Genevieve M. Klug

Ultrasensitive human prion detection in cerebrospinal fluid by real-time quaking-induced conversion

The development of technologies for the in vitro amplification of abnormal conformations of prion protein (PrPSc) has generated the potential for sensitive detection of prions. Here we developed a new PrPSc amplification assay, called real-time quaking-induced conversion (RT-QUIC), which allows the detection of ≥1 fg of PrPSc in diluted Creutzfeldt-Jakob disease (CJD) brain homogenate. Moreover, we assessed the technique first in a series of Japanese subjects and then in a blind study of 30 cerebrospinal fluid specimens from Australia, which achieved greater than 80% sensitivity and 100% specificity. These findings indicate the promising enhanced diagnostic capacity of RT-QUIC in the antemortem evaluation of suspected CJD.

Mortality from Creutzfeldt–Jakob disease and related disorders in Europe, Australia, and Canada

Background: An international study of the epidemiologic characteristics of Creutzfeldt–Jakob disease (CJD) was established in 1993 and included national registries in France, Germany, Italy, the Netherlands, Slovakia, and the United Kingdom. In 1997, the study was extended to Australia, Austria, Canada, Spain, and Switzerland. Methods: Data were pooled from all participating countries for the years 1993 to 2002 and included deaths from definite or probable CJD of all etiologic subtypes. Results: Four thousand four hundred forty-one cases were available for analysis and included 3,720 cases of sporadic CJD, 455 genetic cases, 138 iatrogenic cases, and 128 variant cases. The overall annual mortality rate between 1999 and 2002 was 1.67 per million for all cases and 1.39 per million for sporadic CJD. Mortality rates were similar in all countries. There was heterogeneity in the distribution of cases by etiologic subtype with an excess of genetic cases in Italy and Slovakia, of iatrogenic cases in France and the UK, and of variant CJD in the UK. Conclusions: This study has established overall epidemiologic characteristics for Creutzfeldt–Jakob disease (CJD) of all types in a multinational population–based study. Intercountry comparisons did not suggest any relative change in the characteristics of sporadic CJD in the United Kingdom, and the evidence in this study does not suggest the occurrence of a novel form of human bovine spongiform encephalopathy infection other than variant CJD. However, this remains a possibility, and countries currently unaffected by variant CJD may yet have cases.

11C-PiB PET studies in typical sporadic Creutzfeldt-Jakob disease

Objective: Brain amyloid imaging using positron emission tomography (PET) is of increasing importance in the premortem evaluation of dementias, particularly in relation to Alzheimer disease (AD). The purpose of this study was to explore the premortem diagnostic utility of 11C-PiB PET in sporadic Creutzfeldt–Jakob disease (CJD). Methods: Two patients, 72 and 59 years old, underwent evaluation for rapidly progressive cognitive decline, dying after illness durations of 5 and 7 months, respectively. As part of their comprehensive assessment, 18F-FDG PET and 11C-PiB PET studies were performed approximately 2–4 weeks prior to death, and the brain regional distributions compared with those from cohorts of healthy controls (HC) and AD patients. Results: Routine investigations, including brain MRI scans, revealed changes typical of sporadic CJD, with the diagnosis confirmed at autopsy in both patients. The 18F-FDG PET showed global hypometabolism in one patient and thalamic and frontal hypometabolism with unexpected hypermetabolism in the dentate nuclei of the cerebellum in the other. Neither patient displayed cerebral cortical 11C-PiB PET retention above the levels observed in HC. Conclusions: No grey-matter 11C-PiB retention was observed in two pathologically confirmed cases of typical sporadic CJD. We speculate that low PrP plaque density and small plaque size, as well as a relatively low affinity of the radioligand, explain the absence of 11C-PiB retention. More studies to validate this hypothesis are warranted.

Correlative studies support lipid peroxidation is linked to PrPres propagation as an early primary pathogenic event in prion disease

To assess whether heightened oxidative stress plays an early and primary pathogenic role in transmissible spongiform encephalopathies (TSE), we undertook detailed correlative studies using a mouse-adapted model of human disease. The spatio-temporal evolution of the abnormal, protease-resistant isoform of the prion protein (PrP(res)) and neuropathological changes were correlated with the occurrence and type of oxidative stress. Heightened oxidative stress was demonstrated, but restricted to elevated levels of free aldehydic breakdown products of lipid peroxidation, affecting all brain regions to varying extents. The increase in lipid peroxidation was highest over the mid-incubation period, with the onset showing close temporal and general topographical concordance with the first detection of PrP(res) with both pre-empting the typical neuropathological changes of spongiform change, gliosis and neuronal loss. Further, prion propagation over the disease course was assessed using murine bioassay. This revealed that the initial rapid increase in infectivity titres was contemporaneous with the abrupt onset and maximisation of lipid peroxidation. The present results are an important extension to previous studies, showing that heightened oxidative stress in the form of lipid peroxidation is likely to constitute an early primary pathogenic event in TSE, associated temporally with the integral disease processes of prion propagation and PrP(res) formation, and consistent with causal links between these events and subsequent typical neuropathological changes.

