Polymorphisms of the PRNP gene in Chinese populations and the identification of a novel insertion mutation

Human immunodeficiency virus-associated dementia complex with positive 14-3-3 protein in cerebrospinal fluid: A case report

BACKGROUND

Human immunodeficiency virus (HIV)-associated dementia (HAD) is a subcortical form of dementia characterized by memory deficits and psychomotor slowing. However, HAD often presents with symptoms similar to those of Creutzfeldt-Jakob disease (CJD), particularly in patients with acquired immune deficiency syndrome (AIDS).

CASE SUMMARY

We report the case of a 54-year-old male who exhibited cognitive dysfunction and secondary behavioral changes following HIV infection and suspected prion exposure. The patient was diagnosed with HIV during hospitalization and his cerebrospinal fluid tested positive for 14-3-3 proteins. His electroencephalogram showed a borderline-abnormal periodic triphasic wave pattern. Contrast-enhanced magnetic resonance imaging revealed moderate encephalatrophy and demyelination. Initially, symptomatic treatment and administration of amantadine were pursued for presumed CJD, but the patient's condition continued to deteriorate. By contrast, the patient's condition improved following anti-HIV therapy. This individual is also the only patient with this prognosis to have survived over 4 years. Thus, the diagnosis was revised to HAD.

CONCLUSION

In the diagnostic process of rapidly progressive dementia, it is crucial to rule out as many potential causes as possible and to consider an autopsy to diminish diagnostic uncertainty. The 14-3-3 protein should not be regarded as the definitive marker for CJD. Comprehensive laboratory screening for infectious diseases is essential to enhance diagnostic precision, especially in AIDS patients with potential CJD. Ultimately, a trial of diagnostic treatment may be considered when additional testing is not feasible.

Pooled analysis of patients with inherited prion disease caused by two- to twelve-octapeptide repeat insertions in the prion protein gene (PRNP)

Inherited prion diseases caused by two- to twelve-octapeptide repeat insertions (OPRIs) in the prion protein gene (PRNP) show significant clinical heterogeneity. This study describes a family with two new cases with a 4-OPRI mutation and two asymptomatic mutation carriers. The pooled analysis summarizes all cases reported in the literature to date and describes the relation between survival, age of onset, number of OPRI and codon 129 polymorphism. MEDLINE and Google Scholar were queried from database inception up to December 31, 2022. Age of onset was compared per number of OPRI and per codon 129 polymorphism using the Kruskal-Wallis and Wilcoxon-Mann-Whitney tests, respectively. Disease duration was modeled non-parametrically by a Kaplan-Meier model and semi-parametrically by a Cox model. This study comprised 164 patients. Lower number of OPRI and presence of valine (cis-V) versus methionine (cis-M) on codon 129 were associated with an older age of onset (P < 0.001 and P = 0.025, respectively) and shorter disease duration (P < 0.001 and P = 0.003, respectively). Within patients with 5- or more OPRI codon cis-V remained significantly associated with a shorter disease duration. Codon 129 homozygosity versus heterozygosity was not significantly associated with age of onset or disease duration (P = 0.076 and P = 0.409, respectively). This study summarized the largest cohort of patients with two- to twelve-OPRI to date. Lower number of OPRI and codon 129 cis-V is associated with an older age of onset and shorter disease duration, while homozygosity or heterozygosity on codon 129 was not.

Case Report: Genetic Creutzfeldt–Jakob Disease With a G114V Mutation and One Octapeptide Repeat Deletion as a Mimic of Frontotemporal Dementia

Genetic Creutzfeldt–Jakob disease (gCJD) characterized by mutations in the prion protein (PrP) gene (PRNP) contributes to approximately 10–15% of the overall human prion diseases. Here, we report a rare mutation in the PRNP gene in a Han-Chinese family. A 36-year-old man initiated with anxiety and depression followed by progressive dementia, cogwheel-like rigidity combined with tremors, and he was diagnosed with frontotemporal lobar dementia in the first 2 years. The disease progression was relatively slow, and the patient developed into akinetic mutism in 4 years. To characterize the disease, following the pedigree studies, neuropsychological examination, neuroimaging studies, real-time quaking-induced conversion (RT-QuIC) examination, and so on were conducted. We eventually identified a rare mutation of G114V combined with one octapeptide repeats deletion (1-ORPD) in the PrP in the patient by DNA sequencing. In addition, the same mutation and deletion were subsequently identified in the patient's mother without any syndromes. His maternal grandmother had a late onset of the disease in her 60s. Given that 1-OPRD has never been reported in human prion disease before, our first report that both G114V mutation and 1-OPRD appear in the family would forward our understanding of the etiological mechanisms of the gCJD.

