SORL1, the gene encoding the SORLA protein, has arisen as a potential therapeutic target for Alzheimer's disease (AD). Studies suggest that restoring SORLA function or its trafficking pathways, particularly the SORLA-retromer recycling system, may offer a promising strategy to slow or halt AD progression. While both rare and common SORL1 variants have been associated with increased AD risk, recent evidence suggests a potential involvement of SORL1 in other neurodegenerative conditions. This study assessed the contribution of SORL1 genetic variation to the risk of AD, related dementias (RD), and Parkinson's disease (PD) using data from six large-scale biobanks, comprising 15,043 AD, 9,943 RD, and 42,763 PD cases, along with 111,969 controls across 11 ancestries. We identified 53 potentially disease-related SORL1 variants (CADD score > 20, MAC ≥ 2, annotated as protein-altering or splicing, and with the mutated allele present only in cases), including 41 novel and 12 previously reported variants. Three were found across multiple ancestries. Overall, 13 variants were found in AD-related cohorts, 5 in RD cohorts, and 35 in PD cohorts. Association analysis identified 10 nominally significant variants associated with AD and 5 with PD. The replication of multiple SORL1 variants across neurodegenerative diseases and ancestrally diverse populations underscores its potential broad genetic contribution to neurodegeneration and reinforces its relevance across distinct clinical phenotypes. Burden analysis identified a nominal association of SORL1 variants in PD in the South Asian population (P = 0.048). A family-based analysis identified a rare predicted-damaging variant in two East Asian families (11:121478242:G:A, p.R176Q) and two variants in two families of European ancestry (11:121514222:A:C, p.N371T; 11:121545392:G:A, p.V672M) that show some evidence of segregation in PD families. Although these variants were slightly more frequent in unrelated PD cases vs. controls, none of them showed statistically significant enrichment in PD, likely due to their very low frequency. Overall, our results extend the understanding of SORL1 beyond AD, suggesting a broader role in neurodegeneration and emphasizing the need for diverse population studies when evaluating genetic risk.

Young onset Parkinson's disease may be caused by biallelic mutations in PRKN or other autosomal recessive Parkinson's disease genes, but the majority of patients do not carry known monogenic variants. Previous studies have found an increased cumulative burden of common genetic risk variants for Parkinson's disease in young onset patients, but the specific genetic architecture of non-monogenic young onset Parkinson's disease is not well characterized. We conducted a genome-wide association study of 1,528 Parkinson's disease patients with symptom onset between 18 and 40 years and 20,408 controls of European ancestry using data from The Global Parkinson's Genetic Program, the International Parkinson's Disease Genomics Consortium, and the NeuroGenetics Research Consortium. We performed meta-analyses of additive and recessive regression models and investigated associations between age at onset groups and different polygenic risk scores. An additive model meta-analysis identified six independent loci passing a genome-wide significance threshold, including three loci identified in previous genome-wide association studies (near SNCA, GBA1, and HIP1R) and two loci not previously associated with Parkinson's disease (rs74950462, P = 1.24x10-8 and rs72848817, P = 4.89x10-8). Furthermore, we identified a significant signal at the PRKN locus, prompting a follow-up analysis employing a recessive model. The recessive genome-wide association meta-analysis identified nine loci passing a genome-wide significance threshold, including SNCA, PRKN, and seven novel variants. Patients with onset between 18 and 40 years had significantly higher polygenic risk scores than later onset patients when the score was modelled specifically on genome-wide association statistics from independent young onset Parkinson's disease participants versus healthy controls. This increased polygenic burden was driven in part by loci harbouring mitochondrial pathway genes. Our results indicate that previously unidentified common and low-frequency variants contribute specifically to the young onset subgroup of Parkinson's disease. Association signals detected uniquely with a recessive model suggest that genetic susceptibility to young onset Parkinson's disease may be partially driven by homozygous variation, in line with previous reports of increased runs of homozygosity in this particular group of patients and may be consistent with a loss of function mechanism. The findings support the notion of young onset Parkinson's disease as a partly distinct subphenotype and highlight the mitochondrial pathway. These results may have implications for future precision medicine but should be interpreted with caution pending independent replication.

