Abstract
Objective Thailand is experiencing demographic ageing. 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 NDDs including imposing preventive interventions, planning an integrated care chain, accelerating biomedical research etc. Using neuropathology-specific biomarkers is indispensable for successful implementation of such measures because they can detect NDDs in the long presymptomatic stages at which disability can be prevented. Nevertheless, their use is limited by cost and accessibility, perceived invasiveness and lack of validation in non-white population. 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, and multimodal biomarker evaluation scheme for evaluating idiopathic normal pressure hydrocephalus (iNPH), that is affordable, accessible, non-invasive and accurate with regards to Thai people along with an effective guidance for their use. Materials and methods In-house recombinant truncated hamster prion protein (recPrP) purified using a pre-packed column and simultaneous refolding and dialysis (siphon method) served as the substrate for RT-QuIC, which was performed on two sets of cerebrospinal fluid (CSF) specimens. The first comprised of 30 CSF specimens of patients from various hospitals suspected of having sporadic Creutzfeldt-Jakob disease (sCJD). An identical set of aliquots was transferred to an established RT-QuIC facility to determine the inter-laboratory agreement. The second set comprised of CSF from 39 patients presenting at King Chulalongkorn Memorial Hospital suspected of having sCJD. Complete clinical data are available in this group enabling the evaluation of the diagnostic performance. In-house recombinant human α-synuclein (rec-humα-syn) purified using a single Q-Sepharose column served as the substrate for RT-QuIC, which was performed on 11 control CSF specimens as a pilot experiment. P-tau181 quantification using single-molecule array (SIMOA) were performed on plasma specimens from participants with dementia who had previously undergone 18F-Florbetaben positron emission tomography (PET) to determine the optimal cutoff for diagnosing Alzheimer’s disease (AD). Participants with amnestic mild cognitive impairment (MCI) were consecutively enrolled in another cohort whose plasma samples were collected and full neurocognitive assessment were done. The participants subsequently underwent 18F- fluorodeoxyglucose- PET 18F-Florbetaben PET and 18F- PI2620 PET to determined AD biomarker status and prospectively evaluated the diagnostic performance of plasma p-tau181. Participants who were suspected of having iNPH were and evaluated with the proposed multimodal biomarker evaluation scheme. NDD biobank was established for future research use of biological specimen. Results RT-QuIC using in-house recPrP conferred 90% (95% confidence interval (CI) 74.4% – 96.5%) agreement with the results from an established RT-QuIC facility whereas the Cohen’s kappa is 0.876 (95%CI 0.871 - 0.882). The sensitivity and specificity when tested on 39 CSF specimens from possible sCJD patients were 0.92 (95%CI 0.67-0.99) and 1.00 (95%CI 0.87-1.00) respectively. RT-QuIC using in-house rec-humα-syn was positive in 1 out of 6 positive controls and negative in all 5 negative control specimens. The optimal plasma p-tau181 cutoff for diagnosing AD (2.46 pg/mL) were derived from 29 individuals with known AD status. Using this cutoff, the sensitivity, specificity and accuracy of plasma p-tau181 were 0.80 (95%CI 0.64-0.90), 0.75 (95%CI 0.51-0.90) and 0.78 (95%CI 0.65-0.88), respectively, when tested prospectively on 51 amnestic MCI participants. The study had enrolled 6 iNPH participants to undergo the multimodal biomarker evaluation scheme. The NDD biobank is currently fully functional with 902 plasma specimens and 251 other types of specimens from 838 individuals and are operating according to consensus biobanking standard. Conclusion This research project focuses on developing accurate and assessable fluid biomarkers for ND including prion diseases, synucleinopathies, AD etc. Its second year had completed with substantial success. RT-QuIC for prion disease achieved near-perfect agreement with establish laboratory and equal diagnostic performance. Plasma p-tau SIMOA were completely evaluated in real-life settings and is considerably accurate. The results of other tests and biomarkers are underway.
