Preventive or promotive effects of PRNP polymorphic heterozygosity on the onset of prion disease

The polymorphic heterozygosity of PRNP at codon 129 or 219 prevents the onset of sporadic Creutzfeldt-Jakob disease (sCJD). We investigated the association between polymorphic genotypes at codon 129 or 219 and comprehensive prion disease onset using non-CJD as a reference. EK heterozygotes at codon 219, versus EE homozygotes, showed a preventive effect on the extensive prion diseases-sCJD, genetic CJD (gCJD) with V180I or M232R mutation, and Gerstmann-Straussler-Scheinker disease with P102L mutation. No preventive effect was observed for E200K-gCJD and dura-grafted CJD (dCJD) in 129 MV and 219 EK heterozygotes. It was suggested that unlike other prion diseases, E200K-gCJD may not benefit from the preventive effect of 219 EK heterozygosity because complementary electrostatic interactions between PrP molecules at K200 and E219 might make homodimer formation easier. Comparison of sCJD and dCJD indicates that 219 EK heterozygosity strongly inhibits de novo synthesis of PrP^Sc (initial PrP^Sc formation), but does not inhibit accelerated propagation of existing PrP^Sc.

Analysis of a large case series of fatal familial insomnia to determine tests with the highest diagnostic value

Fatal familial insomnia (FFI) is a rare prionopathy with unusually high incidence in the Basque Country. We report detailed data on clinical, diagnostic, histopathological, and biochemical characteristics of a recent FFI case series. The Basque Brain Bank database was screened for patients diagnosed from 2010 to 2021 with standard genetic and/or neuropathological criteria. This series includes 16 patients, 25% without family history, with 12 cases from 9 unrelated (but geographically-linked, Basque country) kindreds, onset ranging from 36 to 70 years, and disease course from 7 to 11.5 months. Insomnia was the initial symptom in most cases, with consistent polysomnography in 92% of the cases. In contrast, 14-3-3 and RT-QuIC from cerebrospinal fluid were negative. Most patients were homozygous for methionine. Gliosis and neuronal loss in basal ganglia and thalamus were the main histopathological findings; Western blotting identified preferentially the protease-resistant prion protein (PrPres) type 2, although detection of the scrapie isoform of the prion protein (PrPSc) identified using brain tissue RT-QuIC was more successful. This is one of the largest current studies on FFI patients performed to provide improvements in diagnostic reliability. Among the analyzed tests, polysomnography and the genetic study show the highest diagnostic value in FFI.

Genetic Prion Disease: Insight from the Features and Experience of China National Surveillance for Creutzfeldt-Jakob Disease

Human genetic prion diseases (gPrDs) are directly associated with mutations and insertions in the PRNP (Prion Protein) gene. We collected and analyzed the data of 218 Chinese gPrD patients identified between Jan 2006 and June 2020. Nineteen different subtypes were identified and gPrDs accounted for 10.9% of all diagnosed PrDs within the same period. Some subtypes of gPrDs showed a degree of geographic association. The age at onset of Chinese gPrDs peaked in the 50-59 year group. Gerstmann-Sträussler-Scheinker syndrome (GSS) and fatal familial insomnia (FFI) cases usually displayed clinical symptoms earlier than genetic Creutzfeldt-Jakob disease (gCJD) patients with point mutations. A family history was more frequently recalled in P105L GSS and D178N FFI patients than T188K and E200K patients. None of the E196A gCJD patients reported a family history. The gCJD cases with point mutations always developed clinical manifestations typical of sporadic CJD (sCJD). EEG examination was not sensitive for gPrDs. sCJD-associated abnormalities on MRI were found in high proportions of GSS and gCJD patients. CSF 14-3-3 positivity was frequently detected in gCJD patients. Increased CSF tau was found in more than half of FFI and T188K gCJD cases, and an even higher proportion of E196A and E200K gCJD patients. 63.6% of P105L GSS cases showed a positive reaction in cerebrospinal fluid RT-QuIC. GSS and FFI cases had longer durations than most subtypes of gCJD. This is one of the largest studies of gPrDs in East Asians, and the illness profile of Chinese gPrDs is clearly distinct. Extremely high proportions of T188K and E196A occur among Chinese gPrDs; these mutations are rarely reported in Caucasians and Japanese.

Doxycycline rescues recognition memory and circadian motor rhythmicity but does not prevent terminal disease in fatal familial insomnia mice

Fatal familial insomnia (FFI) is a dominantly inherited prion disease linked to the D178N mutation in the gene encoding the prion protein (PrP). Symptoms, including insomnia, memory loss and motor abnormalities, appear around 50 years of age, leading to death within two years. No treatment is available. A ten-year clinical trial of doxycycline (doxy) is under way in healthy individuals at risk of FFI to test whether presymptomatic doxy prevents or delays the onset of disease. To assess the drug's effect in a tractable disease model, we used Tg(FFI-26) mice, which accumulate aggregated and protease-resistant PrP in their brains and develop a fatal neurological illness highly reminiscent of FFI. Mice were treated daily with 10 mg/kg doxy starting from a presymptomatic stage for twenty weeks. Doxy rescued memory deficits and restored circadian motor rhythmicity in Tg(FFI-26) mice. However, it did not prevent the onset and progression of motor dysfunction, clinical signs and progression to terminal disease. Doxy did not change the amount of aggregated and protease-resistant PrP, but reduced microglial activation in the hippocampus. Presymptomatic doxy treatment rescues cognitive impairment and the motor correlates of sleep dysfunction in Tg(FFI-26) mice but does not prevent fatal disease.

