Journal of Parkinson's Disease

Braak and others have proposed that Lewy body pathology LBP in Parkinson disease PD may arise not only in the brain but alternatively from an initial site in the gastrointestinal GI tract with subsequent passage to the central nervous system CNS through the vagus nerve or other routes. We tested this hypothesis by using both immunohistochemistry IHC and RT QuIC a form of alpha synuclein seed amplification assay SAA to detect alpha synuclein LBP in samples from selected brain regions and 10 GI tract sites taken from autopsies of 50 PD subjects and 128 elderly subjects without parkinsonism or dementia including 34 with IHC identified CNS incidental Lewy body disease ILBD and 94 with no Lewy body IHC pathology detected NLB. A positive SAA or IHC result was restricted to the GI tract in only 2 subjects while LBP by either SAA or IHC was restricted to the brain in 11 subjects. To fairly compare GI only with brain only synucleinopathy however we would have to do SAA on brain samples from all ILBD and NLB cases in at least 4 critical brain regions olfactory bulb medulla pons and amygdala. Further SAA of brain regions is estimated based on the proportional results to date to potentially identify 21 additional brain only LBP subjects total of 32 if it were done on all of the NLB subjects. From this brain only LBP is estimated to be 16 times more common than GI only LBP. To assess the clinical impact of SAA positive GI sites we found that the number of positive sites per subject is significantly correlated with UPDRS motor score and SCOPA AUT GI related scores including those for salivation straining constipation and bowel movement.

Background: Reliable biomarkers for Parkinson's disease (PD) pathology detection are essential for research. The alpha-synuclein (aSyn) seed amplification assay (SAA) is a validated biomarker for misfolded aSyn. Objectives: To assess the association between aSyn SAA and LRRK2-related PD (LRRK2-PD) and its link to mitochondrial genetic burden. Methods: We included N=76 LRRK2 p.Gly2019Ser variant carriers (N=22 affected, N=54 unaffected), N=714 patients with idiopathic PD (iPD), and N=411 controls from Norway. We analyzed cerebrospinal fluid (CSF)-based aSyn SAA in N=10 PD patients and N=30 unaffected LRRK2 p.Gly2019Ser carriers, alongside N=6 controls and N=56 iPD patients. A mitochondrial polygenic score (MGS) was derived from genotyping data, using PPMI as an additional cohort (iPD: N=355, LRRK2-PD: N=118). Results: Seeding was observed in 80% of patients with LRRK2-PD, and in one unaffected variant carrier (AUC=0.97, CI 0.92-1.00). In a meta-analysis across two PD cohorts, higher MGS was associated with increased aSyn seeding (pooled beta=0.38, p=0.028). Conclusions: CSF-based aSyn SAA can discriminate between LRRK2-PD and unaffected carriers. Our findings support an association with mitochondrial burden and aSyn seeding.

Background: Gait variability is a hallmark of Parkinson's disease (PD) and has been linked to cognitive deficits and fall risk. Rapid eye movement sleep behavior disorder (RBD) is a strong predictor of synucleinopathies, yet evidence for gait changes in RBD is inconsistent. Performing a dual task increases gait variability, an effect that can be quantified using a cost function. Objective: Determine the degree to which dual task cost differs between control, RBD, and PD participants at baseline, and between RBD converters versus non-converters at follow-up. Methods: 46 RBD, 23 control, and 14 PD participants completed standardized gait analysis at baseline. Parameters chosen for analysis included enhanced gait variability index (eGVI), functional ambulation performance (FAP), velocity, step length, cadence, base of support, and double support time. Medical records were surveilled for 3 years following participant enrollment, determining that 6 RBD participants converted to PD or dementia. Baseline gait indices and dual task costs were compared between control, RBD, and PD groups at enrollment, and between RBD stable and RBD converters at follow-up. Results: The PD group had greater eGVI, as well as greater dual task cost for FAP, cadence, width, and double support time. No differences in gait variability were identified between RBD and control groups at baseline. Compared to the stable group, RBD converters had greater dual task cost for FAP, velocity, cadence, and double support time. Conclusions: Increased gait variability during dual task may identify RBD patients at imminent risk of phenoconversion.

