High diagnostic performance of independent alpha-synuclein seed amplification assays for detection of early Parkinson's disease

Atypical Parkinsonian Disorders

Atypical parkinsonian disorders (APD) include progressive supranuclear palsy, corticobasal degeneration, and multiple system atrophy. Identifying APD is important because they have different pathogenesis, disease course, and prognosis than Parkinson's disease (PD), and require different treatments. Therefore, when encountering patients with parkinsonism, it is of crucial importance to look for "red flags" or signs, such as impairments in higher cortical function, visuomotor system, cerebellar and other motor abnormalities including dystonia, myoclonus, and apraxia that help differentiate them from PD. Although disease-modifying therapies are not yet available, treatments targeting specific symptoms may improve the quality of life in these patients.

Targeted proteomic biomarker profiling using NULISA in a cohort enriched with risk for Alzheimer's disease and related dementias

INTRODUCTION

Targeted proteomic assays may be useful for diagnosing and staging Alzheimer's disease and related dementias (ADRD). We evaluated the performance of a 120-marker central nervous system (CNS) NUcleic acid Linked Immuno-Sandwich Assay (NULISA) panel in samples spanning the Alzheimer's disease (AD) spectrum.

METHODS

Cross-sectional plasma samples (n = 252) were analyzed using NULISAseq CNS panel from Alamar Biosciences. Receiver-operating characteristic (ROC) analyses demonstrated the accuracy from NULISAseq-tau phosphorylated at threonine 217 (pTau217) in detecting amyloid (A) and tau (T) positron emission tomography (PET) positivity. Differentially expressed proteins were identified using volcano plots.

RESULTS

NULISAseq-pTau217 accurately classified A/T PET status with ROC areas under the curve of 0.92/0.86; pTau217 was upregulated in A+, T+, and impaired groups with log2-fold changes of 1.21, 0.57, and 4.63, respectively, compared to A-. Of interest, TAR DNA-binding protein 43 (TDP-43) phosphorylated at serine 409 (pTDP43-409) was also upregulated in the impaired group and correlated with declining hippocampal volume and cognitive trajectories.

DISCUSSION

This study shows the potential of a targeted proteomics panel for characterizing brain changes pertinent to ADRD. The promising pTDP43-409 findings require further replication.

HIGHLIGHTS

The NULISAseq pTau217 assay was comparable to the Simoa pTau217 assay, both utilizing the ALZpath antibody, in detecting amyloid positron emission tomography (PET) positivity, each with areas under the curve greater than 90%. Nineteen proteins were differentially expressed in participants with mild cognitive impairment (MCI) compared to those who were unimpaired. Markers of non-AD proteinopathies such as pTDP43-409, oligomeric alpha-synuclein, and huntingtin (HTT), were among those upregulated in MCI. High levels of plasma pTDP43-409 were associated with worsening hippocampal atrophy and cognitive decline, clinical indicators of limbic-predominant age-related TDP-43 encephalopathy (LATE), compared to those with low pTDP43-409.

Automated Imaging Differentiation for Parkinsonism

Importance

Magnetic resonance imaging (MRI) paired with appropriate disease-specific machine learning holds promise for the clinical differentiation of Parkinson disease (PD), multiple system atrophy (MSA) parkinsonian variant, and progressive supranuclear palsy (PSP). A prospective study is needed to test whether the approach meets primary end points to be considered in a diagnostic workup.

Objective

To assess the discriminative performance of Automated Imaging Differentiation for Parkinsonism (AIDP) using 3-T diffusion MRI and support vector machine (SVM) learning.

Design, Setting, and Participants

This was a prospective, multicenter cohort study conducted from July 2021 to January 2024 across 21 Parkinson Study Group sites (US/Canada). Included were patients with PD, MSA, and PSP with established criteria and unanimous agreement in the clinical diagnosis among 3 independent, blinded neurologists who specialize in movement disorders. Patients were assigned to a training set or an independent testing set.

Exposure

MRI.

Main Outcomes and Measures

Area under the receiver operating characteristic curve (AUROC) in the testing set for primary model end points of PD vs atypical parkinsonism, MSA vs PSP, PD vs MSA, and PD vs PSP. AIDP was also paired with antemortem MRI to test against postmortem neuropathology in a subset of autopsy cases.

Results

A total of 316 patients were screened and 249 patients (mean [SD] age, 67.8 [7.7] years; 155 male [62.2%]) met inclusion criteria. Of these patients, 99 had PD, 53 had MSA, and 97 had PSP. A retrospective cohort of 396 patients (mean [SD] age, 65.8 [8.9] years; 234 male [59.1%]) was also included. Of these patients, 211 had PD, 98 had MSA, and 87 had PSP. Patients were assigned to the training set (78%; 104 prospective, 396 retrospective) or independent testing set, which included 145 (22%; 60 PD, 27 MSA, 58 PSP) prospective patients (mean age, 67.4 [SD 7.7] years; 95 male [65.5%]). The model was robust in differentiating PD vs atypical parkinsonism (AUROC, 0.96; 95% CI, 0.93-0.99; positive predictive value [PPV], 0.91; negative predictive value [NPV], 0.83), MSA vs PSP (AUROC, 0.98; 95% CI, 0.96-1.00; PPV, 0.98; NPV, 0.81), PD vs MSA (AUROC, 0.98; 95% CI, 0.96-1.00; PPV, 0.97; NPV, 0.97), and PD vs PSP (AUROC, 0.98; 95% CI, 0.96-1.00; PPV, 0.92; NPV, 0.98). AIDP predictions were confirmed neuropathologically in 46 of 49 brains (93.9%).

Conclusions and Relevance

This prospective multicenter cohort study of AIDP met its primary end points. Results suggest using AIDP in the diagnostic workup for common parkinsonian syndromes.

Preparing for Parkinson's disease prevention trials: Current progress and future directions

In recent decades, numerous clinical trials have aimed to delay or prevent Parkinson's disease (PD) progression. Despite the theoretical promise and encouraging preclinical data, none have shown clear efficacy in slowing or preventing PD progression, related to several key limitations. Conventional motor and non-motor scales often fall short in detecting early disease changes, while the heterogeneity of PD phenotypes complicates treatment efficacy. The timing of interventions is also critical, as most trials target patients already in advanced stages of neurodegeneration. A deeper understanding of the preclinical phase and the emergence of new pathological frameworks have shifted the focus toward preventing the onset of clinical PD. Recent advances in biomarker research, including tissue, fluid, and imaging markers, are poised to transform PD research by improving patient selection, stratification, and disease progression monitoring. New biologically grounded frameworks for classifying synucleinopathies aim to distinguish biological subtypes from clinical phenotypes, enabling more targeted prevention trials. Successful PD prevention trials will require early enrollment of individuals at the highest risk, employing low-risk personalized interventions, with biomarkers or sensitive clinical markers as endpoints. Early involvement of key stakeholders will be essential to ensure that trials are timely, ethically sound, and aligned with the needs of the PD community.

Alpha-synuclein misfolding as fluid biomarker for Parkinson's disease measured with the iRS platform

Misfolding and aggregation of alpha-synuclein (αSyn) play a key role in the pathophysiology of Parkinson's disease (PD). Despite considerable advances in diagnostics, an early and differential diagnosis of PD still represents a major challenge. We innovated the immuno-infrared sensor (iRS) platform for measuring αSyn misfolding. We analyzed cerebrospinal fluid (CSF) from two cohorts comprising PD cases, atypical Parkinsonian disorders, and disease controls. We obtained an AUC of 0.90 (n = 134, 95% CI 0.85-0.96) for separating PD/MSA from controls by determination of the αSyn misfolding by iRS. Using two thresholds divided individuals as unaffected/affected by misfolding with an intermediate area in between. Comparing the affected/unaffected cases, controls versus PD/MSA cases were classified with 97% sensitivity and 92% specificity. The spectral data revealed misfolding from an α-helical/random-coil αSyn in controls to β-sheet enriched αSyn in PD and MSA cases. Moreover, a first subgroup analysis implied the potential for patient stratification in clinically overlapping cases. The iRS, directly measuring all αSyn conformers, is complementary to the αSyn seed-amplification assays (SAAs), which however only amplify seeding competent conformers.

Alpha-synuclein seed amplification assays: Data sharing, standardization needed for clinical use

Alpha-synuclein seed amplification assays can improve neurodegenerative disease diagnosis and care, but widespread use depends on a framework that standardizes protocols and encourages data sharing.

Baseline α-synuclein seeding activity and disease progression in sporadic and genetic Parkinson's disease in the PPMI cohort

Background

α-Synuclein (α-syn) seed amplification assays (SAAs) have shown remarkable potential in diagnosing Parkinson's disease (PD). Using data from the Parkinson's Progression Markers Initiative (PPMI) cohort, we aimed to test whether baseline α-syn seeding activity was associated with disease progression in sporadic PD, LRRK2-associated PD (LRRK2 PD), and GBA-associated PD (GBA PD).

Methods

We analyzed 7 years of motor, non-motor, and cognitive assessments and 5 years of dopamine transporter imaging along with baseline α-syn SAA results from 564 PPMI participants (n=332 sporadic PD, 162 LRRK2 PD, and 70 GBA PD) using linear mixed-effects models, adjusted for potential confounders, to test whether baseline α-syn SAA positivity (n=315 sporadic PD, 111 LRRK2 PD, and 66 GBA PD) was associated with PD progression.

