Dissecting genetic architecture of rare dystonia: genetic, molecular and clinical insights.

BACKGROUND: Dystonia is one of the most common movement disorders. To date, the genetic causes of dystonia in populations of European descent have been extensively studied. However, other populations, particularly those from the Middle East, have not been adequately studied. The purpose of this study is to discover the genetic basis of dystonia in a clinically and genetically well-characterised dystonia cohort from Turkey, which harbours poorly studied populations. METHODS: Exome sequencing analysis was performed in 42 Turkish dystonia families. Using co-expression network (CEN) analysis, identified candidate genes were interrogated for the networks including known dystonia-associated genes and genes further associated with the protein-protein interaction, animal model-based characteristics and clinical findings. RESULTS: We identified potentially disease-causing variants in the established dystonia genes (PRKRA, SGCE, KMT2B, SLC2A1, GCH1, THAP1, HPCA, TSPOAP1, AOPEP; n=11 families (26%)), in the uncommon forms of dystonia-associated genes (PCCB, CACNA1A, ALDH5A1, PRKN; n=4 families (10%)) and in the candidate genes prioritised based on the pathogenicity of the variants and CEN-based analyses (n=11 families (21%)). The diagnostic yield was found to be 36%. Several pathways and gene ontologies implicated in immune system, transcription, metabolic pathways, endosomal-lysosomal and neurodevelopmental mechanisms were over-represented in our CEN analysis. CONCLUSIONS: Here, using a structured approach, we have characterised a clinically and genetically well-defined dystonia cohort from Turkey, where dystonia has not been widely studied, and provided an uncovered genetic basis, which will facilitate diagnostic dystonia research.

Parkin mRNA Expression Levels in Peripheral Blood Mononuclear Cells in Parkin-Related Parkinson's Disease.

INTRODUCTION: Pathogenic variants in parkin (PRKN gene) are the second most prevalent known monogenic cause of Parkinson's disease (PD). How monoallelic or biallelic pathogenic variants in the PRKN gene may affect its transcription in patient-derived biological material has not been systematically studied. METHODS: PRKN mRNA expression levels were measured with real-time polymerase chain reaction (RT-PCR) in peripheral blood mononuclear cells (PBMCs). PBMCs were derived from PRKN-mutated PD patients (PRKN-PD) (n = 12), sporadic PD (sPD) (n = 21) and healthy controls (n = 21). Six of the PRKN-PD patients were heterozygous, four were compound heterozygous, and two were homozygous for PRKN variants. RESULTS: A statistically significant decrease in PRKN expression levels was present, compared to healthy controls and sPD, in heterozygous (P = 0.019 and 0.031 respectively) and biallelic (P < 0.001 for both) PRKN-PD. PRKN expression levels in biallelic PD patients were uniformly very low and were reduced, albeit not significantly, compared to heterozygotes. Based on receiver operating characteristic analysis, low PRKN expression levels were a sensitive and extremely specific indicator for the presence of PRKN pathogenic variants. CONCLUSIONS: Assessment of PRKN mRNA levels in PBMCs may be a useful way to screen for biallelic pathogenic variants in the PRKN gene. Suspicion for certain variants in a heterozygous state may also be raised based on low PRKN mRNA levels. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

A Novel PINK1 p.F385S Loss-of-Function Mutation in an Indian Family with Parkinson's Disease.

BACKGROUND: Most Parkinson's disease (PD) loci have shown low prevalence in the Indian population, highlighting the need for further research. OBJECTIVE: The aim of this study was to characterize a novel phosphatase tensin homolog-induced serine/threonine kinase 1 (PINK1) mutation causing PD in an Indian family. METHODS: Exome sequencing of a well-characterized Indian family with PD. A novel PINK1 mutation was studied by in silico modeling using AlphaFold2, expression of mutant PINK1 in human cells depleted of functional endogenous PINK1, followed by quantitative image analysis and biochemical assessment. RESULTS: We identified a homozygous chr1:20648535-20648535 T>C on GRCh38 (p.F385S) mutation in exon 6 of PINK1, which was absent in 1029 genomes from India and in other known databases. PINK1 F385S lies within the highly conserved DFG motif, destabilizes its active state, and impairs phosphorylation of ubiquitin at serine 65 and proper engagement of parkin upon mitochondrial depolarization. CONCLUSIONS: We characterized a novel nonconservative mutation in the DFG motif of PINK1, which causes loss of its ubiquitin kinase activity and inhibition of mitophagy. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Team Science Approaches to Unravel Monogenic Parkinson's Disease on a Global Scale.

