Filamentous white matter prion protein deposition is a distinctive feature of multiple inherited prion diseases

Characterization of Prion Disease Associated with a Two-Octapeptide Repeat Insertion

Genetic prion disease accounts for 10-15% of prion disease. While insertion of four or more octapeptide repeats are clearly pathogenic, smaller repeat insertions have an unclear pathogenicity. The goal of this case series was to provide an insight into the characteristics of the 2-octapeptide repeat genetic variant and to provide insight into the risk for Creutzfeldt-Jakob disease in asymptomatic carriers. 2-octapeptide repeat insertion prion disease cases were collected from the National Prion Disease Pathology Surveillance Center (US), the National Prion Clinic (UK), and the National Creutzfeldt-Jakob Disease Registry (Australia). Three largescale population genetic databases were queried for the 2-octapeptide repeat insertion allele. Eight cases of 2-octapeptide repeat insertion were identified. The cases were indistinguishable from the sporadic Creutzfeldt-Jakob cases of the same molecular subtype. Western blot characterization of the prion protein in the absence of enzymatic digestion with proteinase K revealed that 2-octapeptide repeat insertion and sporadic Creutzfeldt-Jakob disease have distinct prion protein profiles. Interrogation of large-scale population datasets suggested the variant is of very low penetrance. The 2-octapeptide repeat insertion is at most a low-risk genetic variant. Predictive genetic testing for asymptomatic blood relatives is not likely to be justified given the low risk.

Molecular Characterization of the Danish Prion Diseases Cohort With Special Emphasis on Rare and Unique Cases

The purpose of this study was to perform an updated reclassification of all definite prion disease cases with available fresh-frozen samples referred to the Danish Reference Center over the past 40 years, putting a special emphasis on the molecular characterization of novel disease subtypes. Investigation of the Danish prion diseases cohort revealed rare sporadic Creutzfeldt-Jakob disease cases with mixed subtypes and subtypes with previously uncharacterized white matter plaques, a new case of sporadic fatal insomnia, and 3 novel mutations, including 2 large octapeptide repeat insertions, and a point mutation in the prion protein gene. The evaluation of methionine and valine distribution at codon 129 among the prion disease patients in the cohort revealed the increased prevalence of methionine homozygotes compared to the general population. This observation was in line with the prevalence reported in other Caucasian prion disease cohort studies. Reclassification of the old prion diseases cohort revealed unique cases, the molecular characterization of which improves prion diseases classification, diagnostic accuracy, genetic counseling of affected families, and the understanding of disease biology.

Evaluating the causality of novel sequence variants in the prion protein gene by example

The estimation of pathogenicity and penetrance of novel prion protein gene (PRNP) variants presents significant challenges, particularly in the absence of family history, which precludes the application of Mendelian segregation. Moreover, the ambiguities of prion disease pathophysiology renders conventional in silico predictions inconclusive. Here, we describe 2 patients with rapid cognitive decline progressing to akinetic mutism and death within 10 weeks of symptom onset, both of whom possessed the novel T201S variant in PRNP. Clinically, both satisfied diagnostic criteria for probable sporadic Creutzfeldt-Jakob disease and in one, the diagnosis was confirmed by neuropathology. While computational analyses predicted that T201S was possibly deleterious, molecular strain typing, prion protein structural considerations, and calculations leveraging large-scale population data (gnomAD) indicate that T201S is at best either of low penetrance or nonpathogenic. Thus, we illustrate the utility of harnessing multiple lines of prion disease-specific evidence in the evaluation of the T201S variant, which may be similarly applied to assess other novel variants in PRNP.

Altered trafficking of abnormal prion protein in atypical scrapie: prion protein accumulation in oligodendroglial inner mesaxons

AIMS

Prion diseases exist in classical and atypical disease forms. Both forms are characterized by disease-associated accumulation of a host membrane sialoglycoprotein known as prion protein (PrPd ). In classical forms of prion diseases, PrPd can accumulate in the extracellular space as fibrillar amyloid, intracellularly within lysosomes, but mainly on membranes in association with unique and characteristic membrane pathology. These membrane changes are found in all species and strains of classical prion diseases and consist of spiral, branched and clathrin-coated membrane invaginations on dendrites. Atypical prion diseases have been described in ruminants and man and have distinct biological, biochemical and pathological properties when compared to classical disease. The purpose of this study was to determine whether the subcellular pattern of PrPd accumulation and membrane changes in atypical scrapie were the same as those found in classical prion diseases.

