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Kalincik T, Roos I, Sharmin S, Malpas CB. Methodological considerations for observational studies of treatment effectiveness in neurology: a clinician's guide. J Neurol Neurosurg Psychiatry 2024; 95:454-460. [PMID: 37890986 DOI: 10.1136/jnnp-2022-330038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Accepted: 09/20/2023] [Indexed: 10/29/2023]
Abstract
Data from cohorts, registries, randomised trials, electronic medical records and administrative claims databases have increasingly been used to inform the use of therapies for neurological diseases. While novel sophisticated methods are enabling us to use existing data to guide treatment decisions, the complexity of statistical methodology is making appraisal of clinical evidence increasingly demanding. In this narrative review, we provide a brief overview of the most commonly used methods for evaluation of treatment effectiveness in neurology. This primer discusses complementarity of randomised and non-randomised study designs, sources of observational data, different forms of bias and the appropriate mitigation strategies, statistical significance, Bayesian approaches and provides an overview of multivariable regression models, propensity score-based models, causal inference, mediation analysis and Mendelian randomisation.
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Affiliation(s)
- Tomas Kalincik
- CORe, Department of Medicine, The University of Melbourne, Melbourne, Victoria, Australia
- Neuroimmunology Centre, Department of Neurology, Royal Melbourne Hospital, Melbourne, Victoria, Australia
| | - Izanne Roos
- CORe, Department of Medicine, The University of Melbourne, Melbourne, Victoria, Australia
- Neuroimmunology Centre, Department of Neurology, Royal Melbourne Hospital, Melbourne, Victoria, Australia
| | - Sifat Sharmin
- CORe, Department of Medicine, The University of Melbourne, Melbourne, Victoria, Australia
- Neuroimmunology Centre, Department of Neurology, Royal Melbourne Hospital, Melbourne, Victoria, Australia
| | - Charles B Malpas
- CORe, Department of Medicine, The University of Melbourne, Melbourne, Victoria, Australia
- Neuroimmunology Centre, Department of Neurology, Royal Melbourne Hospital, Melbourne, Victoria, Australia
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Hu X, Fang Z, Wang F, Mei Z, Huang X, Lin Y, Lin Z. A causal relationship between gut microbiota and subcortical brain structures contributes to the microbiota-gut-brain axis: a Mendelian randomization study. Cereb Cortex 2024; 34:bhae056. [PMID: 38415993 DOI: 10.1093/cercor/bhae056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 01/27/2024] [Accepted: 01/28/2024] [Indexed: 02/29/2024] Open
Abstract
A correlation between gut microbiota and brain structure, referring to as a component of the gut-brain axis, has been observed in observational studies. However, the causality of this relationship and its specific bacterial taxa remains uncertain. To reveal the causal effects of gut microbiota on subcortical brain volume, we applied Mendelian randomization (MR) studies in this study. Genome-wide association study data were obtained from the MiBioGen Consortium (n = 18,340) and the Enhancing Neuro Imaging Genetics through Meta-Analysis Consortium (n = 13,170). The primary estimate was obtained utilizing the inverse-variance weighted, while heterogeneity and pleiotropy were assessed using the Cochrane Q statistic, MR Pleiotropy RESidual Sum and Outlier, and MR-Egger intercept. Our findings provide strong evidence that a higher abundance of the genus Parasutterella is causally correlated with a decrease in intracranial volume (β = -30,921.33, 95% CI -46,671.78 to -15,170.88, P = 1.19 × 10-4), and the genus FamilyXIIIUCG001 is associated with a decrease in thalamus volume (β = -141.96, 95% CI: -214.81 to -69.12, P = 1.0× 10-4). This MR study offers novel perspectives on the intricate interplay between the gut microbiota and subcortical brain volume, thereby lending some support to the existence of the microbiota-gut-brain axis.