BACKGROUND: Until recently, about three-quarters of all monogenic Parkinson's disease (PD) studies were performed in European/White ancestry, thereby severely limiting our insights into genotype-phenotype relationships at a global scale. OBJECTIVE: To identify the multi-ancestry spectrum of monogenic PD. METHODS: The first systematic approach to embrace monogenic PD worldwide, The Michael J. Fox Foundation Global Monogenic PD Project, contacted authors of publications reporting individuals carrying pathogenic variants in known PD-causing genes. In contrast, the Global Parkinson's Genetics Program's Monogenic Network took a different approach by targeting PD centers underrepresented or not yet represented in the medical literature. RESULTS: In this article, we describe combining both efforts in a merger project resulting in a global monogenic PD cohort with the buildup of a sustainable infrastructure to identify the multi-ancestry spectrum of monogenic PD and enable studies of factors modifying penetrance and expressivity of monogenic PD. CONCLUSIONS: This effort demonstrates the value of future research based on team science approaches to generate comprehensive and globally relevant results. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Association of elevated cerebrospinal fluid levels of the longevity protein α-Klotho with a delayed onset of cognitive impairment in Parkinson's disease patients.

BACKGROUND AND PURPOSE: Parkinson's disease (PD) is an age-related condition characterized by substantial phenotypic variability. Consequently, pathways and proteins involved in biological aging, such as the central aging pathway comprising insulin-like growth factor 1-α-Klotho-sirtuin 1-forkhead box O3-peroxisome proliferator-activated receptor γ, may potentially influence disease progression. METHODS: Cerebrospinal fluid (CSF) levels of α-Klotho in 471 PD patients were examined. Of the 471 patients, 96 carried a GBA1 variant (PD GBA1), whilst the 375 non-carriers were classified as PD wild-type (PD WT). Each patient was stratified into a CSF α-Klotho tertile group based on the individual level. Kaplan-Meier survival curves and Cox regression analysis stratified by tertile groups were conducted. These longitudinal data were available for 255 patients. Follow-up times reached from 8.4 to 12.4 years. The stratification into PD WT and PD GBA1 was undertaken to evaluate potential continuum patterns, particularly in relation to CSF levels. RESULTS: Higher CSF levels of α-Klotho were associated with a significant later onset of cognitive impairment. Elevated levels of α-Klotho in CSF were linked to higher Montreal Cognitive Assessment scores in male PD patients with GBA1 mutations. CONCLUSIONS: Our results indicate that higher CSF levels of α-Klotho are associated with a delayed cognitive decline in PD. Notably, this correlation is more prominently observed in PD patients with GBA1 mutations, potentially reflecting the accelerated biological aging profile characteristic of individuals harboring GBA1 variants.

Using Extracellular miRNA Signatures to Identify Patients with LRRK2-Related Parkinson's Disease.

