Abstract
Objective: Thailand is experiencing demographic aging. Consequently, the socioeconomic burden of neurodegenerative diseases (NDDs) is expected to escalate drastically, posing a challenge for the middle-income country. Much can be done to mitigate the consequences of NDDs, including imposing preventive interventions, planning an integrated care chain, accelerating biomedical research, etc. Using neuropathology-specific biomarkers is indispensable for the successful implementation of such measures because they can detect NDDs in the long presymptomatic stages, during which disability can be prevented. Nevertheless, their use is limited by cost and accessibility, perceived invasiveness, and lack of validation in non-white populations. The aim of this project is to develop biomarkers for NDDs, including Real-time Quaking-induced Conversion (RT-QuIC) for diagnosing prion diseases and synucleinopathies, plasma phosphorylated tau (p-tau) for diagnosing Alzheimer's disease (AD), a multimodal biomarker evaluation scheme for evaluating idiopathic normal pressure hydrocephalus (iNPH), and reference values for biomarkers of neuronal injury that are affordable, accessible, non-invasive, and accurate with regards to Thai people, along with effective guidance for their real-world application. Materials and methods: Patients suspected of prion diseases by their attending physicians were evaluated in a nationwide surveillance program. Their cerebrospinal fluid (CSF) samples were tested using prion RT-QuIC. Three previously published methods of performing α-synuclein RT-QuIC were tested on 16 clinical patients, enabling the selection of the method with the most suitable accuracy. The method was subsequently performed on more CSF samples that were better characterized clinically. P-tau217 quantification using electrochemiluminescence (ECL) was performed on plasma specimens from participants with cognitive impairment who had previously undergone 18F-Florbetaben positron emission tomography (PET) or CSF biomarkers to determine its accuracy as well as the optimal cutoff for diagnosing AD. The diagnostic performance was compared with p-tau181 as well as clinical diagnosis. Participants suspected of having iNPH were recruited and evaluated with multimodal biomarkers. The correlation of those biomarkers and objective changes in gait parameters was determined. Healthy participants of various ages were evaluated with plasma neurofilament light chain (NFL) in order to find the optimal age-related threshold for defining an abnormal level of neuronal injury. Results: Nineteen patients joined the national prion surveillance program, of whom 8 (42%) tested positive for prion RT-QuIC. None of the patients had a risk for acquired prion disease except for one RT-QuIC positive patient, who had previous brain surgery without receiving a dura mater graft. Clinical features of all RT-QuIC positive patients were compatible with sporadic Creutzfeldt-Jakob disease. RT-QuIC using commercial rec-humα-synuclein was positive in 3 out of 10 clinical samples suspected of PD and negative in all 6 negative control specimens. It then showed substantial agreement with clinical diagnosis from a movement disorders specialist in a cohort of 26 patients. A total of 132 participants with cognitive impairment were evaluated for plasma p-tau, with 54.5% having AD confirmed by PET or CSF. Plasma p-tau217 measured by ECL achieved an AUC of 0.94 (95% CI 0.90-0.98), whereas plasma p-tau181 and clinical diagnosis only had AUCs of 0.86 (95% CI 0.80-0.93) and 0.84 (95% CI 0.77-0.90), respectively. Using the p-tau217 cutoff of 0.24 pg/mL, the sensitivity and specificity of this assay were 90.3% and 92.0%, respectively. The study had enrolled 13 iNPH participants to undergo the multimodal biomarker evaluation scheme. All but one showed improvement in ankle and knee flexion angles. CSF p-tau181 showed a trend toward correlation with those gait changes, Rho = 0.49 (p=0.09). Two-hundred and thirty-three healthy participants’ plasma was measured for NFL, and their values clearly increased with age. Preliminarily, the reference values obtained were similar to reported values from Western cohorts. Conclusion: This research project continues to focus on developing accurate and assessable fluid biomarkers for ND, including prion diseases, synucleinopathies, AD, etc., as well as testing them in real-life clinical practice. Its third year had completed with substantial success. RT-QuIC for prion disease has been successfully implemented in a nationwide surveillance program. This yielded the output of Thai patients receiving the test with short waiting time and achieved the outcome of guiding physician management in improved quality of life for the patients. The main output of the memory clinic study is showing that plasma p-tau217 was evaluated in real-life settings and considerably outperformed the former assay and specialist’s diagnosis leading to the outcome of a potential guideline for the use of blood-based AD biomarkers in Thailand. The study showed that CSF AD biomarkers could be related to the emergence of NPH physiology resulting in the output of abstract presentation at an international conference and outcome of insights on the mechanisms of NPH. The results for other studies are underway, possibly leading to tangible outputs and outcomes in the following years.
