Genome sequencing analysis identifies new loci associated with Lewy body dementia and provides insights into its genetic architecture

Systematic identification of SNCA as a key gene in ischemic cardiomyopathy via integrated weighted gene co-expression network analysis and experimental validation

Ischemic cardiomyopathy (ICM) is associated with high mortality and hospitalization rates, and current treatments are suboptimal. The aim of this research was to identify novel therapeutic targets for ICM. The datasets GSE57338 and GSE5406 were obtained from the Gene Expression Omnibus (GEO) database. Gene modules were constructed using weighted gene co-expression network analysis (WGCNA), and the three relevant modules associated with ICM were identified. The biological functions and signaling pathways of the genes in these modules were further explored through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. Protein-protein interaction (PPI) networks were employed to identify hub genes within these modules. Least Absolute Shrinkage and Selection Operator (LASSO) logistic regression was performed to establish gene models, and 16 genes associated with left ventricular ejection fraction (LVEF) in ICM were identified. The genes were validated in heart tissues from human using quantitative real-time polymerase chain reaction (qRT-PCR). Among them, growth factor receptor-bound protein 14 (GRB14), ubiquitin C-terminal hydrolase L1 (UCHL1), and synuclein alpha (SNCA) were identified as key genes significantly associated with ICM. Additionally, key genes correlated with immune and stromal cell-related types were screened using xCell. In vivo and in vitro experiments demonstrated that inhibiting SNCA could improve cardiac dysfunction, inflammatory infiltration, and fibrosis in ICM. In conclusion, this study identified 16 genes closely related to LVEF and revealed that SNCA was a key gene in ICM, providing potential biomarkers and therapeutic targets for ICM.

Apolipoprotein E genotypes and amyloid burden associated with cognitive decline in non-demented Parkinson's disease patients: A preliminary analysis

BACKGROUND

Cognitive impairment is a common non-motor manifestation in Parkinson's disease (PD). Amyloidosis seems to accelerate the onset of dementia in PD. The Apolipoprotein (APOE) ε4 genotype is linked to amyloid aggregation and has been suggested to be a candidate for development of PD dementia, while other APOE alleles have been less investigated.

METHODS

Forty-eight non-demented PD patients were included (ε2/ε3 carriers: n = 8; ε3/ε3 carriers: n = 35; and ε3/ε4 carriers: n = 5). Patients underwent APOE genotyping, a neuropsychological exam and a [18F]-Flutemetamol PET. Statistical Parametric Mapping 12 was used to analyze regional amyloid differences by APOE genotypes. Cognitive assessment was re-administered after follow-up.

RESULTS

APOE ε3/ε4 carriers showed significant amyloid load in left middle occipital areas in comparison with APOE ε3/ε3, whereas APOE ε3/ε4 exhibited several areas of amyloid accumulation in comparison with APOE ε2/ε3 that disappeared after family-wise error cluster level correction, but which hold in nonparametric analyses. No amyloid load differences were found between APOE ε2/ε3 and APOE ε3/ε3. The frequency of progression of cognitive decline was 80 % in ε3/ε4, 50 % in ε2/ε3, and 22.86 % in ε3/ε3 carriers.

CONCLUSIONS

This compared regional amyloid deposition and cognitive evolution among APOE genotypes. Our preliminary findings suggest an association between APOE ε4 and amyloid burden in posterior cortical areas in non-demented PD and a tendency to a higher frequency of cognitive decline. Larger studies should explore cognition and amyloid burden in APOE ε2 carriers.

Genetically Proxied Phosphodiesterase Type 5 (PDE5) Inhibition and Risk of Dementia: A Drug Target Mendelian Randomization Study

Phosphodiesterase-5 (PDE5) inhibitors have gained interest as a potential treatment for dementia. However, current evidence is limited to observational and pre-clinical studies. We conducted a drug-target Mendelian randomization (MR) analysis to investigate the on-target effects of pharmacological PDE5 inhibition on dementia subtypes and related phenotypes. We selected variants from around the PDE5A locus associated with diastolic and systolic blood pressure, as well as circulating PDE5A levels, to create three instruments for genetically proxied PDE5A inhibition. Using two-sample MR, we validated the instruments against erectile dysfunction and pulmonary arterial hypertension before assessing their associations with dementia subtypes, dementia-related proteins, and neuroimaging traits. After correcting for multiple comparisons, genetically proxied PDE5 inhibition, per one SD lower in diastolic blood pressure, was associated with higher odds of Alzheimer's disease (OR 1.09, 95% CI 1.07-1.11) and Lewy body dementia (OR 1.32, 95% CI 1.23-1.41), but a trend towards lower odds of vascular dementia across all instruments. Genetically proxied PDE5 inhibition was associated with both beneficial and adverse effects on brain MRI traits. This included lower volumes of white matter hyperintensities (SD change - 0.035, 95% CI - 0.025, - 0.045), indicating potential benefits, but also reduced volumes of other structures, including the thalamus, suggesting potential adverse effects. PDE5 inhibition was associated with the concentrations of several proteins implicated in dementia pathophysiology. Our findings suggest that while PDE5 inhibition may be associated with a lower risk of vascular dementia, possibly by preventing white matter hyperintensities, it may increase risk of Alzheimer's disease and Lewy body dementia, warranting further investigation before clinical trials.

Genetic risk and plasma biomarkers of dementia with Lewy bodies in a Chinese population

Genetic investigations and associations with plasma biomarkers of dementia with Lewy bodies (DLB) in East Asian populations are lacking. The aim of our study is to identify candidate pathogenic variants and assess the diagnostic performance of plasma biomarkers among DLB patients in the Chinese population. This cohort included 151 DLB patients and 2010 controls, all of whom underwent whole genome sequencing. Plasma glial fibrillary acidic protein (GFAP), α-synuclein(αSyn), neurofilament light (NfL), and phosphorylated tau 217 (p-tau217) were detected in a subgroup. As a result, the APOE ε4 allele significantly increased DLB risk (p = 1.84E-11), while rare missense variants of USP13 gene were first found to be suggestively associated with DLB risk (p = 1.31E-5). Higher levels of plasma GFAP, αSyn, NfL, and p-tau217 were detected in DLB patients compared to controls (p < 0.001), which combined with polygenic risk scores (PRS) achieving an AUC of 0.927 for DLB diagnosis. Besides, significant correlations were observed between PRS of DLB and age at onset, the cumulative incidence rate, as well as plasma GFAP levels. In conclusion, this is the first study to simultaneously investigate the genetics and plasma biomarkers of DLB, highlighting the discriminative ability for DLB using PRS and plasma biomarker assay.

The Association Between Herpes Zoster, Antiherpetic Therapies, and Alzheimer's Disease: A Comprehensive Systematic Review

Background: Alzheimer's Disease (AD) represents a significant public health challenge with a rising global burden. Emerging evidence suggests a potential link between herpes zoster (HZ) and an increased risk of AD. These findings indicate that HZ may contribute to neuroinflammation and other pathophysiological processes associated with AD, pointing out the potential role of the virus infection in the initiation and/or progression of AD pathology. Objective: This systematic review evaluates the relationships between HZ and the risk of AD, highlighting the potential neuroprotective role of HZ vaccination and antiherpetic drug (AHD) use. Methods: Adhering to the (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) PRISMA guidelines, a comprehensive search of databases (e.g., PubMed) until October 2024 was conducted. Observational studies reporting risk estimates were included. Extracted data were synthesized and analyzed narratively due to study heterogeneity. Results: Eleven studies (out of two hundred) met the inclusion criteria, offering preliminary insights that could form a foundation for further investigation. Reports on HZ showed mixed outcomes, with some studies suggesting a potential increased risk of AD, while others showed no clear correlation. Interestingly, HZ vaccination led to a potential preventive role in reducing the risk of AD, with risk estimates ranging from 0.57 to 0.99. Additionally, the use of AHDs was linked to a reduced risk of AD, with risk estimates ranging from 0.65 to 0.96. Conclusions: Published findings suggest that HZ vaccination and AHD use could represent potential interventions to reduce the risk of AD; however, further research is necessary to validate these findings and better understand the underlying protective mechanisms.

Dementia with Lewy bodies and Parkinson disease dementia - the same or different and is it important?

Biological definitions of neurological diseases are now becoming a reality, although still in the research phase. This development will recategorize neurological diseases, providing objective diagnostics and the promise of therapeutics that target biological mechanisms - similar to the strategy that has proven successful in tumours and other conditions. In this Perspective article, we discuss this development for dementias with dominant Lewy pathology, as the availability of biological assays for this pathology has sparked new interest in a single disease diagnosis for all individuals positive for α-synuclein. On the basis of current evidence, we argue that an α-synuclein assay alone is unlikely to be a specific criterion for a spectrum of clinical syndromes with Lewy pathology or a definitive diagnostic marker for Lewy body dementia. We advocate that one biological assay will not reflect the complex spatiotemporal features of brain pathology. Diverse sequential mechanisms underpin the highly heterogeneous phenotypes and clinicopathological processes of Lewy body dementias. Disease modification, if possible, will be most effective when it targets the early underlying mechanisms, especially those leading to aggressive phenotypes.

