Abstract Body

Tau and alpha-synuclein aggregates are neuropathological hallmarks of neurodegenerative dementias and movement disorders with parkinsonism, highlighting the etiological resemblance and topological distinction between these two disease categories. We recently developed a PET imaging agent capable of capturing tau fibrils in Alzheimer’s disease and frontotemporal lobar degeneration with high contrast, enabling separations of AD and progressive supranuclear palsy patients from controls with high sensitivity and specificity. The intensity and extent of PET signals in these disorders are intimately correlated with the disease severity, according to cross-sectional and longitudinal assays. Moreover, enhanced tau PET probe binding has been noted in diverse other neuropsychiatric conditions, including chronic traumatic encephalopathy and late-onset bipolar illness. As our tau probe is also self-fluorescent, it is applicable to in-vivo two-photon microscopy of the tauopathy model mouse brain, leading to the revelation that progressive tau accumulation detected by PET is based on a dynamic turnover of tau inclusions formed by the generation of tau tangles and subsequent primary phagocytosis of tangle-bearing neurons by microglia. Similar to the tau ligand, we generated bimodal optical and PET probes for alpha-synuclein assemblies and applied them to mouse and marmoset models of propagating alpha-synuclein pathologies. At in-vivo microscopic and macroscopic levels, these imaging agents allowed the longitudinal pursuit of disseminating alpha-synuclein fibrillogenesis along the neuronal circuits accompanied by neurodegeneration. Encouraged by our nonclinical data, we are currently preparing the clinical application of these two compounds to PET assays of Parkinson’s disease, Lewy body dementia, and multiple system atrophy in comparison with controls.

Aims

The microtubule-associated protein tau is strongly involved in many neurodegenerative disorders. Even though abnormal accumulation of tau is a characteristic feature of tauopathies, modified tau has been observed also in alpha-synucleinopathies like Parkinson's Disease (PD) and Multiple System Atrophy (MSA). Due to the common involvement of peripheral nervous system (PNS) in several neurodegenerative diseases, in this study we characterized tau expression in the skin PNS of patients with PD, MSA, tauopathies and healthy subjects (HC) as a possible biomarker of disease.

Methods

We recruited 27 patients with idiopathic PD, 8 MSA, 10 atypical parkinsonisms with possible tauopathies (AP-Tau) and 20 HC. A double 3mm punch skin biopsy was performed at two anatomical sites (cervical and ankle). We evaluated the expression of physiological and phosphorylated tau by immunofluorescence assays and western blot and quantified tau expression by ELISA.

Results

Physiological tau was abundantly expressed in skin somatosensory and autonomic nerve fibers. Western-blot analysis revealed the presence of two different tau isoforms (~70 and 55 KDa) and a different pattern of phosphorylation between synucleinopathies and tauopathies patients. ELISA assay showed higher levels of tau in AP-Tau compared to other groups. Finally, ROC curves analysis displayed an optimal diagnostic performance for AP-Tau patients especially compared to PD (sensitivity 90%, specificity 69%) and MSA (sensitivity 90%, specificity 86%).

Conclusions

Characterisation of tau in skin peripheral nervous system shows a differential expression of the protein between groups and suggests that tau profiling in skin biopsy is a promising biomarker to discriminate neurodegenerative diseases.

Aims

The goal of this research is to determine whether the tau-PET tracer AV-1451 can help differentiate corticobasal syndrome (CBS)cases of varying underlying pathologies.

Methods

In this cross-sectional study, 11 subjects with CBS underwent structural MR, tau-PET with AV-1451 and amyloid-PET with PiB imaging, along with detailed clinical and neuropsychological examinations. Neuropathological examinations were conducted on 6 of the 11 individuals. Mixed effects general linear models were used to compare AV-1451 retention and atrophy to those features in 34 normal control subjects.