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Affiliation(s)
- Xuequn Hu
- Department of Neurosurgery, National Regional Medical Center, Binhai Campus of the First Affiliated Hospital, Fujian Medical University, 999 Huashan Road, Changle District, Fuzhou 350209, Fujian Province, China
- Department of Neurosurgery, Neurosurgery Research Institute, The First Affiliated Hospital, Fujian Medical University, 20 Chazhong Road, Taijiang District, Fuzhou 350005, Fujian Province, China
| | - Zhiyong Fang
- Department of Neurosurgery, National Regional Medical Center, Binhai Campus of the First Affiliated Hospital, Fujian Medical University, 999 Huashan Road, Changle District, Fuzhou 350209, Fujian Province, China
- Department of Neurosurgery, Neurosurgery Research Institute, The First Affiliated Hospital, Fujian Medical University, 20 Chazhong Road, Taijiang District, Fuzhou 350005, Fujian Province, China
| | - Feng Wang
- Department of Neurosurgery, National Regional Medical Center, Binhai Campus of the First Affiliated Hospital, Fujian Medical University, 999 Huashan Road, Changle District, Fuzhou 350209, Fujian Province, China
- Department of Neurosurgery, Neurosurgery Research Institute, The First Affiliated Hospital, Fujian Medical University, 20 Chazhong Road, Taijiang District, Fuzhou 350005, Fujian Province, China
| | - Zhen Mei
- Department of Neurosurgery, National Regional Medical Center, Binhai Campus of the First Affiliated Hospital, Fujian Medical University, 999 Huashan Road, Changle District, Fuzhou 350209, Fujian Province, China
- Department of Neurosurgery, Neurosurgery Research Institute, The First Affiliated Hospital, Fujian Medical University, 20 Chazhong Road, Taijiang District, Fuzhou 350005, Fujian Province, China
| | - Xiaofen Huang
- Department of Neurosurgery, National Regional Medical Center, Binhai Campus of the First Affiliated Hospital, Fujian Medical University, 999 Huashan Road, Changle District, Fuzhou 350209, Fujian Province, China
- Department of Neurosurgery, Neurosurgery Research Institute, The First Affiliated Hospital, Fujian Medical University, 20 Chazhong Road, Taijiang District, Fuzhou 350005, Fujian Province, China
| | - Yuanxiang Lin
- Department of Neurosurgery, National Regional Medical Center, Binhai Campus of the First Affiliated Hospital, Fujian Medical University, 999 Huashan Road, Changle District, Fuzhou 350209, Fujian Province, China
- Department of Neurosurgery, Neurosurgery Research Institute, The First Affiliated Hospital, Fujian Medical University, 20 Chazhong Road, Taijiang District, Fuzhou 350005, Fujian Province, China
| | - Zhangya Lin
- Department of Neurosurgery, National Regional Medical Center, Binhai Campus of the First Affiliated Hospital, Fujian Medical University, 999 Huashan Road, Changle District, Fuzhou 350209, Fujian Province, China
- Department of Neurosurgery, Neurosurgery Research Institute, The First Affiliated Hospital, Fujian Medical University, 20 Chazhong Road, Taijiang District, Fuzhou 350005, Fujian Province, China
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Huang LY, Ou YN, Yang YX, Wang ZT, Tan L, Yu JT. Associations of cardiovascular risk factors and lifestyle behaviors with neurodegenerative disease: a Mendelian randomization study. Transl Psychiatry 2023; 13:267. [PMID: 37488110 PMCID: PMC10366095 DOI: 10.1038/s41398-023-02553-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Revised: 06/29/2023] [Accepted: 06/30/2023] [Indexed: 07/26/2023] Open
Abstract
Previous observational studies reported that midlife clustering of cardiovascular risk factors and lifestyle behaviors were associated with neurodegenerative disease; however, these findings might be biased by confounding and reverse causality. This study aimed to investigate the causal associations of cardiovascular risk factors and lifestyle behaviors with neurodegenerative disease, using the two-sample Mendelian randomization design. Genetic variants for the modifiable risk factors and neurodegenerative disease were extracted from large-scale genome-wide association studies. The inverse-variance weighted method was used as the main analysis method, and MR-Egger regression and leave-one-out analyses were performed to identify potential violations. Genetically predicted diastolic blood pressure (DBP: OR per 1 mmHg, 0.990 [0.979-1.000]), body mass index (BMI: OR per 1 SD, 0.880 [0.825-0.939]), and educational level (OR per 1 SD, 0.698 [0.602-0.810]) were associated with lower risk of late-onset Alzheimer's disease (LOAD), while genetically predicted low-density lipoprotein (LDL: OR per 1 SD, 1.302 [1.066-1.590]) might increase LOAD risk. Genetically predicted exposures (including LDL and BMI) applied to familial AD showed the same effect. The association of LDL was also found with Amyotrophic lateral sclerosis (ALS) (LDL: OR per 1 SD, 1.180 [1.080-1.289]). This MR analysis showed that LDL, BMI, BP, and educational level were causally related to AD; a significant association between LDL and ALS risk, as well as the potential effect of sleep duration on PD risk, were also revealed. Targeting these modifiable factors was a promising strategy of neurodegenerative disease prevention.
