OBJECTIVE:Biallelic variants in PRKN cause autosomal recessive Parkinson's disease (PD) with a median age at onset of 31 years. When evaluating the 16 previously published carriers of a homozygous deletion of Exon 2 from the International Parkinson's Disease and Movement Disorder Society Gene Database (MDSGene) database, the median age at onset is later (39.5 years) than in carriers of other PRKN pathogenic variants. We investigated whether these carriers show delayed disease onset compared with carriers of other pathogenic PRKN variants and explored the underlying molecular mechanism. METHODS:We compared 26 homozygous PRKN Exon 2 deletion carriers with carriers of other pathogenic variants. Using human-induced pluripotent stem cell (hiPSC)-derived neuronal cell models from an unaffected 86-year-old carrier, genome-edited control lines, neuroblastoma cell lines, and in silico prediction, we investigated the underlying mechanism. RESULTS:Patients with PRKN Exon 2 deletions showed a later age at onset compared with carriers of other pathogenic variants. We discovered elevated levels of an N-terminally truncated Parkin proteoform lacking amino acids 1-79 due to internal translation initiation. This truncated protein partially retained ubiquitin ligase activity at endogenous levels. Treatment with Parkin modulator BIO-2007817 enhanced this residual function but reduced endogenous full-length Parkin activity. INTERPRETATION:Residual truncated Parkin function provides a molecular explanation for a delayed disease onset in PRKN Exon 2 deletion carriers. Whereas this retained activity can be pharmacologically enhanced, the modulator's inhibitory effect on endogenous full-length Parkin may mandate strict patient stratification based on genotype. This finding offers mutation-specific counseling opportunities and highlights a potential therapeutic approach for appropriately selected patients with PARK-PRKN. ANN NEUROL 2026;99:1379-1393.

BACKGROUND:Parkinsonism is a motor syndrome traditionally considered sporadic, but genetic factors are increasingly recognized. While next-generation sequencing (NGS) has identified pathogenic variants in Parkinson's disease (PD) and related disorders, data from admixed populations like Brazilians remain limited. This study aimed to evaluate the utility of whole-exome sequencing (WES) in identifying pathogenic variants in Brazilian patients with early-onset parkinsonism or a family history of the condition. METHODS:Patients from the Federal University of Paraná's movement disorders clinic were recruited between December 2019 and July 2023. Inclusion criteria included parkinsonism, symptom onset before 45 years, and/or family history. WES was performed, with variant pathogenicity assessed using ACMG criteria. Clinical data included MDS-UPDRS-III and MoCA scores. RESULTS:Of 52 patients evaluated, 44 met PD criteria (pathogenic variants in 20.45%), while 8 had syndromic parkinsonism (pathogenic variants in 50%). The most commonly implicated genes were GBA and LYST, followed by LRRK2, PRKN, and NPC1. A novel C19Orf12 variant (c.362T > G, p.Leu121Arg) was identified in juvenile parkinsonism. Additionally, a LYST variant (c.9320G > A, p.Arg3107His), associated with Chédiak-Higashi syndrome but without classic hematological features, was reported. CONCLUSION:WES proved valuable in detecting rare pathogenic variants in Brazilian patients, uncovering atypical phenotypes and expanding the spectrum of genetic findings. These results highlight the need for broader genetic studies in admixed populations to refine diagnostics and better characterize such unique cohorts.

To investigate whether antidiabetic drugs have a biological basis to be repurposed in PD prevention, we applied a drug target Mendelian randomization framework to assess associations between genetic variation in antidiabetic drug targets and PD risk or age at onset (AAO). Instrumental variables (IVs) were derived from GWAS summary statistics on fasting glucose (FG), glycated hemoglobin (HbA1c), and gene expression data from GTEx. Apart from SGLT2 inhibitors, all other antidiabetic drugs of interest could be instrumented through our methods. Positive and negative control analyses were carried out to validate 20 IVs in the FG arm and 23 IVs in the HbA1c arm. DPP-4 inhibitors failed the positive control. GWAS summary statistics for PD risk and AAO data were sourced from the IPDGC and COURAGE-PD consortia, resulting in 42 083 cases/457 090 controls for risk and 37 103 PD cases for AAO. MR analyses showed no significant associations across consortia or in meta-analysis. These findings do not support a causal role of genetic variation in antidiabetic drug targets in PD risk or AAO.