METHODS

Immunogold electron microscopy was used to examine brains of atypical scrapie-affected sheep and Tg338 mice.

RESULTS

Classical prion disease-associated membrane lesions were not found in atypical scrapie-affected sheep, however, white matter PrPd accumulation was localized mainly to the inner mesaxon and paranodal cytoplasm of oligodendroglia. Similar lesions were found in myelinated axons of atypical scrapie Tg338-infected mice. However, Tg338 mice also showed the unique grey matter membrane changes seen in classical forms of disease.

CONCLUSIONS

These data show that atypical scrapie infection directs a change in trafficking of abnormal PrP to axons and oligodendroglia and that the resulting pathology is an interaction between the agent strain and host genotype.

Comparison of abnormal isoform of prion protein in prion-infected cell lines and primary-cultured neurons by PrPSc-specific immunostaining

We established abnormal isoform of prion protein (PrPSc)-specific double immunostaining using mAb 132, which recognizes aa 119-127 of the PrP molecule, and novel PrPSc-specific mAb 8D5, which recognizes the N-terminal region of the PrP molecule. Using the PrPSc-specific double immunostaining, we analysed PrPSc in immortalized neuronal cell lines and primary cerebral-neuronal cultures infected with prions. The PrPSc-specific double immunostaining showed the existence of PrPSc positive for both mAbs 132 and 8D5, as well as those positive only for either mAb 132 or mAb 8D5. This indicated that double immunostaining detects a greater number of PrPSc species than single immunostaining. Double immunostaining revealed cell-type-dependent differences in PrPSc staining patterns. In the 22 L prion strain-infected Neuro2a (N2a)-3 cells, a subclone of N2a neuroblastoma cell line, or GT1-7, a subclone of the GT1 hypothalamic neuronal cell line, granular PrPSc stains were observed at the perinuclear regions and cytoplasm, whereas unique string-like PrPSc stains were predominantly observed on the surface of the 22 L strain-infected primary cerebral neurons. Only 14 % of PrPSc in the 22 L strain-infected N2a-3 cells were positive for mAb 8D5, indicating that most of the PrPSc in N2a-3 lack the N-terminal portion. In contrast, nearly half PrPSc detected in the 22 L strain-infected primary cerebral neurons were positive for mAb 8D5, suggesting the abundance of full-length PrPSc that possesses the N-terminal portion of PrP. Further analysis of prion-infected primary neurons using PrPSc-specific immunostaining will reveal the neuron-specific mechanism for prion propagation.

Rapidly progressive dementia with thalamic degeneration and peculiar cortical prion protein immunoreactivity, but absence of proteinase K resistant PrP: a new disease entity?

Background

Human prion diseases are a group of rare fatal neurodegenerative conditions with well-developed clinical and neuropathological diagnostic criteria. Recent observations have expanded the spectrum of prion diseases beyond the classically recognized forms.

Results

In the present study we report six patients with a novel, apparently sporadic disease characterised by thalamic degeneration and rapidly progressive dementia (duration of illness 2–12 months; age at death: 55–81 years). Light and electron microscopic immunostaining for the prion protein (PrP) revealed a peculiar intraneuritic distribution in neocortical regions. Proteinase K resistant PrP (PrP^res) was undetectable by Western blotting in frontal cortex from the three cases with frozen tissue, even after enrichment for PrP^res by centrifugation or by phosphotungstic acid precipitation. Conformation-dependent immunoassay analysis using a range of PK digestion conditions (and no PK digestion) produced only very limited evidence of meaningful D-N (denatured/native) values, indicative of the presence of disease-associated PrP (PrP^Sc) in these cases, when the results were compared with appropriate negative control groups.

Conclusions

Our observation expands the spectrum of conditions associated with rapidly progressive dementia and may have implications for the understanding of the pathogenesis of prion diseases.