Chorea can arise from genetic, metabolic, pharmacologic, and autoimmune causes. In clinical practice, however, non-genetic causes are rare. The most common genetic cause is a CAG repeat expansion in HTT, leading to Huntington’s disease (HD). Beyond HD, systematic studies have been lacking and many individuals with non-HD chorea remain without a molecular diagnosis. We conducted whole-exome and genome sequencing analysis on 190 non-HD chorea cases, leveraging data from the All of Us Research Program (n = 134), UK Biobank (n = 26), and a clinically ascertained multicenter Spanish cohort recruited by the Spanish Study Group for Genetics of Chorea (SSGGC) (n = 30). Variant calling was performed without pre-filtering based on a disease or gene list, and variants were clinically contextualized using OMIM, ClinVar, and in silico predictions. We identified thirteen protein-altering variants, including six previously described as pathogenic or likely pathogenic. Notably, we identified a pathogenic JPH3 expansion in a patient of Black race and c9orf72 expansions in individuals of European and South Asian ancestry. These findings explained 23% of cases in the SSGGC, 12% in UK Biobank, and 4% in All of Us. Our results broaden the genetic architecture of non-HD chorea and highlight the value of multi-ancestry genomic approaches for rare movement disorders.

Elucidating the genetic contributions to Parkinson's disease aetiology across diverse ancestries is a critical priority for the development of targeted therapies in a global context. We conducted the largest sequencing characterization of potentially disease-causing, protein-altering and splicing mutations in 710 cases and 11 827 controls from genetically predicted African or African admixed ancestries. We explored copy number variants (CNVs) and runs of homozygosity in prioritized early onset and familial cases. Our study identified rare GBA1 coding variants to be the most frequent mutations among patients with Parkinson's disease, with a frequency of 4% in our case cohort. Of the 18 GBA1 variants identified, 10 were previously classified as pathogenic or likely pathogenic, four were novel and four were reported as of uncertain clinical significance. The most common known disease-associated GBA1 variants in the Ashkenazi Jewish and European populations, p.Asn409Ser, p.Leu483Pro, p.Thr408Met and p.Glu365Lys, were not identified among the screened Parkinson's disease cases of African and African admixed ancestry. Similarly, the European and Asian LRRK2 disease-causing mutational spectrum, including LRRK2 p.Gly2019Ser and p.Gly2385Arg genetic risk factors, did not appear to play a major role in Parkinson's disease aetiology among West African ancestry populations. However, we found three heterozygous novel missense LRRK2 variants of uncertain significance, with two (p.Glu268Ala and p.Arg1538Cys) displaying higher frequencies in the African ancestry population reference datasets. Structural variant analyses revealed the presence of PRKN CNVs with a frequency of 0.7% in African and African admixed cases, with 66% of CNVs detected being compound heterozygous or homozygous in early-onset cases, providing further insights into the genetic underpinnings in early-onset juvenile Parkinson's disease in these populations. Short tandem repeat analysis also identified ATXN3 CAG repeat expansions within the pathogenic range (CAGn > 45) in three patients with Parkinson's disease of African ancestry. Novel genetic variation among screened genes warrants further replication and functional prioritization to unravel their pathogenic potential. Here, we created the most comprehensive genetic catalogue of both known and novel coding and splicing variants potentially linked to Parkinson's disease aetiology in an underserved population and further conducted global and local ancestry analyses to further explore population-specific effects. Our study has the potential to guide the development of targeted therapies in the emerging era of precision medicine. By expanding genetics research to involve underrepresented populations, we hope that future Parkinson's disease treatments are not only effective but also inclusive, addressing the needs of diverse ancestral groups.

In the Global Parkinson's Genetics Program (GP2) we aim to advance precision medicine by integrating large-scale clinico-genetic data from diverse populations worldwide. We investigated potentially trial-eligible carriers of pathogenic and high-risk GBA1 and LRRK2 variants and conducted a global precision-medicine survey across GP2 sites. Among 65,509 individuals with Parkinson's disease, we identified 9,019 (13.8%) potentially trial-eligible genetic variant carriers, including 6,789 GBA1, 2,084 LRRK2, and 146 dual GBA1-LRRK2 carriers. Individuals were distributed across multiple global regions, many of which currently lack active gene-targeted trials, highlighting a global disparity between relevant variant carriers and the availability of disease modifying treatment trials. GP2's unified framework supports equitable recruitment for gene-targeted therapeutic studies and helps address critical gaps in Parkinson's disease genetics and future therapeutic development.

