Prion diseases are fatal neurodegenerative disorders that can be idiopathic, associated with genetic mutations, or acquired by infection with misfolded prion protein. We developed two complementary transgenic mouse models to investigate how the L108I substitution in mouse prion protein (PrP) influences spontaneous prion formation and transmission characteristics. The transgenic mouse model overexpressing the variant at approximately three times wild-type (WT) PrP levels (TgMo(L108I)3x) consistently developed a spontaneous neurodegenerative disorder between 219 and 536 days of age with 100% penetrance. This spontaneous disease exhibited biochemical and neuropathological characteristics of atypical prion disorders, featuring a distinctive 7-10 kDa protease-resistant PrP fragment and pathology comparable to small ruminants' atypical scrapie and certain forms of Gerstmann-Sträussler-Scheinker syndrome (GSS). In contrast, the knock-in model expressing the same variant at physiological levels (TgMo(L108I)1x) showed no spontaneous disease beyond 600 days, demonstrating that both the specific amino acid substitution and elevated expression levels are necessary for spontaneous prion formation. The spontaneously generated prions transmitted efficiently to models expressing the I108 variant and to Tga20 mice overexpressing WT PrP but encountered a robust transmission barrier toward WT mice, indicating strain-specific replication requirements. The TgMo(L108I)3x model demonstrated exceptional versatility as a universal acceptor for heterogeneous prion isolates, demonstrating superior efficiency in propagating atypical variants like GSS A117V (57 ± 0.6 days) and rapid propagation of classical scrapie-derived mouse prion strains, including Rocky Mountains Laboratory mouse prion strain (RML) (85 ± 3.8 days) and 22L (95 ± 1 days). Comparative analysis revealed that the L108I substitution differentially impacts strain propagation, with greater acceleration of RML (~33% shorter incubation) than 22L (~0.5% shorter) compared to WT mice. These complementary systems offer powerful experimental platforms for investigating the molecular determinants of spontaneous prion formation, strain selection and transmission barriers, providing insights into idiopathic prion pathogenesis and developing therapeutic interventions.

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.

Transgenic mice overexpressing bank vole prion protein with the isoleucine 109 polymorphism, TgVole(I109)4x, develop spontaneous neurodegenerative disease with sex-dependent onset, averaging 170 days in females and 200 days in males at terminal stage. The clinical and pathological features closely resemble Gerstmann-Sträussler-Scheinker syndrome (GSS), with characteristic ataxia, dysmetria, kyphosis, and prominent PrP plaques. Biochemical analysis reveals an atypical prion protein banding pattern with a distinctive low molecular weight band (7-10 kDa) following proteinase K digestion, similar to other atypical prion diseases such as small ruminants atypical scrapie (AS). Importantly, these spontaneously generated prions are highly infectious when passaged to mice expressing the same I109 polymorphism as well as to wild bank voles carrying the I109 polymorphism, but not to models expressing the methionine variant at this position, demonstrating the critical role of this specific polymorphism in atypical prion propagation. Temporal analysis reveals that infectious prions emerge significantly (2-3 months) before clinical signs appear, offering important insights into the pre-clinical phase of prion diseases. Serum neurofilament light chain levels increase significantly at 80 days of age, approximately 100 days before clinical onset, providing a wide therapeutic window with a reliable biomarker. The TgVole(I109)4× model exhibits extraordinary versatility in propagating diverse prion strains, showing remarkable susceptibility to atypical prions (including GSS and AS) with exceptionally short incubation periods, while maintaining the ability to efficiently propagate classical and recombinant prion strains. We present here a thoroughly characterized transgenic mouse model that spontaneously develops an atypical, bona fide prion disease with sex-related differences in disease onset. This model offers valuable insights into spontaneous and atypical prionopathies while demonstrating exceptional versatility for studying diverse prion strains and potential utility for evaluating therapeutic interventions when used with appropriate study designs that account for individual variability.

Gerstmann-Sträussler-Scheinker syndrome is an extremely rare hereditary human prion disease caused by distinct mutations in the prion protein-encoding gene and is frequently associated with a positive family history. The disease typically presents with progressive cerebellar symptoms such as gaze apraxia with limb ataxia and axial ataxia; thus, the diagnostic process is often challenging due to nonspecific clinical presentation. We present a case of a 73-year-old patient with no family history of dementia and cerebellar symptomatology during the course of rapidly progressing dementia. Owing to the clinical suspicion of prion disease, antemortem analysis of cerebrospinal fluid using a real-time quaking-induced conversion (RT-QuIC) assay was performed, with positive results. Postmortem histopathological examination confirmed a familiar form of human prion disease with concomitant asymptomatic tauopathy. An additional finding was a novel 6 octapeptide repeat insertion mutation in the prion gene. Familiar cases with an increasing number of repeated insertions seem to be associated with a longer overall disease course, milder clinical deterioration and often false-negative RT-QuIC results. The performance of RT-QuIC in inherited prion diseases may vary. Our case, involving a 6 octapeptide repeat insertion mutation, is particularly noteworthy due to the rapidly progressive clinical course and positive RT-QuIC results in both antemortem and postmortem tissue analyses.