Quaking-induced conversion (QuIC) tests, which detect prion-seeding activity in cerebrospinal fluid (CSF), have markedly advanced the antemortem diagnosis of prion diseases such as Creutzfeldt-Jakob disease (CJD). These tests provide high diagnostic accuracy and enable timely differentiation from other rapidly progressive neurodegenerative disorders. However, a key limitation of current QuIC tests are the reduced sensitivity in detecting inherited prion diseases and rare sporadic subtypes, including variably protease-sensitive prionopathy (VPSPr). To address this gap, we evaluated a simplified QuIC test, end-point QuIC (EP-QuIC), incorporating a novel recombinant prion protein substrate derived from the North American deer mouse (Peromyscus maniculatus). The diagnostic performance of the modified QuIC test was evaluated using CSF samples from 61 sporadic CJD, 50 inherited prion disease, and 5 VPSPr cases. EP-QuIC with the deer mouse substrate achieved 96.6% sensitivity (111/116) and 100% specificity (35/35), outperforming both standard EP-QuIC (87.1%) and next-generation (IQ-CSF) real-time-QuIC (72.4%) across the same cohort. Notably, this enhanced assay detected inherited mutations, such as D178N, that were previously undetectable with existing diagnostic tests. These findings demonstrate that adapting EP-QuIC with an optimized substrate, termed enhanced sensitivity QuIC (ES-QuIC), significantly improves diagnostic performance for inherited and atypical prion diseases. By expanding the diagnostic reach of QuIC tests, this study strengthens antemortem surveillance, reduces reliance on postmortem confirmation, and improves opportunities for early intervention and clinical trial enrollment, particularly for genetic cases most likely to benefit from emerging therapeutic strategies. ANN NEUROL 2026.

Prions are unprecedented infectious pathogens that cause a group of rare and inevitably fatal neurodegenerative diseases, affecting approximately 1 person per 1 million inhabitants worldwide each year. These diseases include Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome (GSS), kuru, fatal insomnia (FI) and variably protease-sensitive prionopathy (VPSPr), all of which involve a conformational change of normal cellular prion protein (PrPC) into abnormal scrapie prion protein (PrPSc) through a posttranslational process. This structural change is associated with profound alterations in the physicochemical properties of PrPC, making the molecule resistant to proteolysis. The conformational alteration of PrPC can occur either due to spontaneous conversion, dominant mutations in the prion protein gene (PRNP) which codes for PrPC or due to an infection with the pathogenic isoform PrPSc from exogenous sources. There is general consensus that PrPC serves as the substrate for the conversion to abnormal PrPSc. The latter multiplies exponentially and accumulates in the brain, forming deposits which are associated with the neurodegenerative changes. Although the understanding of the main causes of prion-induced neurodegeneration is still limited, the spread of PrPSc and neurotoxic signal transfer in the pathogenic process of prions appear to show an interaction. Prion diseases sometimes have long incubation times but also short clinical trajectories. Sporadic and genetic forms occur worldwide of which genetic forms are associated with mutations in PRNP. Zoonotic forms of prion diseases are also associated with bovine diseases. Substantial progress has been made in the diagnosis of these disorders and the diagnostics include magnetic resonance imaging (MRI) and laboratory investigations, particularly of the cerebrospinal fluid. Prionen sind beispiellose infektiöse Krankheitserreger, die eine Gruppe seltener und unweigerlich tödlicher neurodegenerativer Erkrankungen verursachen, die weltweit jährlich etwa 1 Person pro 1 Mio. Einwohner betreffen. Zu diesen Erkrankungen gehören die Creutzfeld-Jacob-Krankheit (CJK), Gerstmann-Sträussler-Scheinker-Syndrom (GSS), Kuru, fatale Schlaflosigkeit (FI) und variable Protease-sensitive Prionopathie (VPSPr), die alle eine konformationelle Veränderung des normalen zellulären Prionproteins (PrPC) in das abnormale Scrapie-Prionprotein (PrPSc) durch einen posttranslationalen Prozess beinhalten. Diese strukturelle Veränderung geht mit tiefgreifenden Veränderungen in den physikochemischen Eigenschaften von PrPC einher, wodurch das Molekül widerstandsfähig gegen Proteolyse wird. Die konformationelle Veränderung von PrPC kann entweder durch spontane Umwandlung, dominante Mutationen im Prionprotein(PRNP)-Gen, das für PrPC codiert, oder durch eine Infektion mit der pathogenen Isoform PrPsc aus exogenen Quellen entstehen. Es besteht allgemeine Einigkeit darüber, dass PrPC als Substrat für die Umwandlung zu abnormalem PrPSc dient. Letzteres vermehrt sich exponentiell und sammelt sich im Gehirn, wodurch Ablagerungen entstehen, die mit den neurodegenerativen Veränderungen verbunden sind. Obwohl das Verständnis der Hauptursachen der prioninduzierten Neurodegeneration noch begrenzt ist, scheint zwischen der Ausbreitung von PrPSc und neurotoxischer Signalübertragung im pathogenen Prozess der Prionen eine Wechselwirkung zu bestehen. Prionenerkrankungen weisen z. T. lange Inkubationszeiten auf und andererseits kurze klinische Verläufe. Weltweit kommen sporadische und genetische Formen vor, von denen genetische Formen mit Mutationen in PRNP assoziiert sind. Zoonotische Formen von Prionenerkrankungen sind u. a. mit Rinderkrankheiten verbunden. Bei der Diagnose dieser Störungen wurden erhebliche Fortschritte erzielt, die Diagnose umfassen Magnetresonanztomographie (MRT) und laborchemische Untersuchungen, insbesondere des Liquor cerebrospinalis.