Incidence of and Mortality Due to Human Prion Diseases in Taiwan: A Prospective 20-Year Nationwide Surveillance Study from 1998 to 2017

Introduction

Epidemiologic studies of Creutzfeldt-Jakob disease (CJD) have been undertaken worldwide since the new variant CJD outbreak in 1996 in the United Kingdom. A nationwide report system, the Creutzfeldt-Jakob Disease Surveillance Unit (CJDSU), directed by the Centers for Disease Control of Taiwan, was established in 1997 to identify human prion diseases.

Methods

From 1998 to 2017, 647 cases were referred to the committee for confirmation. The report to CJDSU included a structured questionnaire recording the clinical, demographic data, and potential iatrogenic exposure, and the results of the clinical and laboratory examination, including tests of blood and cerebrospinal fluid, electroencephalography, and brain magnetic resonance imaging.

Results

In total, 356 cases (women, n=178) were ascertained to be human prion diseases, and 97.4% (n=347) were sporadic CJD, including three definite, 314 probable, and 30 possible cases; one probable variant CJD and 8 cases of the genetic form human prion diseases. The age- and gender-specific average annual incidence were also significantly higher in the second decade (0.95/1,000,000) than in the first decade (0.63/1,000,000), with an incidence rate ratio of 1.51. The incidences increased with increasing age, reaching a peak at the age of 70-79 years. The 10-year survival curve for sCJD patients showed that the 1-, 5-, and 10-year cumulative survival rate were 52%, 5%, and 1%, respectively. PRNP polymorphisms in 170 patients showed that 98.8% were M129M and 97.6% E219E.

Discussion

The significant increase in incidence after 2008 suggests the increase in the awareness of this rare disease among physicians. The longer disease duration in patients with sCJD in Taiwan than in other countries indicates that the comprehensive support of the health care system, as well as the end-of-life care culture in Taiwan, may prolong survival time in patients with such a progressive and fatal disease.

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

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

Genetic PrP Prion Diseases

Genetic prion diseases (gPrDs) caused by mutations in the prion protein gene (PRNP) have been classified as genetic Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker disease, or fatal familial insomnia. Mutations in PRNP can be missense, nonsense, and/or octapeptide repeat insertions or, possibly, deletions. These mutations can produce diverse clinical features. They may also show varying ancillary testing results and neuropathological findings. Although the majority of gPrDs have a rapid progression with a short survival time of a few months, many also present as ataxic or parkinsonian disorders, which have a slower decline over a few to several years. A few very rare mutations manifest as neuropsychiatric disorders, with systemic symptoms that include gastrointestinal disorders and neuropathy; these forms can progress over years to decades. In this review, we classify gPrDs as rapid, slow, or mixed types based on their typical rate of progression and duration, and we review the broad spectrum of phenotypes manifested by these diseases.

Genetic prion disease: Experience of a rapidly progressive dementia center in the United States and a review of the literature

Although prion diseases are generally thought to present as rapidly progressive dementias with survival of only a few months, the phenotypic spectrum for genetic prion diseases (gPrDs) is much broader. The majority have a rapid decline with short survival, but many patients with gPrDs present as slowly progressive ataxic or parkinsonian disorders with progression over a few to several years. A few very rare mutations even present as neuropsychiatric disorders, sometimes with systemic symptoms such as gastrointestinal disorders and neuropathy, progressing over years to decades. gPrDs are caused by mutations in the prion protein gene (PRNP), and have been historically classified based on their clinicopathological features as genetic Jakob-Creutzfeldt disease (gJCD), Gerstmann-Sträussler-Scheinker (GSS), or Fatal Familial Insomnia (FFI). Mutations in PRNP can be missense, nonsense, and octapeptide repeat insertions or a deletion, and present with diverse clinical features, sensitivities of ancillary testing, and neuropathological findings. We present the UCSF gPrD cohort, including 129 symptomatic patients referred to and/or seen at UCSF between 2001 and 2016, and compare the clinical features of the gPrDs from 22 mutations identified in our cohort with data from the literature, as well as perform a literature review on most other mutations not represented in our cohort. E200K is the most common mutation worldwide, is associated with gJCD, and was the most common in the UCSF cohort. Among the GSS-associated mutations, P102L is the most commonly reported and was also the most common at UCSF. We also had several octapeptide repeat insertions (OPRI), a rare nonsense mutation (Q160X), and three novel mutations (K194E, E200G, and A224V) in our UCSF cohort. © 2016 Wiley Periodicals, Inc.