Background: Historically, OFF burden in Parkinsons disease has been primarily attributed to motor features. Recent studies highlight that non motor symptoms, and the predictability of OFF episodes also drive functional impairment, yet they are rarely measured in clinical practice. Objective: To identify which clinical features are most closely associated with OFF time and OFF impact, and to quantify the added explanatory value of temporal predictability, non-motor, and behavioural domains beyond a core motor model. Methods: We analysed 1,252 OFF only visits from 430 PPMI participants. Outcomes were MDS UPDRS IV 4.3 (OFF time) and 4.4 (OFF impact). Linear mixed effects models with a participant random intercept were fitted. The core motor model included OFF state motor severity, freezing, tremor, levodopa responsiveness, and dyskinesia, plus covariates. Predictability (IV; 4.5), non motor (mood, fatigue/sleep, autonomic/GI), and behavioural (impulse control behaviours) domains were then added to assess added influence beyond motor. Analyses were stratified by time since diagnosis (Pooled; [≤] 4y; [≥] 6y). Results: Clinical features explained more variance in OFF impact than OFF time (25.9% vs 8.1%). OFF time was primarily linked to OFF state motor severity/freezing, with levodopa responsiveness important early. For OFF impact, predictability produced the largest increment in marginal R squared beyond the core motor model (pooled and Late). Within the core motor model, tremor was the largest contributor to OFF impact. Conclusions: Predictability is a prominent correlate of OFF impact. Asking about predictability may help tailor therapy, from timing optimisation to on demand rescue for unpredictable episodes.

Background: Visual dysfunction is a common but underrecognized contributor to disability in Parkinsons disease (PD), particularly deficits in binocular vision and vergence that impair reading, near work, and quality of life. The relationship between objective oculomotor abnormalities and patient-reported visual disability remains incompletely understood. Methods: We studied 25 individuals with PD and 11 age-matched controls who completed the National Eye Institute Visual Function Questionnaire 25 (VFQ25) and the Convergence Insufficiency Symptom Survey (CISS). Participants underwent comprehensive clinical ophthalmologic assessment and high resolution binocular eye tracking to quantify vergence latency, gain, fixation dynamics, and drift variability. Associations between objective measures and patient reported outcomes were examined, and predictive models were developed using clinic-only and combined clinical plus eye tracking approaches. Results: Compared with controls, PD participants demonstrated significantly worse VFQ25 composite scores and higher CISS scores, driven primarily by impairments in near activities and mental health. Clinically, PD was characterized by convergence insufficiency rather than generalized visual loss. Objective eye tracking revealed delayed vergence initiation, reduced gain, and increased instability. In PD, both clinical convergence measures (notably nearpoint convergence) and dynamic eye tracking metrics strongly correlated with VFQ25 and CISS scores, whereas such relationships were absent in controls. Predictive models showed limited performance using clinic measures alone, but improved with inclusion of eye racking variables. Conclusions: Visual disability in PD is tightly linked to convergence insufficiency and dynamic oculomotor instability. Simple clinical measures such as nearpoint convergence, augmented by eye tracking when available, provide meaningful insight into patient reported visual quality of life.

BackgroundLRRK2-Parkinsons disease (LRRK2-PD) is biologically heterogeneous with approximately 30% lacking aggregated alpha synuclein (Syn) in cerebrospinal fluid by seed amplification assay (SAA). Prior work has suggested slower progression in LRRK2-PD compared to sporadic PD (sPD). ObjectiveWe aimed to assess how LRRK2-PD with Syn aggregates on SAA (S+ LRRK2-PD) compares to S+ sPD. MethodsData from the Parkinsons Progression Markers Initiative were used to compare S+ LRRK2-PD and S+ sPD cohorts propensity score-matched on age, disease duration, sex and levodopa equivalent dose (N = 79 per cohort). Baseline clinical and biological features and 4-year longitudinal features were assessed. ResultsAt baseline, S+ LRRK2-PD participants had lower motor scores and dopaminergic deficit. Among measures showing within group progression, longitudinal trajectories did not differ significantly between groups. ConclusionsLongitudinal clinical progression of S+ LRRK2-PD and sPD in the PPMI study is similar despite differences in baseline features.