Results

While non-statistically significant, there was a trend towards faster motor decline in participants with α-syn SAA positive LRRK2 PD compared to those with α-syn SAA negative LRRK2 PD (MDS-UPDRS III points per year: 2.39 (95% confidence interval: 1.86 - 2.92) vs. 1.76 (0.93 - 2.60); difference=0.63 (-0.29 - 1.55, p=0.18). There was no difference in motor decline between α-syn SAA positive and α-syn SAA negative participants with sporadic PD (2.46 (2.20 - 2.72) vs. 2.39 (1.36 - 3.42); difference=0.07 (-0.99 - 1.12), p=0.90) or GBA PD (2.67 (1.91 - 3.44) vs. 2.40 (-0.18 - 4.99); difference=0.27 (-2.42 - 2.96), p=0.84). No statistically significant differences were seen in the progression of non-motor symptoms, cognition, or DAT imaging.

Conclusions

We found no statistically significant associations between baseline α-syn seeding activity and PD progression among manifest patients in the PPMI cohort. Future studies are needed to further investigate relationships among baseline α-syn seeding activity, disease heterogeneity, disease stage, and PD progression.

Aggregated α-synuclein in erythrocytes as a potential biomarker for idiopathic Parkinson's Disease

BACKGROUND

Mostly known for its implication in synucleinopathies, including Parkinson's disease (PD), α-synuclein is predominantly expressed in the nervous system. Most of the peripheral α-synuclein is found in erythrocytes, and several studies have examined a possible association between erythrocytic α-synuclein and PD.

METHODS

We have used a recently developed ELISA that selectively detects fibrillar and oligomeric α-synuclein to measure aggregated α-synuclein in red blood cells (RBCs) collected from PD patients and age/sex-matched control individuals (n = 35). The PD group included patients without any common mutation (genetically undetermined group, GU-PD, n = 56) as well as mutation carriers in the α-synuclein gene (A53T-PD, n = 28) and glucocerebrosidase gene (GBA-PD, n = 24).

RESULTS

We found that the concentration of aggregated α-synuclein in erythrocytes was significantly increased in GU-PD patients compared to controls. A53T-PD and GBA-PD patients exhibited similar levels of erythrocytic aggregated α-synuclein as the control group. The levels of fibrillar/oligomeric α-synuclein in RBCs were reduced in respect to the age of control individuals suggesting that the observed increase in the GU-PD cohort was not due to normal aging. Parallel assessment of monomeric α-synuclein revealed that aggregated, but not total, α-synuclein could discriminate PD patients from control individuals.

CONCLUSIONS

The elevation of aggregated α-synuclein in GU-PD erythrocytes, which is not related to aging, suggests that these forms may be indicative of PD pathology and possibly accumulate upon disease establishment. As such, aggregated α-synuclein in RBCs could be a potential biomarker for PD diagnosis.

High Agreement Across Laboratories Between Different Alpha-Synuclein Seed Amplification Protocols

BACKGROUND

Seed amplification assays (SAA) detect alpha-synuclein (aSYN) pathology in patient biomatrices such as cerebrospinal fluid (CSF)-potentially even before clinical manifestations. As CSF-based SAA are approaching broader use in clinical trials and research, ensuring that different laboratories obtain the same results becomes increasingly important.

METHODS

In this cross-laboratory, cross-aSYN-recombinant substrate and cross-protocol round-robin test, we compared SAA results from a common set of 38 CSF samples measured independently in four research laboratories of the German Center for Neurodegenerative diseases. Three laboratories (A-C) used an assay protocol adapted from Parchi's group at ISNB (Bologna, Italy); laboratory D used an assay protocol adapted from Amprion Inc. Two different manufacturers of aSYN protein were used as substrates for the SAA reaction.

RESULTS

Qualitative results were identical in at least three of the four laboratories for 37 out of 38 samples (20 positive, 17 negative). Fleiss Kappa for all four laboratories was 0.751 (z = 12, p < 0.001). For each laboratory, agreement with laboratory A was > 92%. For the number of positive replicates, Fleiss Kappa was 0.45 for a score of zero positive replicates and 0.42 for a score of four positive replicates.

CONCLUSIONS

The qualitative SAA results showed a high level of agreement across research laboratories, aSYN monomers, and assay protocols. Small differences between laboratories were systematic, consistent with the notion that SAA reports biologically relevant properties. These results also underline that round-robin tests can be helpful in assessing and ensuring SAA quality across laboratories.

α-Synuclein Seed Amplification Assay Amplification Parameters and the Risk of Progression in Prodromal Parkinson Disease

OBJECTIVES

Tools are needed to evaluate the risk of developing Parkinson disease (PD) in at-risk populations. In this study, we examine differences in alpha-synuclein seed amplification assay (αSyn-SAA) qualitative results and amplification parameters between nonmanifesting carriers (NMCs) of PD-related pathogenic variants, prodromal PD, and PD and the risk of developing a synucleinopathy in participants with prodromal PD.

METHODS

Cross-sectional and longitudinal CSF αSyn-SAA results from participants in the Parkinson's Progression Markers Initiative were analyzed. αSyn-SAA positivity and amplification parameters (maximum fluorescence [Fmax], time-to-threshold [TTT], time-to-50% Fmax [T50], and area under the curve [AUC]) were compared between NMCs, participants with prodromal PD, and participants with PD, and their relationship with the likelihood of phenoconversion in participants with prodromal PD was investigated.

RESULTS

Samples from 1,027 participants were analyzed (159 healthy controls [HCs], 247 NMCs, 96 participants with prodromal PD, and 525 participants with PD). TTT and T50 were faster, and AUC was higher in αSyn-SAA+ participants with prodromal PD and PD than αSyn-SAA+ NMCs and HC participants (Kruskal-Wallis χ2 = 4.15-13.96, p < 0.0002-0.04). Participants with prodromal PD with positive αSyn-SAA tests and faster TTT had higher rates of phenoconversion (log-rank p = 0.001 and log-rank test-for-trend p < 0.0001). There were no changes in 48 participants with prodromal PD with longitudinal assays.

DISCUSSION

αSyn-SAA positivity and faster seed amplification are associated with a greater risk of developing PD in at-risk individuals and may aid in predicting phenoconversion.

Neuropathology meets chemical and genetic pathology head-on: a personal perspective

Medical science has made revolutionary discoveries around the nosology and aetiology of the neurodegenerative diseases. Dementia is the second leading cause of death in Australia. My colleagues and I are now looking at therapeutics which potentially can delay or prevent the onset of Alzheimer's disease (AD). Advances in diagnosis allow detection of preclinical AD. Neuropathologists working closely with chemical and genetic pathologists have a major role to play in pushing diagnostics and therapeutics to the forefront of clinical management of these diseases.

PIDGN: An explainable multimodal deep learning framework for early prediction of Parkinson's disease

BACKGROUND

Parkinson's disease (PD), the second most common neurodegenerative disease in the world, is usually not diagnosed until the later stages of the disease, when patients might have already missed the best treatment period. Therefore, more effective prediction methods based on artificial intelligence (AI) are needed to assist physicians in timely diagnosis.

NEW METHODS

An explainable deep learning-based early Parkinson's disease diagnostic model, Parkinson's Integrative Diagnostic Gated Network (PIDGN), was designed by fusing Single Nucleotide Polymorphism (SNP) and brain sMRI data. Firstly, unimodal internal information was extracted using EmsembleTree dimensionality reduction method, Transformer encoder and 3D ResNet. Secondly, gated attention fusion technique was utilized to explore the inter-modal interactions. Finally, the classification results were output through the fully connected layer. SHapley additive interpretation (SHAP) values and Gradient-weighted Class Activation Mapping (Grad-CAM) techniques were used to help explain the importance of SNPs and brain regions for PD.

RESULTS

The results showed that the PIDGN model achieved the best results with the accuracy of 0.858 and AUROC of 0.897. Top 20 SNPs and the brain regions near the midbrain potentially related to PD were identified using two explainable techniques via SHAP values and Grad-CAM respectively.

COMPARISON WITH EXISTING METHODS AND CONCLUSION

The PIDGN model trained by fusing genetic and imaging data outperforms 13 other commonly used unimodal or bimodal models. Explainable PIDGN model helps deepen understanding of several SNPs and sMRI key factors that may affect PD. This study provides a potentially effective solution for automated early diagnosis of PD using AI.

Exenatide once a week versus placebo as a potential disease-modifying treatment for people with Parkinson's disease in the UK: a phase 3, multicentre, double-blind, parallel-group, randomised, placebo-controlled trial

BACKGROUND

GLP-1 receptor agonists have neurotrophic properties in in-vitro and in-vivo models of Parkinson's disease and results of epidemiological studies and small randomised trials have suggested possible benefits for risk and progression of Parkinson's disease. We aimed to establish whether the GLP-1 receptor agonist, exenatide, could slow the rate of progression of Parkinson's disease.

