Potential Protective Link Between Type I Diabetes and Parkinson's Disease Risk and Progression

BACKGROUND: Epidemiological studies suggested an association between Parkinson's disease (PD) and type 2 diabetes, but less is known about type 1 diabetes (T1D) and PD. OBJECTIVE: This study sought to explore the association between T1D and PD. METHODS: We used Mendelian randomization, linkage disequilibrium score regression, and multi-tissue transcriptome-wide analysis to examine the association between PD and T1D. RESULTS: Mendelian randomization showed a potentially protective role of T1D for PD risk (odds ratio [OR], 0.97; 95% confidence interval [CI], 0.94-0.99; P = 0.039), as well as motor (OR, 0.94; 95% CI, 0.88-0.99; P = 0.044) and cognitive progression (OR, 1.50; 95% CI, 1.08-2.09; P = 0.015). We further found a negative genetic correlation between T1D and PD (rg = -0.17; P = 0.016), and we identified eight genes in cross-tissue transcriptome-wide analysis that were associated with both traits. CONCLUSIONS: Our results suggest a potential genetic link between T1D and PD risk and progression. Larger comprehensive epidemiological and genetic studies are required to validate our findings. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Heritability enrichment implicates microglia in Parkinson's disease pathogenesis

OBJECTIVE: Understanding how different parts of the immune system contribute to pathogenesis in Parkinson's disease is a burning challenge with important therapeutic implications. We studied enrichment of common variant heritability for Parkinson's disease stratified by immune and brain cell types. METHODS: We used summary statistics from the most recent meta-analysis of genome-wide association studies in Parkinson's disease and partitioned heritability using linkage disequilibrium score regression, stratified for specific cell types as defined by open chromatin regions. We also validated enrichment results using a polygenic risk score approach and intersected disease-associated variants with epigenetic data and expression quantitative loci to nominate and explore a putative microglial locus. RESULTS: We found significant enrichment of Parkinson's disease risk heritability in open chromatin regions of microglia and monocytes. Genomic annotations overlapped substantially between these two cell types, and only the enrichment signal for microglia remained significant in a joint model. We present evidence suggesting P2RY12, a key microglial gene and target for the anti-thrombotic agent clopidogrel, as the likely driver of a significant Parkinson's disease association signal on chromosome 3. INTERPRETATION: Our results provide further support for the importance of immune mechanisms in PD pathogenesis, highlight microglial dysregulation as a contributing etiological factor and nominate a targetable microglial gene candidate as a pathogenic player. Immune processes can be modulated by therapy, with potentially important clinical implications for future treatment in Parkinson's disease

Revisiting protein aggregation as pathogenic in sporadic Parkinson and Alzheimer diseases.

The gold standard for a definitive diagnosis of Parkinson disease (PD) is the pathologic finding of aggregated α-synuclein into Lewy bodies and for Alzheimer disease (AD) aggregated amyloid into plaques and hyperphosphorylated tau into tangles. Implicit in this clinicopathologic-based nosology is the assumption that pathologic protein aggregation at autopsy reflects pathogenesis at disease onset. While these aggregates may in exceptional cases be on a causal pathway in humans (e.g., aggregated α-synuclein in SNCA gene multiplication or aggregated β-amyloid in APP mutations), their near universality at postmortem in sporadic PD and AD suggests they may alternatively represent common outcomes from upstream mechanisms or compensatory responses to cellular stress in order to delay cell death. These 3 conceptual frameworks of protein aggregation (pathogenic, epiphenomenon, protective) are difficult to resolve because of the inability to probe brain tissue in real time. Whereas animal models, in which neither PD nor AD occur in natural states, consistently support a pathogenic role of protein aggregation, indirect evidence from human studies does not. We hypothesize that (1) current biomarkers of protein aggregates may be relevant to common pathology but not to subgroup pathogenesis and (2) disease-modifying treatments targeting oligomers or fibrils might be futile or deleterious because these proteins are epiphenomena or protective in the human brain under molecular stress. Future precision medicine efforts for molecular targeting of neurodegenerative diseases may require analyses not anchored on current clinicopathologic criteria but instead on biological signals generated from large deeply phenotyped aging populations or from smaller but well-defined genetic-molecular cohorts

SORL1 mutation in a Greek family with Parkinson's disease and dementia

Whole exome sequencing and linkage analysis were performed in a three generational pedigree of Greek origin with a broad phenotypic spectrum spanning from Parkinson’s disease and Parkinson’s disease dementia to dementia of mixed type (Alzheimer disease and vascular dementia). We identified a novel heterozygous c.G1135T (p.G379W) variant in SORL1 which segregated with the disease in the family. Mutation screening in sporadic Greek PD cases identified one additional individual with the mutation, sharing the same 12.8Mb haplotype. Our findings provide support for SORL1 mutations resulting in a broad range of additional phenotypes and warrants further studies in neurodegenerative diseases beyond AD