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Affiliation(s)
- Liang-Yu Huang
- Department of Neurology, Qingdao Municipal Hospital, Qingdao University, Qingdao, China
| | - Ya-Nan Ou
- Department of Neurology, Qingdao Municipal Hospital, Qingdao University, Qingdao, China
| | - Yu-Xiang Yang
- Department of Neurology and Institute of Neurology, Huashan Hospital, State Key Laboratory of Medical Neurobiology and MOE Frontier Center for Brain Science, Shanghai Medical College, Fudan University, Shanghai, China
| | - Zuo-Teng Wang
- Department of Neurology, Qingdao Municipal Hospital, Qingdao University, Qingdao, China
| | - Lan Tan
- Department of Neurology, Qingdao Municipal Hospital, Qingdao University, Qingdao, China.
| | - Jin-Tai Yu
- Department of Neurology and Institute of Neurology, Huashan Hospital, State Key Laboratory of Medical Neurobiology and MOE Frontier Center for Brain Science, Shanghai Medical College, Fudan University, Shanghai, China.
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Cao J, Wang N, Luo Y, Ma C, Chen Z, Chenzhao C, Zhang F, Qi X, Xiong W. A cause-effect relationship between Graves' disease and the gut microbiome contributes to the thyroid-gut axis: A bidirectional two-sample Mendelian randomization study. Front Immunol 2023; 14:977587. [PMID: 36865531 PMCID: PMC9974146 DOI: 10.3389/fimmu.2023.977587] [Citation(s) in RCA: 17] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 01/23/2023] [Indexed: 02/16/2023] Open
Abstract
Background An association between Graves' disease (GD) and the gut microbiome has been identified, but the causal effect between them remains unclear. Methods Bidirectional two-sample Mendelian randomization (MR) analysis was used to detect the causal effect between GD and the gut microbiome. Gut microbiome data were derived from samples from a range of different ethnicities (18,340 samples) and data on GD were obtained from samples of Asian ethnicity (212,453 samples). Single nucleotide polymorphisms (SNPs) were selected as instrumental variables according to different criteria. They were used to evaluate the causal effect between exposures and outcomes through inverse-variance weighting (IVW), weighted median, weighted mode, MR-Egger, and simple mode methods. F-statistics and sensitivity analyses were performed to evaluate bias and reliability. Results In total, 1,560 instrumental variables were extracted from the gut microbiome data (p< 1 × 105). The classes Deltaproteobacteria [odds ratio (OR) = 3.603] and Mollicutes, as well as the genera Ruminococcus torques group, Oxalobacter, and Ruminococcaceae UCG 011 were identified as risk factors for GD. The family Peptococcaceae and the genus Anaerostipes (OR = 0.489) were protective factors for GD. In addition, 13 instrumental variables were extracted from GD (p< 1 × 10-8), causing one family and eight genera to be regulated. The genus Clostridium innocuum group (p = 0.024, OR = 0.918) and Anaerofilum (p = 0.049, OR = 1.584) had the greatest probability of being regulated. Significant bias, heterogeneity, and horizontal pleiotropy were not detected. Conclusion A causal effect relationship exists between GD and the gut microbiome, demonstrating regulatory activity and interactions, and thus providing evidence supporting the involvement of a thyroid-gut axis.