We investigated whether people with Parkinson's disease who are dual GBA1+LRRK2 carriers have a milder, LRRK2-like phenotype as previously reported. This was accomplished by comparing clinical features and alpha-synuclein seed amplification assay (SAA) positivity rates between dual GBA1+LRRK2-PD(n=13), GBA1-PD(n=169) and LRRK2-PD(n=175) carriers in a cross-sectional retrospective study of Parkinson's Progression Markers Initiative (PPMI) data. Our results show that GBA1+LRRK2-PD rate(83%) is closer to GBA1-PD rate(87%) rather than LRRK2-PD rate (62%mp-value>0.05). GBA1+LRRK2-PD have both non-motor and motor phenotypic similarity of GBA1-PD(p-value>0.05). This small PPMI cohort indicates that dual GBA1+LRRK2-PD carriers' SAA positivity and phenotype are aligned with GBA1-PD.

Background Neuropsychiatric fluctuations in Parkinson's disease (PD) often accompany motor fluctuations, but their temporal relationship during the acute levodopa response remains unclear. Objectives To determine whether motor and neuropsychiatric responses occur synchronously during the OFF-to-ON transition. Methods Nineteen fluctuating PD patients underwent a high-resolution levodopa challenge with repeated assessments every 10 minutes for 60 minutes after levodopa administration. Motor symptoms (akinesia, rigidity) and neuropsychiatric fluctuations were quantified. Transition times (t25%-t50%-t75%-t100%) and response profiles were analyzed using correlation and clustering approaches. Results Motor and neuropsychiatric transition times were not correlated at any threshold (all FDR-corrected p>0.05; Bayes factors <1), supporting temporal dissociation. Among 18 patients with complete data, clustering revealed synchronous (6/18), neuropsychiatric-preceding (7/18), and motor-preceding (3/18) profiles. Conclusion Motor and neuropsychiatric responses to levodopa during PD fluctuations are partly independent and follow heterogeneous, patient-specific temporal profiles, supporting the search for distinct biomarkers and future individualized adaptative therapies

BackgroundPhenoconversion to Parkinsons disease (PD) or dementia with Lewy bodies (DLB) currently relies on established clinical diagnostic criteria. Availability of in vivo biomarkers--CSF -synuclein seed amplification assay (CSFaSynSAA) and dopamine transporter (DAT) imaging--offer the opportunity to investigate congruency between clinical phenoconversion and biologically defined disease. MethodsWe analyzed Parkinso[n]s Progression Markers Initiative participants who phenoconverted to PD, DLB, multiple system atrophy (MSA), Alzheimers disease (AD) or other dementias from prodromal and non-manifesting genetic carrier (NMC) groups and controls. Site investigators determined phenoconversion based on established diagnostic criteria. All phenoconverters with [&ge;]1 annual follow-up visit, with available biomarkers and persistent clinically defined diagnosis at last observation were included. Neuronal alpha-Synuclein Disease Integrated Staging System (NSD-ISS) staging was applied. ResultsAmong 121 phenoconverters, 103 had evaluable CSFaSynSAA and DAT data and were included in analysis: 92 PD, 7 DLB, 2 MSA, 2 AD/other dementias. Phenoconversion annual rates varied widely across groups: iRBD 7.9%, hyposmia 4.2%, GBA1 0.3%, LRRK2 1.3%, LRRK2+GBA1 0.9%, and controls 0.5%. Median time from baseline to phenoconversion ranged from 13-14 months in iRBD and hyposmia to 36-85 months in NMCs. The expected biomarker profile (CSFaSynSAA+/DAT+) for clinically-diagnosed synucleinopathy occurred in 74 (71.8%) participants. Biological alignment (CSFaSynSAA+/DAT+) was present in 87% hyposmics and 72% iRBD phenoconverters. CSFaSynSAA negativity was high among LRRK2 phenoconverters (67%), who also were more likely to have a preserved sense of smell (83%). Phenoconversion occurred later than onset of functional impairment: 15/47 (31.9%) iRBDs and 7/38 (18.4%) hyposmics were already NSD-ISS stage [&ge;]4 at time of phenoconversion. ConclusionsClinical phenoconversion did not necessarily align with biological evidence of synucleinopathy or dopaminergic loss and can be delayed compared to onset of meaningful functional impairment. Longitudinal follow up on converters without biological evidence of PD is required to confirm conversion diagnosis and evaluate for a later occurrence of biomarker positivity.