Results

Subjects with low amyloid burden, including 3 pathologically-confirmed CBD, showed greater retention of AV-1451 and greater regional atrophy in areas commonly associated with CBD than healthy control subjects, especially in the precentral gyrus and pallidum (p < 0.05). AV-1451 retention and atrophy were greater in the clinically affected hemisphere; retention was greater in subcortical than cortical regions (p < 0.0001). Three subjects had evidence of high amyloid burden consistent with Alzheimer disease that was confirmed pathologically in 2 cases; as expected, they had greater and more widespread tau burden and atrophy than in the amyloid negative cases. In a single subject without tau pathology, there was thalamic AV-1451 retention but minimal cortical and basal ganglia uptake.

Conclusions

AV-1451 retention detects the asymmetric cortical and basal ganglia pattern of degeneration consonant with the clinical manifestations of CBD, whereas the cortical retention associated with Alzheimer disease is greater and more diffuse.

Aims

Several studies have confirmed alpha-synuclein (aSyn) real-time quaking-induced conversion (RT-QuIC) assay to have high sensitivity and specificity for Lewy body disorders. Here, we study less understood robustness and reproducibility of the assay as well as its use as a quantitative measure to monitor disease progression, stratifying between different synucleinopathies and predicting disease conversion in idiopathic RBD (iRBD).

Methods

We performed aSyn RT-QuIC in 93 cerebrospinal fluid (CSF) samples from longitudinally followed Parkinson’s disease (PD) patients and controls and examined how quantitative readouts extrapolated from the assay correlated with clinical symptoms. We also examined CSF from 23 longitudinally followed MSA patients and 45 polysomnographically verified iRBD patients derived from four different cohorts.

Results

aSyn RT-QuIC showed 89% sensitivity and 94% specificity for PD. None of the assay parameters correlated with clinical symptoms but V_max across the different phenotype clusters differed significantly (p=0.018). Adding any of the assay parameters to the logistic regression model of PD vs. control with the MDS prodromal PD score showed strong association with PD status. The sensitivity in our MSA samples was 74% and MSA CSF showed longer T₅₀ and significantly lower V_max and Max Fluorescence compared to PD. The sensitivity between different RBD cohorts varied from 39% to 91%, probably representing how close the patients are to disease conversion.

Conclusions

aSyn RT-QuIC adds value in diagnosing PD but the quantitative data does not correlate to disease severity. This assay can clearly distinguish MSA patients and could identify prodromal subjects with iRBD and risk of conversion.

Aims

Alpha-synuclein inclusions in the brain are the molecular hallmark of synucleinopathies. In the absence of validated imaging ligands for alpha-synuclein, biofluidic biomarkers are particularly important to support differential diagnosis and follow the progression of alpha-synuclein pathology.

Methods

We developed and validated a seeded aggregation assay (SAA) detecting alpha-synuclein seeds in human cerebrospinal fluid (CSF) with a sensitivity of at least 70 fg/ml. Using SAA we analyzed three cross-sectional cohorts including healthy controls (HC) and patients with Parkinson’s disease (PD), multiple system atrophy (MSA), dementia with Lewy bodies (DLB), Alzheimer’s disease (AD), corticobasal degeneration (CBD), and progressive supranuclear palsy (PSP).

Results

SAA discriminated PD patients from healthy controls with high sensitivity (78-96%) and specificity (83-96%). The tauopathy groups were predominantly SAA negative indicating high analytical specificity for alpha-synuclein pathology. Interestingly, 87% of MSA patients were SAA negative suggesting that the alpha-synuclein strains present in MSA CSF behave fundamentally different from the ones in PD CSF. By combining SAA with CSF Neurofilament light the HC, PD, and MSA patients could be clearly discriminated from each other, whereas DLB patients showed a higher variability. Quantification of SAA revealed a correlation of seeding kinetics with symptom duration in the PD groups.

Conclusions

Here, we demonstrate that SAA is a powerful CSF biomarker to support the differential diagnosis of parkinsonian disorders with overlapping symptoms like PD and MSA. Our data also provides first evidence that SAA may be used to monitor progression of alpha-synulcein pathology in PD patients.