Progression from Parkinson's disease (PD) to Lewy body dementia is a major clinical concern. Although several progression-associated loci have been identified, their cumulative effects on cognitive decline have not been systematically evaluated. To assess the dose-dependent effect of five candidate progression loci linked to synaptic vulnerability (RIMS2, TMEM108, GBA1) and amyloid-tau pathology (APOE, WWOX), we analyzed 7745 participants from 24 cohorts with 28,737 longitudinal visits over 15 years using random-effects meta-analyses of cohort-specific Cox proportional hazards models. Dementia risk increased monotonically with the number of progression loci (0, 1, 2, or ≥3). A single locus conferred a 1.56-fold increase in risk (hazard ratio (HR) = 1.56, 95% CI: 1.28-1.89), rising to 3.21-fold for two loci (HR = 3.21, 95% CI: 2.19-4.70) and 7.49-fold for three or more loci (HR = 7.49, 95% CI: 4.98-11.28). Individually, GBA1 (HR = 2.09), APOE ε4 (HR = 1.71), RIMS2 (HR = 1.90), TMEM108 (HR = 2.05), and WWOX (HR = 1.56) were associated with dementia risk, but there was heterogeneity between clinical trials, biomarkers, and population-based cohorts. Multi-locus dosage increases dementia risk in a monotonic manner and may improve stratification and clinical trial design in PD.

We investigated the role of copy number variations (CNVs) in Parkinson's disease (PD) using genotyping data from 10,815 patients (2731 early-onset PD, EOPD) and 8901 controls from the COURAGE-PD consortium. CNVs were analyzed using a sliding window genome-wide association and burden approach. No genome-wide significant CNVs were detected in the overall cohort, but a robust deletion spanning exons 2-6 of PRKN was identified in EOPD cases, validated by MLPA, and replicated in the GP2 dataset (23,089 cases, 18,824 controls). CNV burden was significantly enriched in PD-related genes, primarily driven by PRKN, with the strongest effect observed in EOPD. PRKN CNV carriers showed earlier age at onset, confirmed by survival analysis. No association was observed for genome-wide or large CNV burden. Our findings reinforce the pivotal role of PRKN deletions in early-onset PD and highlight the need for high-resolution CNV analysis in large cohorts to uncover additional rare contributors to PD risk.

Dissecting biological pathways highlighted by Mendelian gene discovery has provided critical insights into the pathogenesis of Parkinson's disease (PD) and neurodegeneration. This approach ultimately catalyzes the identification of potential biomarkers and therapeutic targets. Here we identify PSMF1 as a gene implicated in parkinsonism and childhood neurodegeneration. We find that biallelic PSMF1 missense and loss-of-function variants co-segregate with phenotypes from early-onset PD to perinatal lethality with neurological manifestations across 18 pedigrees with 25 affected subjects, showing clear genotype-phenotype correlation. PSMF1 encodes the proteasome regulator PSMF1/hPI31, a highly conserved, ubiquitously expressed partner of the 20S proteasome and neurodegeneration-associated F-box-O 7 and valosin-containing proteins. We demonstrate that PSMF1 variants may affect proteasomal abundance and assembly, and are associated with alterations of mitochondrial membrane potential, respiration, dynamics and mitophagy in patient-derived fibroblasts. Furthermore, Drosophila and mouse models of PI31 loss of function exhibit age-dependent motor impairment, as well as brain-wide mitochondrial membrane depolarization and dopaminergic neurodegeneration in aged flies, and diffuse gliosis in mice. Collectively, our findings unequivocally link defective PSMF1/hPI31 to early-onset parkinsonism and neurodegeneration, and suggest proteasomal and mitochondrial dysfunction as pathogenic contributors.

Rare loss-of-function variants in ITSN1 were recently reported to confer a high risk for Parkinson’s disease (PD). From our local large exome sequencing dataset of PD cases, we identified five carriers from three families. Clinical features of ITSN1-PD are typical and responsive to standard treatments. Additionally, we discuss whether ITSN1 loss-of-function variants should only be considered as a high-risk factor or a Mendelian PD gene.