Causal relationship between schizophrenia and five types of dementia: A bidirectional two-sample Mendelian randomization study

BACKGROUND

Although observational research indicates an association between schizophrenia and dementia, it is unclear whether the two are causally related. In order to examine the causal relationship between schizophrenia and five types of dementia (all-cause dementia, Alzheimer's disease, vascular dementia, frontotemporal dementia, and dementia with Lewy bodies), we performed a bidirectional two-sample Mendelian randomization analysis.

METHODS

In this study, pooled statistics of schizophrenia and dementia were obtained from the Large-scale genome-wide association study (GWAS) in individuals of European ancestry. Inverse variance weighted (IVW) was the primary statistical approach used in this Mendelian randomization, to further support our findings, we also used MR-Egger, weighted median, and cML-MA. We also used a number of sensitivity analyses to evaluate pleiotropy and heterogeneity.

RESULTS

In the study of the effect of schizophrenia on dementia, findings from the IVW analysis suggested that schizophrenia is associated with an increased risk of all-cause dementia (OR = 1.065, 95%CI: 1.027 ～ 1.104, P = 0.001, FDR-corrected P = 0.003), Alzheimer's disease (OR = 1.029, 95%CI: 1.003 ～ 1.054, P = 0.027, FDR-corrected P = 0.045), and vascular dementia (OR = 1.106, 95%CI: 1.023 ～ 1.197, P = 0.012, FDR-corrected P = 0.029). In the study of the effect of dementia on schizophrenia, no form of dementia assessed in this study was found to be a risk factor for schizophrenia.

CONCLUSION

Our findings suggest that schizophrenia may be a risk factor for all-cause dementia, Alzheimer's disease, and vascular dementia, but no dementia of any kind was found to be a risk factor for schizophrenia. Our study provides insights into the potential genetic relationship between schizophrenia and dementia.

Evidence from a Mendelian randomization study: Delirium's noncausal role in dementia onset

BACKGROUND

Previous observational studies have suggested a possible association between dementia and delirium. However, these findings might be influenced by confounding variables. Thus, our study aimed to investigate the causal relationship between dementia and delirium using a bidirectional Mendelian randomization (MR) analysis.

METHODS

In our investigation, bidirectional MR analysis was conducted by summary statistics from genome-wide association studies (GWAS). This enabled us to evaluate the causal impact of delirium and different types of dementia, such as Alzheimer's dementia (AD), vascular dementia (VaD) and Lewy body dementia (LD).

RESULTS

According to MR analysis, there was a significant positive correlation between delirium risk and AD (odds ratio [OR] = 1.363; 95 % confidence interval [CI], 1.223-1.519; p = 2.140E-08) and LD (OR = 1.403; 95 % CI, 1.151-1.711; p = 8.226E-04). However, the analysis also revealed that there was no causal relationship between VaD (OR = 1.044; 95 % CI = 1.136-1.027; p = 0.316) and the risk of delirium. Additionally, our study does not provide evidence to support a causal correlation between delirium and the risk of developing any form of dementia.

CONCLUSION

The results of the MR analysis suggest a potential causal link between dementia and an increased risk of delirium. Nevertheless, it should be emphasized that the existing evidence does not provide support for a causal connection in the reverse direction, implying that delirium may not play a causative role in the onset of dementia.

Comparative mapping of single-cell transcriptomic landscapes in neurodegenerative diseases

INTRODUCTION

Alzheimer's disease (AD), dementia with Lewy bodies (DLB), and Parkinson's disease (PD) represent a spectrum of neurodegenerative diseases (NDDs). Here, we performed the first direct comparison of their transcriptomic landscapes.

METHODS

We profiled whole transcriptomes of NDD cortical tissue by single-nucleus RNA sequencing, using computational analyses to identify common and distinct differentially expressed genes (DEGs), pathways, vulnerable and disease-driver cell subtypes, and altered cell-to-cell interactions.

RESULTS

The same inhibitory neuron subtype was depleted in both AD and DLB. Potentially disease-driving neuronal cell subtypes were identified in both PD and DLB. Cell-cell communication was predicted to be increased in AD but decreased in DLB and PD. DEGs were most commonly shared across NDDs within inhibitory neuron subtypes. Overall, AD and PD showed greatest transcriptomic divergence, while DLB exhibited an intermediate signature.

DISCUSSION

These results may help explain the clinicopathological spectrum of these NDDs and provide unique insights into shared and distinct molecular mechanisms underlying pathogenesis.

HIGHLIGHTS

The same vulnerable inhibitory neuron subtype population was depleted in both Alzheimer's disease (AD) and dementia with Lewy bodies (DLB). Potentially disease-driving neuronal cell subtypes were discovered in both Parkinson's disease (PD) and DLB. Cell-cell communication was predicted to be increased in AD but decreased in DLB and PD. Differentially expressed genes were most commonly shared across neurodegenerative diseases in inhibitory neuron types. AD and PD had the greatest transcriptomic divergence, with DLB showing an intermediate signature.

Investigating the causal relationships between mitochondrial proteins and dementia with Lewy bodies

BackgroundDisruptions in mitochondrial function have been implicated in various neurodegenerative diseases. However, the specific role of mitochondrial proteins in the pathogenesis of dementia with Lewy bodies (DLB) remains poorly understood.ObjectiveThis study aims to investigate potential causal relationships between mitochondrial proteins and DLB risk using Mendelian randomization (MR) analysis.MethodsCausal associations between 66 mitochondrial proteins (MPs) and DLB were assessed by MR analysis, utilizing data from comprehensive genome-wide association studies (GWAS), with various analytical methods, including the inverse variance weighted, MR-Egger, and weighted median. Cochran's Q statistics assessed the heterogeneity of instrumental variables.ResultsGenetic predispositions to increased levels of ES1 protein homolog and apoptosis-inducing factor 1 (AIF-1) were associated with an elevated risk of DLB. Conversely, genetic predispositions to increased levels of glutaredoxin-2 (GLRX-2), complement component 1 Q subcomponent-binding protein (C1QBP), and mitochondrial glutamate carrier 2 (GC2) were found to be protective against DLB. Sensitivity analyses revealed no heterogeneity or horizontal pleiotropy among the selected instrumental variables.ConclusionsOur MR study identifies specific MPs potentially causally linked to DLB risk. These findings offer new insights into the MP-related mechanisms underlying DLB pathogenesis and highlight potential therapeutic targets.

BIN1 and Alzheimer's disease: the tau connection

Bridging integrator 1 (BIN1) is a ubiquitously expressed protein that plays a critical role in endocytosis, trafficking and cytoskeletal dynamics. In 2010, BIN1 gene was reported as a major genetic risk factor for Alzheimer's disease (AD), which shifted the focus on its physiological and pathophysiological roles in the brain (at a time when data available were scarce). In this review, we discuss the multiple cerebral roles of BIN1, especially in regulating synaptic function, and the strong link between BIN1 and tau pathology, supported by recent evidence ranging from genetic and clinical/postmortem observations to molecular interactions.

Combining GWAS Summary Data and Proteomics Identified Potential Drug Targets in Dementia

Due to progressive cognitive loss and subsequent incapability of daily life, the development of novel therapeutics is urgently needed for dementia patients. We performed a two-sample bi-directional Mendelian randomization (MR) analysis using summary-level statistics to identify causality between peripheral and cerebrospinal fluid (CSF) proteins and the risk of dementia. Genetic variants were subtracted from the Genome-Wide Association Studies (GWAS) results. Wald ratio (WR) and inverse-variance weighted (IVW) ratio were utilized to estimate the causal effects of plasma and CSF proteins on dementia. Reverse MR, Steiger filtering, Bayesian co-localization phenotype scanning, and external validation were integrated to strengthen the robustness of primary MR results. After sensitivity analysis, six circulating proteins were identified in three dementia classifications, whereas no causality was found in frontotemporal dementia (FTD). Elevated levels of circulating C1R protein increased the odds of developing Alzheimer's disease (AD), while PILRA and CELA2A were estimated to protect against the pathogenesis of AD; genetically predicted increase of α-synuclein and APOE elevated the occurrence of Dementia of Lewy Bodies (DLB); elevated level of circulating CRP was assessed to increase the onset of vascular dementia (VD). Our MR analyses identified a genetically predicted association between circulating C1R, PILRA, and CELA2A and the risk of AD, causal estimates between α-syn, APOE protein, and the onset of DLB, and a robust correlation between CRP and the etiology of VD. This study might guide the discovery of disease etiology and build up a novel disease-modifying paradigm of dementia.