METHODS

We did a phase 3, multicentre, double-blind, parallel-group, randomised, placebo-controlled trial at six research hospitals in the UK. Participants were aged 25-80 years with a diagnosis of Parkinson's disease, were at Hoehn and Yahr stage 2·5 or less when on dopaminergic treatment, and were on dopaminergic treatment for at least 4 weeks before enrolment. Participants were randomly assigned (1:1) using a web-based system with minimisation according to Hoehn and Yahr stage and study site to receive extended-release exenatide 2 mg by subcutaneous pen injection once per week over 96 weeks, or visually identical placebo. All participants and all research team members at study sites were masked to randomisation allocation. The primary outcome was the Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III score, off dopaminergic medication at 96 weeks, analysed in the intention-to-treat population using a linear mixed modelling approach. This study is registered with ISRCTN (14552789), EudraCT (2018-003028-35), and ClinicalTrials.gov (NCT04232969).

FINDINGS

Between Jan 23, 2020, and April 23, 2022, 215 participants were screened for eligibility, of whom 194 were randomly assigned to exenatide (n=97) or placebo (n=97). 56 (29%) participants were female and 138 (71%) were male. 92 participants in the exenatide group and 96 in the placebo group had at least one follow-up visit and were included in analyses. At 96 weeks, MDS-UPDRS III OFF-medication scores had increased (worsened) by a mean of 5·7 points (SD 11·2) in the exenatide group, and by 4·5 points (SD 11·4) points in the placebo group (adjusted coefficient for the effect of exenatide 0·92 [95% CI -1·56 to 3·39]; p=0·47). Nine (9%) participants in the exenatide group had at least one serious adverse event compared with 11 (11%) in the placebo group.

INTERPRETATION

Our findings suggest that exenatide is safe and well tolerated. We found no evidence to support exenatide as a disease-modifying treatment for people with Parkinson's disease. Studies with agents that show better target engagement or in specific subgroups of patients are needed to establish whether there is any support for the use of GLP-1 receptor agonists for Parkinson's disease.

FUNDING

National Institute for Health and Care Research and Cure Parkinson's.

A quantitative Lewy-fold-specific alpha-synuclein seed amplification assay as a progression marker for Parkinson's disease

Misfolded α-synuclein (αSyn) is the hallmark of α-synucleinopathies such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). While seed amplification assays (SAA) have demonstrated ultrasensitive detection of misfolded αSyn, they have been primarily used reliably to provide binary (positive/negative) results for diagnostic purposes. We developed an SAA with enhanced specificity for Lewy-fold α-synucleinopathies and introduced a quantifiable measure correlating with clinical severity. Cerebrospinal fluid (CSF) of 170 patients with neurodegenerative diseases and controls was analyzed. Blinded measurements demonstrated 97.8% sensitivity and 100% specificity for Lewy-fold α-synucleinopathies, correctly identifying PD and DLB while excluding MSA. In addition, we validated the strain specificity of the assay by testing brain homogenates from 30 neuropathologically confirmed cases. A novel Lewy-fold pathology (LFP) score based on positive signals in a dilution series provided a quantitative measure of αSyn seeds. The LFP score significantly correlated with motor and cognitive impairment presented by Hoehn and Yahr stage, MDS-UPDRS III, and MoCA. Longitudinal tracking in seven PD cases showed progressive LFP score increases corresponding with clinical deterioration, highlighting the assay's potential for monitoring disease progression at an individual level. Our Lewy-fold-specific SAA enhances ante-mortem diagnosis and differentiates Lewy-fold α-synucleinopathies from MSA. Unlike previous assays, the LFP score offers a quantitative assessment, showing promise as a progression marker and pharmacodynamic biomarker for αSyn-targeting therapies. This represents an important step toward developing an αSyn SAA that could help to track disease progression quantitatively, with potential applications in both clinical diagnostics and therapeutic trials.

Deciphering the role of neuropeptides as biomarkers for early diagnosis of Parkinson's disease

Parkinson's disease (PD) is a neurological condition and is characterized by both motor and non-motor symptoms. Early diagnosis is essential for effective therapy and management; nevertheless, present diagnostic methods are frequently insufficient and primarily rely on clinical symptoms that appear later in the disease. Neuropeptides, such as alpha-synuclein (α-syn), Substance P (SP), neurotensin (Nts), Neuropeptide Y (NPY), and somatostatin (SST), exhibit significant potential as biomarkers for the early identification of Parkinson's disease (PD). The pathophysiology of Parkinson's disease is closely associated with the dysregulation of these neuropeptides, which are essential in many neurophysiological processes. Advancements in detection technologies, including the Enzyme-Linked Immunosorbent Assay (ELISA), have rendered it possible to precisely and sensitively quantify neuropeptides in a variety of bodily fluids, including blood, saliva, tears, urine, and cerebrospinal fluid (CSF). Studies show that PD patients have different amounts of neuropeptides in their biological fluids. These differences are correlated with the severity of the disease and help to distinguish PD patients apart from individuals with other neurodegenerative conditions. Despite being less investigated, Nts and SST are also involved in neuroprotection and dopaminergic transmission, they too hold significant characteristics as diagnostic biomarkers. This article highlights the possible use of neuropeptides as PD diagnostic biomarkers. Integrating neuropeptide biomarkers into normal diagnostic processes can substantially enhance early diagnosis. This enables early therapeutic interventions and improves outcomes for individuals with PD.

The Amplification of Alpha-Synuclein Amyloid Fibrils is Suppressed under Fully Quiescent Conditions

Seed amplification assays (SAAs) are a promising avenue for the early diagnosis of neurodegenerative diseases. However, when amplifying fibrils from patient-derived samples in multiwell plates, it is currently highly challenging to accurately quantify the aggregates. It is therefore desirable to transfer such assays into a digital format in microemulsion droplets to enable direct quantification of aggregate numbers. To achieve transfer from conventional plate-based to the microfluidic digital format, effective seed amplification needs to be achieved inside the microdroplets. Therefore, we establish a new set of assay conditions that enable highly efficient seed amplification in plates without any shaking. However, the same set of conditions displayed a very different behavior upon transfer to a microfluidic platform where no amplification was observed. We demonstrate that this is caused by the suppression of all secondary processes that could amplify the seeds in the complete absence of mechanical perturbations inside the microdroplets. We further show that the amplification inside droplets can be achieved by subjecting the microemulsions to high-frequency vibrations using a piezo device. Taken together, our results provide novel insights into the physical requirements of alpha-synuclein seed amplification and demonstrate a pathway towards the development of effective digital SAAs.

The α-synuclein seed amplification assay: Interpreting a test of Parkinson's pathology

The α-synuclein seed amplification assay (αSyn-SAA) sensitively detects Lewy pathology, the amyloid state of α-synuclein, in the cerebrospinal fluid (CSF) of patients with Parkinson's disease (PD). The αSyn-SAA harnesses the physics of seeding, whereby a superconcentrated solution of recombinant α-synuclein lowers the thermodynamic threshold (nucleation barrier) for aggregated α-synuclein to act as a nucleation catalyst ("seed") to trigger the precipitation (nucleation) of monomeric α-synuclein into pathology. This laboratory setup increases the signal for identifying a catalyst if one is present in the tissue examined. The result is binary: positive, meaning precipitation occurred, and a catalyst is present, or negative, meaning no precipitation, therefore no catalyst. Since protein precipitation via seeding can only occur at a concentration many-fold higher than the human brain, laboratory-elicited seeding does not mean human brain seeding. We suggest that a positive αSyn-SAA reveals the presence of pathological α-synuclein but not the underlying etiology for the precipitation of monomeric α-synuclein into its pathological form. Thus, a positive αSyn-SAA supports a clinical diagnosis of PD but cannot inform disease pathogenesis, ascertain severity, predict the rate of progression, define biology or biological subtypes, or monitor treatment response.

Association between the Amplification Parameters of the α-Synuclein Seed Amplification Assay and Clinical and Genetic Subtypes of Parkinson's Disease

BACKGROUND

α-Synuclein seed amplification assay on cerebrospinal fluid (CSF-αSyn-SAA) has shown high accuracy for Parkinson's disease (PD) diagnosis. The analysis of CSF-αSyn-SAA parameters may provide useful insight to dissect the heterogeneity of synucleinopathies.

OBJECTIVE

To assess differences in CSF-αSyn-SAA amplification parameters in participants with PD stratified by rapid eye movement (REM) sleep behavior disorder (RBD), dysautonomia, GBA, and LRRK2 variants.

METHODS

Clinical and CSF-αSyn-SAA data from the Parkinson's Progression Marker Initiative dataset were used. CSF-αSyn-SAA parameters included maximum fluorescence (Fmax), time to reach 50% of Fmax (T50), time to threshold (TTT), slope, and area under the curve (AUC). Sporadic PD (n = 371) was stratified according to RBD and dysautonomia (DysA) symptoms. Genetic PD included carriers of pathogenic variants of GBA (GBA-PD, n = 52) and LRRK2 (LRRK2-PD, n = 124) gene.

RESULTS

CSF-αSyn-SAA was positive in 77% of LRRK2-PD, 92.3% of GBA-PD, and 93.8% of sporadic PD. The LRRK2-PD cohort showed longer T50 and TTT, and smaller AUC than GBA-PD (P = 0.029, P = 0.029, P = 0.016, respectively) and sporadic PD (P = 0.034, P = 0.033, P = 0.014, respectively). In the sporadic cohort, CSF-αSyn-SAA parameters were similar between PD with (n = 157) and without (n = 190) RBD, whereas participants with DysA (n = 193) presented shorter T50 (P = 0.026) and larger AUC (P = 0.029) than those without (n = 150).