Objective:To investigate the impact of copy number variations (CNVs) on Parkinson's disease (PD) pathogenesis using genome-wide data and explore their role in sporadic PD. Methods:We analyzed CNV data from 11,035 PD patients (including 2,731 early-onset PD (EOPD)) and 8,901 controls from the COURAGE-PD consortium using a sliding window CNV-GWAS and genome-wide burden analysis. The independent dataset from the Global Parkinson Genetics Program (GP2) consisted of 23,089 cases and 18,824 controls were used to validate our initial findings. Results:The exploratory dataset identifies multiple CNV regions associated with PD risk. The nominated CNV loci were not confirmed in an independent dataset, except that only a deletion in the PRKN gene, a well-established EOPD locus, remained genome-wide significant and robustly supported. CNV burden analysis showed a higher prevalence of CNVs in PD-related genes in patients compared to controls (OR=1.56 [1.18-2.09], p=0.0013), with PRKN showing the highest burden (OR=1.47 [1.10-1.98], p=0.026). Patients with CNVs in PRKN had an earlier disease onset. Burden analysis with controls and EOPD patients showed similar results. Interpretation:The largest CNV-based GWAS on PD highlights both the promise and pitfalls of array-based CNV detection in PD and underscores the relevance of whole-genome sequencing approaches in resolving the role of CNV in PD. The array-based findings are prone towards false positive findings that might arise either from platform limitations and/or cohort biases. Future studies require improved genotyping resolution and rigorous cross-cohort validation to reliably assess CNV contributions to PD risk.

Dissecting biological pathways highlighted by Mendelian gene discovery has provided critical insights into the pathogenesis of Parkinson's disease (PD) and neurodegeneration. This approach ultimately catalyzes the identification of potential biomarkers and therapeutic targets. Here, we identify PSMF1 as a novel gene implicated in parkinsonism and childhood neurodegeneration. We find that biallelic PSMF1 missense and loss-of-function variants co-segregate with phenotypes from early-onset PD to perinatal lethality with neurological manifestations across 17 pedigrees with 24 affected subjects, showing clear genotype-phenotype correlation. PSMF1 encodes the proteasome regulator PSMF1/PI31, a highly conserved, ubiquitously expressed partner of the 20S proteasome and neurodegeneration-associated F-box-O 7 and valosin-containing proteins. We demonstrate that PSMF1 variants impair mitochondrial membrane potential, dynamics and mitophagy, and may affect proteasomal abundance and assembly in patient-derived fibroblasts. Furthermore, Drosophila and mouse models of PSMF1 loss of function exhibit age-dependent motor impairment, as well as brain-wide mitochondrial membrane depolarization and dopaminergic neurodegeneration in aged flies, and diffuse gliosis in mice. Collectively, our findings unequivocally link defective PSMF1 to early-onset parkinsonism and neurodegeneration, and suggest proteasomal and mitochondrial dysfunction as mechanistic contributors.

Background: Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by motor and nonmotor symptoms, with a significant genetic component. Early-onset Parkinson's disease (EOPD), manifesting before age 45, is often linked to mutations in genes such as PARK2, PINK1, and PARK7, the latter coding for the protein DJ-1. Objective: We present the first reported cases of EOPD carrying a previously undescribed homozygous PARK7 mutation, p.Thr110Pro. Methods: Whole exom sequencing was performed on two inbred Moroccan siblings with early-onset Parkinson's disease (EOPD). Detailed clinical assessments, including neurological evaluations and cognitive testing, were conducted to understand the clinical presentation of the patients. Genetic analysis was also carried out to examine their genetic background. Therapeutic responses to treatments were monitored to assess the effectiveness of management strategies. Results: The sequencing revealed that both siblings carried the homozygous PARK7 mutation, p.Thr110Pro. Both siblings presented with typical EOPD features, including motor and non-motor symptoms. The patients both presented with cognitive impairment, with the male sibling exhibiting more pronounced symptoms. He also developed compulsive behaviors, which underscore the varied clinical presentations and therapeutic responses associated with this genetic variant. Conclusion: This case study expands the genetic and geographic diversity of PD presentations, highlighting cognitive and behavioral challenges and variable therapeutic outcomes. It underscores the necessity for genetic screening and individualized management strategies for patients with PD.