Increased Proportions of C1 Truncated Prion Protein Protect Against Cellular M1000 Prion Infection

Prion disease pathogenesis is linked to the cell-associated propagation of misfolded protease-resistant conformers (PrPres) of the normal cellular prion protein (PrPC). Ongoing PrPC expression is the only known absolute requirement for successful prion disease transmission and PrPres propagation. Further typifying prion disease is selective neuronal dysfunction and loss, although the precise mechanisms underlying this are undefined. We utilized a single prion strain (M1000) and a range of neuronal and nonneuronal, PrPC endogenously expressing and transgenically modified overexpressing cell lines, to evaluate whether PrPC glycosylation patterns or constitutive N-terminal cleavage events may be determinants of sustained PrPres propagation. Our data demonstrates that relative proportions offull-length and C1 truncated PrPC are the most important characteristics influencing susceptibility to sustained M1000 prion infection, supporting PrPC &agr;-cleavage as a protective event, which may contribute to the selective neuronal vulnerability observed in vivo.

Australian sporadic CJD analysis supports endogenous determinants of molecular-clinical profiles

Objective: To define the protease-resistant prion protein (PrPres) types and associated clinical profiles in Australian patients with sporadic Creutzfeldt–Jakob disease (CJD) to allow comparison with those reported from other continents and concomitantly reaffirm absence of variant CJD (vCJD). Methods: Reassessment of available clinical and neuropathologic data on patients referred to the Australian National Creutzfeldt–Jakob Disease Registry (ANCJDR) who died between January 1, 1992, and June 30, 2003, was conducted. Molecular classification of PrPres was determined by immunoblot analysis of available frozen brain tissue. Brain homogenate pH and codon 129 genotype on the prion protein gene (PRNP) were established. Results: PrPres patterns in 35 of 37 patients with sporadic CJD conformed to one of three common reported types. Of a range of clinical features assessed, illness duration was the only clinical feature significantly associated with PrPres type. Two patients displayed coexistence of more than one PrP type, with one displaying a novel pattern of three PrPres types in a single brain region. The absence of vCJD was reconfirmed, supported by the lack of the typical PrPres glycoform pattern. Conclusions: Given Australia’s geographic isolation and environmental uniqueness, the general congruity of these results with those reported from other continents suggests that endogenous factors predominantly determine sporadic Creutzfeldt–Jakob disease (CJD) phenotypic subtypes or “strains.” These results support a clinicopathologic classification system whereby both PrPres type and codon 129 genotype are utilized to most accurately depict phenotypic subtypes or strains of sporadic CJD.

Enhanced geographically restricted surveillance simulates sporadic Creutzfeldt-Jakob disease cluster

Spatio-temporal clustering of sporadic Creutzfeldt-Jakob disease (sCJD) has been recognized and investigated previously in various global settings including Australia. Generally, despite often extensive investigation, explanations such as point source outbreaks and plausible case-to-case transmission links have not been identified to explain the apparently higher case rates than expected. In the context of national surveillance during the period 1993-2006, an increased number of cases of sCJD were recognized in a circumscribed coastal region of eastern Australia. To assess the significance of this apparent clustering, the Spatial Scan Statistic was used to examine for geographic excess of CJD mortality at spatial and temporal combined, spatial only and temporal only levels. A significant spatial cluster was confirmed, encompassing three contiguous statistical local areas within the state of New South Wales (NSW). Detailed epidemiological analysis did not reveal a plausible cross-over or point source transmission event. Further evaluation prompted the conclusion that vigilant and motivated managing clinicians in this geographically circumscribed area of NSW evinced a sustained higher level of clinical awareness for the broad phenotypic spectrum of CJD with reliable referral of suspect cases for further investigation. In addition, these physicians established and maintained a well-coordinated and active approach to suspect CJD autopsy. This combination of factors translated into a higher intensity of surveillance at approximately twice the rate per population observed in the entire state, culminating in twice the incidence of sCJD at around 2.28 cases/million population/year. The hypothesis that intensity of surveillance for rare disorders can be objectively measured and that this can positively correlate with disease incidence deserves further exploration. It may prove to be an important insight into the varying incidence rates over periods of time within individual nations and between different countries.