Background: PD GENEration (NCT04057794, NCT04994015), sponsored by the Parkinson's Foundation in partnership with Aligning Science Across Parkinson's (ASAP) through the Global Parkinson's Genetics Program (GP2), is an international, observational, clinical research study that offers genetic testing and counseling to people living with Parkinson's disease (PwP) at no cost. PD GENEration has aimed to empower PwP and their clinicians with knowledge of their genetic status, to accelerate recruitment into precision medicine trials, and to advance research through data sharing. Since its launch in 2019, the study has expanded to enroll over 32,000 PwP (as of March 31, 2026), from 10 countries across North, Central, and South America, the Caribbean, and Israel. Methods: Over the course of 6 years, PD GENEration has evolved to accommodate the growing scientific and research needs of the Parkinson's community while also increasing the ability to return genetic test results to PwP at a greater scale. Participants with a diagnosis of Parkinson's disease (PD) may enroll in-person or virtually where informed consent and blood sample collection can occur. Samples are analyzed at a College of American Pathologists/Clinical Laboratory Improvement Amendments (CAP/CLIA)-certified laboratory using whole genome sequencing, with variants curated for a primary panel of seven PD-associated genes. Results are disclosed during a genetic counseling visit, where further testing is offered for two optional additional gene panels. Those who consent undergo analysis of additional genes, and results are returned during a genetic counseling visit for those that test positive for a variant. In addition to returning genetic results to PwP, a central pillar of the study design has been the open sharing of genomic data to advance discovery in PD research in partnership with ASAP and GP2. Discussion: PD GENEration applies a flexible framework, allowing for country specific considerations and the integration of multiple site models, evolving based on participant needs and the prioritization of equity and accessibility. We summarize PD GENEration's implementation and scaling, highlight key accomplishments and lessons learned, and provide guidance for those interested in implementing large-scale clinical genetic testing studies across other diseases and therapeutic domains.

BackgroundParkinsons disease (PD) is a progressive neurodegenerative disorder with complex pathophysiology. The potential of integrating biomarkers of neuronal injury, neuroinflammation, and modulators of Wnt signaling for PD diagnosis remains largely unexplored. ObjectiveThis study aimed to evaluate the diagnostic and clinical predictive value of a ten-biomarker serum panel encompassing markers of neuronal injury (NSE, UCHL1), neuroinflammation (GFAP, HMGB1), synaptic plasticity (BDNF), proteinopathy (-Synuclein, {beta}-Amyloid-42), and Wnt signaling (R-spondin-1, DKK1, Sclerostin), with a particular focus on chronic fatigue in PD. MethodsIn this case-control study, 90 PD patients and 45 healthy controls were enrolled. Serum biomarkers were quantified using ELISA. Clinical severity was assessed using the Movement Disorder Society-Unified Parkinsons Disease Rating Scale (MDS-UPDRS) and Fibro-Fatigue (FF) scales. Binary logistic regression and multiple linear regression analyses were used to evaluate the diagnostic and predictive value of biomarkers for PD diagnosis, psychiatric and motoric scores, and an FF score reflecting chronic fatigue syndrome (CFS) severity. ResultsA model incorporating NSE, DKK1, and {beta}-Amyloid-42 effectively discriminated PD patients from controls, yielding an area under the curve (AUC) of 0.932 and an overall accuracy of 83.0%. NSE and DKK1 emerged as the main predictors of overall disease severity, motor symptoms, and CFS severity. Regression analyses indicated that 41.3% of the variance in the FF score was explained by increased NSE, DKK1, {beta}-amyloid, and UCHL1, while 42.9% of the variance in psychiatric symptoms was explained by increased NSE, DKK1, and {beta}-amyloid. Increased GFAP levels were significantly associated with motor dysfunction. ConclusionThe combined presence of neuronal injury, Wnt signaling dysregulation, and amyloid pathology may represent a key pathophysiological component underlying PD, CFS-like fatigue, and psychiatric symptoms in PD. Targeting neuronal injury and Wnt signaling pathways may offer novel therapeutic strategies for managing fatigue and psychiatric manifestations in PD.