CONCLUSION

CSF-αSyn-SAA parameters vary across genetic and non-genetic PD subtypes at the group level. These differences are mostly driven by the presence of LRRK2 variants and DysA. Significant overlaps in the amplification parameter values exist between groups and limit their use at the individual level. Further studies are necessary to understand the mechanisms of CSF-αSyn-SAA parameter differences. © 2024 International Parkinson and Movement Disorder Society.

Behavioral variant frontotemporal dementia with pathogenic variant in MAPT presenting as dementia with Lewy body disease

A 75-year-old Chinese American man presented to behavioral neurology clinic for a second opinion of dementia with Lewy body disease (DLB). The clinical manifestations met the criteria for a probable DLB diagnosis. Yet, in-depth evaluation unveiled clinical history, family history, and neuroimaging evidences that suggested a diagnosis of behavioral variant frontotemporal dementia (FTD). A heterozygous pathogenic variant in the microtubule-associated protein Tau (MAPT) was identified through genetic testing and confirmed the diagnosis of autosomal dominant MAPT-related FTD. This case is the first reported instance of MAPT-related FTD presenting with well-formed visual hallucinations in an elderly Chinese American.

Toward a biological definition of neuronal and glial synucleinopathies

Cerebral accumulation of alpha-synuclein (αSyn) aggregates is the hallmark event in a group of neurodegenerative diseases-collectively called synucleinopathies-which include Parkinson's disease, dementia with Lewy bodies and multiple system atrophy. Currently, these are diagnosed by their clinical symptoms and definitively confirmed postmortem by the presence of αSyn deposits in the brain. Here, we summarize the drawbacks of the current clinical definition of synucleinopathies and outline the rationale for moving toward an earlier, biology-anchored definition of these disorders, with or without the presence of clinical symptoms. We underscore the utility of the αSyn seed amplification assay to detect aggregated αSyn in living patients and to differentiate between neuronal or glial αSyn pathology. We anticipate that a biological definition of synucleinopathies, if well-integrated with the current clinical classifications, will enable further understanding of the disease pathogenesis and contribute to the development of effective, disease-modifying therapies.

Increased plasma DOPA decarboxylase levels in Lewy body disorders are driven by dopaminergic treatment

DOPA Decarboxylase (DDC) has been proposed as a cerebrospinal fluid (CSF) biomarker with increased concentrations in Lewy body disorders (LBDs) and highest levels in patients receiving dopaminergic treatment. Here we evaluate plasma DDC, measured by proximity extension assay, and the effect of dopaminergic treatment in three independent LBD (with a focus on dementia with Lewy bodies (DLB) and Parkinson's disease (PD)) cohorts: an autopsy-confirmed cohort (n = 71), a large multicenter, cross-dementia cohort (n = 1498) and a longitudinal cohort with detailed treatment information (n = 66, median follow-up time[IQR] = 4[4, 4] years). Plasma DDC was not altered between different LBDs and other disease groups or controls in absence of treatment. DDC levels increased over time in PD, being significantly associated to higher dosages of dopaminergic treatment. This emphasizes the need to consider treatment effect when analyzing plasma DDC, and suggests that plasma DDC, in contrast to CSF DDC, is of limited use as a diagnostic biomarker for LBD, but could be valuable for treatment monitoring.

Nanodiamond-mediated delivery of microRNA-7 for the neuroprotection of dopaminergic neurons

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the gradual loss of dopaminergic neurons in the substantia nigra and the accumulation of α-synuclein aggregates known as Lewy bodies. MicroRNA-7 (miR-7) targets the gene SNCA, which encodes α-synuclein, reducing its expression and alleviating neuronal damage in PD. Regulating the post-transcriptional levels of α-synuclein through miR-7 effectively inhibits its production. Herein, we use nanodiamonds as carriers to deliver miR-7 (N-7), which can effectively protect dopaminergic neurons. Dopaminergic neurons efficiently take up N-7 and express miR-7. N-7 inhibits the expression of α-synuclein, reduces oxidative stress and restores dopamine levels effectively. These findings suggest that nanocomposites have significant potential in treating PD.

Advancing Parkinson's diagnosis: seed amplification assay for α-synuclein detection in minimally invasive samples

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by tremor, rigidity, and bradykinesia, beginning with early loss of dopaminergic neurons in the ventrolateral substantia nigra and advancing to broader neurodegeneration in the midbrain. The clinical heterogeneity of PD and the lack of specific diagnostic tests present significant challenges, highlighting the need for reliable biomarkers for early diagnosis. Alpha-synuclein (α-Syn), a protein aggregating into Lewy bodies and neurites in PD patients, has emerged as a key biomarker due to its central role in PD pathophysiology and potential to reflect pathological processes. Additionally, α-Syn allows earlier differentiation between PD and other neurodegenerative disorders with similar symptoms. Currently, detection of α-Syn pathology in post-mortem brain tissue remains the primary means of achieving a conclusive diagnosis, often revealing significant misdiagnoses. Seed amplification assay (SAA), initially developed for prion diseases, has been adapted to detect α-Syn aggregates in cerebrospinal fluid, showing promise for early diagnosis. Recent studies have demonstrated that SAA can also detect α-Syn aggregates in peripheral samples collected via minimally invasive procedures, such as skin, olfactory mucosa, saliva, and blood. However, the lack of standardized protocols limits clinical application. Standardizing protocols is essential to improve assay reliability and enable accurate patient identification for emerging therapies. This review examines studies on SAA for detecting α-Syn aggregates in minimally invasive samples, focusing on sample collection, processing, and reaction conditions.

Radiological markers of CSF α-synuclein aggregation in Parkinson's disease patients

Alpha-synuclein (αS) aggregation is a widely regarded hallmark of Parkinson's disease (PD) and can be detected through synuclein amplification assays (SAA). This study investigated the association between cerebrospinal fluid (CSF) radiological measures in 41 PD patients (14 iPD, 14 GBA1-PD, 13 LRRK2-PD) and 14 age-and-sex-matched healthy controls. Quantitative measures including striatal binding ratios (SBR), whole-brain and deep gray matter volumes, neuromelanin-MRI (NM-MRI), functional connectivity (FC), and white matter (WM) diffusion-tensor imaging (DTI) were calculated. Nine LRRK2-PD patients were SAA-negative (PD-SAA-). PD-SAA+ patients showed lower whole-brain gray matter, putamenal, brainstem, and substantia nigra volumes, reduced FC in the left caudate, and lower fractional anisotropy in the left fronto-occipital fasciculus compared to PD-SAA-. Taken together, αS aggregation was observed in iPD, GBA1-PD, and 38% of LRRK2-PD patients, and this was associated with reduced regional brain volumes, altered caudal FC, and SBRs. These changes were less pronounced in PD-SAA-, possibly suggesting a milder neurodegenerative process.

What is the future for dementia with Lewy bodies?

Dementia with Lewy bodies (DLB) is the second most common neurodegenerative dementia after Alzheimer's disease (AD), yet it remains under-recognized and frequently misdiagnosed due to heterogenous clinical presentations, the presence of co-pathology, and the lack of specific diagnostic tools. Pathologically, DLB is characterized by the accumulation of misfolded alpha-synuclein (aSyn) aggregates, known as Lewy bodies. Recent advancements have improved in vivo detection of aSyn pathology through techniques such as seed amplification assays, monoclonal antibodies, and positron emission tomography using novel small-molecule ligands. The ability to detect aSyn in vivo has sparked dialogue about using biomarkers to identify individuals with aSyn, similar to the approach influencing the field of AD. Proponents argue that biological staging could facilitate the detection of preclinical disease stages, allowing for earlier intervention and targets for disease modification, and could improve diagnostic sensitivity and accuracy in selecting patients for clinical trials. However, critics caution that this method may oversimplify the complexity of DLB and overlook its clinical heterogeneity, also highlighting practical challenges related to implementation, cost, and global access to advanced diagnostic technologies. Importantly, although significant progress has been made in detecting aSyn for diagnostic purposes, disease-modifying therapies targeting aSyn have yet to demonstrate clear efficacy in slowing disease progression. Elucidating the physiological and pathophysiological roles of aSyn remains an urgent priority in neurodegenerative research. Other experimental research priorities for DLB include developing improved cellular and animal models that reflect epigenetic and environmental factors, mapping post-translational modifications, and systematically characterizing neurons that are vulnerable and resistant to lewy pathology using a multi-omic approach. Clinically, there is an urgent need for international, prospective, longitudinal studies and for validated, disease-specific outcome measures. Addressing these priorities is essential for advancing our understanding of DLB and developing effective therapies.

Evaluation of Cerebrospinal Fluid α-Synuclein Seed Amplification Assay in Progressive Supranuclear Palsy and Corticobasal Syndrome

BACKGROUND

Seed amplification assay (SAA) testing has been developed as a biomarker for the diagnosis of α-synuclein-related neurodegenerative disorders.

OBJECTIVE

The objective of this study was to assess the rate of α-synuclein SAA positivity in progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS) and to analyze clinical and pathological features of SAA-positive and -negative cases.

METHODS

A total of 96 cerebrospinal fluid samples from clinically diagnosed PSP (n = 59) and CBS (n = 37) cases were analyzed using α-synuclein SAA.