Parkinson's disease is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc), and neuromelanin-sensitive MRI provides a biomarker to track this neuronal loss. Isolated REM sleep behaviour disorder (iRBD), associated with cognitive decline, may represent a distinct subtype of synucleinopathy. Polygenic risk scores for these conditions may be associated with neuronal degeneration. This study investigates whether genetic risk scores for Parkinson's disease (PGS000903) or iRBD (PGS003414) are associated with neuromelanin signal loss in the SNc in the ICEBERG cohort. The analysis included 123 individuals with Parkinson's disease, 37 with iRBD and 48 healthy individuals. Neuromelanin signal intensity was analysed through linear mixed models by status and genetic risk, adjusted for age and sex. Compared with healthy controls, patients with Parkinson's disease had higher genetic risk scores for both disorders, while patients with iRBD had higher genetic risk scores only for RBD. Both patient groups showed significant signal loss over time (P < 0.001). In Parkinson's disease, higher genetic risk for the condition was associated with greater neuromelanin signal decline (P = 0.008), particularly in sensorimotor (P = 0.04) and limbic (P = 0.02) regions. No significant association was found in iRBD. In Parkinson's disease, genetic susceptibility was linked to neuromelanin signal loss, indicating genetic susceptibility to neuronal degeneration. The absence of a significant effect in iRBD may be due to a lack of power. These results should be replicated in independent studies.

BACKGROUND:Loss of Y chromosome (LOY), an age-related somatic mutation, is associated with various age-related diseases, but its role in the onset and progression of Parkinson's disease (PD) remains unclear. This study investigated the relationship between blood LOY levels and the risk of PD onset and progression. METHODS:We estimated the LOY level for each male participant based on genome-wide arrays or whole genome sequencing data. We performed Cox proportional hazards regression analysis among 222,598 male participants in the UK Biobank and linear mixed model analysis involving 2574 male individuals with PD across 14 cohorts, encompassing 19,562 visits. In the Parkinson's Progression Markers Initiative (PPMI) cohort, we further compared brain structure using T1-weighted magnetic resonance imaging (MRI) scans, and carried out brain network functional connectivity analysis based on resting-state functional MRI (rs-fMRI) datasets. Additionally, we assessed the LOY status in single-nucleus RNA sequencing (snRNA-seq) data, which included 1,303,531 cells from 279 post-mortem samples across five brain regions, and performed temporal dynamic gene expression analysis. FINDINGS:Male participants with LOY had a slightly higher risk of developing PD during follow-up (HR = 1·16, 95% CI = 1·01-1·34, P = 0·04). Among males affected by PD, LOY carriers experienced accelerated neurodegenerative progression, manifesting as more rapid motor impairment (P = 0·0072) and cognitive decline (P = 0·0005) compared to non-LOY carriers. Patients with PD carrying LOY also exhibited decreased network functional connectivity in certain brain regions. Notably, LOY cells were particularly enriched in microglia/immune and vascular/epithelial cells, and a subset of genes in LOY-Mic P2RY12 cells were associated with PD progression. INTERPRETATION:This data-driven study highlights the potential association of LOY with the onset and progression of PD through the analysis of multi-scale data, including clinical phenotypes, brain neuroimaging maps, and molecular profiles from single-nucleus transcriptome across multi-brain regions. These findings suggest that LOY may be an accomplice to the onset and progression of PD. FUNDING:G.L.'s work is supported by the Shenzhen Fundamental Research Program (JCYJ20240813151132042), National Natural Science Foundation of China (32270701, 32470708), Young Talent Recruitment Project of Guangdong (2019QN01Y139), the Science and Technology Planning Project of Guangdong Province (2023B1212060018) and Shenzhen Key Laboratory for Systems Medicine in Inflammatory Diseases (ZDSYS20220606100803007). This study is supported by High-performance Computing Public Platform (Shenzhen Campus) of Sun Yat-sen University. C.R.S.'s work is supported by NIH grants NINDS/NIA R01NS115144, the U.S. Department of Defense, and the American Parkinson Disease Association Center for Advanced Parkinson Research. C.R.S.'s research work was funded in part by Aligning Science Across Parkinson's 000301 through the Michael J. Fox Foundation for Parkinson's Research (MJFF). The study was made possible in part by a philanthropic support for Illumina MEGA chip genotyping (to Brigham & Women's Hospital and C.R.S.). CHWG received funding support from an RCUK/UKRI Research Innovation Fellowship awarded by the Medical Research Council (MR/R007446/1; MR/W029235/1) and from the NIHR Cambridge Biomedical Research Centre (NIHR203312). The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care. For the purpose of open access, the author has applied a CC BY public copyright licence to all Author Accepted Manuscripts arising from this submission.