Knowledge and attitudes about dementia and dementia genetics in a cohort of geriatric clinic attendees in Nigeria

BackgroundPopulation ageing in Africa will increase the burden of Alzheimer's disease and related dementias within the next few decades. Despite the potential for discovery of novel genetic risks in African populations, there is still a paucity of dementia genetic research among indigenous Africans.ObjectiveWe aimed to investigate the knowledge and attitudes of elderly population in Nigeria about dementia and dementia genetics.MethodsOne hundred clinic attendees (aged ≥60 years) recruited at the University College Hospital, Ibadan, Nigeria were surveyed using an interviewer-administered questionnaire consisting of the Dementia Knowledge Assessment Scale (DKAS) and other items assessing knowledge and attitudes about dementia genetics.ResultsThe mean age (±SD) of participants was 71.0 (±7.1) years, and the mean (±SD) DKAS score was 8.87 (±10.84). Only 10% were considered to have good knowledge of dementia (i.e., DKAS score ≥26). Attempts by participants to translate "dementia" in their local languages revealed misleading themes in their perception of the condition. Of the 42 participants who claimed to know what dementia is, 32 (76.2%) of them had poor knowledge (i.e., DKAS <26). Twenty-one participants were aware of the existence of genetic risk factors for dementia, but none could name a dementia risk gene. Seventy participants expressed willingness to undergo genetic testing to assess their risk of dementia.ConclusionsThere is a poor level of knowledge about dementia and dementia genetics among the elderly population in Nigeria. Public health education and community engagement is important for maximizing the impact of dementia genetic studies in Africa.

The role of the hippocampus and SLC39A8 in chronic musculoskeletal pain-induced dementia: a Mendelian randomization study

Despite observational studies suggesting a link between chronic musculoskeletal pain (CMP) and increased risk of cognitive decline and dementia, the causal nature of this relationship remains uncertain due to potential confounding factors and reverse causality. We employed two-sample Mendelian Randomization (TSMR), bidirectional MR, mediation MR, drug-target MR, and colocalization analysis, along with gene set enrichment and protein-protein interaction (PPI) analyses. TSMR assessed the causal associations between CMP and the risk of dementia and its subtypes, including Alzheimer's disease (AD), vascular dementia (VaD), Lewy body dementia (LBD), frontotemporal dementia (FTD), and Parkinson's disease (PD). Bidirectional MR evaluated reverse causality, while mediation analyses identified potential mediators, focusing on neuroimaging and cognitive phenotypes. Drug-target MR investigated the role of the SLC39A8 gene, and colocalization analysis determined shared causal genetic variants. Gene set enrichment and PPI analyses elucidated the biological pathways implicated in the CMP-dementia relationship. Robust evidence established a causal relationship between chronic low back pain (LBP) and increased risk of PD, with knee osteoarthritis identified as a partial mediator, suggesting a pathway involving chronic inflammation. Bidirectional MR analysis revealed no evidence of reverse causality, further supporting the unidirectional causal link from LBP to PD. Colocalization analysis confirmed distinct genetic architectures for LBP and PD, while drug-target MR implicated the SLC39A8 gene as a potential mediator. Gene set enrichment and PPI analyses highlighted critical biological pathways, such as purine metabolism and glutamate receptor signaling. Suggestive evidence indicated potential causal links between limb pain and overall dementia, myalgia and VaD, as well as potential protective effects of Polymyalgia Rheumatica (PMR) against AD and rheumatism against PD. This study reveals a complex causal relationship between CMP and neurodegenerative diseases, particularly the robust link between LBP and PD. The findings underscore the need for further research to elucidate the underlying mechanisms and inform targeted prevention and treatment strategies.

Decoding the genetic blueprints of neurological disorders: disease mechanisms and breakthrough gene therapies

Neurological disorders pose a rapidly growing global health burden, significantly affecting cognitive and motor functions with profound societal repercussions. This comprehensive review probe into the genetic foundations of various neurological conditions while exploring innovative RNA-based therapeutics particularly gene therapies as cutting edge treatment strategies. Through an in-depth analysis of existing literature, the study examines the genetic landscape, disease mechanisms, and gene-based intervention possibilities across a range of neurological disorders, including Cerebellar Ataxias, Autosomal Recessive Ataxia, Mitochondrial Cerebellar Ataxia, Multiple System Atrophy (MSA), Idiopathic Late-Onset Cerebellar Ataxia, Hereditary Spastic Paraplegias, Alzheimer's Disease, Vascular Dementia, Lewy Body Dementia, Frontotemporal Dementias, Inherited Prion Diseases, and Huntington's Disease. It uncovers the intricate network of genetic mutations driving these disorders, shedding light on their mechanisms and uncovering promising therapeutic targets. The review also highlights the remarkable potential of RNA-based therapeutics, with gene therapies standing at the forefront of precision treatment approaches. By offering an up-to-date understanding of the genetic intricacies and emerging therapeutic possibilities in neurological disorders, this study significantly contributes to the advancement of precision medicine in neurology. It also paves the way for future research and clinical applications aimed at improving patient care and outcomes.

Commander complex regulates lysosomal function and is implicated in Parkinson's disease risk

Variants in GBA1 resulting in decreased lysosomal glucocerebrosidase (GCase) activity are a common risk factor for Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Incomplete penetrance of GBA1 variants suggests that additional genes contribute to PD and DLB manifestation. By using a pooled genome-wide CRISPR interference screen, we identified copper metabolism MURR1 domain-containing 3 (COMMD3) protein, a component of the COMMD/coiled-coil domain-containing protein 22 (CCDC22)/CCDC93 (CCC) and Commander complexes, as a modifier of GCase and lysosomal activity. Loss of COMMD3 increased the release of lysosomal proteins through extracellular vesicles, leading to their impaired delivery to endolysosomes and consequent lysosomal dysfunction. Rare variants in the Commander gene family were associated with increased PD risk. Thus, COMMD genes and related complexes regulate lysosomal homeostasis and may represent modifiers in PD and other neurodegenerative diseases associated with lysosomal dysfunction.

GWAS by Subtraction to Disentangle RBD Genetic Background from α-Synucleinopathies

Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia characterized by loss of muscle atonia and abnormal behaviors occurring during REM sleep. Idiopathic RBD (iRBD) is recognized as the strongest prodromal hallmark of α-synucleinopathies, with an established conversion rate to a neurodegenerative condition that reaches up to 96.6% at 15 years of follow-up. Moreover, RBD-converters display a more severe clinical trajectory compared to those that do not present with RBD. However, the extent to which iRBD represents a distinct genetic entity or an early manifestation of neurodegeneration remains unclear. To address this, we applied Genomic Structural Equation Modeling (GenomicSEM) using a GWAS-by-subtraction approach to disentangle the genetic architecture of iRBD from the shared genomic liability across α-synucleinopathies. Our findings highlight the SNCA locus as a key genetic regulator of iRBD susceptibility. While iRBD exhibits a partially distinct genetic signature, residual genomic overlap with neurodegenerative traits suggests that its genetic architecture exists along a continuum of α-synucleinopathy risk. In this scenario, the associations with neuroanatomical correlates may serve as early indicators of a trajectory toward future neurodegeneration. These findings provide a framework for identifying biomarkers that could aid in disease stratification and risk prediction, potentially improving early intervention strategies.

Identification of Common Brain Protein and Genetic Loci Between Parkinson's Disease and Lewy Body Dementia

BACKGROUND

Parkinson's disease (PD) and Lewy body dementia (LBD) have many common features, including clinical manifestations, neurochemistry, and pathology, but little is known about their shared brain proteins and genetic factors.

METHODS

To identify susceptibility-related brain proteins that are shared between PD and LBD patients, proteome-wide association studies (PWASs) were conducted by integrating human brain protein quantitative trait loci (pQTLs) with large-scale genome-wide association studies (GWASs) of both diseases. Subsequently, pleiotropy-informed conditional false discovery rate (pleioFDR) analysis was performed to identify common risk genetic loci between PD and LBD. Finally, the downregulation of these risk genes in different disease states was validated by differential gene expression analysis.

RESULTS

PWASs identified 12 PD risk proteins and nine LBD risk proteins, among which TMEM175 (zPD = -7.25, PPD = 4.12E-13; zLBD = -6.02, PLBD = 1.75E-09) and DOC2A (zPD = -4.13, PPD = 3.71E-05; zLBD = -3.91, PLBD = 9.08E-05) were shared. PleioFDR analysis revealed that five genetic risk loci mapped to eight genes associated with PD and LBD, including the proteome-wide significant risk gene TMEM175 (ConjFDR = 5.74E-03). Differential expression analysis verified that TMEM175 was significantly downregulated in the midbrains of PD patients (p = 1.19E-02), and further exploration revealed that TMEM175 was also dramatically downregulated in the substantia nigra of PD patients (p = 1.16E-02) and incidental Lewy body disease patients (p = 7.52E-03). Moreover, TMEM175 was significantly downregulated in induced pluripotent stem cell-derived dopaminergic neurons from PD patients (p = 4.60E-02).

CONCLUSION

Dysregulation of TMEM175 may confer PD and LBD risk and may be partly responsible for their comorbidity. Our results revealed the common genetic risk factors between PD and LBD, which elucidated the shared genetic basis of these diseases.

Genome-wide association analysis identifies APOE as a mitophagy modifier in Lewy body disease

INTRODUCTION

Phosphorylated ubiquitin (p-S65-Ub) is generated during PINK1-PRKN mitophagy as a specific marker of mitochondrial damage. Despite the widespread deposition of p-S65-Ub in aged and diseased human brain, the genetic contribution to its accumulation remains unclear.

METHODS

To identify novel mitophagy regulators, we performed a genome-wide association study using p-S65-Ub level as a quantitative trait in 1012 autopsy-confirmed Lewy body disease (LBD) samples.