RESULTS

Six of 59 (10.2%) PSP cases were α-synuclein SAA positive, including one case who was MSA-type positive. An exploratory analysis showed that PSP cases who were Parkinson's disease-type positive were older and had a shorter disease duration compared with SAA-negative cases. In contrast, 11 of 37 (29.7%) CBS cases were α-synuclein SAA positive, including two cases who were MSA-type positive.

CONCLUSIONS

Our results suggest that α-synuclein seeds can be detected in PSP and CBS using a cerebrospinal fluid α-synuclein SAA, and in PSP this may impact on clinical course.

Disease-modifying therapies for Parkinson disease: lessons from multiple sclerosis

The development of disease-modifying therapies (DMTs) for neurological disorders is an important goal in modern neurology, and the associated challenges are similar in many chronic neurological conditions. Major advances have been made in the multiple sclerosis (MS) field, with a range of DMTs being approved for relapsing MS and the introduction of the first DMTs for progressive MS. By contrast, people with Parkinson disease (PD) still lack such treatment options, relying instead on decades-old therapeutic approaches that provide only symptomatic relief. To address this unmet need, an in-person symposium was held in Toronto, Canada, in November 2022 for international researchers and experts in MS and PD to discuss strategies for advancing DMT development. In this Roadmap article, we highlight discussions from the symposium, which focused on therapeutic targets and preclinical models, disease spectra and subclassifications, and clinical trial design and outcome measures. From these discussions, we propose areas for novel or deeper exploration in PD using lessons learned from therapeutic development in MS. In addition, we identify challenges common to the PD and MS fields that need to be addressed to further advance the discovery and development of effective DMTs.

Targeted Proteomic Biomarker Profiling Using NULISA in a cohort enriched with risk for Alzheimer's Disease and Related Dementias

INTRODUCTION

Targeted proteomic assays may be useful for diagnosing and staging Alzheimer's disease and related dementias (ADRD). We evaluated the performance of a 120-marker central nervous system (CNS) NUcleic acid-Linked Immuno-Sandwich Assay (NULISA) panel in samples spanning the AD spectrum.

METHODS

Cross-sectional plasma samples (n=252) were analyzed using Alamar's NULISAseq CNS panel. ROC analyses demonstrated NULISAseq-pTau217 accuracy in detecting amyloid (A) and tau (T) PET positivity. Differentially expressed proteins were identified using volcano plots.

RESULTS

NULISAseq-pTau217 accurately classified A/T PET status with ROC AUCs of 0.92/0.86. pTau217 was upregulated in A+, T+, and impaired groups with log2-fold changes of 1.21, 0.57 and 4.63, respectively, compared to A-. Interestingly, pTDP43-409 was also upregulated in the impaired group and correlated with declining hippocampal volume and cognitive trajectories.

DISCUSSION

This study shows the potential of a targeted proteomics panel for characterizing brain changes pertinent to ADRD. The promising pTDP43-409 findings require further replication.

α-Synuclein seeding amplification assays for diagnosing synucleinopathies: an innovative tool in clinical implementation

The spectrum of synucleinopathies, including Parkinson's disease (PD), multiple system atrophy (MSA), and dementia with Lewy bodies (DLB), is characterized by α-synuclein (αSyn) pathology, which serves as the definitive diagnostic marker. However, current diagnostic methods primarily rely on motor symptoms that manifest years after the initial neuropathological changes, thereby delaying potential treatment. The symptomatic overlap between PD and MSA further complicates the diagnosis, highlighting the need for precise and differential diagnostic methods for these overlapping neurodegenerative diseases. αSyn misfolding and aggregation occur before clinical symptoms appear, suggesting that detection of pathological αSyn could enable early molecular diagnosis of synucleinopathies. Recent advances in seed amplification assay (SAA) offer a tool for detecting neurodegenerative diseases by identifying αSyn misfolding in fluid and tissue samples, even at preclinical stages. Extensive research has validated the effectiveness and reproducibility of SAAs for diagnosing synucleinopathies, with ongoing efforts focusing on optimizing conditions for detecting pathological αSyn in more accessible samples and identifying specific αSyn species to differentiate between various synucleinopathies. This review offers a thorough overview of SAA technology, exploring its applications for diagnosing synucleinopathies, addressing the current challenges, and outlining future directions for its clinical use.

Parkinson's Disease: A Narrative of the Evolving Understanding of the Role of α-Synuclein in Screening

The present investigation aims to examine the role of α-synuclein seed amplification assays for screening Parkinson's disease. Parkinson's disease (PD) is a debilitating neurodegenerative disorder caused by the loss of dopaminergic neurons in the midbrain, leading to symptoms such as tremors, bradykinesia, postural instability, dementia, and depression. It is classified as an α-synucleinopathy related to the role of α-synuclein aggregates in neuron degeneration. Diagnosis relies on clinical assessment without premortem diagnostic tests or imaging, often resulting in delayed detection and impaired symptom management. In this regard, our study explores a screening technique using an amplification assay to measure α-synuclein levels in cerebrospinal fluid, which could potentially identify early pathological changes and improve diagnostic accuracy and patient outcomes. While preliminary results are promising, further studies are needed to evaluate this approach's accuracy and clinical feasibility. A review of numerous trials demonstrates that α-synuclein seeding amplification assays (SAA) are a highly reliable, sensitive, and specific diagnostic tool for PD. This assay offers a promising opportunity to improve early diagnosis and quantify severity, especially for asymptomatic individuals or those with a family history of PD, allowing for earlier intervention and more effective disease management. In summary, the emerging body of evidence supporting α-synuclein as a biomarker should allow patients with PD to be detected and treated sooner, enhancing patients' quality of life and potentially changing the disease trajectory.

Safety, Tolerability, and Pharmacokinetics of Single Doses of Exidavnemab (BAN0805), an Anti-α-Synuclein Antibody, in Healthy Western, Caucasian, Japanese, and Han Chinese Adults

Exidavnemab is a monoclonal antibody (mAb) with a high affinity and selectivity for pathological aggregated forms of α-synuclein and a low affinity for physiological monomers, which is in clinical development as a disease-modifying treatment for patients with synucleinopathies such as Parkinson's disease. Safety, tolerability, pharmacokinetics, immunogenicity, and exploratory biomarkers were assessed in two separate Phase 1 single ascending dose studies, including single intravenous (IV) (100 to 6000 mg) or subcutaneous (SC) (300 mg) administration of exidavnemab in healthy volunteers (HVs). Across the two studies, a total of 98 Western, Caucasian, Japanese, and Han Chinese HVs were enrolled, of which 95 completed the study. Exidavnemab was generally well tolerated. There were no serious adverse events or safety issues identified in laboratory analyses. Headache, asymptomatic COVID-19, back pain, and post lumbar puncture syndrome were the most frequently reported treatment-emergent adverse events. Following IV infusion, the pharmacokinetics of exidavnemab was approximately dose linear in the range 100-6000 mg. The terminal half-life was approximately 30 days, and the exposure was comparable across Western, Caucasian, Japanese, and Han Chinese volunteers. The absolute SC bioavailability was ∼71%. Cerebrospinal fluid exposure relative to serum after single dose was within the range expected for mAbs (approximately 0.2%). The anti-drug antibody rates were low and there was no effect of immunogenicity on the pharmacokinetics or safety. Dose-dependent reduction of free α-synuclein in plasma was observed. In summary, exidavnemab was found to have an excellent pharmacokinetic profile and was well tolerated in HVs, supporting the continued clinical development.

Cerebrospinal fluid in the differential diagnosis of Alzheimer's disease: an update of the literature

INTRODUCTION

The importance of cerebrospinal fluid (CSF) biomarkers in Alzheimer's disease (AD) diagnosis is rapidly increasing, and there is a growing interest in the use of CSF biomarkers in monitoring the response to therapy, especially in the light of newly available approaches to the therapy of neurodegenerative diseases.

AREAS COVERED

In this review we discuss the most relevant measures of neurodegeneration that are being used to distinguish patients with AD from healthy controls and individuals with mild cognitive impairment, in order to provide an overview of the latest information available in the scientific literature. We focus on markers related to amyloid processing, markers associated with neurofibrillary tangles, neuroinflammation, neuroaxonal injury and degeneration, synaptic loss and dysfunction, and markers of α-synuclein pathology.

EXPERT OPINION

In addition to neuropsychological evaluation, core CSF biomarkers (Aβ42, t-tau, and p-tau181) have been recommended for improvement of timely, accurate and differential diagnosis of AD, as well as to assess the risk and rate of disease progression. In addition to the core CSF biomarkers, various other markers related to synaptic dysfunction, neuroinflammation, and glial activation (neurogranin, SNAP-25, Nfl, YKL-40, TREM2) are now investigated and have yet to be validated for future potential clinical use in AD diagnosis.