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Affiliation(s)
- Jiamin Cao
- Department of Ophthalmology, The Third Xiangya Hospital, Central South University, Hunan, China
| | - Nuo Wang
- Department of Ophthalmology, The Third Xiangya Hospital, Central South University, Hunan, China
| | - Yong Luo
- Department of Ophthalmology, The Third Xiangya Hospital, Central South University, Hunan, China
| | - Chen Ma
- Department of Ophthalmology, The Third Xiangya Hospital, Central South University, Hunan, China
| | - Zhuokun Chen
- Department of Ophthalmology, The Third Xiangya Hospital, Central South University, Hunan, China
| | - Changci Chenzhao
- Department of Ophthalmology, The Third Xiangya Hospital, Central South University, Hunan, China
| | - Feng Zhang
- Department of Ophthalmology, The Third Xiangya Hospital, Central South University, Hunan, China
| | - Xin Qi
- Department of Ophthalmology, The Second Xiangya Hospital, Central South University, Hunan, China
| | - Wei Xiong
- Department of Ophthalmology, The Third Xiangya Hospital, Central South University, Hunan, China
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Taschler B, Smith SM, Nichols TE. Causal inference on neuroimaging data with Mendelian randomisation. Neuroimage 2022; 258:119385. [PMID: 35714886 PMCID: PMC10933777 DOI: 10.1016/j.neuroimage.2022.119385] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Revised: 05/30/2022] [Accepted: 06/12/2022] [Indexed: 10/18/2022] Open
Abstract
While population-scale neuroimaging studies offer the promise of discovery and characterisation of subtle risk factors, massive sample sizes increase the power for both meaningful associations and those attributable to confounds. This motivates the need for causal modelling of observational data that goes beyond statements of association and towards deeper understanding of complex relationships between individual traits and phenotypes, clinical biomarkers, genetic variation, and brain-related measures of health. Mendelian randomisation (MR) presents a way to obtain causal inference on the basis of genetic data and explicit assumptions about the relationship between genetic variables, exposure and outcome. In this work, we provide an introduction to and overview of causal inference methods based on Mendelian randomisation, with examples involving imaging-derived phenotypes from UK Biobank to make these methods accessible to neuroimaging researchers. We motivate the use of MR techniques, lay out the underlying assumptions, introduce common MR methods and focus on several scenarios in which modelling assumptions are potentially violated, resulting in biased effect estimates. Importantly, we give a detailed account of necessary steps to increase the reliability of MR results with rigorous sensitivity analyses.
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Affiliation(s)
- Bernd Taschler
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
| | - Stephen M Smith
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Thomas E Nichols
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, City Oxford, UK
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Julian TH, Boddy S, Islam M, Kurz J, Whittaker KJ, Moll T, Harvey C, Zhang S, Snyder MP, McDermott C, Cooper-Knock J, Shaw PJ. A review of Mendelian randomization in amyotrophic lateral sclerosis. Brain 2022; 145:832-842. [PMID: 34791088 PMCID: PMC9050546 DOI: 10.1093/brain/awab420] [Citation(s) in RCA: 28] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2021] [Revised: 10/02/2021] [Accepted: 10/29/2021] [Indexed: 11/13/2022] Open
Abstract
Amyotrophic lateral sclerosis is a relatively common and rapidly progressive neurodegenerative disease that, in the majority of cases, is thought to be determined by a complex gene-environment interaction. Exponential growth in the number of performed genome-wide association studies combined with the advent of Mendelian randomization is opening significant new opportunities to identify environmental exposures that increase or decrease the risk of amyotrophic lateral sclerosis. Each of these discoveries has the potential to shape new therapeutic interventions. However, to do so, rigorous methodological standards must be applied in the performance of Mendelian randomization. We have reviewed Mendelian randomization studies performed in amyotrophic lateral sclerosis to date. We identified 20 Mendelian randomization studies, including evaluation of physical exercise, adiposity, cognitive performance, immune function, blood lipids, sleep behaviours, educational attainment, alcohol consumption, smoking and type 2 diabetes mellitus. We have evaluated each study using gold standard methodology supported by the Mendelian randomization literature and the STROBE-Mendelian randomization checklist. Where discrepancies exist between Mendelian randomization studies, we suggest the underlying reasons. A number of studies conclude that there is a causal link between blood lipids and risk of amyotrophic lateral sclerosis; replication across different datasets and even different populations adds confidence. For other putative risk factors, such as smoking and immune function, Mendelian randomization studies have provided cause for doubt. We highlight the use of positive control analyses in choosing exposure single nucleotide polymorphisms (SNPs) to make up the Mendelian randomization instrument, use of SNP clumping to avoid false positive results due to SNPs in linkage and the importance of multiple testing correction. We discuss the implications of survival bias for study of late age of onset diseases such as amyotrophic lateral sclerosis and make recommendations to mitigate this potentially important confounder. For Mendelian randomization to be useful to the amyotrophic lateral sclerosis field, high methodological standards must be applied to ensure reproducibility. Mendelian randomization is already an impactful tool, but poor-quality studies will lead to incorrect interpretations by a field that includes non-statisticians, wasted resources and missed opportunities.