BackgroundEffective screening for Parkinson disease (PD) is important for both symptomatic treatment and recruitment into intervention trials. We recently developed a toolkit to quantify PD risk. Here, we examined the PREDIGT models diagnostic performance when deployed at home. MethodsWe contacted 613 subjects following outpatient clinic encounters. Between 2022-2024, 305 participants (range, 40-85 years) were recruited: 93 with typical PD; 66 had other neurological diseases (OND); 146 were neurologically healthy. Two versions of the toolkit were completed: First, an original, 69-item-long questionnaire paired with a 40-scent smell test; thereafter, a simplified, 11-item-long questionnaire and a newly developed, 8-scent smell test. PREDIGT summary scores were calculated for each subject to examine diagnostic classifications. Area-under-the-ROC-curve, sensitivity, specificity, and likelihood ratios were used to evaluate performances and to determine clinically relevant thresholds. ResultsIn both versions, PD patients had higher questionnaire scores and lower smell test scores than neurologically healthy controls (p<0.001); scores for OND subjects ranked at intermediate levels. The simplified questionnaire outperformed the original version in diagnostic accuracy. The abbreviated smell test performed as well as the 40-item version in identifying hyposmia. At a value of 22.94 (range 0-100) for the threshold that separates PD subjects from other participants, the simplified PREDIGT summary score showed a sensitivity of 0.98, a specificity of 0.83, and revealed positive and negative likelihood ratios of 5.88 and 0.02, respectively. InterpretationOur study reveals that unsupervised screening for typical PD can be effectively carried out at home using an 11-item questionnaire and 8-scent smell test.

IntroductionMotor complications are major determinants of disability in Parkinsons disease (PD), yet clinician-rated motor complication severity does not fully explain variability in health-related quality of life (HRQoL). Research questionTo examine the contribution of illness perceptions and cognitive-behavioural responses to HRQoL alongside motor complication severity in people with PD. MethodsThis multi-centre, cross-sectional study recruited 58 people with idiopathic PD (median age 68 years; 55.2% male; 48.3% from minoritised ethnic backgrounds; Hoehn & Yahr stage 2-3). All underwent assessment of motor complications (Movement Disorder Society-Unified Parkinsons Disease Rating Scale; MDS-UPDRS Part IV) and HRQoL (Parkinsons Disease Questionnaire-39 Summary Index; PDQ-39 SI). Illness perceptions were measured with Illness Perception Questionnaire-Revised (IPQ-R) Part 2, and cognitive-behavioural responses with Cognitive and Behavioural Responses Questionnaire (CBRQ). Regression models were adjusted for age, sex, disease duration, motor severity (MDS-UPDRS Part III), levodopa equivalent daily dose (LEDD), anxiety, depression, and cognitive function. A subset (n=47) completed 7-day Parkinsons KinetiGraph monitoring. ResultsDemographic and clinical covariates explained 77.3% of variance in HRQoL (R{superscript 2}=0.773). Adding motor complication severity explained a significant additional 3.7% ({Delta}R{superscript 2}=0.037, P=0.004). Subsequent inclusion of illness consequences (IPQ-R) and catastrophising (CBRQ) explained a further 4.1% ({Delta}R{superscript 2}=0.041, P=0.004), yielding a final adjusted R{superscript 2} of 0.815. In the fully adjusted model, catastrophising (B=0.797, P=0.027) and perceived consequences (B=0.767, P=0.013) remained independently associated with HRQoL. ConclusionHRQoL in PD appears to depend not only on motor complication severity, but also on patients interpretations and responses. Clinicians should assess both to guide holistic care and support adaptive coping.

Background: Most trials of Parkinson's disease (PD) measure progression over a short to medium time-period using continuous rating scales that may be hard to interpret and less meaningful for patients. There is a lack of evidence connecting changes in these scales to changes in outcomes important to patients. Objectives: We present causal modelling to translate the causal, short-term disease-modifying treatment effects on functional rating scales to the 10-year risk of serious clinical progression milestones. Methods: We selected four important clinical milestones of disease progression from the Oxford Parkinson's Disease Centre "Discovery" cohort: dementia, any falls, frequent falls, and mortality. We proposed a causal framework for our research objectives so we could model the potential impact of a 30% reduction in disease progression slopes ("treatment effect") using the summation of parts I and II of the Movement Disorders Society Unified Parkinson's Disease Rating Scale (UPDRS12). This outcome was regressed on time to milestone using flexible parametric survival models. Marginal predictions of survival and survival difference at year 10 were then calculated for the Discovery cohort, and a counterfactual cohort applying the treatment effect to estimate the relative and absolute reductions for the four clinical milestones. Results: The model increase in risk for each unit change in the UPDRS12 were as follows: dementia hazard ratio (HR)=1.52 (95% Confidence Interval (CI) 1.36-1.70), any falls HR=1.37 (95% CI 1.29-1.46), frequent falls HR=1.68 (95% CI 1.49-1.89), mortality=1.29 (95% CI 1.17-1.42). These models led to marginal predictions of absolute reductions, when the progression was reduced by 30%, between 4.0% (mortality) and 7.5% (frequent falls) at 10 years follow up. Conclusions: We have demonstrated how a treatment effect in a trial specified in terms of a progression change of a rating scale can be contextualised into a long-term reduction in the probability of clinically relevant milestones. Whilst we have used PD as our exemplar, we believe this methodological approach is generalisable to other chronic progressive diseases where trials are often limited to a relatively short follow-up period and use some scalar measure of progression, but significant clinical milestones usually take longer to be observed. Keywords: Clinical trials; disease modifying therapies; causal estimation; prediction models