RESULTS

We identified a significant genome-wide association with p-S65-Ub for rs429358 (apolipoprotein E ε4 [APOE4]) and a suggestive association for rs6480922 (ZMIZ1). APOE4 was associated with higher p-S65-Ub levels and greater neuropathological burden. Functional validation in mouse and human induced pluripotent stem cell (iPSC) models confirmed APOE4-mediated mitophagy alterations. Intriguingly, ZMIZ1 rs6480922 was associated with lower p-S65-Ub levels, reduced neuropathological load, and increased brain weight, indicating a potential protective role.

DISCUSSION

Our findings underscore the importance of mitochondrial quality control in LBD pathogenesis and nominate regulators that may contribute to disease risk or resilience.

HIGHLIGHTS

p-S65-Ub levels were used as a quantitative marker of mitochondrial damage. A GWAS identified two genetic variants that modify mitophagy in LBD autopsy brain. APOE4 was associated with increased p-S65-Ub accumulation and neuropathology. APOE4 altered mitophagy via pathology-dependent and pathology-independent mechanisms. ZMIZ1 was linked to reduced p-S65-Ub and neuropathology indicative of protection.

Blood biomarker profiles in young-onset neurocognitive disorders: A cohort study

INTRODUCTION

Young-onset neurocognitive symptoms result from a heterogeneous group of neurological and psychiatric disorders which present a diagnostic challenge. To identify such factors, we analysed the Biomarkers in Younger-Onset Neurocognitive Disorders cohort, a study of individuals <65 years old presenting with neurocognitive symptoms for a diagnosis and who have undergone cognitive and biomarker analyses.

METHODS

Sixty-five participants (median age at assessment of 56 years, 45% female) were recruited during their index presentation to the Royal Melbourne Hospital Neuropsychiatry Centre, a tertiary specialist service in Melbourne, Australia, and categorized as either early-onset Alzheimer's disease (n = 18), non-Alzheimer's disease neurodegeneration (n = 23) or primary psychiatric disorders (n = 24). Levels of neurofilament light chain, glial fibrillary acidic protein and phosphorylated-tau 181, apolipoprotein E genotype and late-onset Alzheimer's disease polygenic risk scores were determined. Information-theoretic model selection identified discriminatory factors.

RESULTS

Neurofilament light chain, glial fibrillary acidic protein and phosphorylated-tau 181 levels were elevated in early-onset Alzheimer's disease compared with other diagnostic categories. A multi-omic model selection identified that a combination of cognitive and blood biomarkers, but not the polygenic risk score, discriminated between early-onset Alzheimer's disease and primary psychiatric disorders (area under the curve ⩾ 0.975, 95% confidence interval: 0.825-1.000). Phosphorylated-tau 181 alone significantly discriminated between early-onset Alzheimer's disease and non-Alzheimer's disease neurodegeneration causes (area under the curve = 0.950, 95% confidence interval: 0.877-1.00).

DISCUSSION

Discriminating between early-onset Alzheimer's disease, non-Alzheimer's disease neurodegeneration and primary psychiatric disorders causes of young-onset neurocognitive symptoms is possible by combining cognitive profiles with blood biomarkers. These results support utilizing blood biomarkers for the work-up of young-onset neurocognitive symptoms and highlight the need for the development of a young-onset Alzheimer's disease-specific polygenic risk score.

Genomic and epigenomic insights into purkinje and granule neurons in Alzheimer's disease and related dementia using single-nucleus multiome analysis

Although the human cerebellum is known to be neuropathologically impaired in Alzheimer's disease (AD) and AD-related dementias (ADRD), the cell type-specific transcriptional and epigenomic changes that contribute to this pathology are not well understood. Here, we report single-nucleus multiome (snRNA-seq and snATAC-seq) analysis of 103,861 nuclei isolated from both cerebellum and frontal cortex of AD/ADRD patients and normal controls. Using peak-to-gene linkage analysis, we identified 431,834 significant linkages between gene expression and cell subtype-specific chromatin accessibility regions enriched for candidate cis-regulatory elements (cCREs). These cCREs were associated with AD/ADRD-specific transcriptomic changes and disease-related gene regulatory networks, especially for RAR Related Orphan Receptor A (RORA) and E74 Like ETS Transcription Factor 1 (ELF1) in cerebellar Purkinje cells and granule cells, respectively. Trajectory analysis of granule cell populations further identified disease-relevant transcription factors, such as RORA, and their regulatory targets. Finally, we pinpointed two likely causal genes, Seizure Related 6 Homolog Like 2 (SEZ6L2) in Purkinje cells and KAT8 Regulatory NSL Complex Subunit 1 (KANSL1) in granule cells, through integrative analysis of cCREs derived from snATAC-seq, genome-wide AD/ADRD loci, and three-dimensional (3D) genome data. Via CRISPRi experiments, we found that perturbation of rs4788201 and rs62056801 significantly inhibited the expression of their target genes, SEZ6L2 and KANSL1, in human iPSC-derived neurons. This cell subtype-specific regulatory landscape in the human cerebellum identified here offers novel genomic and epigenomic insights into the neuropathology and pathobiology of AD/ADRD and other neurological disorders if broadly applied.

Genetic insights of lipid metabolism and lipid-lowering drugs with Lewy body dementia risk: Evidence from Mendelian randomization

BACKGROUND

Lewy body dementia (LBD) is the second common dementia, with unclear mechanisms and limited treatment options. Dyslipidemia has been implicated in LBD, but the role of lipid-lowering drugs remains underexplored. This study aims to investigate the association between lipid traits, drug targets, and LBD risk using Mendelian Randomization (MR) analysis.

METHODS

We performed univariable and multivariable MR analyses to evaluate the causal effects of lipid traits on the risk of LBD. Then, drug-target MR analysis and subtype analysis were conducted to evaluate the effects of lipid-lowering therapies on LBD.

RESULTS

In univariable MR, genetically predicted low-density lipoprotein cholesterol (LDL-C) and remnant cholesterol (RC) levels were associated with an increased risk of LBD. Mediation analysis suggested a potential interaction between LDL-C and RC in influencing LBD risk. Drug-target MR analysis identified significant associations between genetically proxied inhibition of ANGPTL3, CETP, and HMGCR and LBD risk.

CONCLUSION

This MR analysis provided evidence that elevated LDL-C and RC may increase the risk of LBD. Additionally, targeting ANGPTL3, CETP, and HMGCR may represent potential therapeutic strategies for the prevention or treatment of LBD.

Extensive perivascular spaces burden causally affects neurodegenerative diseases and brain structure: A two-sample bidirectional Mendelian randomization study

BACKGROUND

Extensive perivascular spaces (PVS) burden has been reported to be associated with neurodegenerative diseases and brain structure; however, the causal effects has not been determined yet. Therefore, this study aimed to investigate the causal effect of extensive PVS burden on neurodegenerative diseases and brain structure through Mendelian randomization (MR) analysis.

METHODS

Two-sample bidirectional MR was conducted based on publicly available genome-wide association studies (GWAS) summary statistics. Causal estimates of extensive PVS burden on neurodegenerative diseases and brain structure were primarily assessed using the inverse-variance weighted (IVW) method, supplemented by additional methods, including MR-Egger, weighted median, simple mode, and weighted mode. Sensitivity analyses were performed to assess heterogeneity and pleiotropy. In addition, we explored whether brain structure act as a mediating factor in the pathway from extensive PVS burden to neurodegenerative diseases.

RESULTS

Our MR study found that extensive PVS burden in white matter (WM-PVS) burden was associated with lower Alzheimer's disease (AD) risk (IVW OR (95 % CI) = 0.963(0.929 to 0.999), P = 0.0428), with no heterogeneity and pleiotropy detected. In addition, following FDR correction, we found bidirectional causal relationships between extensive PVS burden and brain structure. Moreover, our results of the mediated analysis showed that the surface area of parahippocampal, as a mediating variable, plays an important role in the causal relationship between WM-PVS and AD. The mediation effect is 18 %.

CONCLUSIONS

Our study provides evidence for the causal associations of different extensive PVS burden phenotypes with neurodegenerative diseases and brain structures, improving our understanding of the complex relationships between different brain injuries.

Interrogating DNA methylation associated with Lewy body pathology in a cross brain-region and multi-cohort study

Lewy body (LB) diseases are an umbrella term encompassing a range of neurodegenerative conditions all characterized by the hallmark of intra-neuronal α-synuclein associated with the development of motor and cognitive dysfunction. In this study, we have conducted a large meta-analysis of DNA methylation across multiple cortical brain regions, in relation to increasing burden of LB pathology. Utilizing a combined dataset of 1239 samples across 855 unique donors, we identified a set of 30 false discovery rate (FDR) significant loci that are differentially methylated in association with LB pathology, the most significant of which were located in UBASH3B and PTAFR, as well as an intergenic locus. Ontological enrichment analysis of our meta-analysis results highlights several neurologically relevant traits, including synaptic, inflammatory and vascular alterations. We leverage our summary statistics to compare DNA methylation signatures between different neurodegenerative pathologies and highlight a shared epigenetic profile across LB diseases, Alzheimer's disease and Huntington's disease, although the top-ranked loci show disease specificity. Finally, utilizing summary statistics from previous large-scale genome-wide association studies we report FDR significant enrichment of DNA methylation differences with respect to increasing LB pathology in the SNCA genomic region, a gene previously associated with Parkinson's disease and dementia with Lewy bodies.