Transgenic mouse models for the study of prion diseases

Prions are unique agents that challenge the molecular biology dogma by transmitting information on the protein level. They cause neurodegenerative diseases that lack of any cure or treatment called transmissible spongiform encephalopathies. The function of the normal form of the prion protein, the exact mechanism of prion propagation between species as well as at the cellular level and neuron degeneration remains elusive. However, great amount of information known for all these aspects has been achieved thanks to the use of animal models and more precisely to transgenic mouse models. In this chapter, the main contributions of these powerful research tools in the prion field are revised.

Cerebrospinal Fluid Total Prion Protein in the Spectrum of Prion Diseases

Cerebrospinal fluid (CSF) total prion protein (t-PrP) is decreased in sporadic Creutzfeldt-Jakob disease (sCJD). However, data on the comparative signatures of t-PrP across the spectrum of prion diseases, longitudinal changes during disease progression, and levels in pre-clinical cases are scarce. T-PrP was quantified in neurological diseases (ND, n = 147) and in prion diseases from different aetiologies including sporadic (sCJD, n = 193), iatrogenic (iCJD, n = 12) and genetic (n = 209) forms. T-PrP was also measured in serial lumbar punctures obtained from sCJD cases at different symptomatic disease stages, and in asymptomatic prion protein gene (PRNP) mutation carriers. Compared to ND, t-PrP concentrations were significantly decreased in sCJD, iCJD and in genetic prion diseases associated with the three most common mutations E200K, V210I (associated with genetic CJD) and D178N-129M (associated with fatal familial insomnia). In contrast, t-PrP concentrations in P102L mutants (associated with the Gerstmann-Sträussler-Scheinker syndrome) remained unaltered. In serial lumbar punctures obtained at different disease stages of sCJD patients, t-PrP concentrations inversely correlated with disease progression. Decreased mean t-PrP values were detected in asymptomatic D178-129M mutant carriers, but not in E200K and P102L carriers. The presence of low CSF t-PrP is common to all types of prion diseases regardless of their aetiology albeit with mutation-specific exceptions in a minority of genetic cases. In some genetic prion disease, decreased levels are already detected at pre-clinical stages and diminish in parallel with disease progression. Our data indicate that CSF t-PrP concentrations may have a role as a pre-clinical or early symptomatic diagnostic biomarker in prion diseases as well as in the evaluation of therapeutic interventions.

Biochemical features of genetic Creutzfeldt-Jakob disease with valine-to-isoleucine substitution at codon 180 on the prion protein gene

Valine-to-isoleucine substitution at codon 180 of the prion protein gene is only observed in patients with Creutzfeldt-Jakob disease and accounts for approximately half of all cases of genetic prion disease in Japan. In the present study, we investigated the biochemical characteristics of valine-to-isoleucine substitution at codon 180 in the prion protein gene, using samples obtained from the autopsied brains of seven patients with genetic Creutzfeldt-Jakob disease exhibiting this mutation (diagnoses confirmed via neuropathological examination). Among these patients, we observed an absence of diglycosylated and monoglycosylated forms of PrP^res at codon 181. Our findings further indicated that the abnormal prion proteins were composed of at least three components, although smaller carboxyl-terminal fragments were predominant. Western blot analyses revealed large amounts of PrP^res in the cerebral neocortices, where neuropathological examination revealed marked spongiosis. Relatively smaller amounts of PrP^res were detected in the hippocampus, where milder spongiosis was observed, than in the cerebral neocortex. These findings indicate that abnormal prion proteins in the neocortex are associated with severe toxicity, resulting in severe spongiosis. Our findings further indicate that the valine-to-isoleucine substitution is not a polymorphism, but rather an authentic pathogenic mutation associated with specific biochemical characteristics that differ from those observed in sporadic Creutzfeldt-Jakob disease.

Transgenic mice recapitulate the phenotypic heterogeneity of genetic prion diseases without developing prion infectivity: Role of intracellular PrP retention in neurotoxicity

Genetic prion diseases are degenerative brain disorders caused by mutations in the gene encoding the prion protein (PrP). Different PrP mutations cause different diseases, including Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker (GSS) syndrome and fatal familial insomnia (FFI). The reason for this variability is not known. It has been suggested that prion strains with unique self-replicating and neurotoxic properties emerge spontaneously in individuals carrying PrP mutations, dictating the phenotypic expression of disease. We generated transgenic mice expressing the FFI mutation, and found that they developed a fatal neurological illness highly reminiscent of FFI, and different from those of similarly generated mice modeling genetic CJD and GSS. Thus transgenic mice recapitulate the phenotypic differences seen in humans. The mutant PrPs expressed in these mice are misfolded but unable to self-replicate. They accumulate in different compartments of the neuronal secretory pathway, impairing the membrane delivery of ion channels essential for neuronal function. Our results indicate that conversion of mutant PrP into an infectious isoform is not required for pathogenesis, and suggest that the phenotypic variability may be due to different effects of mutant PrP on intracellular transport.