Dementia diagnosis increasingly relies on blood-based biomarkers, yet their performance in diverse populations remains insufficiently characterized. Latin America, with substantial genetic and environmental heterogeneity, is particularly underrepresented in biomarker research. Here we show that plasma AT(N) biomarkers can distinguish Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) in a multinational Latin American cohort (N = 605). Aβ42/Aβ40 amyloid-β ratios were reduced and levels of phosphorylated tau (p-tau217, p-tau181) and neurofilament light chain (NfL) were elevated in both disorders, with NfL showing greater increases in FTLD. Classification models achieved receiver operating characteristic areas under the curve (ROC AUCs) of 83% for AD and 88% for FTLD. Meta-analyses confirmed consistency across countries, and these markers correlated with executive, memory and global cognitive impairment. Biomarker alterations combined with disease-specific neuroimaging patterns and cognitive measures further improved accuracy (ROC AUCs of 89% for AD and 95% for FTLD). These findings indicate that plasma AT(N) biomarkers, combined with neuroimaging and clinical assessments, can enhance dementia diagnosis across diverse Latin American populations.

ABSTRACT The genetics of Parkinson’s disease (PD) in underrepresented populations remain poorly characterized, potentially overlooking population-specific contributions. We analyzed 461 Chilean PD cases from a movement disorders center. Pathogenic, likely pathogenic, or GBA1 risk variants were identified in 58 individuals (12.6%), mainly in LRRK2 (50%) and GBA1 (44.8%), while PRKN, SNCA , and SQSTM1 collectively represented 5.2%. All LRRK2 variants were p.G2019S, with an overall frequency of 6.3%, the highest reported in South America, and enrichment of Ashkenazi Jewish ancestry at this locus. These findings characterize the genetic landscape of PD in Chile and support its relevance for LRRK2 -targeted studies.

Latin America's diverse genetic landscape provides a unique opportunity to study Alzheimer's disease (AD) and frontotemporal dementia (FTD). The Multi-Partner Consortium to Expand Dementia Research in Latin America (ReDLat) recruited 2162 participants with AD, FTD, or healthy controls from six countries: Argentina, Brazil, Chile, Colombia, Mexico, and Peru. Participants underwent genomic sequencing, and population structure analyses were conducted using Principal Component Analysis and ADMIXTURE. The study revealed a predominant mix of American, African, and European ancestries, with an additional East Asian component in Brazil. Variant curation identified 17 pathogenic variants, a pathogenic C9orf72 expansion, and 44 variants of uncertain significance. Seventy families showed autosomal dominant inheritance, with 48 affected by AD and 22 by FTD. This represents the first large-scale genetic study of AD and FTD in Latin America, highlighting the need to consider diverse ancestries, social determinants of health, and cultural factors when assessing genetic risk for neurodegenerative diseases.

Pathogenic GAA repeat expansions in FGF14 are an established cause of late-onset cerebellar ataxia, but have not been linked to Parkinson's disease (PD). Given emerging evidence that repeat expansions in ataxia-associated genes like RFC1, can contribute to atypical or familial forms of PD, we investigated whether FGF14 expansions might play a similar role. Using long-read whole-genome sequencing on 411 individuals with PD and 197 neurologically healthy controls from the PPMI cohort, alongside 1,429 additional controls from the NIH CARD initiative, the 1000 Genomes Project, and the All of Us program, representing globally diverse populations. We identified pathogenic FGF14 GAA repeat expansions in five individuals with PD and one control. All five individuals fit the clinical criteria of PD and showed typical patterns of neurodegeneration on DaTSCAN imaging; α-synuclein aggregation was confirmed by a positive seeding assay among four individuals with available data. These findings broaden the phenotypic spectrum of FGF14 repeat-associated disease and suggest a rare, previously unrecognized genetic contributor to PD. To our knowledge, this is the first report implicating FGF14 in PD and underscores the utility of long-read sequencing for detecting hidden forms of pathogenic variation in unresolved cases.