No causal link between smoking and dementia with Lewy bodies

This letter addresses the findings of Goodheart and Gomperts (2024), which observed an association between smoking and reduced odds of dementia with Lewy bodies (DLB). In contrast, our Mendelian randomization analysis found no causal link, suggesting that further research using genetically informed methods is needed to clarify these results.

A genome-wide association study identifies a novel East Asian-specific locus for dementia with Lewy bodies in Japanese subjects

BACKGROUND

Dementia with Lewy bodies (DLB) is the second most common type of degenerative dementia in older patients. As with other multifactorial diseases, the pathogenesis results from interactions of environmental and genetic factors. The genetic basis of DLB is not yet fully understood. Recent genomic analyses of DLB in Caucasian cohorts identified genetic susceptibility loci for DLB, but the comprehensive genomic analysis in Asians was still not performed.

METHODS

We conducted a genome-wide association study (GWAS) in Japanese subjects (211 DLB cases and 6113 controls) to clarify the genetic architecture of DLB pathogenesis.

RESULTS

We identified the East Asian-specific DHTKD1 locus (rs138587229) on chromosome 10 with genome-wide significance (GWS; P = 3.27 × 10-8) and the ICOS/PARD3B locus on chromosome 2 with suggestive significance (P = 3.95 × 10-7) as novel DLB genetic risk loci. We also confirmed the APOE locus (rs429358, P < 5.0 × 10-8), a known risk locus for DLB and Alzheimer's disease in Caucasians. The DHTKD1 locus was associated with the gene expression of SEC61A2 and showed a causal relationship with cholinesterase levels. In a trans-ethnic meta-analysis that included Japanese, UK Biobank, and other Caucasian GWAS, we confirmed the risk for DLB at APOE and SNCA loci with GWS. Transcriptome-wide association analysis identified ZNF155 and ZNF284 in the brain cortex and GPRIN3 in the substantia nigra as putative causal genes for DLB.

CONCLUSIONS

This is the first GWAS for DLB in East Asians, and our findings provide new biological and clinical insights into the pathogenesis of DLB.

Structural variants linked to Alzheimer's disease and other common age-related clinical and neuropathologic traits

BACKGROUND

Alzheimer's disease (AD) is a complex neurodegenerative disorder with substantial genetic influence. While genome-wide association studies (GWAS) have identified numerous risk loci for late-onset AD (LOAD), the functional mechanisms underlying most of these associations remain unresolved. Large genomic rearrangements, known as structural variants (SVs), represent a promising avenue for elucidating such mechanisms within some of these loci.

METHODS

By leveraging data from two ongoing cohort studies of aging and dementia, the Religious Orders Study and Rush Memory and Aging Project (ROS/MAP), we performed genome-wide association analysis testing 20,205 common SVs from 1088 participants with whole genome sequencing (WGS) data. A range of Alzheimer's disease and other common age-related clinical and neuropathologic traits were examined.

RESULTS

First, we mapped SVs across 81 AD risk loci and discovered 22 SVs in linkage disequilibrium (LD) with GWAS lead variants and directly associated with the phenotypes tested. The strongest association was a deletion of an Alu element in the 3'UTR of the TMEM106B gene, in high LD with the respective AD GWAS locus and associated with multiple AD and AD-related disorders (ADRD) phenotypes, including tangles density, TDP-43, and cognitive resilience. The deletion of this element was also linked to lower TMEM106B protein abundance. We also found a 22-kb deletion associated with depression in ROS/MAP and bearing similar association patterns as GWAS SNPs at the IQCK locus. In addition, we leveraged our catalog of SV-GWAS to replicate and characterize independent findings in SV-based GWAS for AD and five other neurodegenerative diseases. Among these findings, we highlight the replication of genome-wide significant SVs for progressive supranuclear palsy (PSP), including markers for the 17q21.31 MAPT locus inversion and a 1483-bp deletion at the CYP2A13 locus, along with other suggestive associations, such as a 994-bp duplication in the LMNTD1 locus, suggestively linked to AD and a 3958-bp deletion at the DOCK5 locus linked to Lewy body disease (LBD) (P = 3.36 × 10-4).

CONCLUSIONS

While still limited in sample size, this study highlights the utility of including analysis of SVs for elucidating mechanisms underlying GWAS loci and provides a valuable resource for the characterization of the effects of SVs in neurodegenerative disease pathogenesis.

The causal association between resting state intrinsic functional networks and neurodegeneration

Alterations of resting state intrinsic functional networks have been associated with neurodegenerative diseases even before the onset of cognitive symptoms. Emerging hypotheses propose a role of resting state intrinsic functional networks alterations in the risk or vulnerability to neurodegeneration. It is unknown whether intrinsic functional network alterations can be causal for neurodegenerative diseases. We sought to answer this question using two-sample Mendelian randomization. Using the largest genome-wide association study of resting state intrinsic functional connectivity (n = 47 276), we generated genetic instruments (at the significance level 2.8 ×10-11) to proxy resting state intrinsic functional network features. Based on the known brain regions implicated in different neurodegenerative diseases, we generated genetically proxied resting state intrinsic functional features and tested their association with their paired neurodegenerative outcomes: features in parieto-temporal regions and Alzheimer dementia (111 326 cases, 677 663 controls); frontal region and frontotemporal dementia (2154 cases, 4308 controls); temporal pole region and semantic dementia (308 cases, 616 controls), and occipital region with Lewy body dementia (LBD) (2591 cases, 4027 controls). Major depressive disorder outcome (170 756 cases, 329 443 controls) was included as a positive control and tested for its association with genetically proxied default mode network (DMN) exposure. Inverse-variance weighted analysis was used to estimate the association between the exposures (standard deviation units) and outcomes. Power and sensitivity analyses were completed to assess the robustness of the results. None of the genetically proxied functional network features were significantly associated with neurodegenerative outcomes (adjusted P value >0.05), despite sufficient calculated power. Two resting state features in the visual cortex showed a nominal level of association with LBD (P = 0.01), a finding that was replicated using a different instrument (P = 0.03). The genetically proxied DMN connectivity was associated with the risk of depression (P = 0.024), supporting the validity of the genetic instruments. Sensitivity analyses were supportive of the main results. This is the first study to comprehensively assess the potential causal effect of resting state intrinsic functional network features on the risk of neurodegeneration. Overall, the results do not support a causal role for the tested associations. However, we report a nominal association between visual network connectivity and Lewy body dementia that requires further evaluation.

Identification of Potential Causal Genes for Neurodegenerative Diseases by Mitochondria-Related Genome-Wide Mendelian Randomization

Current research lacks comprehensive investigations into the potential causal link between mitochondrial-related genes and the risk of neurodegenerative diseases (NDDs). We aimed to identify potential causative genes for five NDDs through an examination of mitochondrial-related gene expression levels. Through the integration of summary statistics from expression quantitative trait loci (eQTL) datasets (human blood and brain tissue), mitochondrial DNA copy number (mtDNA-CN), and genome-wide association studies (GWAS) datasets of five NDDs from European ancestry, we conducted a Mendelian randomization (MR) analysis to explore the potential causal relationship between mitochondrial-related genes and Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Lewy body dementia (LBD). Sensitivity analysis and Bayesian colocalization were employed to validate this causal relationship. Through MR analysis, we have identified potential causal relationships between 12 mitochondria-related genes and AD, PD, ALS, and FTD overlapping with motor neuron disease (FTD_MND) in human blood or brain tissue. Bayesian colocalization analysis further confirms 9 causal genes, including NDUFS2, EARS2, and MRPL41 for AD; NDUFAF2, MALSU1, and METTL8 for PD; MYO19 and MRM1 for ALS; and FASTKD1 for FTD_MND. Importantly, in both human blood and brain tissue, NDUFS2 exhibits a significant pathogenic effect on AD, while NDUFAF2 demonstrates a robust protective effect on PD. Additionally, the mtDNA-CN plays a protected role in LBD (OR = 0.62, p = 0.031). This study presents evidence establishing a causal relationship between mitochondrial dysfunction and NDDs. Furthermore, the identified candidate genes may serve as potential targets for drug development aimed at preventing NDDs.

Quantitative trait loci mapping of circulating metabolites in cerebrospinal fluid to uncover biological mechanisms involved in brain-related phenotypes

Genomic studies of molecular traits have provided mechanistic insights into complex disease, though these lag behind for brain-related traits due to the inaccessibility of brain tissue. We leveraged cerebrospinal fluid (CSF) to study neurobiological mechanisms in vivo, measuring 5543 CSF metabolites, the largest panel in CSF to date, in 977 individuals of European ancestry. Individuals originated from two separate cohorts including cognitively healthy subjects (n = 490) and a well-characterized memory clinic sample, the Amsterdam Dementia Cohort (ADC, n = 487). We performed metabolite quantitative trait loci (mQTL) mapping on CSF metabolomics and found 126 significant mQTLs, representing 65 unique CSF metabolites across 51 independent loci. To better understand the role of CSF mQTLs in brain-related disorders we integrated our CSF mQTL results with pre-existing summary statistics on brain traits, identifying 34 genetic associations between CSF metabolites and brain traits. Over 90% of significant mQTLs demonstrated colocalized associations with brain-specific gene expression, unveiling potential neurobiological pathways.