We describe two patients with variably protease-sensitive prionopathy (VPSPr) who developed progressive upper motor neuron symptoms, insomnia, behavioral and cognitive decline, compatible with primary lateral sclerosis associated with frontotemporal dementia (FTD). Neuropathology revealed a spongiform encephalopathy with frontotemporal and pronounced thalamic involvement, associated with fine synaptic abnormal prion protein conformer (PrPSc) deposits, microplaques, and intraneuronal aggregates. Western blot analysis revealed a characteristic VPSPr proteolytic profile, lacking the diglycosylated band. Both patients were methionine homozygous at PRNP codon 129 and carried no pathogenic mutations. These cases illustrate that VPSPr can present with a prominent motor neuron syndrome and FTD features.

Variably protease-sensitive prionopathy (VPSPr) is a rare, atypical subtype of prion disease currently classified as sporadic. We performed exome sequencing and targeted sequencing of PRNP non-coding regions on genomic DNA from autopsy-confirmed VPSPr patients (N = 67) in order to search for a possible genetic cause. Our search identified no potentially causal variants for VPSPr. The common polymorphism PRNP M129V was the largest genetic risk factor for VPSPr, with an odds ratio of 7.0. Other variants in and near PRNP exhibited association to VPSPr risk only in proportion to their linkage disequilibrium with M129V, and upstream expression quantitative trait loci showed no evidence of independent association to VPSPr risk. We cannot rule out the possibility of causal variants hiding in genomic regions or classes of genetic variation that our search did not canvas. Nevertheless, our data support the classification of VPSPr as a sporadic prion disease.

Variably protease-sensitive prionopathy (VPSPr) is a rare, atypical subtype of prion disease currently classified as sporadic. We performed exome sequencing and targeted sequencing of PRNP non-coding regions on genomic DNA from autopsy-confirmed VPSPr patients (N=67) in order to search for a possible genetic cause. Our search identified no potentially causal variants for VPSPr. The common polymorphism PRNP M129V was the largest genetic risk factor for VPSPr, with an odds ratio of 7.0. Other variants in and near PRNP exhibited association to VPSPr risk only in proportion to their linkage disequilibrium with M129V, and upstream expression quantitative trait loci showed no evidence of independent association to VPSPr risk. We cannot rule out the possibility of causal variants hiding in genomic regions or classes of genetic variation that our search did not canvas. Nevertheless, our data support the classification of VPSPr as a sporadic prion disease.