Mitochondria function associated genes contribute to Parkinson’s Disease risk and later age at onset

Mitochondrial dysfunction has been implicated in the etiology of monogenic Parkinson’s disease (PD). Yet the role that mitochondrial processes play in the most common form of the disease; sporadic PD, is yet to be fully established. Here, we comprehensively assessed the role of mitochondrial function-associated genes in sporadic PD by leveraging improvements in the scale and analysis of PD GWAS data with recent advances in our understanding of the genetics of mitochondrial disease. We calculated a mitochondrial-specific polygenic risk score (PRS) and showed that cumulative small effect variants within both our primary and secondary gene lists are significantly associated with increased PD risk. We further reported that the PRS of the secondary mitochondrial gene list was significantly associated with later age at onset. Finally, to identify possible functional genomic associations we implemented Mendelian randomization, which showed that 14 of these mitochondrial function-associated genes showed functional consequence associated with PD risk. Further analysis suggested that the 14 identified genes are not only involved in mitophagy, but implicate new mitochondrial processes. Our data suggests that therapeutics targeting mitochondrial bioenergetics and proteostasis pathways distinct from mitophagy could be beneficial to treating the early stage of P

The Parkinson's Disease Mendelian Randomization Research Portal

Background Mendelian randomization is a method for exploring observational associations to find evidence of causality. Objective To apply Mendelian randomization between risk factors/phenotypic traits (exposures) and PD in a large, unbiased manner, and to create a public resource for research. Methods We used two‐sample Mendelian randomization in which the summary statistics relating to single‐nucleotide polymorphisms from 5,839 genome‐wide association studies of exposures were used to assess causal relationships with PD. We selected the highest‐quality exposure genome‐wide association studies for this report (n = 401). For the disease outcome, summary statistics from the largest published PD genome‐wide association studies were used. For each exposure, the causal effect on PD was assessed using the inverse variance weighted method, followed by a range of sensitivity analyses. We used a false discovery rate of 5% from the inverse variance weighted analysis to prioritize exposures of interest. Results We observed evidence for causal associations between 12 exposures and risk of PD. Of these, nine were effects related to increasing adiposity and decreasing risk of PD. The remaining top three exposures that affected PD risk were tea drinking, time spent watching television, and forced vital capacity, but these may have been biased and were less convincing. Other exposures at nominal statistical significance included inverse effects of smoking and alcohol. Conclusions We present a new platform which offers Mendelian randomization analyses for a total of 5,839 genome‐wide association studies versus the largest PD genome‐wide association studies available (https://pdgenetics.shinyapps.io/MRportal/). Alongside, we report further evidence to support a causal role for adiposity on lowering the risk of P

Parkinson's disease age at onset genome-wide association study : Defining heritability, genetic loci, and α-synuclein mechanisms

Background Increasing evidence supports an extensive and complex genetic contribution to PD. Previous genome-wide association studies (GWAS) have shed light on the genetic basis of risk for this disease. However, the genetic determinants of PD age at onset are largely unknown. Objectives To identify the genetic determinants of PD age at onset. Methods Using genetic data of 28,568 PD cases, we performed a genome-wide association study based on PD age at onset. Results We estimated that the heritability of PD age at onset attributed to common genetic variation was similar to 0.11, lower than the overall heritability of risk for PD (similar to 0.27), likely, in part, because of the subjective nature of this measure. We found two genome-wide significant association signals, one at SNCA and the other a protein-coding variant in TMEM175, both of which are known PD risk loci and a Bonferroni-corrected significant effect at other known PD risk loci, GBA, INPP5F/BAG3, FAM47E/SCARB2, and MCCC1. Notably, SNCA, TMEM175, SCARB2, BAG3, and GBA have all been shown to be implicated in alpha-synuclein aggregation pathways. Remarkably, other well-established PD risk loci, such as GCH1 and MAPT, did not show a significant effect on age at onset of PD. Conclusions Overall, we have performed the largest age at onset of PD genome-wide association studies to date, and our results show that not all PD risk loci influence age at onset with significant differences between risk alleles for age at onset. This provides a compelling picture, both within the context of functional characterization of disease-linked genetic variability and in defining differences between risk alleles for age at onset, or frank risk for disease. (c) 2019 International Parkinson and Movement Disorder SocietyPeer reviewe

Insufficient evidence for pathogenicity of SNCA His50Gln (H50Q) in Parkinson's disease

SNCA missense mutations are a rare cause of autosomal dominant Parkinson's disease (PD). To date, 6 missense mutations in SNCA have been nominated as causal. Here, we assess the frequency of these 6 mutations in public population databases and PD case-control data sets to determine their true pathogenicity. We found that 1 of the 6 reported SNCA mutations, His50Gln, was consistently identified in large population databases, and no enrichment was evident in PD cases compared to controls. These results suggest that His50Gln is probably not a pathogenic variant. This information is important to provide counseling for His50Gln carriers and has implications for the interpretation of His50Gln α-synuclein functional investigations