Many non-coding variants influence complex traits and diseases through gene regulation, yet the mechanisms linking these variants to downstream biology remain poorly understood. Here, we present eQTLGen Phase 2, a comprehensive genome-wide analysis of gene expression quantitative trait loci (eQTLs) in 43,301 blood samples from 52 datasets. Beyond local ciseffects, this sample size enabled the first systematic mapping of trans-eQTLs at scale. We identify cis-eQTLs for nearly all expressed genes (94.7%) and trans-eQTLs for over half (56.2%). Second, by colocalizing cis-eQTLs with trans-eQTLs, we infer a directed gene regulatory network comprising 47,554 directed gene regulatory relationships. These networks reveal how genetic perturbations in upstream regulators produce dose-dependent downstream effects, supported by Perturb-seq and ChIP-seq data. Third, integrating this network with 87 genome-wide association studies allows us to systematically prioritize trait-relevant pathways and candidate genes. Variants exerting both cis- and trans-effects are markedly more likely to colocalize with trait associations than cis-only variants, delineating a subset of functionally active cis-eQTLs from a large group with limited downstream impact. This distinction provides a conceptual framework for identifying regulatory variants that truly mediate complex trait biology. Together, these results provide a publicly available resource of cis- and trans-eQTLs and an in vivo scaffold for human gene-regulatory networks, elucidating how propagation of cis-effects modulates complex disease.

ObjectivesEmerging evidence suggests that the genetic architecture of Alzheimer disease (AD) and Parkinson disease (PD) risk varies across ancestries. This study seeks to explore distinct and universal genetic targets across individuals of Latino, African/African-admixed, East Asian, and European populations by implementing population attributable risk (PAR) comparisons using summary statistics from genome-wide association studies (GWASs). MethodsPAR was calculated for the most significant disease variants using summary statistics derived from select multi-ancestry GWAS meta-analyses, followed by fine-mapping analysis to validate genetic contribution of disease variants to European, African/African-admixed, East Asian, and Latino individuals. ResultsFor AD, APOE4 PAR estimates were universally high across all ancestries, with TSPAN14 and PICALM emerging as other common targets. Attributable risk varied across PD-related major risk loci, including variation nearby GBA1 and LRRK2. By contrast, SNCA, MCCC1, VPS13C, and MAPT loci demonstrated comparable attributable risk across ancestries. DiscussionThis cross-ancestry evaluation of PAR reinforces the genetic heterogeneity of AD and PD. In consideration of the complex etiology of these diseases, these findings may inform the strategic prioritization of therapeutic targets and improve global health outcomes.

In Parkinson's disease (PD), inclusive research recruitment practices are essential to ensure that study findings are generalizable to diverse populations. The definition and implementation of inclusive recruitment practices are guided by the principles of equity, justice, engagement, and sustainability. However, practical implementation guidance is lacking. This paper shares insights from the Black and African American Connections to Parkinson's Disease (BLAAC PD) study, a PD genetics research study being conducted in the United States that enrolls individuals with and without PD. The inclusive recruitment strategy in BLAAC PD centers around four areas: training and working with study personnel toward equitable research practices, partnering with community members, creating culturally resonant study materials, and customizing practices at the local level. We provide practical examples implemented by BLAAC PD to address each of these areas. We share the materials and tools that the study utilizes for site training, recruitment, and community outreach and engagement. These approaches have potential for application in other PD research studies, to achieve greater diversity in PD research.