The role of Apolipoprotein E4 on cognitive impairment in Parkinson's disease and Parkinsonisms

Cognitive impairment is a prevalent non-motor symptom of Parkinson's disease (PD), increasing the risk of dementia as the disease progresses. Despite its clinical significance, the etiology of cognitive impairment in PD remains unclear. Apolipoprotein E4 (APOE4), a well-known genetic risk factor of Alzheimer's disease, has been studied for its potential role in PD-related cognitive impairment. However, findings have been conflicting and thus inconclusive, highlighting a need to critically evaluate the current research. Several studies using neuroimaging modalities have explored the brains of individuals with PD and atypical parkinsonian disorders who have APOE4. Some of these studies have identified distinct neuropathological changes that have been previously reported to be associated with cognitive impairments in those with Parkinsonisms. Here, we review the role of APOE4 on cognitive impairment in PD and atypical Parkinsonisms using neuroimaging evidence. We will examine how APOE4 may contribute to pathological changes within the brain and its association with cognitive impairment.

From mechanisms to future therapy: a synopsis of isolated REM sleep behavior disorder as early synuclein-related disease

Parkinson disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy are synucleinopathies, characterized by neuronal loss, gliosis and the abnormal deposition of α-synuclein in vulnerable areas of the nervous system. Neurodegeneration begins however several years before clinical onset of motor, cognitive or autonomic symptoms. The isolated form of REM sleep behavior disorder (RBD), a parasomnia with dream enactment behaviors and excessive muscle activity during REM sleep, is an early stage synucleinopathy. The neurophysiological hallmark of RBD is REM sleep without atonia (RWSA), i.e. the loss of physiological muscle atonia during REM sleep. RBD pathophysiology is not fully clarified yet, but clinical and basic science suggest that ɑ-syn pathology begins in the lower brainstem where REM atonia circuits are located, including the sublaterodorsal tegmental/subcoeruleus nucleus and the ventral medulla, then propagates rostrally to brain regions such as the substantia nigra, limbic system, cortex. Genetically, there is only a partial overlap between RBD, PD and DLB, and individuals with iRBD may represent a specific subpopulation. A genome-wide association study identified five loci, which all seem to revolve around the GBA1 pathway. iRBD patients often show subtle motor, cognitive, autonomic and/or sensory signs, neuroimaging alterations as well as biofluid and tissue markers of neurodegeneration (in particular pathologic α-synuclein aggregates), which can be useful for risk stratification. Patients with iRBD represent thus the ideal population for neuroprotective/neuromodulating trials. This review provides insights into these aspects, highlighting and substantiating the central role of iRBD in treatment development strategies for synucleinopathies.

A brain DNA co-methylation network analysis of psychosis in Alzheimer's disease

INTRODUCTION

The presence of psychosis in Alzheimer's disease (AD) is suggested to be associated with distinct molecular and neuropathological profiles in the brain.

METHODS

We assessed brain DNA methylation in AD donors with psychosis (AD+P) and without psychosis (AD-P) using the EPIC array. Weighted gene correlation network analysis identified modules of co-methylated genes in a discovery cohort (PITT-ADRC: N = 113 AD+P, N = 40 AD-P), with validation in an independent cohort (BDR: N = 79 AD+P, N = 117 AD-P), with Gene Ontology and cell-type enrichment analysis. Genetic data were integrated to identify methylation quantitative trait loci (mQTLs), which were co-localized with GWAS for related traits.

RESULTS

We replicated one AD+P associated module, which was enriched for synaptic pathways and in excitatory and inhibitory neurons. mQTLs in this module co-localized with variants associated with schizophrenia and educational attainment.

DISCUSSION

This represents the largest epigenetic study of AD+P to date, identifying pleiotropic relationships between AD+P and related traits.

HIGHLIGHTS

DNA methylation was assessed in the prefrontal cortex in subjects with AD+P and AD-P. WGCNA identified six modules of co-methylated loci associated with AD+P in a discovery cohort. One of the modules was replicated in an independent cohort. This module was enriched for synaptic genes and in excitatory and inhibitory neurons. mQTLs mapping to genes in the module co-localized with GWAS loci for schizophrenia and educational attainment.

Mapping the microRNA landscape in the older adult brain and its genetic contribution to neuropsychiatric conditions

MicroRNAs (miRNAs) play a crucial role in regulating gene expression and influence many biological processes. Despite their importance, understanding of how genetic variation affects miRNA expression in the brain and how this relates to brain disorders remains limited. Here we investigated these questions by identifying microRNA expression quantitative trait loci (miR-QTLs), or genetic variants associated with brain miRNA levels, using genome-wide small RNA sequencing profiles from dorsolateral prefrontal cortex samples of 604 older adult donors of European ancestry. Here we show that nearly half (224 of 470) of the analyzed miRNAs have associated miR-QTLs, many of which fall in regulatory regions such as brain promoters and enhancers. We also demonstrate that intragenic miRNAs often have genetic regulation independent from their host genes. Furthermore, by integrating our findings with 16 genome-wide association studies of psychiatric and neurodegenerative disorders, we identified miRNAs that likely contribute to bipolar disorder, depression, schizophrenia and Parkinson's disease. These findings advance understanding of the genetic regulation of miRNAs and their role in brain health and disease.

Investigating the causal relationships between lipid traits and dementia with lewy bodies: A mendelian randomization study

BACKGROUND

Disruptions in lipid metabolism have been implicated in various neurodegenerative diseases. However, the specific role of lipid species in the pathogenesis of dementia with Lewy bodies (DLB) remains poorly understood. This study aims to investigate potential causal relationships between lipid traits and DLB risk using Mendelian randomization (MR).

METHODS

We employed MR analysis to assess causal associations between 179 lipid traits and DLB, utilizing data from comprehensive genome-wide association studies (GWAS). The lipid-related GWAS included 7174 participants, and the DLB-related GWAS included 2981 DLB cases and 4391 healthy controls.

RESULTS

Genetic predispositions to increased levels of phosphatidylinositol (PI) (18:1_20:4) were associated with an elevated risk of DLB. Conversely, genetic predispositions to increased levels of specific phosphatidylcholine (PC) species, including PC (O-18:1_20:4), PC (O-16:0_20:4) and PC (O-18:0_20:4), were found to be protective against DLB. Sensitivity analyses revealed no evidence of heterogeneity or horizontal pleiotropy among the selected instrumental variables.

CONCLUSIONS

Our MR study identifies specific lipid species potentially causally linked to DLB risk. Elevated levels of PI (18:1_20:4) were associated with increased DLB risk, while higher levels of certain PC species were found to be protective. These findings offer new insights into the lipid-related mechanisms underlying DLB pathogenesis and highlight potential therapeutic targets.

Genomic and Transcriptomic Approaches Advance the Diagnosis and Prognosis of Neurodegenerative Diseases

Neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS), represent a growing societal challenge due to their irreversible progression and significant impact on patients, caregivers, and healthcare systems. Despite advances in clinical and imaging-based diagnostics, these diseases are often detected at advanced stages, limiting the effectiveness of therapeutic interventions. Recent breakthroughs in genomic and transcriptomic technologies, including whole-genome sequencing, single-cell RNA sequencing (scRNA-seq), and CRISPR-based screens, have revolutionized the field, offering new avenues for early diagnosis and personalized prognosis. Genomic approaches have elucidated disease-specific genetic risk factors and molecular pathways, while transcriptomic studies have identified stage-specific biomarkers that correlate with disease progression and severity. Furthermore, genome-wide association studies (GWAS), polygenic risk scores (PRS), and spatial transcriptomics are enabling the stratification of patients based on their risk profiles and prognostic trajectories. Advances in functional genomics have uncovered actionable targets, such as ATXN2 in ALS and TREM2 in AD, paving the way for tailored therapeutic strategies. Despite these achievements, challenges remain in translating genomic discoveries into clinical practice due to disease heterogeneity and the complexity of neurodegenerative pathophysiology. Future integration of genetic technologies holds promise for transforming diagnostic and prognostic paradigms, offering hope for improved patient outcomes and precision medicine approaches.

Association between osteoarthritis and cognitive function: results from the NHANES 2011-2014 and Mendelian randomization study

Background

Previous meta-analyses have demonstrated osteoarthritis (OA) is associated with an increased risk of dementia, but these studies were prone to bias based on residual confounding factors and reverse causality.

Objectives

We aimed to investigate associations between OA and cognitive function using data from the National Health and Nutrition Examination Survey (NHANES) and to investigate the causality using Mendelian randomization (MR).

Design

This is a cross-sectional study and MR study.

Methods

Data from the NHANES 2011-2014 were used. Multiple linear, logistic regressions and stratified analyses were used to determine the association between OA status and cognitive function. Sample weights were used to ensure result generalizability. Two-sample MR analysis was conducted to examine the association between OA and dementia. Mediation analyses were performed to investigate the mediating effects of depression.