Bi-allelic pathogenic GBA1 variants cause Gaucher disease (GD), whereas certain heterozygous missense variants increase the risk of Parkinson’s disease (PD), although the underlying mechanisms are unclear. Here, we classified GBA1 missense variants using predictive and structural scores, and analysed their associations with enzyme activity, Saposin C (SapC) interaction and PD progression in 639 patients with heterozygous GBA1 variants from five cohorts. Principal component analysis (PCA) identified two components: PC1, associated with reduced β-glucocerebosidase activity, the GD clinical severity classification, younger age at PD diagnosis, and faster cognitive and motor decline; and PC2, associated with surface-exposed, flexible regions involved in SapC interactions, younger age at PD diagnosis, and slightly with motor decline. These findings highlight that impaired SapC interactions, in addition to reduced activity, may contribute to PD severity in GBA1 variant carriers. This is relevant for therapeutic approaches aimed at stabilizing β-glucocerebosidase or enhancing its enzymatic activity in PD.

Biallelic pathogenic variants of PRKN , encoding the Parkin RBR E3 ubiquitin protein ligase, are the most common known cause of autosomal recessive Parkinson's disease (PD). PARK- PRKN is characterized by an early median age at onset (AAO) of 31 years with a wide range (3-81 years). When evaluating the 16 previously published carriers of a homozygous deletion of Exon 2 ( PRKN delEx2) from the MDSGene database, the median AAO is later (39.5 years; range: 25-75 years) than in carriers of other PRKN pathogenic variants. Here, we investigated 26 homozygous PRKN delEx2 patients, including 20 from additional sources, and confirmed the later median AAO (37 years, range: 13-60 years). Furthermore, we investigated one carrier who was still unaffected at the age of 66 years. To elucidate the functional basis for this observation, we used induced pluripotent stem cell (iPSC)-derived dopaminergic neurons (iDN) from this unaffected carrier as well as genome-edited iDNs from two control lines and neuroblastoma cell lines (SH-SY5Y) with the introduction of a homozygous PRKN delEx2. We observed elevated levels of an N-terminally truncated form of Parkin (ParkinΔ1-79), starting at an internal translation initiation site (TIS) in Exon 3 (p.Met80 in the full-length protein) in cells with the Exon 2 deletion. Furthermore, in silico prediction and Parkin quantification in isogenic neuroblastoma cell lines suggested the presence of residual ParkinΔ1-79 also for other PRKN variants upstream of the alternative TIS. iDNs from PRKN delEx2 carriers partially retained Parkin E3 ubiquitin ligase activity in contrast to carriers of other exonic deletions in PRKN ( PRKN delEx3, PRKN delEx7) via the expression of ParkinΔ1-79. Importantly, endogenous Parkin E3 ubiquitin ligase activity of ParkinΔ1-79 was enhanced in neurons derived from a homozygous PRKN delEx2 variant carrier upon treatment with a small molecule allosteric modulator of Parkin (BIO-2007817). In summary, the later AAO in patients with homozygous PRKN delEx2 is associated with partially retained Parkin function. The residual ligase activity can be further increased pharmacologically, providing mutation-specific personalized counseling opportunities and a potential novel therapy for selected patients with PARK- PRKN . ### Competing Interest Statement C.K. serves as consultant for Centogene, Takeda, and Biogen, and has received Speakers' honoraria from Bial. J.C.C. has served in advisory boards for Alzprotect, Bayer, Ferrer, iRegene, Servier, UCB, Roche ; and received grants from AXA and the ICM Foundation outside of this work. ### Funding Statement The study was partially supported by the DFG (FOR2488). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The ethics committee of the University of Luebeck gave ethical approval of this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data presented and analyzed in this study are available from the corresponding authors upon reasonable request.