A minimally invasive biomarker for sensitive and accurate diagnosis of Parkinson's disease

Seeding activities of disease-associated α-synuclein aggregates (αSynD), a hallmark of Parkinson's disease (PD), are detectable by seed amplification assay (αSyn-SAA) and being developed as a diagnostic biomarker for PD. Sensitive and accurate αSyn-SAA for blood or saliva would greatly facilitate PD diagnosis. This prospective diagnostic study conducted αSyn-SAA analyses on serum and saliva samples collected from patients clinically diagnosed with PD or healthy controls (HC). 124 subjects (82 PD, 42 HC) donated blood and had extensive clinical assessments, of whom 74 subjects (48 PD, 26 HC) also donated saliva at the same visits. An additional 57 subjects (35 PD, 22 HC) donated saliva and had more limited clinical assessments. The mean ages were 69.21, 66.55, 69.58, and 64.71 years for PD serum donors, HC serum donors, PD saliva donors, and HC saliva donors, respectively. αSynD seeding activities in either sample type alone or both sample types together were evaluated for PD diagnosis. Serum αSyn-SAA data from 124 subjects showed 80.49% sensitivity, 90.48% specificity, and 0.9006 accuracy (AUC of ROC); saliva αSyn-SAA data from 131 subjects attained 74.70% sensitivity, 97.92% specificity, and 0.8966 accuracy. Remarkably, the combined serum and saliva αSyn-SAA from 74 subjects with both sample types achieved better diagnostic performance: 95.83% sensitivity, 96.15% specificity, and 0.98 accuracy. In addition, serum αSynD seeding activities correlated inversely with Montreal Cognitive Assessment in males and positively with Hamilton Depression Rating Scale in females and in the < 70 age group, whereas saliva αSynD seeding activities correlated inversely with age at diagnosis in males and in the < 70 age group. Our data indicate that serum and saliva αSyn-SAA together can achieve high diagnostic accuracy for PD comparable to that of CSF αSyn-SAA, suggesting their potential utility for highly sensitive, accurate, and minimally invasive diagnosis of PD in routine clinical practice and clinical studies.

α-synuclein seed amplification assay sensitivity may be associated with cardiac MIBG abnormality among patients with Lewy body disease

Although α-synuclein seed amplification assays (α-syn SAA) are promising, its sensitivity may be affected by heterogeneity among patients with Lewy body disease (LBD). We evaluated whether α-syn SAA sensitivity is affected by patient heterogeneity, using 123I-meta-iodobenzylguanidine (MIBG) cardiac scintigraphy in early drug-naïve patients. Thirty-four patients with clinically established or probable Parkinson's disease (PD) and seven with dementia with Lewy bodies (DLB) or prodromal DLB were included. While 85.2% of patients with abnormal cardiac MIBG were α-syn SAA positive, only 14.3% were positive among those with normal scans. Logistic regression analysis showed that MIBG positivity was the only significant variable associated with α-syn SAA positivity (odds ratio 74.2 [95% confidence interval 6.1-909]). Although α-syn SAA is sensitive for LBD in patients with abnormal MIBG, the sensitivity may be lower in those with normal MIBG. Further studies are necessary to evaluate the association between patient heterogeneity and α-syn SAA sensitivity.

Seeding Aggregation Assays in Lewy Bodies Disorders: A Narrative State-of-the-Art Review

Multiple system atrophy and Lewy body diseases (LBDs) such as Parkinson's disease, dementia with Lewy bodies, and Parkinson's disease with dementia, known as synucleinopathies, are defined neuropathologically by the accumulation and deposition of aberrant protein aggregates, primarily in neuronal cells. Seeding aggregation assays (SAA) have significant potential as biomarkers for early diagnosis, monitoring disease progression, and evaluating treatment efficacy for these diseases. Real-time quaking-induced conversion (RT-QuIC) and Protein Misfolding Cyclic Amplification (PMCA) assays represent two ultrasensitive protein amplification techniques that were initially tested for the field of prion disorders. Although the fundamental idea behind the creation of these two methods is very similar, their technical differences resulted in different levels of diagnostic accuracy for the identification of prion proteins, making the RT-QuIC assay the most trustworthy and effective instrument for the detection of suspected cases of LBDs and prion-like diseases.

Research advancement in fluid biomarkers for Parkinson's disease

INTRODUCTION

Diagnostic criteria for Parkinson's disease (PD) rely on clinical, mainly motor, features, implying that pre-motor phase cannot be accurately identified. To achieve a reliable early diagnosis, similar to what has been done for Alzheimer's disease (AD), a shift from clinical to biological identification of PD is being pursued. This shift has taken great advantage from the research on cerebrospinal fluid (CSF) biomarkers as they mirror the ongoing molecular pathogenic mechanisms taking place in PD, thus intercepting the disease timely with respect to clinical manifestations.

AREAS COVERED

CSF α-synuclein seed amplification assay (αS-SAA) has emerged as the most promising biomarker of α-synucleinopathy. CSF biomarkers reflecting AD-pathology and axonal damage (neurofilament light chain) and a novel marker of dopaminergic dysfunction (DOPA decarboxylase) add valuable diagnostic and prognostic information in the neurochemical characterization of PD.

EXPERT OPINION

A biological classification system of PD, encompassing pathophysiological and staging biomarkers, might ensure both early identification and prognostic characterization of the patients. This approach could allow for the best setting for disease-modifying treatments which are currently under investigation.

MRI Signature of α-Synuclein Pathology in Asymptomatic Stages and a Memory Clinic Population

Importance

The lack of an in vivo measure for α-synuclein (α-syn) pathology until recently has limited thorough characterization of its brain atrophy pattern, especially during early disease stages.

Objective

To assess the association of state-of-the-art cerebrospinal fluid (CSF) seed amplification assays (SAA) α-syn positivity (SAA α-syn+) with magnetic resonance imaging (MRI) structural measures, across the continuum from clinically unimpaired (CU) to cognitively impaired (CI) individuals, in 3 independent cohorts, and separately in CU and CI individuals, the latter reflecting a memory clinic population.

Design, Setting, and Participants

Cross-sectional data were used from the Swedish BioFINDER-2 study (inclusion, 2017-2023) as the discovery cohort and the Swedish BioFINDER-1 study (inclusion, 2007-2015) and Alzheimer's Disease Neuroimaging Initiative (ADNI; inclusion 2005-2022) as replication cohorts. All cohorts are from multicenter studies, but the BioFINDER cohorts used 1 MRI scanner. CU and CI individuals fulfilling inclusion criteria and without missing data points in relevant metrics were included in the study. All analyses were performed from 2023 to 2024.

Exposures

Presence of α-syn pathology, estimated by baseline CSF SAA α-syn.

Main Outcomes and Measures

The primary outcomes were cross-sectional structural MRI measures either through voxel-based morphometry (VBM) or regions of interest (ROI) including an automated pipeline for cholinergic basal forebrain nuclei CH4/4p (nucleus basalis of Meynert [NBM]) and CH1/2/3. Secondary outcomes were domain-specific cross-sectional cognitive measures. Analyses were adjusted for CSF biomarkers of Alzheimer pathology.

Results

A total of 2961 participants were included in this study: 1388 (mean [SD] age, 71 [10] years; 702 female [51%]) from the BioFINDER-2 study, 752 (mean [SD] age, 72 [6] years; 406 female [54%]) from the BioFINDER-1 study, and 821 (mean [SD] age, 75 [8] years; 449 male [55%]) from ADNI. In the BioFINDER-2 study, VBM analyses in the whole cohort revealed a specific association between SAA α-syn+ and the cholinergic NBM, even when adjusting for Alzheimer copathology. ROI-based analyses in the BioFINDER-2 study focused on regions involved in the cholinergic system and confirmed that SAA α-syn+ was indeed independently associated with smaller NBM (β = -0.271; 95% CI, -0.399 to -0.142; P <.001) and CH1/2/3 volumes (β = -0.227; 95% CI, -0.377 to -0.076; P =.02). SAA α-syn+ was also independently associated with smaller NBM volumes in the separate CU (β = -0.360; 95% CI, -0.603 to -0.117; P =.03) and CI (β = -0.251; 95% CI, -0.408 to -0.095; P =.02) groups. Overall, the association between SAA α-syn+ and NBM volume was replicated in the BioFINDER-1 study and ADNI cohort. In CI individuals, NBM volumes partially mediated the association of SAA α-syn+ with attention/executive impairments in all cohorts (BioFINDER-2, β = -0.017; proportion-mediated effect, 7%; P =.04; BioFINDER-1, β = -0.096; proportion-mediated effect, 19%; P =.04; ADNI, β = -0.061; proportion-mediated effect, 20%; P =.007).

Conclusions and Relevance

In this cohort study, SAA α-syn+ was consistently associated with NBM atrophy already during asymptomatic stages. Further, in memory clinic CI populations, SAA α-syn+ was associated with NBM atrophy, which partially mediated α-syn-induced attention/executive impairment.

Biosensors for Parkinson's Disease: Where Are We Now, and Where Do We Need to Go?

Parkinson's Disease is the second most common neurological disease in the United States, yet there is no cure, no pinpointed cause, and no definitive diagnostic procedure. Parkinson's is typically diagnosed when patients present with motor symptoms such as slowness of movement and tremors. However, none of these are specific to Parkinson's, and a confident diagnosis of Parkinson's is typically only achieved when 60-80% of dopaminergic neurons are no longer functioning, at which point much of the damage to the brain is irreversible. This Perspective details ongoing efforts and accomplishments in biosensor research with the goal of overcoming these issues for Parkinson's diagnosis and care, with a focus on the potential impact of early diagnosis and associated opportunities to pinpoint a cause and a cure. We critically analyze the strengths and shortcomings of current technologies and discuss the ideal characteristics of a diagnostic technology toolbox to guide future research decisions in this space. Finally, we assess what role biosensors can play in facilitating precision medicine for Parkinson's patients.