Background: Mutations in the Leucine Rich Repeat Kinase 2 gene are highly relevant in both sporadic and familial cases of Parkinson's disease. Specific therapies are entering clinical trials but patient stratification remains challenging. Dysregulated microRNA expression levels have been proposed as biomarker candidates in sporadic Parkinson's disease. Objective: In this proof-of concept study we evaluate the potential of extracellular miRNA signatures to identify LRRK2-driven molecular patterns in Parkinson's disease. Methods: We measured expression levels of 91 miRNAs via RT-qPCR in ten individuals with sporadic Parkinson's disease, ten LRRK2 mutation carriers and eleven healthy controls using both plasma and cerebrospinal fluid. We compared miRNA signatures using heatmaps and t-tests. Next, we applied group sorting algorithms and tested sensitivity and specificity of their group predictions. Results: miR-29c-3p was differentially expressed between LRRK2 mutation carriers and sporadic cases, with miR-425-5p trending towards significance. Individuals clustered in principal component analysis along mutation status. Group affiliation was predicted with high accuracy in the prediction models (sensitivity up to 89%, specificity up to 70%). miRs-128-3p, 29c-3p, 223-3p, and 424-5p were identified as promising discriminators among all analyses. Conclusions: LRRK2 mutation status impacts the extracellular miRNA signature measured in plasma and separates mutation carriers from sporadic Parkinson's disease patients. Monitoring LRRK2 miRNA signatures could be an interesting approach to test drug efficacy of LRRK2-targeting therapies. In light of small sample size, the suggested approach needs to be validated in larger cohorts.

We know that alterations in a gene called Leucine Rich Repeat Kinase 2 are important in both inherited and non-inherited cases of Parkinson's disease. We also know that treatments for Parkinson's disease specifically targeting LRRK2 are currently being developed. Challenges for developing such a treatment, however, are how to accurately identify patients who could benefit from these therapies and to observe whether the treatment interacts with its target on a molecular level. In this study, we tested whether individuals with an alteration in the LRRK2 gene display a distinct pattern of small RNA molecules, called microRNAs. We measured the amount of 91 microRNAs present in blood of individuals with an alteration in the LRRK2 gene and compared their pattern to patients with a non-inherited form of Parkinson's disease and healthy controls.We found that the amount of a specific microRNA called miR-29c-3p was different between individuals with or without an alteration of the LRRK2 gene. Additionally, we developed models that could predict whether someone had a LRRK2 mutation based on the microRNA pattern in the plasma. Of course, we have easier methods to find these gene alterations, but our findings suggest that changes of LRRK2 result in a shift of microRNA patterns in the blood. This could help us to observe the effects of a LRRK2 specific treatment which tries to revert these changes. As we know that LRRK2 also plays a role in some patients with a non-inherited form of Parkinson's disease, this microRNA pattern could maybe even help us to identify these individuals. It is important to note that our study involved a small number of individuals, so that further research with larger groups is needed to confirm our findings.

Transcriptomic changes in oligodendrocytes and precursor cells associate with clinical outcomes of Parkinson's disease.

Several prior studies have proposed the involvement of various brain regions and cell types in Parkinson's disease (PD) pathology. Here, we performed snRNA-seq on the prefrontal cortex and anterior cingulate regions from a small cohort of post-mortem control and PD brain tissue. We found a significant association of oligodendrocytes (ODCs) and oligodendrocyte precursor cells (OPCs) with PD-linked risk loci and report several dysregulated genes and pathways, including regulation of tau-protein kinase activity, regulation of inclusion body assembly and protein processing involved in protein targeting to mitochondria. In an independent PD cohort with clinical measures (681 cases and 549 controls), polygenic risk scores derived from the dysregulated genes significantly predicted Montreal Cognitive Assessment (MoCA)-, and Beck Depression Inventory-II (BDI-II)-scores but not motor impairment (UPDRS-III). We extended our analysis of clinical outcome prediction by incorporating differentially expressed genes from three separate datasets that were previously published by different laboratories. In the first dataset from the anterior cingulate cortex, we identified an association between ODCs and BDI-II. In the second dataset obtained from the substantia nigra (SN), OPCs displayed an association with UPDRS-III. In the third dataset from the SN region, a distinct subtype of OPCs, labeled OPC_ADM, exhibited an association with UPDRS-III. Intriguingly, the OPC_ADM cluster also demonstrated a significant increase in PD samples. These results suggest that by expanding our focus to glial cells, we can uncover region-specific molecular pathways associated with PD symptoms.

Resequencing the complete SNCA locus in Indian patients with Parkinson's disease.

