirmation must be sought by additional techniques such as PrP immunoblotting, preparations for electron microscopic examination of scrapie associated fibrils (SAF), molecular biologic studies, or experimental transmission.

The original Gerstmann-Sträussler-Scheinker family of Austria: divergent clinicopathological phenotypes but constant PrP genotype

We present new data on the original Austrian kindred with Gerstmann-Sträussler-Scheinker disease (GSS) which encompasses currently 221 members in 9 generations. The mode of inheritance is autosomal dominant. Predominant clinical features are slowly progressive ataxia and late impairment of higher cerebral functions. In contrast, a recent case with proven P102L mutation of the PRNP gene had rapidly developing dementia and severe cortical damage indistinguishable from the clinicopathological phenotype of Creutzfeldt-Jakob disease (CJD). PRNP codon 129 was homozygous for methionine in both the historic and recent cases. Neuropathology confirms spongiosis of variable degree and numerous protease resistant/prion protein (PrP) amyloid plaques scattered throughout most of the brain as constant features in this family. Some amyloid deposits are surrounded by dystrophic neurites with accumulation of phosphorylated neurofilaments and abnormal organelles, reminiscent of Alzheimer-type plaques. Severe telencephalic damage and a synaptic-type fine granular immunoreactivity in laminar distribution in the cortex with anti-PrP after hydrated autoclaving of sections were seen only in the recent patient. In conclusion, factors in addition to the PRNP genotype at codons 102 and 129 must play a role in determining clinicopathological characteristics of this inherited brain amyloidosis.

New variant prion protein in a Japanese family with Gerstmann-Sträussler syndrome

We found novel variants in the open reading frame of the prion protein (PrP) gene in a family with Gerstmann-Sträussler syndrome (GSS). Codon 219Lys variant is a normal polymorphism which we found recently. Some GSS cases were identified with codon 102 mutation (proline to leucine) and codon 219Lys polymorphism. While two families had a codon 102 mutation and codon 219Lys polymorphism in different alleles, 4 patients in one family had both in the same allele. The clinicopathological features of these 4 patients were clearly different from previously reported GSS patients with codon 102 mutation. These cases should be reported as a new variant of GSS.

Inherited prion diseases and transmission to rodents

Clinico-pathological phenotypes of patients with prion diseases were compared with their PrP genotypes and transmission rate to mice. Sporadic and iatrogenic CJD patients without mutation and familial CJD patients with E200K showed uniform clinico-pathological features, synaptic-type deposition of PrPCJD and high rate of transmission of the disease to mice. GSS patients with P102L showed long duration of ataxia, numerous plaques in cerebellar cortex and transmitted the disease to mice in only one third of inoculated cases. Other mutations such as P105L, A117V, Y145stop, V180I, M232R and various insertions have particular phenotypes, distinct distribution patterns of PrPCJD, and untransmitted or inconclusive transmission to mice. Polymorphism at codon 129 may modify the phenotypes and transmission rate to mice. Therefore, prion diseases have a wide range from infectious disease to non-infectious, hereditary metabolic disease.

Gerstmann-Sträussler-Scheinker disease and the Indiana kindred

Gerstmann-Sträussler-Scheinker disease is an autosomal dominant disorder with a wide spectrum of clinical presentations including ataxia, spastic paraparesis, extrapyramidal signs, and dementia. The patients present with symptoms in the third to sixth decade of life and the mean duration of illness is five years. Mutations at codons 102, 105, 117, 145, 198 and 217 of the open reading frame of the prion protein gene have been associated with GSS disease. As a result of the mutations, a substitution at the corresponding residues of the prion protein occurs, or as in the case of the STOP mutation at codon 145, a truncated protein is produced. Neuropathologically, the common denominator is a cerebral prion protein amyloidosis; however, there is significant variability in the pattern of amyloid deposition in regions of the central nervous system among reported families. Amyloidosis coexists with severe spongiform degeneration in patients with the mutation at codon 102, and with neurofibrillary degeneration in the patients with mutation at codons 145, 198 and 217. The development of a transmissible spongiform encephalopathy in animals inoculated with brain tissue from affected subjects with mutation at codon 102 suggests that in some forms of genetically-determined Gerstmann-Sträussler-Scheinker disease, and particularly those characterized by severe spongiosis, amyloidogenesis and production of an infectious "agent" occur concomitantly via mechanisms that are only partially understood.

The nosology of Creutzfeldt-Jakob disease and conditions related to the accumulation of PrPCJD in the nervous system

Although typical cases of Creutzfeldt-Jakob disease are readily recognized pathologically and clinically, variant forms often pose a diagnostic challenge. From the 1920's, when this disease was first characterized, until quite recently diagnosis relied heavily on morphologic changes. New advances in immunoassays and PrP gene analysis now provide important adjuncts in recognizing the spectrum of disorders of PrP metabolism associated with these transmissible encephalopathies.

Ultrastructural pathology of Gerstmann-Sträussler-Scheinker disease

We report a detailed ultrastructural study based on a large series of samples from a recent case of Gerstmann-Sträussler-Scheinker disease from the original Austrian family. Numerous PrP-immunopositive plaques dominated light microscopic neuropathology. Ultrastructurally, several types of plaques were observed: unicentric "kuru," multicentric, and neuritic. Dystrophic neurites accompanied amyloid plaques to differing degrees. Plaques were enveloped by astrocytic processes and invaded by microglial cells. A prominent astrocytic reaction accompanied abundant spongiform change. Unusual crystalloids were observed in mitochondria while another type of crystalloid was seen within lysosomes. We conclude that Gerstmann-Sträussler-Scheinker disease is distinct also at the ultrastructural level.