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Affiliation(s)
- Thomas H Julian
- Department of Neuroscience, Sheffield Institute for Translational Neuroscience (SITraN), University of Sheffield, Sheffield, UK
| | - Sarah Boddy
- Department of Neuroscience, Sheffield Institute for Translational Neuroscience (SITraN), University of Sheffield, Sheffield, UK
| | - Mahjabin Islam
- Department of Neuroscience, Sheffield Institute for Translational Neuroscience (SITraN), University of Sheffield, Sheffield, UK
| | - Julian Kurz
- Department of Neuroscience, Sheffield Institute for Translational Neuroscience (SITraN), University of Sheffield, Sheffield, UK
| | - Katherine J Whittaker
- Department of Neuroscience, Sheffield Institute for Translational Neuroscience (SITraN), University of Sheffield, Sheffield, UK
| | - Tobias Moll
- Department of Neuroscience, Sheffield Institute for Translational Neuroscience (SITraN), University of Sheffield, Sheffield, UK
| | - Calum Harvey
- Department of Neuroscience, Sheffield Institute for Translational Neuroscience (SITraN), University of Sheffield, Sheffield, UK
| | - Sai Zhang
- Department of Genetics, Stanford University School of Medicine, Stanford, CA, USA
- Center for Genomics and Personalized Medicine, Stanford University School of Medicine, Stanford, CA, USA
| | - Michael P Snyder
- Department of Genetics, Stanford University School of Medicine, Stanford, CA, USA
- Center for Genomics and Personalized Medicine, Stanford University School of Medicine, Stanford, CA, USA
| | - Christopher McDermott
- Department of Neuroscience, Sheffield Institute for Translational Neuroscience (SITraN), University of Sheffield, Sheffield, UK
| | - Johnathan Cooper-Knock
- Department of Neuroscience, Sheffield Institute for Translational Neuroscience (SITraN), University of Sheffield, Sheffield, UK
| | - Pamela J Shaw
- Department of Neuroscience, Sheffield Institute for Translational Neuroscience (SITraN), University of Sheffield, Sheffield, UK
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Lu H, Wu PF, Ma DL, Zhang W, Sun M. Growth Factors and Their Roles in Multiple Sclerosis Risk. Front Immunol 2021; 12:768682. [PMID: 34745143 PMCID: PMC8566812 DOI: 10.3389/fimmu.2021.768682] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Accepted: 10/07/2021] [Indexed: 12/12/2022] Open
Abstract
Background Previous studies have suggested essential roles of growth factors on the risk of Multiple Sclerosis (MS), but it remains undefined whether the effects are causal. Objective We applied Mendelian randomization (MR) approaches to disentangle the causal relationship between genetically predicted circulating levels of growth factors and the risk of MS. Methods Genetic instrumental variables for fibroblast growth factor (FGF) 23, growth differentiation factor 15 (GDF15), insulin growth factor 1 (IGF1), insulin-like growth factor binding proteins 3 (IGFBP3) and vascular endothelial growth factor (VEGF) were obtained from up-to-date genome-wide association studies (GWAS). Summary-level statistics of MS were obtained from the International Multiple Sclerosis Genetics Consortium, incorporating 14,802 subjects with MS and 26,703 healthy controls of European ancestry. Inverse-variance weighted (IVW) MR was used as the primary method and multiple sensitivity analyses were employed in this study. Results Genetically predicted circulating levels of FGF23 were associated with risk of MS. The odds ratio (OR) of IVW was 0.63 (95% confidence interval [CI], 0.49-0.82; p < 0.001) per one standard deviation increase in circulating FGF23 levels. Weighted median estimators also suggested FGF23 associated with lower MS risk (OR = 0.67; 95% CI, 0.51-0.87; p = 0.003). While MR-Egger approach provided no evidence of horizontal pleiotropy (intercept = -0.003, p = 0.95). Results of IVW methods provided no evidence for causal roles of GDF1, IGF1, IGFBP3 and VEGF on MS risks, and additional sensitivity analyses confirmed the robustness of these null findings. Conclusion Our results implied a causal relationship between FGF23 and the risk of MS. Further studies are warranted to confirm FGF23 as a genetically valid target for MS.