Although large-scale genetic association studies have proven opportunistic for the delineation of neurodegenerative disease processes, we still lack a full understanding of the pathological mechanisms of these diseases, resulting in few appropriate treatment options and diagnostic challenges. To mitigate these gaps, the Neurodegenerative Disease Knowledge Portal (NDKP) was created as an open-science initiative with the aim to aggregate, enable analysis, and display all available genomic datasets of neurodegenerative disease, while protecting the integrity and confidentiality of the underlying datasets. The portal contains 218 genomic datasets, including genotyping and sequencing studies, of individuals across ten different phenotypic groups, including neurological conditions such as Alzheimer's disease, amyotrophic lateral sclerosis, Lewy body dementia, and Parkinson's disease. In addition to securely hosting large genomic datasets, the NDKP provides accessible workflows and tools to effectively utilize the datasets and assist in the facilitation of customized genomic analyses. Here, we summarize the genomic datasets currently included within the portal, the bioinformatics processing of the datasets, and the variety of phenotypes captured. We also present example use-cases of the various user interfaces and integrated analytic tools to demonstrate their extensive utility in enabling the extraction of high-quality results at the source, for both genomics experts and those in other disciplines. Overall, the NDKP promotes open-science and collaboration, maximizing the potential for discovery from the large-scale datasets researchers and consortia are expending immense resources to produce and resulting in reproducible conclusions to improve diagnostic and therapeutic care for neurodegenerative disease patients.

Among LRRK2-associated parkinsonism cases with nigral degeneration, over two-thirds demonstrate evidence of pathologic alpha-synuclein, but many do not. Understanding the clinical phenotype and underlying biology in such individuals is critical for therapeutic development. Our objective was to compare clinical and biomarker features, and rate of progression over 4 years of follow-up, among LRRK2-associated parkinsonism cases with and without in vivo evidence of alpha-synuclein aggregates. Data were from the Parkinson's Progression Markers Initiative, a multicentre prospective cohort study. The sample included individuals diagnosed with Parkinson disease with pathogenic variants in LRRK2. Presence of CSF alpha-synuclein aggregation was assessed with seed amplification assay. A range of clinician- and patient-reported outcome assessments were administered. Biomarkers included dopamine transporter scan, CSF amyloid-beta1-42, total tau, phospho-tau181, urine bis(monoacylglycerol)phosphate levels and serum neurofilament light chain. Linear mixed-effects (LMMs) models examined differences in trajectory in CSF-negative and CSF-positive groups. A total of 148 LRRK2 parkinsonism cases (86% with G2019S variant), 46 negative and 102 positive for CSF alpha-synuclein seed amplification assay, were included. At baseline, the negative group was older than the positive group [median (inter-quartile range) 69.1 (65.2-72.3) versus 61.5 (55.6-66.9) years, P < 0.001] and a greater proportion were female [28 (61%) versus 43 (42%), P = 0.035]. Despite being older, the negative group had similar duration since diagnosis and similar motor rating scale [16 (11-23) versus 16 (10-22), P = 0.480] though lower levodopa equivalents. Only 13 (29%) of the negative group were hyposmic, compared with 75 (77%) of the positive group. The negative group, compared with the positive group, had higher per cent-expected putamenal dopamine transporter binding for their age and sex [0.36 (0.29-0.45) versus 0.26 (0.22-0.37), P < 0.001]. Serum neurofilament light chain was higher in the negative group compared with the positive group [17.10 (13.60-22.10) versus 10.50 (8.43-14.70) pg/mL; age-adjusted P-value = 0.013]. In terms of longitudinal change, the negative group remained stable in functional rating scale score in contrast to the positive group who had a significant increase (worsening) of 0.729 per year (P = 0.037), but no other differences in trajectory were found. Among individuals diagnosed with Parkinson disease with pathogenic variants in the LRRK2 gene, we found clinical and biomarker differences in cases without versus with in vivo evidence of CSF alpha-synuclein aggregates. LRRK2 parkinsonism cases without evidence of alpha-synuclein aggregates as a group exhibit less severe motor manifestations and decline. The underlying biology in LRRK2 parkinsonism cases without evidence of alpha-synuclein aggregates requires further investigation.