The genetic loci implicated in familial Parkinson's disease (PD) have limited generalizability to the Indian PD population. We tested mutations and the frequency of known mutations in the SNCA gene in a PD cohort from India. We selected 298 PD cases and 301 age-matched controls for targeted resequencing (before QC), along with 363 PD genomes of Indian ancestry and 1029 publicly available whole genomes from India as healthy controls (IndiGenomes), to determine the frequency of monogenic SNCA mutations. The raw sequence reads were analyzed using an in-house analysis pipeline, allowing the detection of small variants and structural variants using Manta. The in-depth analysis of the SNCA locus did not identify missense or structural variants, including previously identified SNCA mutations, in the Indian population. The familial forms of SNCA gene variants do not play a major role in the Indian PD population and this warrants further research in the under-represented population.

Longitudinal cognitive decline characterizes the profile of non-PD-manifest GBA1 mutation carriers.

With disease-modifying treatment for Parkinson's disease (PD) associated with variants in the glucocerebrosidase gene (GBA1) under way, the challenge to design clinical trials with non-PD-manifest GBA mutation carriers (GBA1NMC) comes within close reach. To delineate trajectories of motor and non-motor markers as well as serum neurofilament light (sNfL) levels and to evaluate clinical endpoints as outcomes for clinical trials in GBA1NMC, longitudinal data of 56 GBA1NMC carriers and 112 age- and sex-matched GBA1 wildtype participants (GBA1wildtype) with up to 9 years of follow-up was analyzed using linear mixed-effects models (LMEM) and Kaplan-Meier survival analysis of clinical endpoints for motor and cognitive function. GBA1NMC showed worse performance in Pegboard, 20 m fast walking, global cognition as well as in executive and memory function at baseline. Longitudinally, LMEM revealed a higher annual increase of the MDS-UPDRS III bradykinesia subscore in GBA1NMC compared to GBA1wildtype, but comparable trajectories of all other motor and non-motor markers as well as sNfL. Kaplan-Meier survival analysis showed a significantly earlier progression to clinical endpoints of cognitive decline in GBA1NMC. Incidence of PD was significantly higher in GBA1NMC. In conclusion, our study extends data on GBA1NMC indicating early cognitive decline as a potentially characteristic feature. Comprehensive longitudinal assessments of cognitive function are crucial to delineate the evolution of early changes in GBA1NMC enabling a more accurate stratification and allow for a more precise definition of trial design and sample size.

CSF α-synuclein seed amplification kinetic profiles are associated with cognitive decline in Parkinson's disease.

Seed amplification assays have been implemented in Parkinson's disease to reveal disease-specific misfolded alpha-synuclein aggregates in biospecimens. While the assays' qualitative dichotomous seeding response is valuable to stratify and enrich cohorts for alpha-synuclein pathology in general, more quantitative parameters that are associated with clinical dynamics of disease progression and that might potentially serve as exploratory outcome measures in clinical trials targeting alpha-synuclein would add important information. To evaluate whether the seeding kinetic parameters time required to reach the seeding threshold (LAG phase), the peak of fluorescence response (Imax), and the area under the curve (AUC) are associated with clinical trajectories, we analyzed LAG, Imax, and AUC in relation to the development of cognitive decline in a longitudinal cohort of 199 people with Parkinson's disease with positive CSF alpha-synuclein seeding status. Patients were stratified into tertiles based on their individual CSF alpha-synuclein seeding kinetic properties. The effect of the kinetic parameters on longitudinal development of cognitive impairment defined by MoCA ≤25 was analyzed by Cox-Regression. Patients with a higher number of positive seeding replicates and tertile groups of shorter LAG, higher Imax, and higher AUC showed a higher prevalence of and a shorter duration until cognitive impairment longitudinally (3, 6, and 3 years earlier with p ≤ 0.001, respectively). Results remained similar in separate subgroup analyses of patients with and without GBA mutation. We conclude that a more prominent alpha-synuclein seeding kinetic profile translates into a more rapid development of cognitive decline.