Hereditary Human Prion Diseases: an Update

Prion diseases in humans are neurodegenerative diseases which are caused by an accumulation of abnormal, misfolded cellular prion protein known as scrapie prion protein (PrP^Sc). Genetic, acquired, or spontaneous (sporadic) forms are known. Pathogenic mutations in the human prion protein gene (PRNP) have been identified in 10-15 % of CJD patients. These mutations may be single point mutations, STOP codon mutations, or insertions or deletions of octa-peptide repeats. Some non-coding mutations and new mutations in the PrP gene have been identified without clear evidence for their pathogenic significance. In the present review, we provide an updated overview of PRNP mutations, which have been documented in the literature until now, describe the change in the DNA, the family history, the pathogenicity, and the number of described cases, which has not been published in this complexity before. We also provide a description of each genetic prion disease type, present characteristic histopathological features, and the PrP^Sc isoform expression pattern of various familial/genetic prion diseases.

Protective V127 prion variant prevents prion disease by interrupting the formation of dimer and fibril from molecular dynamics simulations

Recent studies uncovered a novel protective prion protein variant: V127 variant, which was reported intrinsically resistant to prion conversion and propagation. However, the structural basis of its protective effect is still unknown. To uncover the origin of the protective role of V127 variant, molecular dynamics simulations were performed to explore the influence of G127V mutation on two key processes of prion propagation: dimerization and fibril formation. The simulation results indicate V127 variant is unfavorable to form dimer by reducing the main-chain H-bond interactions. The simulations of formed fibrils consisting of β1 strand prove V127 variant will make the formed fibril become unstable and disorder. The weaker interaction energies between layers and reduced H-bonds number for V127 variant reveal this mutation is unfavorable to the formation of stable fibril. Consequently, we find V127 variant is not only unfavorable to the formation of dimer but also unfavorable to the formation of stable core and fibril, which can explain the mechanism on the protective role of V127 variant from the molecular level. Our findings can deepen the understanding of prion disease and may guide the design of peptide mimetics or small molecule to mimic the protective effect of V127 variant.

Coomassie brilliant blue R-250 as a new surface-enhanced Raman scattering probe for prion protein through a dual-aptamer mechanism

Surface-enhanced Raman scattering (SERS) spectra, which can provide large information about trace amount of chemical and biological species have been widely performed as a well-established tool in complex biological system. In this work, coomassie brilliant blue (R-250) with high affinity to proteins and high Raman activity was employed as a Raman reporter to probe prion protein (PrP) through a dual-aptamer mechanism, and thus an original strategy for PrP determination was proposed, which showed great potential to turn on the SERS response through specific recognition of anti-prion aptamers towards the target protein. Aptamers (Apt1 and Apt 2) recognizing distinct epitopes of PrP with high affinity were first conjugated to Ag@Si NPs, and Ag@Si-PrP/R-250-Ag@Si conjugates were obtained in the presence of PrP/R-250, inducing dramatically enhanced Raman signal. SERS responses enhanced with increasing amount of PrP and a linear equation of ISERS=6729.7+3091.2 cPrP was obtained in the range of 3.0-12.0×10(-9)M with the determination coefficient of 0.988. The proposed strategy is simple, rapid, and high specificity to probe protein-aptamer recognition in the solution.

Metal-enhanced fluorescence of nano-core-shell structure used for sensitive detection of prion protein with a dual-aptamer strategy

Metal-enhanced fluorescence (MEF) as a newly recognized technology is widespread throughout biological research. The use of fluorophore-metal interactions is recognized to be able to alleviate some of fluorophore photophysical constraints, favorably increase both the fluorophore emission intensity and photostability. In this contribution, we developed a novel metal-enhanced fluorescence (MEF) and dual-aptamer-based strategy to achieve the prion detection in solution and intracellular protein imaging simultaneously, which shows high promise for nanostructure-based biosensing. In the presence of prion protein, core-shell Ag@SiO2, which are functionalized covalently by single stranded aptamer (Apt1) of prions and Cyanine 3 (Cy3) decorated the other aptamer (Apt2) were coupled together by the specific interaction between prions and the anti-prion aptamers in solution. By adjusting shell thickness of the pariticles, a dual-aptamer strategy combined MEF can be realized by the excitation and/or emission rates of Cy3. It was found that the enhanced fluorescence intensities followed a linear relationship in the range of 0.05-0.30 nM, which is successfully applied to the detection of PrP in mice brain homogenates.

