Variant CJD: Reflections a Quarter of a Century on

The epidemiological and clinical characteristics of patients with young-onset genetic Creutzfeldt-Jakob disease

OBJECTIVES

The onset of Creutzfeldt-Jakob disease (CJD) is usually around the age of 60, but younger patients have been described as well. Our study characterizes the demographic and clinical features of young-onset CJD patients.

METHODS

The CJD Israeli National Database was reviewed, and the patients were divided into groups of young (<40-year-old) (Y|) and older disease onset (>40-year-old) (O). Each group was further divided into sporadic (sCJD) and genetic (gCJD) patients. Clinical and demographic parameters were compared between the groups.

RESULTS

The study included 731 patients (Y- 18 patients, O- 713 patients). MRI showed classical features more often in the older population (O-76.9%, Y-36%, p = 0.006). Rapidly progressive dementia as a presenting feature was more common in the older group (O = 58%, Y = 27.7%, p = 0.019) whereas cerebellar onset (gait instability, dysarthria) was more common in the younger group (O = 6.7%, Y = 27.7%, p = 0.036)). Among gCJD patients, rapidly progressive dementia was commonly seen in older patients (O = 54%, Y = 21% p = 0.008) whereas cerebellar symptoms were seen in young patients (O = 7%, Y = 30% p = 0.01) Typical MRI findings were seen in 37% of young people compared to 87% of older patients (p = 0.002). No significant differences were between young and older patients in the sCJD group.

CONCLUSION

Young-onset gCJD patients have unique disease features including less typical brain MRI changes, a lower prevalence of dementia, and a higher prevalence of cerebellar signs at disease onset.

The advances in the early and accurate diagnosis of Creutzfeldt-Jakob disease and other prion diseases: where are we today?

INTRODUCTION

Before the introduction of MRI diffusion-weighted images (DWI), the diagnosis of Creutzfeldt-Jakob disease (CJD) relied upon nonspecific findings including clinical symptoms, EEG abnormalities, and elevated levels of cerebrospinal fluid 14-3-3 protein. Subsequently, the use of DWI has improved diagnostic accuracy, but it sometimes remains difficult to differentiate CJD from encephalitis, epilepsy, and other dementing disorders. The revised diagnostic criteria include real-time quaking-induced conversion (RT-QuIC), detecting small amounts of CJD-specific prion protein, and clinically sensitive DWI. Combining these techniques has further improved diagnostic accuracy, enabling earlier diagnosis.

AREAS COVERED

Herein, the authors review the recent advances in diagnostic methods and revised diagnostic criteria for sporadic CJD. They also discuss other prion diseases, such as variant CJD and chronic wasting disease, where the emergence of new types is a concern.

EXPERT OPINION

Despite improvements in diagnostic methods and criteria, some subtypes of prion disease are still difficult to diagnose, and even the diagnosis using the most innovative RT-QuIC test remains a challenge in terms of accuracy and standardization. However, these revised criteria can be adapted to the emergence of new types of prion diseases. It is essential to continue careful surveillance and update information on the latest prion disease phenotypes.

Kinetics of Abnormal Prion Protein in Blood of Transgenic Mice Experimentally Infected by Multiple Routes with the Agent of Variant Creutzfeldt-Jakob Disease

Transmissible spongiform encephalopathies (TSEs) or prion diseases are characterized by the accumulation in affected tissues of the abnormal prion protein PrP^TSE. We previously demonstrated PrP^TSE in the blood of macaques experimentally infected with variant Creutzfeldt-Jakob disease (vCJD), a human TSE, months to years prior to clinical onset. That work supported the prospect of using PrP^TSE as a blood biomarker to detect vCJD and possibly other human TSEs before the onset of overt illness. However, our results also raised questions about the origin of PrP^TSE detected in blood early after inoculation and the effects of dose and route on the timing of the appearance of PrP^TSE. To investigate these questions, we inoculated vCJD-susceptible transgenic mice and non-infectable prion protein-knockout mice under inoculation conditions resembling those used in macaques, with additional controls. We assayed PrP^TSE in mouse blood using the protein misfolding cyclic amplification (PMCA) method. PrP^TSE from the inoculum cleared from the blood of all mice before 2 months post-inoculation (mpi). Mouse PrP^TSE generated de novo appeared in blood after 2 mpi. These results were consistent regardless of dose or inoculation route. We also demonstrated that a commercial ELISA-like PrP^TSE test detected and quantified PMCA products and provided a useful alternative to Western blots.

Human prion diseases: An overview

Prion diseases are a group of neurodegenerative diseases. The disease-causing agent is a protein (PrP), that is normally produced in the nervous system, aggregated in an abnormal form. The abnormal protein, known as prion (PrP^Sc), is capable of self-propagation promoting the misfolding of the normal protein (PrP). These conditions can be acquired sporadically, genetically, or infectiously either by eating meat contaminated with prions or from iatrogenic exposure. The diagnosis of these diseases is often challenging. The use of highly sensitive and specific diagnostic tools, such as MRI and RT-QuIC, may aid in the diagnosis. Neuropathological examination of brain tissue ensures a definite diagnosis. At present, no treatment significantly improves the course of prion diseases; however, an early diagnosis is of paramount importance for patient care decision planning, infection control purposes, and genetic counseling.