Understanding monogenic Parkinson's disease at a global scale.

Until recently, about three-quarters of all monogenic Parkinson's disease (PD) studies were performed in European/White ancestry, thereby severely limiting our insights into genotype-phenotype relationships at global scale. The first systematic approach to embrace monogenic PD worldwide, The Michael J. Fox Foundation Global Monogenic PD (MJFF GMPD) Project, contacted authors of publications reporting individuals carrying pathogenic variants in known PD-causing genes. In contrast, the Global Parkinson's Genetics Program's (GP2) Monogenic Network took a different approach by targeting PD centers not yet represented in the medical literature. Here, we describe combining both efforts in a "merger project" resulting in a global monogenic PD cohort with build-up of a sustainable infrastructure to identify the multi-ancestry spectrum of monogenic PD and enable studies of factors modifying penetrance and expression of monogenic PD. This effort demonstrates the value of future research based on team science approaches to generate comprehensive and globally relevant results.

Genotype-phenotype correlation in PRKN-associated Parkinson's disease.

Bi-allelic pathogenic variants in PRKN are the most common cause of autosomal recessive Parkinson's disease (PD). 647 patients with PRKN-PD were included in this international study. The pathogenic variants present were characterised and investigated for their effect on phenotype. Clinical features and progression of PRKN-PD was also assessed. Among 133 variants in index cases (n = 582), there were 58 (43.6%) structural variants, 34 (25.6%) missense, 20 (15%) frameshift, 10 splice site (7.5%%), 9 (6.8%) nonsense and 2 (1.5%) indels. The most frequent variant overall was an exon 3 deletion (n = 145, 12.3%), followed by the p.R275W substitution (n = 117, 10%). Exon3, RING0 protein domain and the ubiquitin-like protein domain were mutational hotspots with 31%, 35.4% and 31.7% of index cases presenting mutations in these regions respectively. The presence of a frameshift or structural variant was associated with a 3.4 ± 1.6 years or a 4.7 ± 1.6 years earlier age at onset of PRKN-PD respectively (p < 0.05). Furthermore, variants located in the N-terminus of the protein, a region enriched with frameshift variants, were associated with an earlier age at onset. The phenotype of PRKN-PD was characterised by slow motor progression, preserved cognition, an excellent motor response to levodopa therapy and later development of motor complications compared to early-onset PD. Non-motor symptoms were however common in PRKN-PD. Our findings on the relationship between the type of variant in PRKN and the phenotype of the disease may have implications for both genetic counselling and the design of precision clinical trials.

Plasma extracellular vesicle tau and TDP-43 as diagnostic biomarkers in FTD and ALS.

Minimally invasive biomarkers are urgently needed to detect molecular pathology in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Here, we show that plasma extracellular vesicles (EVs) contain quantifiable amounts of TDP-43 and full-length tau, which allow the quantification of 3-repeat (3R) and 4-repeat (4R) tau isoforms. Plasma EV TDP-43 levels and EV 3R/4R tau ratios were determined in a cohort of 704 patients, including 37 genetically and 31 neuropathologically proven cases. Diagnostic groups comprised patients with TDP-43 proteinopathy ALS, 4R tauopathy progressive supranuclear palsy, behavior variant FTD (bvFTD) as a group with either tau or TDP-43 pathology, and healthy controls. EV tau ratios were low in progressive supranuclear palsy and high in bvFTD with tau pathology. EV TDP-43 levels were high in ALS and in bvFTD with TDP-43 pathology. Both markers discriminated between the diagnostic groups with area under the curve values >0.9, and between TDP-43 and tau pathology in bvFTD. Both markers strongly correlated with neurodegeneration, and clinical and neuropsychological markers of disease severity. Findings were replicated in an independent validation cohort of 292 patients including 34 genetically confirmed cases. Taken together, the combination of EV TDP-43 levels and EV 3R/4R tau ratios may aid the molecular diagnosis of FTD, FTD spectrum disorders and ALS, providing a potential biomarker to monitor disease progression and target engagement in clinical trials.