A visual dual-aptamer logic gate for sensitive discrimination of prion diseases-associated isoform with reusable magnetic microparticles and fluorescence quantum dots

Molecular logic gates, which have attracted increasing research interest and are crucial for the development of molecular-scale computers, simplify the results of measurements and detections, leaving the diagnosis of disease either "yes" or "no". Prion diseases are a group of fatal neurodegenerative disorders that happen in human and animals. The main problem with a diagnosis of prion diseases is how to sensitively and selectively discriminate and detection of the minute amount of PrP(Res) in biological samples. Our previous work had demonstrated that dual-aptamer strategy could achieve highly sensitive and selective discrimination and detection of prion protein (cellular prion protein, PrP(C), and the diseases associated isoform, PrP(Res)) in serum and brain. Inspired by the advantages of molecular logic gate, we further conceived a new concept for dual-aptamer logic gate that responds to two chemical input signals (PrP(C) or PrP(Res) and Gdn-HCl) and generates a change in fluorescence intensity as the output signal. It was found that PrP(Res) performs the "OR" logic operation while PrP(C) performs "XOR" logic operation when they get through the gate consisted of aptamer modified reusable magnetic microparticles (MMPs-Apt1) and quantum dots (QDs-Apt2). The dual-aptamer logic gate simplifies the discrimination results of PrP(Res), leaving the detection of PrP(Res) either "yes" or "no". The development of OR logic gate based on dual-aptamer strategy and two chemical input signals (PrP(Res) and Gdn-HCl) is an important step toward the design of prion diseases diagnosis and therapy systems.

Effective detection and cell imaging of prion protein with new prepared targetable yellow-emission silver nanoclusters

Silver nanoclusters (AgNCs) have gained considerable attention over a wide range from chemical detection to bioimaging applications. Herein we developed a facile way to synthesize water-soluble, intense fluorescent targetable AgNCs with yellow-emission by using DNA via a chemical reduction method. The sequence of DNA was designed to contain two fragments, one of which is the DNA aptamer fragment which can selectively bind to the target, and the other is rich in cytosine sequence fragments that can result in a high quantum efficiency. The as-prepared targetable AgNCs (Apt-AgNCs) through the reduction of silver ions (Ag(+)) by NaBH(4) have a very strong fluorescence emission, which, was greatly quenched upon specific binding to prion protein (PrP(C)). As a result, Apt-AgNCs were demonstrated as a novel, effective and sensitive probe for both detection and intracellular fluorescent imaging with high selectivity through the strong binding affinity between the aptamer and its target.

Label-free detection of prion protein with its DNA aptamer through the formation of T-Hg2+-T configuration

Though rapid tests were developed for mass screening of prion diseases in the last century, bovine spongiform encephalopathy (BSE) was still epidemic in some European countries. The main reason is that the sensitivity of such tests is insufficient for detecting animals that are incubating with prion diseases at the presymptomatic stage. Driven by this, in this contribution, we developed a novel sensitive label-free method taking advantage of DNA aptamer for prion proteins (PrP) detection through the formation of T-Hg(2+)-T configuration. In the presence of Hg(2+) ions, double-strand structures formed due to the strong binding affinity of Hg(2+) ions to the T bases of DNA aptamer, which dramatically enhanced the fluorescence of Syber Green I, a double-strand indicator. With the addition of prion protein, however, the specific interaction between prion protein and its aptamer forced the destruction of the double-strand structures, and thus the fluorescence of Syber Green I decreased. It was found that there is a linear relationship between the decreased fluorescence intensities and prion protein concentration ranging from 13.0 to 156.0 nmol/L. Compared with other methods, the method presented here holds the advantages of being label-free, rapid, highly sensitive, and selective, which shows great promise for clinical application.

An overview of human prion diseases

Prion diseases are transmissible, progressive and invariably fatal neurodegenerative conditions associated with misfolding and aggregation of a host-encoded cellular prion protein, PrP^C. They have occurred in a wide range of mammalian species including human. Human prion diseases can arise sporadically, be hereditary or be acquired. Sporadic human prion diseases include Cruetzfeldt-Jacob disease (CJD), fatal insomnia and variably protease-sensitive prionopathy. Genetic or familial prion diseases are caused by autosomal dominantly inherited mutations in the gene encoding for PrP^C and include familial or genetic CJD, fatal familial insomnia and Gerstmann-Sträussler-Scheinker syndrome. Acquired human prion diseases account for only 5% of cases of human prion disease. They include kuru, iatrogenic CJD and a new variant form of CJD that was transmitted to humans from affected cattle via meat consumption especially brain. This review presents information on the epidemiology, etiology, clinical assessment, neuropathology and public health concerns of human prion diseases. The role of the PrP encoding gene (PRNP) in conferring susceptibility to human prion diseases is also discussed.