Abstract/SummaryO_ST_ABSBackgroundC_ST_ABSCerebrospinal fluid (CSF) -synuclein seed amplification assay (SAA) has emerged as a diagnostic biomarker for Parkinsons disease (PD) and has been linked to differences in disease severity and progression. However, whether SAA status predicts responsiveness to levodopa remains unknown. We investigated the longitudinal association between SAA status, levodopa responsiveness, dopaminergic denervation, and motor complications in sporadic PD. MethodsIn this longitudinal analysis, PD participants from the Parkinsons Progression Markers Initiative (PPMI) cohort with CSF SAA testing who initiated levodopa treatment were included. SAA- and SAA+ patients were matched on sex, age, and disease duration at treatment initiation. Motor severity was assessed using MDS-UPDRS Part III, with proportional and absolute responsiveness derived from ON and OFF medication states. Motor complications were assessed using MDS-UPDRS Part IV, and dopaminergic dysfunction was quantified using caudate DAT-SPECT. Linear mixed-effects models examined longitudinal differences as a function of SAA status. FindingsIn this analysis, 40 SAA- patients were compared to 183 matched SAA+ patients. SAA+ patients showed a slower rate of ON-state motor progression than SAA- patients (0.87 vs 3.47 points/year; p = 0.01). Consistently, proportional levodopa responsiveness increased over time in SAA+ patients while declining in SAA- patients (p = 0.036). These differences were accompanied by lower caudate DAT binding at treatment initiation in SAA- patients (p = 0.002) and faster dopaminergic decline over time (p = 0.008). Although SAA+ patients had fewer motor complications at treatment initiation, their progression was similar. InterpretationCSF -synuclein SAA status is associated with divergent levodopa response in PD, with SAA+ patients showing sustained and progressively greater motor benefit, while SAA- patients show declining responsiveness. Faster dopaminergic denervation in SAA- patients may underlie this difference. SAA status captures clinically relevant heterogeneity that may inform patient stratification and therapeutic decision-making.

ImportanceDementia is common in Parkinsons disease (PD), causing greater disability than other symptoms, but varies in timing. Although visual deficits are linked with PD dementia, how these interact with genetic factors to predict PD dementia has not been characterised. ObjectiveTo investigate whether visual deficits and genetic factors predict PD dementia. DesignLarge prospective longitudinal case-control study, mean follow-up 32.7 (SD=12.3) months. SettingCases were recruited between 2017-2020 at 35 UK PD clinics. ParticipantsPeople with PD without dementia at baseline were included. Main outcomes and measuresVisual function was measured using a web-based platform. The main outcome measure was global cognition, measured as the Montreal Cognitive Assessment (MoCA). Blood samples were collected for genetics. Results450 patients with PD were included. Mean age of PD patients was 71.7 (SD=7.8), 68% male. Mean baseline MoCA was 27.7 (SD=1.7). 263 patients with PD were classed as poor-vision based on baseline visual tests: mean age 74.4 (SD=6.8) compared to 69.7 (SD=7.5) with good-vision. Poor-vision PD patients had higher rates of progression to mild cognitive impairment (PD-MCI) (HR=2.34, CI=1.58-3.48, pFDR=0.00062, age- and sex-corrected). The combination of genetic factors together with vision influenced outcomes. In good-vision PD patients, high-risk GBA1 gene variants were linked with greater progression to PD-MCI (HR=4.61, CI=1.73-12.28, pFDR=0.0068). Polygenic Risk Score (PRS) for both PD and Alzheimers disease (AD) also modified cognitive survival when combined with vision status. High PD-PRS was associated with greater progression to PD-MCI in good-vision patients (HR=2.66, CI=1.21-5.81, pFDR=0.0381); and high AD-PRS with greater progression to PD-MCI in poor-vision PD patients (HR=1.91, CI=1.10-3.32, pFDR=0.04999). Combining high PD- and AD-PRS, compared to low PD- and AD-PRS in good-vision PD showed even higher progression to PD-MCI (HR=6.14, CI=1.36-27.83, pFDR=0.046). Simulations showed that adding visual and genetic stratification reduced sample size from n=705 to n=160 for clinical trials. Conclusions and relevancePoor vision in PD predicts progression to PD-MCI and dementia. This combines with the effects of genetic factors including GBA risk variants and PD- and AD-PRS. These findings can enable enrichment of clinical trials for patients at higher risk of PD dementia, for more efficient trial design for interventions to slow progression. Key pointsO_ST_ABSQuestionC_ST_ABSDo clinical factors, measured by performance on visual tests, and genetic factors help predict which patients are more likely to develop cognitive involvement in Parkinsons disease? FindingsThis prospective longitudinal study of 450 Parkinsons patients, based in Parkinsons clinics, with mean follow-up 32.7 months, found that Parkinsons patients with poor vision are more likely to develop cognitive impairment; and that genetic factors in combination with poor vision further predict poor prognostic groups for Parkinsons dementia. MeaningThese data could enable selection of Parkinsons patients at highest risk of dementia for clinical trials aimed at slowing Parkinsons dementia.