Improving protocols for α-synuclein seed amplification assays: analysis of preanalytical and analytical variables and identification of candidate parameters for seed quantification

OBJECTIVES

The effect of preanalytical and analytical factors on the α-synuclein (α-syn) seed amplification assay's (SAA) performance has not been fully explored. Similarly, there is limited knowledge about the most suitable assay protocol and kinetic parameters for misfolded α-syn seed quantification.

METHODS

We studied the effect of centrifugation, repeated freeze-thaw cycles (up to seven), delayed freezing, detergent addition, and blood contamination on the performance of the cerebrospinal fluid (CSF) α-syn SAA real-time quaking-induced conversion (RT-QuIC). Moreover, we analysed the inter- and intra-plate variability, the recombinant protein batch effect, and the RT-QuIC parameters' variability when multiple samples were run in controlled conditions. Finally, we evaluated the assay potential of quantifying α-syn seed by assessing kinetic curves in serial CSF dilutions.

RESULTS

Among tested preanalytical variables, a ≥0.01 % blood contamination and adding detergents significantly affected the RT-QuIC kinetic parameters and the number of positive replicates. Increasing the number of replicates improved result reproducibility. The number of positive replicates in serially diluted CSF samples improved discrimination between samples with high and low seeding activity, and the time to threshold (LAG) was the most reliable kinetic parameter in multiple experiment settings.

CONCLUSIONS

Preanalytical variables affecting α-syn RT-QuIC performance are limited to blood contamination and detergent addition. The number of positive replicates and the LAG are the most reliable variables for quantifying α-syn seeding activity. Their consistent measurement in serial dilution experiments, especially when associated with an increased number of sample replicates, will help to develop the α-syn RT-QuIC assay further into a quantitative test.

Single-Molecule Fingerprinting Reveals Different Growth Mechanisms in Seed Amplification Assays for Different Polymorphs of α-Synuclein Fibrils

α-Synuclein (αSyn) aggregates, detected in the biofluids of patients with Parkinson's disease (PD), have the ability to catalyze their own aggregation, leading to an increase in the number and size of aggregates. This self-templated amplification is used by newly developed assays to diagnose Parkinson's disease and turns the presence of αSyn aggregates into a biomarker of the disease. It has become evident that αSyn can form fibrils with slightly different structures, called "strains" or polymorphs, but little is known about their differential reactivity in diagnostic assays. Here, we compared the properties of two well-described αSyn polymorphs. Using single-molecule techniques, we observed that one of the polymorphs had an increased tendency to undergo secondary nucleation and we showed that this could explain the differences in reactivity observed in in vitro seed amplification assay and cellular assays. Simulations and high-resolution microscopy suggest that a 100-fold difference in the apparent rate of growth can be generated by a surprisingly low number of secondary nucleation "points" (1 every 2000 monomers added by elongation). When both strains are present in the same seeded reaction, secondary nucleation displaces proportions dramatically and causes a single strain to dominate the reaction as the major end product.

Navigating the Neurobiology of Parkinson's: The Impact and Potential of α-Synuclein

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease worldwide; therefore, since its initial description, significant progress has been made, yet a mystery remains regarding its pathogenesis and elusive root cause. The widespread distribution of pathological α-synuclein (αSyn) aggregates throughout the body raises inquiries regarding the etiology, which has prompted several hypotheses, with the most prominent one being αSyn-associated proteinopathy. The identification of αSyn protein within Lewy bodies, coupled with genetic evidence linking αSyn locus duplication, triplication, as well as point mutations to familial Parkinson's disease, has underscored the significance of αSyn in initiating and propagating Lewy body pathology throughout the brain. In monogenic and sporadic PD, the presence of early inflammation and synaptic dysfunction leads to αSyn aggregation and neuronal death through mitochondrial, lysosomal, and endosomal functional impairment. However, much remains to be understood about αSyn pathogenesis, which is heavily grounded in biomarkers and treatment strategies. In this review, we provide emerging new evidence on the current knowledge about αSyn's pathophysiological impact on PD, and its presumable role as a specific disease biomarker or main target of disease-modifying therapies, highlighting that this understanding today offers the best potential of disease-modifying therapy in the near future.

Rapid iPSC inclusionopathy models shed light on formation, consequence, and molecular subtype of α-synuclein inclusions

The heterogeneity of protein-rich inclusions and its significance in neurodegeneration is poorly understood. Standard patient-derived iPSC models develop inclusions neither reproducibly nor in a reasonable time frame. Here, we developed screenable iPSC "inclusionopathy" models utilizing piggyBac or targeted transgenes to rapidly induce CNS cells that express aggregation-prone proteins at brain-like levels. Inclusions and their effects on cell survival were trackable at single-inclusion resolution. Exemplar cortical neuron α-synuclein inclusionopathy models were engineered through transgenic expression of α-synuclein mutant forms or exogenous seeding with fibrils. We identified multiple inclusion classes, including neuroprotective p62-positive inclusions versus dynamic and neurotoxic lipid-rich inclusions, both identified in patient brains. Fusion events between these inclusion subtypes altered neuronal survival. Proteome-scale α-synuclein genetic- and physical-interaction screens pinpointed candidate RNA-processing and actin-cytoskeleton-modulator proteins like RhoA whose sequestration into inclusions could enhance toxicity. These tractable CNS models should prove useful in functional genomic analysis and drug development for proteinopathies.

Limitations of the α-Synuclein Seed Amplification Assay in Clinical Practice: Understanding the Pathological Diversity of Parkinson Syndrome

This Viewpoint cautions against premature adoption of the α-synuclein seed amplification assay as a biomarker test for Parkinson disease in general neurology practice.

Enhanced quantitation of pathological α-synuclein in patient biospecimens by RT-QuIC seed amplification assays

Disease associated pathological aggregates of alpha-synuclein (αSynD) exhibit prion-like spreading in synucleinopathies such as Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Seed amplification assays (SAAs) such as real-time quaking-induced conversion (RT-QuIC) have shown high diagnostic sensitivity and specificity for detecting proteopathic αSynD seeds in a variety of biospecimens from PD and DLB patients. However, the extent to which relative proteopathic seed concentrations are useful as indices of a patient's disease stage or prognosis remains unresolved. One feature of current SAAs that complicates attempts to correlate SAA results with patients' clinical and other laboratory findings is their quantitative imprecision, which has typically been limited to discriminating large differences (e.g. 5-10 fold) in seed concentration. We used end-point dilution (ED) RT-QuIC assays to determine αSynD seed concentrations in patient biospecimens and tested the influence of various assay variables such as serial dilution factor, replicate number and data processing methods. The use of 2-fold versus 10-fold dilution factors and 12 versus 4 replicate reactions per dilution reduced ED-RT-QuIC assay error by as much as 70%. This enhanced assay format discriminated as little as 2-fold differences in αSynD seed concentration besides detecting ~2-16-fold seed reductions caused by inactivation treatments. In some scenarios, analysis of the data using Poisson and midSIN algorithms provided more consistent and statistically significant discrimination of different seed concentrations. We applied our improved assay strategies to multiple diagnostically relevant PD and DLB antemortem patient biospecimens, including cerebrospinal fluid, skin, and brushings of the olfactory mucosa. Using ED αSyn RT-QuIC as a model SAA, we show how to markedly improve the inter-assay reproducibility and quantitative accuracy. Enhanced quantitative SAA accuracy should facilitate assessments of pathological seeding activities as biomarkers in proteinopathy diagnostics and prognostics, as well as in patient cohort selection and assessments of pharmacodynamics and target engagement in drug trials.

Association of CSF α-Synuclein Seeding Amplification Assay Results With Clinical Features of Possible and Probable Dementia With Lewy Bodies

BACKGROUND AND OBJECTIVES

The clinical diagnosis of dementia with Lewy bodies (DLB) depends on identifying significant cognitive decline accompanied by core features of parkinsonism, visual hallucinations, cognitive fluctuations, and REM sleep behavior disorder (RBD). Hyposmia is one of the several supportive features. α-Synuclein seeding amplification assays (αSyn-SAAs) may enhance diagnostic accuracy by detecting pathologic αSyn seeds in CSF. In this study, we examine how different clinical features associate with CSF αSyn-SAA positivity in a large group of clinically diagnosed participants with DLB.

METHODS

Cross-sectional and longitudinal CSF samples from the multicentered observational cohort study of the DLB Consortium and similar studies within the Parkinson's Disease Biomarker Program, contributed by academic medical centers in the United States, underwent αSyn-SAA testing. Participants included those clinically diagnosed with DLB and 2 control cohorts. Associations between core DLB features and olfaction with αSyn-SAA positivity were evaluated using logistic regression.

RESULTS

CSF samples from 191 participants diagnosed with DLB (mean age 69.9 ± 6.8, 15% female), 50 age-matched and sex-matched clinical control participants, and 49 younger analytical control participants were analyzed. Seventy-two percent (137/191) of participants with DLB had positive αSyn-SAAs vs 4% of the control groups. Among participants with DLB, those who were αSyn-SAA-positive had lower Montreal Cognitive Assessment scores (18.8 ± 5.7 vs 21.2 ± 5.2, p = 0.01), had worse parkinsonism on the Movement Disorders Society Unified Parkinson's Disease Rating Scale part III (33.8 ± 15.1 vs 25.6 ± 16.4, p = 0.001), were more likely to report RBD (114/133 [86%] vs 33/53 [62%], p < 0.0001), and had worse hyposmia on the University of Pennsylvania Smell Identification Test (UPSIT) (94/105 [90%] below 15th percentile vs 14/44 [32%], p < 0.0001). UPSIT percentile had the highest area under the curve (0.87, 95% CI 0.81-0.94) in predicting αSyn-SAA positivity and participants scoring at or below the 15th percentile of age and sex normative values had 18.3 times higher odds (95% CI 7.52-44.6) of having a positive αSyn-SAA test. Among 82 participants with longitudinal CSF samples, 81 (99%) had the same αSyn-SAA result for initial and follow-up specimens.