Frequency distribution of PRNP polymorphisms in the Pakistani population

Prion diseases are neurodegenerative conditions caused by misfolding of a normal host-encoded prion protein (PrPC) into pathogenic scrapie prion protein (PrPSc). In human prion diseases, the M129V prion protein polymorphism is known to confer susceptibility to the disease, determines PrPSc conformation and alters clinicopathological phenotypes. To date, all clinicopathologically confirmed cases of a variant form of Cruetzfeldt-Jacob disease (vCJD) have been 129MM homozygotes. There is also predominance of 129MM homozygotes in sporadic CJD (sCJD). No information regarding prion disorders is available from Pakistan. Although only invasive procedures like brain biopsy can confirm the diagnosis of prion disorders, testing a corresponding human population for variation in the prion protein gene (PRNP) may provide some insights into the presence of these disorders in a locality. The current study therefore aimed at exploring the genetic susceptibility of Pakistani population to CJD. A total of 909 unrelated individuals including 221 hemophiliacs representing all 4 major provinces of Pakistan were screened for M129V polymorphism and insertions or deletions of octapeptide repeats (OPRIs/OPRDs) using Polymerase Chain Reaction coupled with Restriction Fragment Length Polymorphism (PCR-RFLP). Concordance of the results of some PCR-RFLP reactions was also confirmed by dideoxy automated Sanger sequencing. The frequencies of M129V alleles (129M and 129V) and genotypes (129MM, 129MV and 129VV) were found in all 909 individuals to be 0.7101, 0.2899, 0.5270, 0.3663 and 0.1067, respectively. Deletion of 1 octapeptide repeat (1-OPRD) was detected in heterozygous state in PRNP of 10 individuals and in homozygous state in 1 individual. An insertion of 3 octapeptide repeats (3-OPRI) was found in 1 individual and an insertion of 1 octapeptide repeat (1-OPRI) in two individuals. Both 3-OPRI and 1-OPRI were present in heterozygous state and were linked to 129M allele. There were no significant χ2 differences between M129V allelic and genotypic frequencies of healthy individuals and hemophiliacs. However, M129V allelic and genotypic frequencies differed significantly between Pakistani population and East Asian and Western populations. Non-significant χ2 differences between M129V frequencies of healthy individuals and hemophiliacs suggest that individuals manifesting single gene disorders may provide naturally randomized samples for studies aiming at surveying the genetic variation. The combined excess of 129MM and 129VV homozygosity and the presence of 3-OPRI in 1 individual imply that Pakistani population is susceptible to prion disorders. Cases of prion disorders may exist in Pakistan, albeit at lower annual prevalence than other countries where life expectancy is greater than 65 years.

Sensitive discrimination and detection of prion disease-associated isoform with a dual-aptamer strategy by developing a sandwich structure of magnetic microparticles and quantum dots

The major challenge of prion disease diagnosis at the presymptomatic stage is how to sensitively or selectively discriminate and detect the minute quantity of disease-associated prion protein isoform (PrP(Res)) in complex biological systems such as serum and brain homogenate. In this contribution, we developed a dual-aptamer strategy by taking the advantages of aptamers, the excellent separation ability of magnetic microparticles (MMPs), and the high fluorescence emission features of quantum dots (QDs). Two aptamers (Apt1 and Apt2), which can recognize their two corresponding distinct epitopes of prion proteins (PrP), were coupled to the surfaces of MMPs and QDs, respectively, to make MMPs-Apt1 and QDs-Apt2 ready at first, which then could be coassociated together through the specific recognitions of the two aptamers with their two corresponding distinct epitopes of PrP, forming a sandwich structure of MMPs-Apt1-PrP-Apt2-QDs and displaying the strong fluorescence of QDs. Owing to the different binding affinities of the two aptamers with PrP(Res) and cellular prion protein (PrP(C)), both of which have distinct denaturing detergent resistance, our dual-aptamer strategy could be applied to discriminate PrP(Res) and PrP(C) successfully in serum. Further identifications showed that the present dual-aptamer assay could be successfully applied to the detection of PrP in 0.01% brain homogenate, about 1000-fold lower than that of commonly applied antibody-mediated assays, which can detect PrP just in 10% brain homogenate, indicating that the present designed dual-aptamer assay is highly sensitive and adequate for clinical diagnosis without isolation of target protein prior to assay.