Endemic viral infections with low pathogenicity are often overlooked due to their mild symptoms, yet they can exert long-term effects on cellular function and contribute to disease pathogenesis. While viral infections have been implicated in neurodegenerative disorders, their impact on the neuronal proteome remains poorly understood. Here, we differentiated human induced pluripotent stem cells (KOLF2.1J) into mature neurons to investigate virus-induced proteomic changes following infection with five neurotropic endemic human viruses: Herpes simplex virus 1 (HSV-1), Human coronavirus 229E (HCoV-229E), Epstein-Barr virus (EBV), Varicella-Zoster virus (VZV), and Influenza A virus (H1N1). Given that these viruses can infect adults and have the potential to cross the placental barrier, their molecular impact on neurons may be relevant across the lifespan. Using mass spectrometry-based proteomics with a customized library for simultaneous detection of human and viral proteins, we confirmed successful infections and identified virus-specific proteomic signatures. Notably, virus-induced protein expression changes converged on key neuronal pathways, including those associated with neurodegeneration. Gene co-expression network analysis identified protein modules correlated with viral proteins. Pathway enrichment analysis of these modules revealed associations with the nervous system, including pathways linked to Alzheimer's and Parkinson's disease. Remarkably, several viral-induced proteomic alterations overlapped with changes observed in postmortem Alzheimer's patient brains, suggesting a mechanistic connection between viral exposure and neurodegenerative disease progression. These findings provide molecular insights into how common viral infections perturb neuronal homeostasis and may contribute to neurodegenerative pathology, highlighting the need to consider endemic viruses as potential environmental risk factors in neurological disorders.

The iPSC Neurodegenerative Disease Initiative (iNDI) is the largest-ever induced pluripotent stem cell (iPSC) genome engineering project, modeling over 100 ADRD mutations in high-quality isogenic human iPSCs. iNDI leverages unbiased CRISPRi screens as a powerful tool to identify fundamental mechanisms and modifiers of disease. However, current CRISPRi molecular tools are poorly optimized for use in iPSC-derived neurons (iNeurons). Here we develop a Cre-lox inducible CRISPRi system (CRISPRi-Cre), enabling gene knockdown upon Cre delivery to postmitotic iNeurons, and identification of neuron-specific, disease-relevant modifiers. We modified a plasmid carrying a potent Zim3-dCas9 transcriptional repressor to include a strong floxed STOP cassette upstream of the Zim3 start codon. We leveraged HaloTag-TDP43 and HaloTag-FUS iSPCs from the iNDI project paired with flow cytometry to validate leakiness and responsiveness to Cre in iPSCs and iNeurons treated with sgRNAs. We then performed a genome-wide CRISPRi survival screen in iNeurons to demonstrate broad functionality of this inducible CRISPRi system with over 20,000 sgRNAs. Finally, we use CRISPRi-Cre to identify neuron-specific regulators of neuronal activity in iNeurons. We demonstrate that in the absence of Cre, dCas9 is inactive. Delivery of lentivirus-Cre to iNeurons activates dCas9, resulting in potent gene knockdown. In genome-wide CRISPRi screens, we show that CRISPRi-Cre identifies many of the same hits observed in screens using constitutive-active dCas9, and importantly uncovers novel neuron-specific hits not identified in previous CRISPRi screens. Here, we developed a robust Cre-inducible CRISPRi system that enables post-mitotic gene knockdown in iPSC-derived neurons. Our CRISPRi screens identify neuron-specific hits, demonstrating the utility of our tool to help uncover disease-relevant mechanisms, modifiers, and potential therapeutic targets in relevant cell types.

Emerging evidence suggests that the genetic architecture of Alzheimer's (AD) and Parkinson's diseases (PD) risk varies across ancestries. This study seeks to explore distinct and universal genetic targets across individuals of Latino, African/African Admixed, East Asian, and European populations by implementing Population Attributable Risk (PAR) comparisons on summary statistics from genome-wide association studies (GWAS). PAR was calculated for the most significant disease variants using summary statistics derived from select multi-ancestry GWAS meta-analyses, followed by fine-mapping analysis to validate genetic contribution of disease variants to European, African/African Admixed, East Asian, and Latino individuals. For both AD, APOE4 PAR estimates were universally high across all ancestries, with TSPAN14 and PICALM emerging as other common targets. Attributable risk varied across PD-related major risk loci including variation nearby GBA1 and LRRK2. In contrast, SNCA, MCCC1, VPS13C, and MAPT loci demonstrated comparable attributable risk across ancestries. This cross-ancestry evaluation of PAR reinforces the genetic heterogeneity of AD and PD. In consideration of the complex etiology of these diseases, these findings may inform the strategic prioritization of therapeutic targets and improve global health outcomes.