Introduction:Subthalamic nucleus deep brain stimulation (STN-DBS) is an established treatment for early-onset Parkinson's disease (EOPD). While the effect of STN-DBS on patients with LRRK2 G2019S mutation has been largely investigated, data specific to EOPD patients with this mutation remain scarce. This study examines the impact of the LRRK2 G2019S mutation on STN-DBS outcomes in EOPD patients in Morocco, a developing country where such treatment is challenging to provide. Methods:A prospective cohort study was conducted at the University Hospital of Ibn Rochd in Casablanca. Genomic DNA was analyzed for the LRRK2 G2019S mutation, and clinical data were collected before and after surgery. Motor outcomes, including dyskinesia, motor fluctuations, and reduction in levodopa equivalent daily dose (LEDD), were assessed one year post-DBS. Results:Seventeen EOPD patients who underwent STN-DBS were included, with 10(58.8%) being carriers of the LRRK2 G2019S mutation. The mean age of participants was 57.2±8.4 years, with a mean age at onset of 37.9±6.2 years. Motor fluctuations were present in 88.2% of patients, and 94.1% experienced dyskinesia. Following DBS, both mutation carriers and non-carriers demonstrated significant improvements in motor symptoms, with a mean improvement of 61.3% in the unified PD rating scale (UPDRS) III. Dyskinesia and motor fluctuations, as measured by specific UPDRS IV items, improved by 77.1% and 83.8%, respectively, with a mean LEDD reduction of 60.6%. Improvements were comparable between LRRK2 G2019S carriers and non-carriers. All patients were satisfied with the treatment, though one patient had a hardware-related infection. Conclusion:STN-DBS is effective in managing motor symptoms and reducing medication needs in EOPD patients, regardless of LRRK2 G2019S mutation status.

Early-onset Parkinson's disease (EOPD) is usually defined as Parkinson's disease (PD) occurring before the age of 40-50 years. Unlike late-onset PD, EOPD is often due to pathogenic mutations in autosomal recessive genes. Two phenotypes can be distinguished: typical EOPD, which progresses slowly (PRKN, PINK1 and DJ-1), and atypical PD, often associated with additional symptoms (ATP13A2, FBXO7, DNAJC6, VPS13C, SYNJ1, PLA2G6). In this review, we will highlight recent advances and remaining challenges. The frequency of causal genetic mutations and the genotype-phenotype landscape of PRKN-associated PD has been refined. Long-read sequencing has solved several undiagnosed cases with a single PRKN mutation. Five new genes have been reported to contribute to EOPD associated with various neurological signs (PTPA, DAGLB, PSMF1, EPG5, SGIP1). Small molecules targeting PRKN dysfunctions are expected to enter clinical trials in the coming years, paving the way for targeted therapies in EOPD.

Background and Objectives The role of body mass index (BMI) in Parkinson disease (PD) is unclear. Based on the Comprehensive Unbiased Risk Factor Assessment for Genetics and Environment in PD (Courage-PD) consortium, we used 2-sample Mendelian randomization (MR) to replicate a previously reported inverse association of genetically predicted BMI with PD and investigated whether findings were robust in analyses addressing the potential for survival and incidence-prevalence biases. We also examined whether the BMI-PD relation is bidirectional by performing a reverse MR. Methods We used summary statistics from a genome-wide association study (GWAS) to extract the association of 501 single-nucleotide polymorphisms (SNPs) with BMI and from the Courage-PD and international Parkinson Disease Genomics Consortium (iPDGC) to estimate their association with PD. Analyses are based on participants of European ancestry. We used the inverse-weighted method to compute odds ratios (ORIVW per 4.8 kg/m(2) [95% CI]) of PD and additional pleiotropy robust methods. We performed analyses stratified by age, disease duration, and sex. For reverse MR, we used SNPs associated with PD from 2 iPDGC GWAS to assess the effect of genetic liability toward PD on BMI. Results Summary statistics for BMI are based on 806,834 participants (54% women). Summary statistics for PD are based on 8,919 (40% women) cases and 7,600 (55% women) controls from Courage-PD, and 19,438 (38% women) cases and 24,388 (51% women) controls from iPDGC. In Courage-PD, we found an inverse association between genetically predicted BMI and PD (ORIVW 0.82 [0.70-0.97], p = 0.012) without evidence for pleiotropy. This association tended to be stronger in younger participants (<= 67 years, ORIVW 0.71 [0.55-0.92]) and cases with shorter disease duration (<= 7 years, ORIVW 0.75 [0.62-0.91]). In pooled Courage-PD + iPDGC analyses, the association was stronger in women (ORIVW 0.85 [0.74-0.99], p = 0.032) than men (ORIVW 0.92 [0.80-1.04], p = 0.18), but the interaction was not statistically significant (p-interaction = 0.48). In reverse MR, there was evidence for pleiotropy, but pleiotropy robust methods showed a significant inverse association. Discussion Using an independent data set (Courage-PD), we replicate an inverse association of genetically predicted BMI with PD, not explained by survival or incidence-prevalence biases. Moreover, reverse MR analyses support an inverse association between genetic liability toward PD and BMI, in favor of a bidirectional relation.