Prospective 10-year surveillance of human prion diseases in Japan

We analysed the epidemiological data and clinical features of patients with prion diseases that had been registered by the Creutzfeldt-Jakob Disease Surveillance Committee, Japan, over the past 10 years, since 1999. We obtained information on 1685 Japanese patients suspected as having prion diseases and judged that 1222 patients had prion diseases, consisting of definite (n=180, 14.7%) and probable (n=1029, 84.2%) cases, except for dura mater graft-associated Creutzfeldt-Jakob disease which also included possible cases (n=13, 1.1%). They were classified into 922 (75.5%) with sporadic Creutzfeldt-Jakob disease, 216 (17.7%) with genetic prion diseases, 81 (6.6%) with acquired prion diseases, including 80 cases of dura mater graft-associated Creutzfeldt-Jakob disease and one case of variant Creutzfeldt-Jakob disease, and three cases of unclassified Creutzfeldt-Jakob disease (0.2%). The annual incidence rate of prion disease ranged from 0.65 in 1999 to 1.10 in 2006, with an average of 0.85, similar to European countries. Although methionine homozygosity at codon 129 polymorphism of the prion protein gene was reported to be very common (93%) in the general Japanese population, sporadic Creutzfeldt-Jakob disease in Japan was significantly associated with codon 129 homozygosity (97.5%), as reported in western countries. In sporadic Creutzfeldt-Jakob disease, MM1 type (Parchi's classification) is the most common, as in western countries. Among atypical sporadic Creutzfeldt-Jakob disease cases, the MM2 type appeared most common, probably related to the very high proportion of methionine allele in the Japanese population. As for iatrogenic Creutzfeldt-Jakob disease, only dura mater graft-associated Creutzfeldt-Jakob disease cases were reported in Japan and, combined with the data from previous surveillance systems, the total number of dura mater graft-associated Creutzfeldt-Jakob disease was 138, comprising the majority of worldwide dura mater graft-associated Creutzfeldt-Jakob disease patients. Regarding genetic prion diseases, the most common mutation of prion protein gene was V180I (41.2%), followed by P102L (18.1%), E200K (17.1%) and M232R (15.3%), and this distribution was quite different from that in Europe. In particular, V180I and M232R were quite rare mutations worldwide. Patients with V180I or M232R mutations rarely had a family history of prion diseases, indicating that a genetic test for sporadic cases is necessary to distinguish these from sporadic Creutzfeldt-Jakob disease. In conclusion, our prospective 10-year surveillance revealed a frequent occurrence of dura mater graft-associated Creutzfeldt-Jakob disease, and unique phenotypes of sporadic Creutzfeldt-Jakob disease and genetic prion diseases related to the characteristic distribution of prion protein gene mutations and polymorphisms in Japan, compared with those in western countries.

Macromolecular crowding converts the human recombinant PrPC to the soluble neurotoxic beta-oligomers

Prion diseases are fatal neurodegenerative disorders and are linked with the conversion of the cellular isoform of the prion protein (PrP(C)) into the abnormal beta-sheet-rich isoform. It is widely accepted that the soluble oligomers of beta-PrP are neurotoxic and that they are more pathologically significant. To unravel the molecular mechanism under the conversion process, it is critical to identify the factors that can promote the conversion from PrP(C) to the beta-oligomers. By recording circular dichroism spectra and performing a size-exclusion HPLC assay, we found that the conformation of the recombinant human prion protein (rPrP(C)) was converted from an alpha-helical conformation into beta-sheet oligomers under a macromolecular crowding condition. The soluble beta-oligomers of rPrP were resistant to proteinase K digestion and could bind to the dyes thioflavin T and 8-anilino-1-naphthalene sulfonate. Furthermore, by the 3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay, we showed that the soluble beta-oligomers were neurotoxic. These results suggest that macromolecular crowding, which has not been considered before, is a key intracellular factor in the formation of soluble neurotoxic beta-oligomers in prion diseases.

Incidence of Creutzfeldt-Jakob disease in Taiwan: a prospective 10-year surveillance

This study was performed to estimate the incidence of Creutzfeldt-Jakob Disease (CJD) in Taiwan from 1998 to 2007. Suspected cases of CJD were reported to the Taiwan Creutzfeldt-Jakob Disease Surveillance Unit, a nationwide, hospital-based case report system initiated since 1996 to prospectively conduct a CJD epidemiological study. Consecutive patients who met the diagnostic criteria recommended by the World Health Organization were enrolled. The clinical information of each suspected case was collected and case ascertainment was performed by an expert committee. A total of 123 sporadic CJD were identified without any iatrogenic or new variant CJD cases. The overall annual incidence rate (95% CI) was 0.55 (0.46-0.65) cases per million person-year. There was no statistically significant difference between the calendar year of disease onset (P = 0.97). The incidence rates were not significantly different between women and men (P = 0.63). Age was the main factor for the risk of CJD (P < 0.0001). Age-specific incidence rate increased after the age of 40 years with the peak being in the 70-79 years age group. Our data showed low annual incidence rate and high frequency of methionine homozygous prion protein genotype of sCJD in Taiwan. This report provided important epidemiological data on ethnic Chinese.