DISCUSSION

A substantial proportion of clinically diagnosed participants with DLB had negative αSyn-SAA results. Hyposmia was the strongest clinical predictor of αSyn-SAA positivity. Hyposmia and αSyn-SAA may have utility in improving the diagnostic assessment of individuals with potential DLB.

CLASSIFICATION OF EVIDENCE

This study provided Class III evidence that CSF αSyn-SAA distinguishes patients with clinically diagnosed DLB from normal controls.

Aptamer binding footprints discriminate α-synuclein fibrillar polymorphs from different synucleinopathies

Synucleinopathies, including dementia with Lewy bodies (DLB), Parkinson's disease (PD), and multiple system atrophy (MSA), are characterized by the presence of α-synuclein (α-syn) aggregates in the central nervous system. Recent evidence suggests that the heterogeneity of synucleinopathies may be partly explained by the fact that patients may have different α-syn fibrillar polymorphs with structural differences. In this study, we identify nuclease resistant 2'fluoro-pyrimidine RNA aptamers that can differentially bind to structurally distinct α-syn fibrillar polymorphs. Moreover, we introduce a method, AptaFOOT-Seq, designed to rapidly assess the affinity of a mixture of these aptamers for different α-SYN fibrillar polymorphs using next-generation sequencing. Our findings reveal that the binding behavior of aptamers can be very different when they are tested separately or in the presence of other aptamers. In this case, competition and cooperation can occur, providing a higher level of information, which can be exploited to obtain specific 'footprints' for different α-Syn fibrillar polymorphs. Notably, these footprints can distinguish polymorphs obtained from patients with PD, DLB or MSA. This result suggests that aptaFOOT-Seq could be used for the detection of misfolded or abnormal protein conformations to improve the diagnosis of synucleinopathies.

Detecting Misfolded α-Synuclein in Blood Years before the Diagnosis of Parkinson's Disease

BACKGROUND

Identifying individuals with Parkinson's disease (PD) already in the prodromal phase of the disease has become a priority objective for opening a window for early disease-modifying therapies.

OBJECTIVE

The aim was to evaluate a blood-based α-synuclein seed amplification assay (α-syn SAA) as a novel biomarker for diagnosing PD in the prodromal phase.

METHODS

In the TREND study (University of Tuebingen) biennial blood samples of n = 1201 individuals with/without increased risk for PD were taken prospectively over 4 to 10 years. We retrospectively analyzed blood samples of 12 participants later diagnosed with PD during the study to detect and amplify pathological α-syn conformers derived from neuronal extracellular vesicles using (1) immunoblot analyses with an antibody against these conformers and (2) an α-syn-SAA. Additionally, blood samples of n = 13 healthy individuals from the TREND cohort and n = 20 individuals with isolated rapid eye movement sleep behavior disorder (iRBD) from the University Hospital Cologne were analyzed.

RESULTS

All individuals with PD showed positive immunoblots and a positive α-syn SAA at the time of diagnosis. Moreover, all PD patients showed a positive α-syn SAA 1 to 10 years before clinical diagnosis. In the iRBD cohort, 30% showed a positive α-syn SAA. All healthy controls had a negative SAA.

CONCLUSIONS

We here demonstrate the possibility to detect and amplify pathological α-syn conformers in peripheral blood up to 10 years before the clinical diagnosis of PD in individuals with and without iRBD. The findings of this study indicate that this blood-based α-syn SAA assay has the potential to serve as a diagnostic biomarker for prodromal PD. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Ultrasensitive detection of aggregated α-synuclein using quiescent seed amplification assay for the diagnosis of Parkinson's disease

BACKGROUND

Seed amplification assays (SAA) enable the amplification of pathological misfolded proteins, including α-synuclein (αSyn), in both tissue homogenates and body fluids of Parkinson's disease (PD) patients. SAA involves repeated cycles of shaking or sonication coupled with incubation periods. However, this amplification scheme has limitations in tracking protein propagation due to repeated fragmentation.

METHODS

We introduced a modified form of SAA, known as Quiescent SAA (QSAA), and evaluated biopsy and autopsy samples from individuals clinically diagnosed with PD and those without synucleinopathies (control group). Brain biopsy samples were obtained from 14 PD patients and 6 controls without synucleinopathies. Additionally, skin samples were collected from 214 PD patients and 208 control subjects. Data were analyzed from April 2019 to May 2023.

RESULTS

QSAA successfully amplified αSyn aggregates in brain tissue sections from mice inoculated with pre-formed fibrils. In the skin samples from 214 PD cases and 208 non-PD cases, QSAA demonstrated high sensitivity (90.2%) and specificity (91.4%) in differentiating between PD and non-PD cases. Notably, more αSyn aggregates were detected by QSAA compared to immunofluorescence with the pS129-αSyn antibody in consecutive slices of both brain and skin samples.

CONCLUSION

We introduced the new QSAA method tailored for in situ amplification of αSyn aggregates in brain and skin samples while maintaining tissue integrity, providing a streamlined approach to diagnosing PD with individual variability. The integration of seeding activities with the location of deposition of αSyn seeds advances our understanding of the mechanism underlying αSyn misfolding in PD.

α-Synuclein seed amplification technology for Parkinson's disease and related synucleinopathies

Synucleinopathies are a group of neurodegenerative diseases (NDs) associated with cerebral accumulation of α-synuclein (αSyn) misfolded aggregates. At this time, there is no effective treatment to stop or slow down disease progression, which in part is due to the lack of an early and objective biochemical diagnosis. In the past 5 years, the seed amplification technology has emerged for highly sensitive identification of these diseases, even at the preclinical stage of the illness. Much research has been done in multiple laboratories to validate the efficacy and reproducibility of this assay. This article provides a comprehensive review of this technology, including its conceptual basis and its multiple applications for disease diagnosis, as well for understanding of the disease biology and therapeutic development.

Tear α-synuclein as a biomarker for Parkinson's disease: A systematic review and meta-analysis

BACKGROUND

Parkinson's disease symptoms mostly manifest after significant and irreversible neuropathology. Hence, there is a need to identify biomarkers that can provide indications of disease before significant neuronal degeneration occurs.

OBJECTIVE

To estimate the difference in the concentration of α-synuclein protein in tears between individuals with Parkinson's disease and healthy controls.

DATA SOURCES

PubMed, Scopus, and Web of Science. The last database search was on December 20, 2023.

STUDY ELIGIBILITY CRITERIA

Primary prospective studies in humans measuring the level of α-synuclein in tears and clinical outcomes reported using mean or median.

PARTICIPANTS AND INTERVENTIONS

Individuals with Parkinson's disease and healthy controls.

STUDY APPRAISAL AND SYNTHESIS METHODS

The risk of bias was assessed using the Newcastle-Ottawa Scale. The I2 statistic was used to estimate heterogeneity. The outcome measure was the difference in tear total and oligomeric α-synuclein. Mean difference (MD) was used to assess the outcome. The certainty of evidence was rated following the Grading of Recommendations Assessment and Development and Evaluation (GRADE) system.

RESULTS

Three hundred twenty-seven Parkinson's disease and 312 healthy control subjects from five studies and 177 Parkinson's disease and 166 healthy control subjects from two studies were included in total α-synuclein levels and oligomeric α-synuclein levels analysis, respectively. Total α-synuclein level was not different between Parkinson's disease and healthy controls (MD = 0.02 ng/mL [95% confidence interval {CI}: 0.00 to 0.05 ng/mL; I2 = 90%; Z = 1.79; p=0.07; number of studies = 5; GRADE rating = very low]). Stratifying the data based on disease duration, total α-synuclein was higher in subjects with Parkinson's disease duration ≥7 years compared with healthy controls (MD = 0.04 ng/mL [95% CI: 0.03 to 0.05 ng/mL; I2 = 0%; Z = 8.24, p<0.00001; number of studies = 2; GRADE rating = low]) but not different between the two groups (MD = -0.12 ng/mL (95% CI: -0.38 to 0.15 ng/mL; I2 = 93%; Z = 0.84, p=0.40; number of studies = 3; GRADE rating = very low]). Oligomeric α-synuclein level was higher in Parkinson's disease compared with controls (MD = 6.50 ng/mL [95% CI: 2.79 to 10.20 ng/mL; I2 = 94%; Z = 3.44; p=0.0006; number of studies = 2; GRADE rating = very low]).

LIMITATIONS

High heterogeneity between studies. Potential sources of heterogeneity could not be explored due to the limited number of studies.

CONCLUSIONS AND IMPLICATIONS OF KEY FINDINGS

Tear α-synuclein has the potential to be a noninvasive biomarker for Parkinson's disease. Studies are, however, needed to increase certainty in the biomarker and establish how the protein's changes in tears correlate with Parkinson's disease progression and severity.