Results

We did not demonstrate a significant association between OA and cognitive performance after adjusting for relevant covariates (p > 0.05), and the population of individuals with both OA and depression was associated with higher odds of low total word recall cognitive performance (odds ratio (OR) = 4.74, 95% confidence interval (CI): 1.09-20.63; p = 0.04). Genetically predicted specific-site OA was not significantly associated with the risk of dementia (OR = 1.12; 95% CI: 0.96-1.32; p = 0.16), Alzheimer's disease (OR = 0.95, 95% CI: 0.68-1.31, p = 0.74), vascular dementia (OR = 1.32, 95% CI: 0.82-2.13, p = 0.25) with accepted heterogeneity and no evidence of directional pleiotropy. Furthermore, major depression was found to mediate the pathway between OA and vascular dementia (β = 0.044, 95% CI: -0.391 to 0.479, p < 0.05).

Conclusion

Our findings indicate that there is no significant association or causal relationship between OA and cognitive decline. However, depression may serve as an important factor influencing cognitive outcomes. Future research should further explore the bidirectional causal relationship and underlying mechanisms.

The causal role of lipids in dementia: A Mendelian randomization study

Background

Increasing evidence suggests that abnormal lipid metabolism is one of the pathogeneses of dementia. It is necessary to reveal the relationship between lipids and dementia.

Objective

This study used bidirectional two-sample Mendelian randomization to explore the causal relationship between 179 lipid species and the risk of dementia.

Methods

We assessed the causal effects of 179 lipid species and four subtypes of dementia including Alzheimer's disease (AD), vascular dementia (VaD), frontotemporal dementia (FTD), and dementia with Lewy bodies (DLB). Inverse variance weighting, MR-Egger method, weighted median, simple mode, and weighted mode were used to analyze the relationship between lipids and dementia. Cochran's Q, MR-Egger intercept test, and MR-PRESSO test were used to test the heterogeneity and pleiotropy of the results. In addition, we performed an inverse MR analysis testing the causal effects of dementia on lipids.

Results

Our study revealed causal effects of glycerophospholipid, glycerolipid, and sterol on the risk of dementia. Phosphatidylcholine, phosphatidylinositol, and triglycerides play significant roles in AD. Notably, phosphatidylcholine played a protective role in both FTD and DLB. However, this study did not observe a significant effect of phosphatidylinositol on FTD. In the case of VaD, not only glycerophospholipid, but also glycerolipid, exerted an influence, but sterol was also a risk factor.

Conclusions

Our study provided new evidence supporting the causal role of genetically predicted lipid species in dementia. Future clinical trials are necessary to evaluate the potential role of lipid levels in dementia prevention.

Scrutinizing neurodegenerative diseases: decoding the complex genetic architectures through a multi-omics lens

Neurodegenerative diseases present complex genetic architectures, reflecting a continuum from monogenic to oligogenic and polygenic models. Recent advances in multi-omics data, coupled with systems genetics, have significantly refined our understanding of how these data impact neurodegenerative disease mechanisms. To contextualize these genetic discoveries, we provide a comprehensive critical overview of genetic architecture concepts, from Mendelian inheritance to the latest insights from oligogenic and omnigenic models. We explore the roles of common and rare genetic variants, gene-gene and gene-environment interactions, and epigenetic influences in shaping disease phenotypes. Additionally, we emphasize the importance of multi-omics layers including genomic, transcriptomic, proteomic, epigenetic, and metabolomic data in elucidating the molecular mechanisms underlying neurodegeneration. Special attention is given to missing heritability and the contribution of rare variants, particularly in the context of pleiotropy and network pleiotropy. We examine the application of single-cell omics technologies, transcriptome-wide association studies, and epigenome-wide association studies as key approaches for dissecting disease mechanisms at tissue- and cell-type levels. Our review introduces the OmicPeak Disease Trajectory Model, a conceptual framework for understanding the genetic architecture of neurodegenerative disease progression, which integrates multi-omics data across biological layers and time points. This review highlights the critical importance of adopting a systems genetics approach to unravel the complex genetic architecture of neurodegenerative diseases. Finally, this emerging holistic understanding of multi-omics data and the exploration of the intricate genetic landscape aim to provide a foundation for establishing more refined genetic architectures of these diseases, enhancing diagnostic precision, predicting disease progression, elucidating pathogenic mechanisms, and refining therapeutic strategies for neurodegenerative conditions.

Comparative mapping of single-cell transcriptomic landscapes in neurodegenerative diseases

INTRODUCTION

Alzheimer's disease (AD), Dementia with Lewy bodies (DLB), and Parkinson's disease (PD) represent a spectrum of neurodegenerative disorders (NDDs). Here, we performed the first direct comparison of their transcriptomic landscapes.

METHODS

We profiled the whole transcriptomes of NDD cortical tissue by snRNA-seq. We used computational analyses to identify common and distinct differentially expressed genes (DEGs), biological pathways, vulnerable and disease-driver cell subtypes, and alteration in cell-to-cell interactions.

RESULTS

The same vulnerable inhibitory neuron subtype was depleted in both AD and DLB. Potentially disease-driving neuronal cell subtypes were present in both PD and DLB. Cell-cell communication was predicted to be increased in AD but decreased in DLB and PD. DEGs were most commonly shared across NDDs within inhibitory neuron subtypes. Overall, we observed the greatest transcriptomic divergence between AD and PD, while DLB exhibited an intermediate transcriptomic signature.

DISCUSSION

These results help explain the clinicopathological spectrum of this group of NDDs and provide unique insights into the shared and distinct molecular mechanisms underlying the pathogenesis of NDDs.

What is the future for dementia with Lewy bodies?

Dementia with Lewy bodies (DLB) is the second most common neurodegenerative dementia after Alzheimer's disease (AD), yet it remains under-recognized and frequently misdiagnosed due to heterogenous clinical presentations, the presence of co-pathology, and the lack of specific diagnostic tools. Pathologically, DLB is characterized by the accumulation of misfolded alpha-synuclein (aSyn) aggregates, known as Lewy bodies. Recent advancements have improved in vivo detection of aSyn pathology through techniques such as seed amplification assays, monoclonal antibodies, and positron emission tomography using novel small-molecule ligands. The ability to detect aSyn in vivo has sparked dialogue about using biomarkers to identify individuals with aSyn, similar to the approach influencing the field of AD. Proponents argue that biological staging could facilitate the detection of preclinical disease stages, allowing for earlier intervention and targets for disease modification, and could improve diagnostic sensitivity and accuracy in selecting patients for clinical trials. However, critics caution that this method may oversimplify the complexity of DLB and overlook its clinical heterogeneity, also highlighting practical challenges related to implementation, cost, and global access to advanced diagnostic technologies. Importantly, although significant progress has been made in detecting aSyn for diagnostic purposes, disease-modifying therapies targeting aSyn have yet to demonstrate clear efficacy in slowing disease progression. Elucidating the physiological and pathophysiological roles of aSyn remains an urgent priority in neurodegenerative research. Other experimental research priorities for DLB include developing improved cellular and animal models that reflect epigenetic and environmental factors, mapping post-translational modifications, and systematically characterizing neurons that are vulnerable and resistant to lewy pathology using a multi-omic approach. Clinically, there is an urgent need for international, prospective, longitudinal studies and for validated, disease-specific outcome measures. Addressing these priorities is essential for advancing our understanding of DLB and developing effective therapies.

Lewy Body Dementia

OBJECTIVE

Lewy body dementia (LBD) is an umbrella term describing two closely related conditions: Parkinson disease dementia (PDD) and dementia with Lewy bodies (DLB). LBD is the second most common cause of neurodegenerative dementia but is often underrecognized in clinical practice. This review covers the key epidemiologic, clinical, cognitive, behavioral, and biomarker features of LBD and discusses current treatment options.

LATEST DEVELOPMENTS

Indicative biomarkers of LBD improve the ability to make a diagnosis and include single-photon emission computed tomography (SPECT) of the dopamine system (brain) and the noradrenergic system (cardiac), and polysomnography. α-Synuclein-specific biomarkers in spinal fluid, skin, plasma, and brain imaging are in active development with some available for clinical use. Prodromal stages of PDD and DLB have been contextualized, and diagnostic criteria have been published. An emerging theme is whether an integrated staging system focusing on protein aggregation, rather than clinical symptoms, may advance research efforts.

ESSENTIAL POINTS

LBD is a common cause of cognitive impairment in older adults but is often subject to significant delays in diagnosis and treatment, increasing the burden on patients and family care partners. Understanding key features of disease and the use of biomarkers will improve recognition. Earlier detection may also facilitate the development of new therapeutics and enrollment in clinical trials.

