Phenotypic Heterogeneity of Variably Protease-Sensitive Prionopathy: A Report of Three Cases Carrying Different Genotypes at PRNP Codon 129

Characterization of variably protease-sensitive prionopathy by capillary electrophoresis

Variably Protease Sensitive Prionopathy (VPSPr) is a rare human prion disease that, like Creutzfeldt-Jakob disease (CJD), results in the deposition of abnormally folded prion protein aggregates in the brain and is ultimately fatal. Neuropathology and clinical features of VPSPr are heterogeneous. However, the key discriminating feature is the relative sensitivity of the pathological prion protein to proteinase digestion compared to that typically seen in other human prion cases. Three major fragments of 23, 17 and 7 kDa are characteristic of the disease following digestion with proteinase K. We recently reported the utility of the highly adaptive and reproducible ProteinSimple™ capillary electrophoresis (CE) system to perform protein separation of PK digested prion protein in CJD. Consequently, we explored capillary-based electrophoresis (CE) technology as a sensitive method to detect and characterize VPSPr in a cohort of 29 cases. The unique 7 kDa fragment has high intensity, particularly in cases with the codon 129 VV genotype, but can be missed by regular Western blotting due to the small size. However, this fragment is readily detected by CE in all cases. In addition, the flexibility of CE produced highly reproducible, semi-quantitative data for determining relative proteinase K sensitivity and epitope mapping of representative cases from each codon 129 genotype (VV, MV and MM).

Variably protease-sensitive prionopathy with methionine homozygosity at codon 129 in the prion protein gene

Variably protease-sensitive prionopathy (VPSPr) is a recently characterised rare subtype of sporadic prion disease, mainly affecting individuals with valine homozygosity at codon 129 in the prion protein gene, with only seven methionine homozygote cases reported to date. This case presents clinical, neuropathological and biochemical features of the eighth VPSPr case worldwide with methionine homozygosity at codon 129 and compares the features with the formerly presented cases.The patient, a woman in her 70s, presented with cognitive decline, impaired balance and frequent falls. Medical history and clinical presentation were suggestive of a rapidly progressive dementia disorder. MRI showed bilateral thalamic hyperintensity. Cerebrospinal fluid real-time quaking-induced conversion was negative, and the electroencephalogram was unremarkable. The diagnosis was established through post-mortem pathological examinations. VPSPr should be suspected in rapidly progressive dementia lacking typical features or paraclinical results of protein misfolding diseases.

An autopsy case of variably protease-sensitive prionopathy with Met/Met homogeneity at codon 129

The typical clinical manifestations of sporadic Creutzfeldt-Jakob disease (sCJD) are rapid-progressive dementia and myoclonus. However, the diagnosis of atypical sCJD can be challenging due to its wide phenotypic variations. We report an autopsy case of variably protease-sensitive prionopathy (VPSPr) with Met/Met homogeneity at codon 129. An 81-year-old woman presented with memory loss without motor symptoms. Seventeen months after the onset, her spontaneous language production almost disappeared. Diffusion-weighted images (DWI) showed hyperintensity in the cerebral cortex while electroencephalogram (EEG) showed nonspecific change. 14-3-3 protein and real-time qualing-induced conversion (RT-QuIC) of cerebrospinal fluid were negative. She died at age 85, 3.5 years after the onset. Pathological investigation revealed spongiform change, severe neuronal loss, and gliosis in the cerebral cortex. Mild to moderate neuronal loss and gliosis were observed in the basal ganglia. PrP immunostaining revealed plaque-like, dotlike, and synaptic structures in the cerebral cortex and small plaque-like structures in the molecular layer of the cerebellum. Analysis of PRNP showed no pathogenic mutations, and Western blot examination revealed the lack of a diglycosylated band consistent with VPSPr. The present case, which is the first report on a VPSPr case in Japan, supports previously published evidence that VPSPr cases can present variable and nonspecific clinical presentations. Because a small number of VPSPr cases can show typical magnetic resonance imaging (MRI) change in sCJD. We should investigate the possibility of VPSPr in a differential diagnosis with atypical dementia that presented DWIs of high intensity in the cortex, even though 14-3-3 proteins and RT-QuIC are both negative. In addition, VPSPr cases can take a longer clinical course compared to that of sCJD, and long-term follow-up is important.

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.

The Use of Real-Time Quaking-Induced Conversion for the Diagnosis of Human Prion Diseases

Prion diseases are rapidly progressive, invariably fatal, transmissible neurodegenerative disorders associated with the accumulation of the amyloidogenic form of the prion protein in the central nervous system (CNS). In humans, prion diseases are highly heterogeneous both clinically and neuropathologically. Prion diseases are challenging to diagnose as many other neurologic disorders share the same symptoms, especially at clinical onset. Definitive diagnosis requires brain autopsy to identify the accumulation of the pathological prion protein, which is the only specific disease biomarker. Although brain post-mortem investigation remains the gold standard for diagnosis, antemortem clinical, instrumental, and laboratory tests showing variable sensitivities and specificity, being surrogate disease biomarkers, have been progressively introduced in clinical practice to reach a diagnosis. More recently, the ultrasensitive Real-Time Quaking-Induced Conversion (RT-QuIC) assay, exploiting, for the first time, the detection of misfolded prion protein through an amplification strategy, has highly improved the “in-vitam” diagnostic process, reaching in cerebrospinal fluid (CSF) and olfactory mucosa (OM) around 96% sensitivity and close to 100% specificity. RT-QuIC also improved the detection of the pathologic prion protein in several peripheral tissues, possibly even before the clinical onset of the disease. The latter aspect is of great interest for the early and even preclinical diagnosis in subjects at genetic risk of developing the disease, who will likely be the main target population in future clinical trials. This review presents an overview of the current knowledge and future perspectives on using RT-QuIC to diagnose human prion diseases.