BackgroundParkinsons disease (PD) is a neurodegenerative disorder for which there is currently no cure or reliable biomarker for early detection or for evaluating the effectiveness of potential treatments. PD pathology is driven by misfolding and subsequent accumulation of alpha-synuclein (Syn) protein into pathological aggregates within neurons and glial cells. Seed amplification assay (SAA) is a highly sensitive and specific diagnostic tool developed to detect pathological Syn species in the cerebrospinal fluid (CSF) of PD patients. However, Syn aggregates are present in multiple tissues and biosamples, including stools. In this study, we aimed to investigate the potential diagnostic value of SAA using stool samples from PD patients and healthy controls (HC). MethodsStool samples from PD patients (n=45) and healthy controls (n=35) were analysed for the presence of Syn species using slot blot assays with a panel of six Syn antibodies, and ELISA assays. Samples were subjected to SAA, and the end-point products (SAA EP) were characterised using transmission electron microscopy (TEM). Extracellular vesicles (EVs) were isolated from the subset of samples (n=5 per group) using size exclusion chromatography and characterized by TEM. The seeding activity of isolated EVs was evaluated using SAA, followed by TEM analysis of SAA EP. ResultsProtein extracts from both PD and HC stool samples revealed pathological Syn species in the slot blot assay using the phosphorylated Syn antibody, pS129 and conformation-specific antibodies, MJFR-14 and 5G4. ELISA showed significantly elevated total Syn levels in PD samples compared to HC, although no differences in aggregated Syn levels were detected. In stool protein extracts, SAA demonstrated 55.6% sensitivity and 60% specificity. When applied to stool-derived EVs from PD patients and controls, sensitivity increased to 100%, while specificity remained at 60%. Notably, SAA applied to stool-derived EVs pre-incubated with recombinant monomeric Syn achieved 100% sensitivity and 100% specificity. ConclusionThese findings suggest that SAA applied to EVs isolated from stool samples, particularly after pre-incubation with recombinant monomeric Syn, may serve as a valuable, non-invasive screening tool for the diagnosis of PD.

Studies reporting alpha-synuclein seed amplification assay (aSyn-SAA) results are often cross-sectional. Here we investigated the intra-individual consistency of aSyn-SAA results over time from participants in the Parkinson's Progression Marker Initiative (PPMI). A total of 1238 participants had >1 CSF aSyn-SAA result for analysis (Parkinson's disease [PD]=633, prodromal =563, healthy control [HC]=42) which were collected over a median (min, max) of 2.0 (0.4, 11.4) years. Emphasis was placed on evaluating consistency in less common results such as aSyn-SAA- PD participants, aSyn-SAA+ HC and conversion rates from aSyn-SAA negative to positive results prodromal participants. Of aSyn-SAA+ PD participants, 96% (474/493, 95%CI 94-98%) remained positive in subsequent samples, and 92% (116/126, 95%CI 86-96%) of aSyn-SAA- PD participants remained negative. 99% (303/307, 95%CI 97-99%) of aSyn-SAA+ prodromal participants remained positive, and 95% (234/247, 95%CI 91-97%) of aSyn-SAA- prodromal participants remained negative. 89% (16/18, 95%CI 67-97%) of aSyn-SAA+ HC participants remained positive, and 87% (20/23, 95%CI 68-95%) of aSyn-SAA- HC participants remained negative. These results confirm a high consistency of aSyn-SAA results over time, even in less expected results.