Function of PrPC (1-OPRD) in biological activities of gastric cancer cell lines

Approximately 10–15% of the human prion disease is inherited and one of the important genetic mutations occurs in the octapeptide repeat region of prion protein gene. One of the variants, one octapeptide repeat deletion (1-OPRD), existed in several gastric cancer cell lines and its mutation frequency was higher in gastric cancer cases. However, the biological functions of it remain unknown. Wild-type and mutation forms of PrP^C were cloned and transfected into gastric cancer cells. Cell apoptosis, adhesion, invasion, multidrug resistance (MDR) and proliferation were, respectively, investigated. Different expressed genes were screened by gene array and proved by PT-PCR. Further, luciferase report assay was used to explore the transcriptional activation of target genes. Forced overexpression PrP^C (1-OPRD) could promote the gastric cancer cells SGC7901 growth through facilitating G1- to S-phase transition in the cell cycle. PrP^C (1-OPRD) could also inhibit apoptosis, and promote adhesion, invasion and MDR in SGC7901. However, it exhibited no significant difference between wild-type PrP^C (1-OPRD) and PrP^C on apoptosis, invasion or MDR effects. Further experiments indicated that PrP^C (1-OPRD) could trigger the transactivation of cyclinD3 besides cyclinD1 to promote cell transition and proliferation. Overexpression of PrP^C (1-OPRD) might promote the proliferation of gastric cancer cells at least partially through transcriptional activation of cyclinD3 to accelerate the G1-/S-phase transition. The promoting proliferation effect of PrP^C (1-OPRD) was more than that of wild-type PrP^C. However, they showed no difference on apoptosis, adhesion, invasion or MDR effects of gastric cancer cells.

Comparative genomic analysis of the whale (Pseudorca crassidens) PRNP locus

There have been many studies of the morphology, behavioral audiograms, and population structure of the false killer whale ( Pseudorca crassidens ), but sequencing, mapping, and functional and comparative genomics studies are still largely unknown. In this paper, we sequenced three novel BAC clones corresponding to a total length of 308 kb and spanning the PRNP, PRND, and RASSF2 loci, and conducted comparative genomic analysis to examine the genomic structure of the false killer whale PRNP locus. We determined that the three genes show a high degree of conservation in their syntenic regions with respect to gene order, gene orientation, and the predicted coding sequence (CDS) between human and whale, whereas PRNT was not detected in whale. Interestingly, the predicted CDS in whale PRNP contained a novel type of 4-copy octarepeat resulting from a 24 bp deletion when compared with the human sequence. In addition, we identified a novel 1869 bp repeat unit in a region that is non-syntenic to human and cow sequences and is therefore considered to be whale-specific sequence. Our results will provide novel insights into the genomic changes that have occurred during evolution of mammalian PRNP loci, and may also have implications for research into prion disease.

Polymorphism distribution of prion protein codon 117, 129 and 171 in Taiwan

Prion diseases compass transmissible spongiform neurodegenerative diseases from various causes, including the genetic and infectious ones. We investigated the prevalence of codon 117, 129 and 171 polymorphism in prion protein (PrP) in Taiwanese, mainly for the sake of the informative absence of this genetic distribution. Our subjects were 419 aged ones of Han ethic origin. We evaluated the PrP gene (PRNP) polymorphism by restriction fragment length polymorphism, after amplification of their genomic DNAs by polymerase chain reactions with specific primers, digested by restriction enzyme PvuII (for codon 117), NspI (for codon 129), and BbvI (for codon 171), respectively, and confirmed by nucleotide sequencing. All of the subjects were homozygotes at codon 117 (Ala/Ala, gca/gca) and 171 (Asn/Asn, aac/aac). There were no valine homozygotes (Val/Val) in our 419 subjects, and nine subjects (2.1%) showed methionine-valine heterozygosity (Mal/Val, atg/gtg). The methionine homozygotes (Met/Met) comprised the major population (97.9%), and the prevalence of distribution is different to that seen in Caucasians. The almost 100% conservation of the domain from codon 117 to 171 implies the warranty of PrP in cellular functions. The high prevalence of Met/Met alleles in Taiwan did not imply an increased risk of CJD, and the genetic susceptibility of CJD by codon 129 of PrP may be still elusive for the infectivity.

High frequency occurrence of 1-OPRD variant of PRNP gene in gastric cancer cell lines and Chinese population with gastric cancer

The prion protein gene PRNP encodes PrPc and PrPsc, causing a number of neurological disorders. Approximately 10-15% of human prion disease is inherited and more than 20 pathogenic mutations have been found. Most of the genetic alterations are point mutations, with the exception of genetic insertions of one to nine extra octapeptide repeats occurring in the important octapeptide-coding region. Our previous work showed that PrPc was overexpressed in gastric cancer. We wondered whether mutations of PrPc existed in human gastric cancer. DNA sequencing and gel electrophoresis were used to determine the possible mutation of PrPc in patients and cell lines of gastric cancer. We found that 1-OPRD (one octapeptide-repeat deletion) homozygosity or heterozygosity exists in several gastric cancer cell lines, e.g. MKN28 and KatoIII are homozygous for 1-OPRD, and SGC7901 and BGC-823 are heterozygous for 1-OPRD. The mutation frequency in tissues of gastric cancer cases is significantly higher than that in the common population (p<0.05). All positive cases in gastric cancer were found to be heterozygous for 1-OPRD. Further study of the variant may be helpful in understanding the mechanisms of occurrence and development of clinical gastric carcinoma as well as the biology of the mysterious gene PRNP.