Aims

The relationship between neurofilament light (NfL) and the burden of non-motor symptoms (NMS) in Parkinson’s disease (PD) is unclear. The aim of this study is to investigate whether NfL levels are associated with worsening NMS burden in PD.

Methods

Baseline and longitudinal NfL levels were measured in the cerebrospinal fluid (CSF) and serum in a large cohort of PD patients and healthy controls from the Parkinson’s Progression Marker Initiative. NMS were assessed using composite measures from the Movement Disorder Society Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) part I, the Geriatric Depression Scale (GDS) and the State-Trait Anxiety Inventory (STAI). We compared CSF and serum NfL between patients and controls and assessed their relationship with baseline and longitudinal NMS with correlations or linear mixed effects models. In all analyses, NfL levels were adjusted for potential confounders.

Results

Serum NfL levels were higher at baseline (p=0.043) and showed significant longitudinal increases (p<0.001) in PD patients compared to controls. Baseline and longitudinal serum and CSF NfL predicted worse MDS-UPDRS-I and depression (GDS) scores over time in PD (p<0.01). Furthermore, longitudinal changes in serum and CSF NfL were associated with worse longitudinal anxiety (STAI) scores in PD (p<0.05). These results were similar after adjusting for cognitive and motor deficits.

Conclusions

Our findings suggest that serum NfL levels are elevated in PD and that both serum and CSF NfL are associated with worse NMS. Serum NfL could potentially be used in the clinic as a non-invasive marker of NMS progression for PD patients.

Aims

Biomarker discovery from large patient cohorts is a complex process due to the heterogeneous nature of such data. Our aim is to minimise the noise or confounding factors and accurately identify markers of Parkinson's disease progression.

Methods

We created a novel tool to objectively predict which confounders need to be accounted for to optimise the underlying biological information in a given cohort. We applied this tool to the whole blood, bulk RNA sequencing data from the PPMI cohort, consisting of Parkinson’s disease patients and equivalent controls. Furthermore, we adjusted for noise arising from cell type variation using existing cell devolution methods.

Results

We find that confounding variables in the PPMI cohort are primarily related to alignment differences, input sample concentrations and handling variations. Correcting for these variables reproducibly improved gene-gene associations in the dataset by up to 5% and indirectly minimised the explanatory power of other unwanted variables while preserving the explanatory power of variables of interest.

Conclusions

Stringent confounder prediction and adjustment serves to improve the explanatory power of disease progression in the PPMI cohort and aids in the identification of markers for Parkinson’s disease progression. This methodology may be utilised not only for the PPMI cohort but also for processing other large, complex populations.

Abstract Body

The Parkinson Progression Marker Initiative (PPMI) is a longitudinal, observational, multi-center study to assess progression of clinical features, digital outcomes, and imaging, biologic and genetic markers of Parkinson’s disease (PD) progression. During the past ten years, the PPMI study has established a robust clinical and biomarker dataset. PPMI has now expanded to increase the number of participants across the PD continuum from prodromal to moderate PD and identify and explore the use of biomarkers to test hypotheses of the underlying molecular pathobiology of PD, enable modeling of PD progression to identify clinical and/or biologic data driven PD progression sub-sets, and inform studies testing PD therapeutics.

The expanded PPMI will will include the current PPMI cohorts plus approximately 1000 early PD and healthy participants and 2000 participants with Prodromal PD. The prodromal cohort will be enrolled based on a staged risk paradigm with initial assessment via PPMI online followed by DAT imaging to determine eligibility to participate in a five-year densely phenotypes longitudinal study.

We will present examples of PPMI data on that demonstrates the staged risk paradigm for prodromal PD and will provide exploratory data identifying clinical subsets of PD that may predict disease progression. PPMI will expand the existing data set and biorepository already available from PPMI. The PPMI expansion has the potential to establish a framework for developing a prodromal PD cohort and to identify meaningful clinical and biomarker outcomes that could accelerate clinical trials of both manifest and prodromal PD.