Oral vaccination as a potential strategy to manage chronic wasting disease in wild cervid populations

Prion diseases are a novel class of infectious disease based in the misfolding of the cellular prion protein (PrPC) into a pathological, self-propagating isoform (PrPSc). These fatal, untreatable neurodegenerative disorders affect a variety of species causing scrapie in sheep and goats, bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in cervids, and Creutzfeldt-Jacob disease (CJD) in humans. Of the animal prion diseases, CWD is currently regarded as the most significant threat due its ongoing geographical spread, environmental persistence, uptake into plants, unpredictable evolution, and emerging evidence of zoonotic potential. The extensive efforts to manage CWD have been largely ineffective, highlighting the need for new disease management tools, including vaccines. Development of an effective CWD vaccine is challenged by the unique biology of these diseases, including the necessity, and associated dangers, of overcoming immune tolerance, as well the logistical challenges of vaccinating wild animals. Despite these obstacles, there has been encouraging progress towards the identification of safe, protective antigens as well as effective strategies of formulation and delivery that would enable oral delivery to wild cervids. In this review we highlight recent strategies for antigen selection and optimization, as well as considerations of various platforms for oral delivery, that will enable researchers to accelerate the rate at which candidate CWD vaccines are developed and evaluated.

Diagnostic performance of CSF biomarkers in a well-characterized Australian cohort of sporadic Creutzfeldt-Jakob disease

The most frequently utilized biomarkers to support a pre-mortem clinical diagnosis of sporadic Creutzfeldt-Jakob disease (sCJD) include concentrations of the 14-3-3 and total tau (T-tau) proteins, as well as the application of protein amplification techniques, such as the real time quaking-induced conversion (RT-QuIC) assay, in cerebrospinal fluid (CSF). Utilizing CSF from a cohort of neuropathologically confirmed (definite) sCJD (n = 50) and non-CJD controls (n = 48), we established the optimal cutpoints for the fully automated Roche Elecsys^® immunoassay for T-tau and the CircuLexTM 14-3-3 Gamma ELISA and compared these to T-tau protein measured using a commercially available assay (INNOTEST hTAU Ag) and 14-3-3 protein detection by western immunoblot (WB). These CSF specimens were also assessed for presence of misfolded prion protein using the RT-QuIC assay. T-tau showed similar diagnostic performance irrespective of the assay utilized, with ~90% sensitivity and specificity. The 14-3-3 protein detection by western blot (WB) has 87.5% sensitivity and 66.7% specificity. The 14-3-3 ELISA demonstrated 81.3% sensitivity and 84.4% specificity. RT-QuIC was the single best performing assay, with a sensitivity of 92.7% and 100% specificity. Our study indicates that a combination of all three CSF biomarkers increases sensitivity and offers the best chance of case detection pre-mortem. Only a single sCJD case in our cohort was negative across the three biomarkers, emphasizing the value of autopsy brain examination on all suspected CJD cases to ensure maximal case ascertainment.

Human prion diseases and the prion protein - what is the current state of knowledge?

Prion diseases and the prion protein are only partially understood so far in many aspects. This explains the continued research on this topic, calling for an overview on the current state of knowledge. The main objective of the present review article is to provide a comprehensive up-to-date presentation of all major features of human prion diseases bridging the gap between basic research and clinical aspects. Starting with the prion protein, current insights concerning its physiological functions and the process of pathological conversion will be highlighted. Diagnostic, molecular, and clinical aspects of all human prion diseases will be discussed, including information concerning rare diseases like prion-associated amyloidoses and Huntington disease-like 1, as well as the question about a potential human threat due to the transmission of prions from prion diseases of other species such as chronic wasting disease. Finally, recent attempts to develop future therapeutic strategies will be addressed.

Recent Advances in Prion Inactivation by Plasma Sterilizer

Prions, which cause transmissible spongiform encephalopathies (TSEs), are a notorious group of infectious agents with possibly the highest resistance to complete inactivation. Although various gas plasma instruments have been developed, studies on prion inactivation using gas plasma instruments are limited. Among them, the hydrogen peroxide gas plasma instrument, STERRAD® (Advanced Sterilization Products; ASP, Johnson & Johnson, Irvine, CA, USA), is recommended for prion inactivation of heat-sensitive medical devices. However, STERRAD® is not a plasma sterilizer but a hydrogen peroxide gas sterilizer. In STERRAD®, plasma generated by radio frequency (RF) discharge removes excess hydrogen peroxide gas and does not contribute to sterilization. This is also supported by evidence that the instrument was not affected by the presence or absence of RF gas plasma. However, recent studies have shown that other gas plasma instruments derived from air, nitrogen, oxygen, Ar, and a mixture of gases using corona, dielectric barrier, microwave, and pulse discharges can inactivate scrapie prions. As inactivation studies on prions other than scrapie are limited, further accumulation of evidence on the effectiveness of gas plasma using human-derived prion samples is warranted for practical purposes.

Recombinant Mammalian Prions: The “Correctly” Misfolded Prion Protein Conformers

Generating a prion with exogenously produced recombinant prion protein is widely accepted as the ultimate proof of the prion hypothesis. Over the years, a plethora of misfolded recPrP conformers have been generated, but despite their seeding capability, many of them have failed to elicit a fatal neurodegenerative disorder in wild-type animals like a naturally occurring prion. The application of the protein misfolding cyclic amplification technique and the inclusion of non-protein cofactors in the reaction mixture have led to the generation of authentic recombinant prions that fully recapitulate the characteristics of native prions. Together, these studies reveal that recPrP can stably exist in a variety of misfolded conformations and when inoculated into wild-type animals, misfolded recPrP conformers cause a wide range of outcomes, from being completely innocuous to lethal. Since all these recPrP conformers possess seeding capabilities, these results clearly suggest that seeding activity alone is not equivalent to prion activity. Instead, authentic prions are those PrP conformers that are not only heritable (the ability to seed the conversion of normal PrP) but also pathogenic (the ability to cause fatal neurodegeneration). The knowledge gained from the studies of the recombinant prion is important for us to understand the pathogenesis of prion disease and the roles of misfolded proteins in other neurodegenerative disorders.