Toshiaki Nonaka

Prion diseases, including Creutzfeldt–Jakob disease (CJD), are deadly neurodegenerative disorders characterized by the buildup of abnormal prion proteins in the brain. This accumulation disrupts neuronal functions, leading to the rapid onset of psychiatric symptoms, ataxia, and cognitive decline. The urgency of timely diagnosis for effective treatment necessitates the identification of strongly correlated biomarkers in bodily fluids, which makes our research crucial. In this study, we employed a fully automated multiplex ELISA (Ella^®) to measure the concentrations of 14-3-3 protein, total tau protein, and neurofilament light chain (NF-L) in cerebrospinal fluid (CSF) and serum samples from patients with prion disease and analyzed their link to disease prognosis. However, in North American and European cases, we did not confirm a correlation between NF-L levels and survival time. This discrepancy is believed to stem from differences in treatment policies and measurement methods between Japan and the United States. Nonetheless, our findings suggest that NF-L concentrations could be an early diagnostic marker for CJD patients with further enhancements. The potential impact of our findings on the early diagnosis of CJD patients is significant. Future research should focus on increasing the number of sCJD cases studied in Japan and gathering additional evidence using next-generation measurement techniques.

Background/Objectives: Sporadic Creutzfeldt–Jakob disease (sCJD) is a fatal neurodegenerative disorder traditionally diagnosed based on the World Health Organization (WHO) criteria in 1998. Recently, Hermann et al. proposed updated diagnostic criteria incorporating advanced biomarkers to enhance early detection of sCJD. This study aimed to evaluate the sensitivity and specificity of Hermann’s criteria compared with those of the WHO criteria in a large cohort of patients suspected of prion disease in Japan. Methods: In this retrospective cohort study, we examined the new criteria using data of 2004 patients with suspected prion disease registered with the Japanese Prion Disease Surveillance (JPDS) between January 2009 and May 2023. Patients with genetic or acquired prion diseases or incomplete data necessary for the diagnostic criteria were excluded, resulting in 786 eligible cases. The sensitivity and specificity of the WHO and Hermann’s criteria were calculated by comparing diagnoses with those made by the JPDS Committee. Results: Of the 786 included cases, Hermann’s criteria helped identify 572 probable cases compared with 448 by the WHO criteria. The sensitivity and specificity of the WHO criteria were 96.4% and 96.6%, respectively. Hermann’s criteria demonstrated a sensitivity of 99.3% and a specificity of 95.2%, indicating higher sensitivity but slightly lower specificity. Fifty-five cases were classified as “definite” by both criteria. Conclusions: The findings suggest that Hermann’s criteria could offer improved sensitivity for detecting sCJD, potentially reducing diagnostic oversight. However, caution is advised in clinical practice to avoid misdiagnosis, particularly in treatable neurological diseases, by ensuring thorough exclusion of other potential conditions.

Background: Recently, the investigation of cerebrospinal fluid (CSF) biomarkers for diagnosing human prion diseases (HPD) has garnered significant attention. Reproducibility and accuracy are paramount in biomarker research, particularly in the measurement of total tau (T-tau) protein, which is a crucial diagnostic marker. Given the global impact of the coronavirus disease pandemic, the frequency of measuring this protein using one of the world’s fully automated assays, chemiluminescent enzyme immunoassay (CLEA), has increased. At present, the diagnosis and monitoring of neurological diseases mainly rely on traditional methods, but their accuracy and responsiveness are limited. There is limited knowledge of the accuracy of CLEA in tau measurements. We aimed to measure T-tau protein using CLEA and to elucidate its merits and limitations. Methods: We randomly selected 60 patients with rapidly progressive dementia, using ELISA and CLEA analysis of cerebrospinal fluid specimens. Additionally, we used Western blotting to detect the presence of 14-3-3 protein and employed real-time quaking-induced conversion (RT-QuIC) assays to analyze the same set of samples. Furthermore, we examined the correlation coefficient between ELISA and CLEA results in a subset of 60 samples. Moreover, using CLEA, we evaluated the diurnal reproducibility, storage stability, dilutability, and freeze–thaw effects in three selected samples. Results: In 172 patients, 172 samples were extracted, with each patient providing only one sample, and a total of 88 (35 men and 53 women) tested positive for HPD in the RT-QuIC assay. In contrast, all CSF samples from the remaining 84 patients without HPD (50 men and 34 women) tested negative in the RT-QuIC assay. Both ELISA and CLEA showed perfect sensitivity and specificity (100%) in measuring T-tau protein levels. In addition, ELISA and CLEA are similar in terms of measurement sensitivity and marginal effect of detection extrema. CLEA analysis exhibited instability for certain samples with T-tau protein levels exceeding 2000 pg/mL, leading to low reproducibility during dilution analysis. Conclusions: Our findings indicate that CLEA outperforms ELISA in terms of diurnal reproducibility, storage stability, and freeze–thaw effects. However, ELISA demonstrated superior performance in the dilution assay. Therefore, it is imperative to develop innovative approaches for the dilution of biomarker samples for CLEA measurements during clinical trials.

Human prion diseases (HPDs) are fatal neurodegenerative disorders characterized by abnormal prion proteins (PrPSc). Numerous techniques have been devised to detect prion seeding activity, each with limitations. Here, we developed a technology for in vitro amplification of abnormal prion proteins (PrPSc), thereby enabling their sensitive detection. Using the real-time quaking-induced conversion (RT-QuIC) PrPSc amplification assay, we could detect ≥1 fg of PrPSc in diluted human prion disease brain homogenate. Although RT-QuIC assay is suitable for detecting prion seeding activity in a variety of specimens, its accuracy in whole blood, blood plasma, or blood-contaminated tissues is reduced. To circumvent this issue and move toward developing a blood test for prions, we introduced an immunoprecipitation step at the beginning of the RT-QuIC reaction. We refer to this enhanced method as “eQuIC”. eQuIC utilizes three types of human monoclonal antibodies, which significantly increased its sensitivity—making it approximately 1000 times more sensitive than the original RT-QuIC assay. Nevertheless, when we tested the blood (serum, plasma, and whole blood) of six patients with sporadic human prion disease using eQuIC, we were unable to detect prion activity. Therefore, we concluded that the detection of prion seeding activities in blood samples from patients with sporadic prion disease remains challenging; thus, alternative methods beyond RT-QuIC and eQuIC will be necessary for future research.