Polymorphism of PRNP codons in the normal Icelandic population

OBJECTIVES

Polymorphisms in the prion protein gene in humans influence susceptibility to, and phenotype of, prion diseases. Methionine-methionine (MM) homozygosity at codon 129 is a risk factor for sporadic Creutzfeldt-Jakob disease (CJD). Polymorphism at codon 117 and changes in the octapeptide repeat region have been associated with genetic CJD. Knowledge of genetic background in normal populations may contribute to better understanding of prion diseases.

MATERIALS AND METHODS

Polymorphism at codon 129, codon 117 and deletions of octapetide repeats were studied in 208 healthy blood donors of both genders and of different age.

RESULTS

Polymorphism at codon 129 was: MM 46.6%, methionine-valine 44.7%, valine-valine 8.7%. Polymorphism at codon 117 was observed in 4.8%. Deletions of octapeptide repeats were not detected. There were no gender or age differences in the distribution of codon 129 polymorphism. The frequency of codon 129 polymorphisms was, with one exception, not significantly different from that observed elsewhere in Europe.

Prion disease genetics

Prion diseases have stimulated intense scientific scrutiny since it was proposed that the infectious agent was devoid of nucleic acid. Despite this finding, genetics has played a key role in understanding the pathobiology and clinical aspects of prion disease through the effects of a series of polymorphisms and mutations in the prion protein gene (PRNP). The advent of variant Creutzfeldt-Jakob disease has confirmed one of the most powerful human genetic susceptibility factors, as all tested patients have an identical genotype at polymorphic codon 129 of PRNP. This review will also consider the accrued reports of inherited prion disease and attempt a genotype-phenotype correlation. The prospects for detection of novel genetic susceptibility factors using mouse models and human genetic association studies will be explored.

Complete sequence data support lack of balancing selection on PRNP in a natural Chinese population

The M129V mutation in the human prion protein gene (PRNP) is the primary site linked to susceptibility to prion diseases in humans. The heterozygous state of this allele has been proven to be more resistant to prion-related diseases such as Creutzfeldt-Jakob disease. Based on a study of the common genetic variations, it has been proposed that balancing selection has played a critical role in shaping the distribution of 129V in worldwide populations. Kreitman and Di-Rienzo [Kreitman and Di-Rienzo (2004)Trend Genet 20:300-304] challenged this hypothesis by pointing out that the exclusion of polymorphisms with low frequency may introduce an ascertainment bias and, in turn, lead to a wrong conclusion. By studying sequence variations in samples from the Human Genome Diversity Project, Soldevila et al. [Soldevila et al. (2005) Trends Genet 21:389-391] showed that this ascertainment bias does exist. We argue that the evidence presented by Soldevila et al. may be compromised by the samples tested since they were selected from a population that may be substructured. In this study, we re-evaluated the hypothesis of balancing selection in a natural Chinese population using a much longer segment encompassing the entire genomic region of the PRNP gene (15 kb). We showed that the pattern of genetic variation in PRNP is not consistent with the presence of balancing selection in this gene.

Prion proteins with insertion mutations have altered N-terminal conformation and increased ligand binding activity and are more susceptible to oxidative attack

We compared the biochemical properties of a wild type recombinant normal human cellular prion protein, rPrP(c), with a recombinant mutant human prion protein that has three additional octapeptide repeats, rPrP(8OR). Monoclonal antibodies that are specific for the N terminus of rPrP(c) react much better with rPrP(8OR) than rPrP(c), suggesting that the N terminus of rPrP(8OR) is more exposed and hence more available for antibody binding. The N terminus of PrP(c) contains a glycosaminoglycan binding motif. Accordingly, rPrP(8OR) also binds more glycosaminoglycan than rPrP(c). In addition, the divalent cation copper modulates the conformations of rPrP(c) and rPrP(8OR) differently. When compared with rPrP(c), rPrP(8OR) is also more susceptible to oxidative damage. Furthermore, the abnormalities associated with rPrP(8OR) are recapitulated, but even more profoundly, in another insertion mutant, which has five extra octapeptide repeats, rPrP(10OR). Therefore, insertion mutants appear to share common features, and the degree of abnormality is proportional to the number of insertions. Any of these anomalies may contribute to the pathogenesis of inherited human prion disease.