Ascertainment Bias Causes False Signal of Anticipation in Genetic Prion Disease

Anticipation is the phenomenon whereby age of onset in genetic disease decreases in successive generations. Three independent reports have claimed anticipation in Creutzfeldt-Jakob disease (CJD) caused by the c.598G > A mutation in PRNP encoding a p.Glu200Lys (E200K) substitution in the prion protein. If confirmed, this finding would carry clear implications for genetic counseling. We analyzed pedigrees with this mutation from four prion centers worldwide (n = 217 individuals with the mutation) to analyze age of onset and death in affected and censored individuals. We show through simulation that selective ascertainment of individuals whose onset falls within the historical window since the mutations 1989 discovery is sufficient to create robust false signals both of anticipation and of heritability of age of onset. In our data set, the number of years of anticipation observed depends upon how strictly the data are limited by the ascertainment window. Among individuals whose disease was directly observed at a study center, a 28-year difference between parent and child age of onset is observed (p = 0.002), but including individuals ascertained retrospectively through family history reduces this figure to 7 years (p = 0.005). Applying survival analysis to the most thoroughly ascertained subset of data eliminates the signal of anticipation. Moreover, even non-CJD deaths exhibit 16 years anticipation (p = 0.002), indicating that ascertainment bias can entirely explain observed anticipation. We suggest that reports of anticipation in genetic prion disease are driven entirely by ascertainment bias. Guidelines for future studies claiming statistical evidence for anticipation are suggested.

Intensity of human prion disease surveillance predicts observed disease incidence

Background Prospective national screening and surveillance programmes serve a range of public health functions. Objectively determining their adequacy and impact on disease may be problematic for rare disorders. We undertook to assess whether objective measures of disease surveillance intensity could be developed for the rare disorder sporadic Creutzfeldt–Jakob disease (CJD) and whether such measures correlate with disease incidence. Method From 10 countries with national human prion disease surveillance centres, the annual number of suspected prion disease cases notified to each national unit (n=17 610), referrals for cerebrospinal fluid (CSF) 14-3-3 protein diagnostic testing (n=28 780) and the number of suspect cases undergoing diagnostic neuropathological examination (n=4885) from 1993 to 2006 were collected. Age and survey year adjusted incidence rate ratios with 95% CIs were estimated using Poisson regression models to assess risk factors for sporadic, non-sporadic and all prion disease cases. Results Age and survey year adjusted analysis showed all three surveillance intensity measures (suspected human prion disease notifications, 14-3-3 protein diagnostic test referrals and neuropathological examinations of suspect cases) significantly predicted the incidence of sporadic CJD, non-sporadic CJD and all prion disease. Conclusions Routine national surveillance methods adjusted as population rates allow objective determination of surveillance intensity, which correlates positively with reported incidence for human prion disease, especially sporadic CJD, largely independent of national context. The predictive relationship between surveillance intensity and disease incidence should facilitate more rapid delineation of aberrations in disease occurrence and assessment of the adequacy of disease monitoring by national registries.

Unusual Clinical and Molecular-Pathological Profile of Gerstmann-Sträussler-Scheinker Disease Associated With a Novel PRNP Mutation (V176G)

IMPORTANCE Here we describe the unusual clinical and molecular-neuropathological profile of a case of Gerstmann-Sträussler-Scheinker disease associated with a novel prion protein (PRNP) gene mutation. OBSERVATIONS This case report from the Australian National Creutzfeldt-Jakob Disease Registry concerns a 61-year-old British-born woman with no history of neurodegenerative disorder in first-degree relatives. Rapidly progressive dementia, altered behavior, and cerebellar ataxia dominated the clinical picture in the period immediately following minor elective surgery, with death 1 month later in an akinetic-mute state. Brain histopathological examination revealed neuronal loss, scant foci of spongiform change, and diffuse multicentric amyloid plaques, selectively immunoreactive for prion protein, within the cerebral and cerebellar cortices and deep gray matter. Tau immune-reactive neurofibrillary tangles and neuritic threads were present in the cerebral cortex. PRNP sequencing demonstrated a valine to glycine mutation at codon 176, with valine homozygosity at polymorphic codon 129. Western-blot analysis of frozen brain tissue displayed a nonclassic protease-resistant prion protein banding pattern, with a prominent approximately 8-kDa protease-resistant fragment. CONCLUSIONS AND RELEVANCE Reported is a proband with a novel PRNP mutation associated with neuropathologically confirmed Gerstmann-Sträussler-Scheinker disease displaying a somewhat unusual constellation of clinicopathological features, which overall subserve to further broaden an already diverse phenotypic spectrum.