Adeno-associated viral (AAV)-mediated overexpression of human wildtype -synuclein (-syn) in the substantia nigra (SN) is a widely used approach to model Parkinsons disease (PD) in rodents. However, variability in the ability of AAV-based systems to induce nigrostriatal pathology and motor deficits has limited reproducibility across studies, especially in mice. Here, we systematically optimized key vector features - AAV serotype, promoter, viral titer - to establish a highly efficient and reliable mouse model of PD. We compared the tropism and expression efficiency of mixed AAV2/1 and AAV2/rh10 serotypes combined with three promoters - CMV enhancer/chicken {beta}-actin (CBA), human Synapsin (hSYN), and rat Tyrosine Hydroxylase (TH) - to drive human -syn gene (SNCA) expression in nigral dopaminergic neurons. The AAV.TH.SNCA vector, delivered at an optimized titer, achieved selective and sustained -syn overexpression in nigral neurons, resulting in nigro-striatal neurochemical changes and progressive motor deficits preceding overt neuronal loss. Fine tuning -syn expression proved critical for detecting early disease processes: lower AAV.TH.SNCA titer induced early pathological signatures, including -syn hyperphosphorylation and neuroinflammation, whereas higher titers produced robust nigrostriatal degeneration not achieved with other promoter constructs. Notably, we demonstrate that motor and neurochemical impairments can occur prior to dopaminergic cell death, implicating microglial activation and -syn pathology as primary drivers of dysfunction. This observation is consistent with human genetic evidence showing that triplication of the wild-type SNCA gene alone can cause Parkinsonian pathology, highlighting that our model enables the use of a single experimental reagent to investigate the molecular, cellular, and behavioral consequences of controlled increases in -syn expression. This novel AAV.TH.SNCA model provides a powerful and versatile platform for investigating mechanisms of a -syn-mediated neurotoxicity and for evaluating disease modifying interventions targeting early, pre-degenerative stages of PD. HighlightsO_LITitrated -syn expression uncouples early dysfunction from dopaminergic neuron loss C_LIO_LIAAV2/rh10-TH-SNCA model captures prodromal and degenerative PD stages C_LIO_LIMotor deficits arise from -syn pathology and nigral molecular changes before neurodegeneration. C_LI

BackgroundParkinsons disease (PD) is a multifactorial neurodegenerative disorder shaped by, amongst others, high-impact variants and common polygenic factors. The Personalized Parkinson Project (PPP) offers deep phenotyping and longitudinal follow-up of Dutch people with PD. Here, we characterize the genetic landscape and its interaction with lifestyle factors within PPP. MethodsWe utilized three complementary approaches in N=507 persons with PD: 1) short-read PD gene panel sequencing of eight PD genes, 2) genome-wide genotyping array, and 3) targeted long-read sequencing of the GBA1 gene. Additionally, we calculated the mitochondrial-function polygenic score (MGS). Associations between genetic factors, smoking status, and age at onset (AAO) were assessed using non-parametric tests, correlation analyses, and multiple regression models. ResultsGenetic screening of the participants revealed N=79 GBA1 ([~]15%), N=3 LRRK2, N=1 CHCHD2, N=1 SNCA variant carrier, and N=9 heterozygous PRKN/PINK1 variants. We also observed an interaction between MGS and smoking: MGS was associated with earlier AAO in non-smokers in persons with iPD (N=414, {beta}=-1.87, p=0.038). ConclusionOur findings corroborate previously reported frequencies of variants in PD-associated genes in European populations, and suggest a potential association between smoking and a mitochondrial dysfunction signature in PD. Thus, even in persons without rare variants (iPD subgroup), complex genetic contributions remained relevant. Our study supports future downstream stratification and personalized medicine approaches with high-impact variants and polygenic risk scores.