African ancestry neurodegeneration risk variant disrupts an intronic branchpoint in GBA1

Recently, an African ancestry-specific Parkinson disease (PD) risk signal was identified at the gene encoding glucocerebrosidase (GBA1). This variant ( rs3115534 -G) is carried by ~50% of West African PD cases and imparts a dose-dependent increase in risk for disease. The risk variant has varied frequencies across African ancestry groups but is almost absent in European and Asian ancestry populations. GBA1 is a gene of high clinical and therapeutic interest. Damaging biallelic protein-coding variants cause Gaucher disease and monoallelic variants confer risk for PD and dementia with Lewy bodies, likely by reducing the function of glucocerebrosidase. Interestingly, the African ancestry-specific GBA1 risk variant is a noncoding variant, suggesting a different mechanism of action. Using full-length RNA transcript sequencing, we identified partial intron 8 expression in risk variant carriers (G) but not in nonvariant carriers (T). Antibodies targeting the N terminus of glucocerebrosidase showed that this intron-retained isoform is likely not protein coding and subsequent proteomics did not identify a shorter protein isoform, suggesting that the disease mechanism is RNA based. Clustered regularly interspaced short palindromic repeats editing of the reported index variant ( rs3115534 ) revealed that this is the sequence alteration responsible for driving the production of these transcripts containing intron 8. Follow-up analysis of this variant showed that it is in a key intronic branchpoint sequence and, therefore, has important implications in splicing and disease. In addition, when measuring glucocerebrosidase activity, we identified a dose-dependent reduction in risk variant carriers. Overall, we report the functional effect of a GBA1 noncoding risk variant, which acts by interfering with the splicing of functional GBA1 transcripts, resulting in reduced protein levels and reduced glucocerebrosidase activity. This understanding reveals a potential therapeutic target in an underserved and underrepresented population.

Pervasive biases in proxy genome-wide association studies based on parental history of Alzheimer's disease

Almost every recent Alzheimer's disease (AD) genome-wide association study (GWAS) has performed meta-analysis to combine studies with clinical diagnosis of AD with studies that use proxy phenotypes based on parental disease history. Here, we report major limitations in current GWAS-by-proxy (GWAX) practices due to uncorrected survival bias and nonrandom participation in parental illness surveys, which cause substantial discrepancies between AD GWAS and GWAX results. We demonstrate that the current AD GWAX provide highly misleading genetic correlations between AD risk and higher education, which subsequently affects a variety of genetic epidemiological applications involving AD and cognition. Our study sheds light on potential issues in the design and analysis of middle-aged biobank cohorts and underscores the need for caution when interpreting genetic association results based on proxy-reported parental disease history.

Genetics and Neuropathology of Neurodegenerative Dementias

OBJECTIVE

This article provides an overview of the current understanding of the genetic and pathologic features of neurodegenerative dementias, with an emphasis on Alzheimer disease and related dementias.

LATEST DEVELOPMENTS

In recent years, there has been substantial progress in genetic research, contributing significant knowledge to our understanding of the molecular risk factors involved in neurodegenerative dementia syndromes. Several genes have been linked to monogenic forms of dementia (eg, APP, PSEN1, PSEN2, SNCA, GRN, C9orf72, MAPT) and an even larger number of genetic variants are known to influence susceptibility for developing dementia. As anti-amyloid therapies for patients with early-stage Alzheimer disease have entered the clinical arena, screening for the apolipoprotein E ε4 high-risk allele has come into focus, emphasizing the importance of genetic counseling. Similarly, advances in the pathologic classifications of neurodegenerative dementia syndromes and molecular pathology highlight their heterogeneity and overlapping features and provide insights into the pathogenesis of these conditions.

ESSENTIAL POINTS

Recent progress in neurogenetics and molecular pathology has improved our understanding of the complex pathogenetic changes associated with neurodegenerative dementias, facilitating improved disease modeling, enhanced diagnostics, and individualized counseling. The hope is that this knowledge will ultimately pave the way for the development of novel therapeutics.

Association between dementia, Alzheimer's disease, and liver cancer: A Mendelian randomization analysis

Background

Epidemiological studies have indicated an inverse association between neurodegenerative diseases and cancer. However, the relationship between liver cancer and dementia, particularly Alzheimer's disease (AD), remains underexplored.

Objective

This study aimed to determine the association between dementia, specifically AD, and liver cancer using Mendelian randomization (MR) analysis.

Methods

We conducted a bidirectional, two-sample MR analysis using publicly available genome-wide association studies data. The inverse-variance weighted method was employed as the primary analytical approach. To detect and correct for the effects of horizontal pleiotropy, we applied three complementary methods: MR Egger, weighted median, and Maximum likelihood.

Results

The analysis indicated significant associations between dementia and a reduced risk of hepatocellular carcinoma (HCC) (OR: 0.87; 95%CI: 0.81-0.95; p < 0.001) and intrahepatic cholangiocarcinoma (ICC) (OR: 0.81; 95%CI: 0.72-0.92; p < 0.001). AD was significantly associated with a decreased risk of HCC (OR: 0.94; 95%CI: 0.88-0.99; p = 0.033), ICC (OR: 0.85; 95%CI: 0.78-0.93; p < 0.001), and combined hepatocellular-cholangiocarcinoma (CHC) (OR: 0.64; 95%CI: 0.43-0.93; p = 0.020). Conversely, inverse MR analyses indicated that ICC was associated with increased dementia risk (OR: 1.05; 95%CI: 1.01-1.09; p = 0.019) and CHC with increased AD risk (OR: 1.03; 95%CI: 1.00-1.04; p = 0.014).

Conclusions

This study suggests that dementia, particularly AD, is associated with a reduced risk of liver cancer. Conversely, liver cancer may be associated with a slightly increased risk of developing dementia and AD, although some observational studies have reported a lower risk of these conditions among cancer survivors.

Whole-genome sequencing to identify rare variants in East Asian patients with dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is the second most common form of age-related dementia, following Alzheimer's disease (AD). DLB is associated with a worse prognosis than AD and is characterized by a more rapid progression of cognitive impairment and a poorer quality of life. In addition, the pathogenesis of DLB is less understood than that of AD, and only three genes-SNCA (α-synuclein), APOE (apolipoprotein E), and GBA1 (glucosylceramidase beta 1)-have been convincingly demonstrated to be associated with DLB. In this study, we utilized whole-genome sequencing data from 1744 Japanese individuals, comprising 45 DLB patients and 1699 cognitively normal older adults, aiming to identify new genes associated with DLB. Our genome-wide association studies of genes with potentially deleterious mutations identified the CDH23 gene as being associated with DLB, reaching a Bonferroni-corrected significance (P = 7.43 × 10-4). The gene contained three ethnicity-specific heterozygous missense variants (rs181275139, rs563688802, and rs137937502). CDH23 has been linked to deafness syndromes, and DLB patients carrying these mutations displayed symptoms of subjective hearing loss, suggesting a potential association between DLB onset and auditory impairment. Additionally, we explored human leukocyte antigen (HLA) genotypes associated with DLB but found no significant associations. This result suggests that the pathology of DLB differs from that of Parkinson's disease, which has been reported to have an association with HLA. Although a limitation of this study is the lack of replication of our findings, which require further validation in independent cohorts, our study enhances the understanding of the etiology of DLB in the Japanese population and provides new insights into the underlying mechanisms of its pathogenesis.

Genetic-based diagnostics of Parkinson's disease and other Parkinsonian syndromes

INTRODUCTION

Parkinson's disease (PD) is a complex disorder with vast clinical heterogeneity. Recent genetic, imaging and clinical evidence suggest that there are multiple subtypes of PD, and perhaps even distinct clinical entities, which are being diagnosed under the umbrella of PD. These might have similar clinical presentation, but potentially different underlying mechanisms, which, in future, will require different treatments. Despite extensive genetic research progress, genetic testing is still not a common practice in clinical patient care.

AREAS COVERED

This review examines the numerous genes that have been discovered to affect the risk of, or cause, PD. We also outline genetic variants that affect PD age at onset, its progression, and the presence or severity of motor and non-motor symptoms. We differentiate between PD, other synucleinopathies, and atypical parkinsonism syndromes, and describe genes responsible for familial forms of typical PD and atypical parkinsonism. Lastly, we present current clinical trails that are underway for targeted therapies, particularly for GBA1-PD and LRRK2-PD which are the most significant subtypes.

EXPERT OPINION

While genetic studies alone cannot be diagnostic for PD, proper utilization of genetic screening for PD could improve diagnostic accuracy and predictions for prognosis, guide treatment, and identify individuals that qualify for clinical trials.

Mechanism-free repurposing of drugs for C9orf72-related ALS/FTD using large-scale genomic data

Repeat expansions in the C9orf72 gene are the most common genetic cause of (ALS) and frontotemporal dementia (FTD). Like other genetic forms of neurodegeneration, pinpointing the precise mechanism(s) by which this mutation leads to neuronal death remains elusive, and this lack of knowledge hampers the development of therapy for C9orf72-related disease. We used an agnostic approach based on genomic data (n = 41,273 ALS and healthy samples, and n = 1,516 C9orf72 carriers) to overcome these bottlenecks. Our drug-repurposing screen, based on gene- and expression-pattern matching and information about the genetic variants influencing onset age among C9orf72 carriers, identified acamprosate, a γ-aminobutyric acid analog, as a potentially repurposable treatment for patients carrying C9orf72 repeat expansions. We validated its neuroprotective effect in cell models and showed comparable efficacy to riluzole, the current standard of care. Our work highlights the potential value of genomics in repurposing drugs in situations where the underlying pathomechanisms are inherently complex. VIDEO ABSTRACT.