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Affiliation(s)
- Hui Lu
- Department of Neurology, Xuanwu Hospital, Capital Medical University, Beijing, China
| | - Peng-Fei Wu
- Center for Medical Genetics & Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, China.,Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States
| | - Deng-Lei Ma
- Department of Pharmacy, Xuanwu Hospital, Capital Medical University, Beijing, China
| | - Wan Zhang
- Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States.,Department of Biology, Boston University, Boston, MA, United States
| | - Meichen Sun
- Department of Neurology, Xuanwu Hospital, Capital Medical University, Beijing, China
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Gan-Or Z, Wood NW. Mendelian Randomization Studies: A Path to Better Understand Sex and Gender Differences in Parkinson's Disease? Mov Disord 2021; 36:2220-2222. [PMID: 34658065 DOI: 10.1002/mds.28765] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 07/30/2021] [Indexed: 11/09/2022] Open
Affiliation(s)
- Ziv Gan-Or
- The Neuro (Montreal Neurological Institute-Hospital), McGill University, Montreal, Quebec, Canada.,Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada.,Department of Human Genetics, McGill University, Montreal, Quebec, Canada
| | - Nicholas W Wood
- Department of Clinical and Movement Neurosciences, University College London Queen Square Institute of Neurology, London, UK
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Rawji V, Latorre A, Sharma N, Rothwell JC, Rocchi L. On the Use of TMS to Investigate the Pathophysiology of Neurodegenerative Diseases. Front Neurol 2020; 11:584664. [PMID: 33224098 PMCID: PMC7669623 DOI: 10.3389/fneur.2020.584664] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Accepted: 10/05/2020] [Indexed: 12/22/2022] Open
Abstract
Neurodegenerative diseases are a collection of disorders that result in the progressive degeneration and death of neurons. They are clinically heterogenous and can present as deficits in movement, cognition, executive function, memory, visuospatial awareness and language. Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation tool that allows for the assessment of cortical function in vivo. We review how TMS has been used for the investigation of three neurodegenerative diseases that differ in their neuroanatomical axes: (1) Motor cortex-corticospinal tract (motor neuron diseases), (2) Non-motor cortical areas (dementias), and (3) Subcortical structures (parkinsonisms). We also make four recommendations that we hope will benefit the use of TMS in neurodegenerative diseases. Firstly, TMS has traditionally been limited by the lack of an objective output and so has been confined to stimulation of the motor cortex; this limitation can be overcome by the use of concurrent neuroimaging methods such as EEG. Given that neurodegenerative diseases progress over time, TMS measures should aim to track longitudinal changes, especially when the aim of the study is to look at disease progression and symptomatology. The lack of gold-standard diagnostic confirmation undermines the validity of findings in clinical populations. Consequently, diagnostic certainty should be maximized through a variety of methods including multiple, independent clinical assessments, imaging and fluids biomarkers, and post-mortem pathological confirmation where possible. There is great interest in understanding the mechanisms by which symptoms arise in neurodegenerative disorders. However, TMS assessments in patients are usually carried out during resting conditions, when the brain network engaged during these symptoms is not expressed. Rather, a context-appropriate form of TMS would be more suitable in probing the physiology driving clinical symptoms. In all, we hope that the recommendations made here will help to further understand the pathophysiology of neurodegenerative diseases.
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Affiliation(s)
| | | | | | | | - Lorenzo Rocchi
- Department of Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom
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10
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Lowry JL, Ryan ÉB, Esengul YT, Siddique N, Siddique T. Intricacies of aetiology in intrafamilial degenerative disease. Brain Commun 2020; 2:fcaa120. [PMID: 33134917 PMCID: PMC7585693 DOI: 10.1093/braincomms/fcaa120] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Revised: 06/23/2020] [Accepted: 07/10/2020] [Indexed: 02/07/2023] Open
Abstract
The genetic underpinnings of late-onset degenerative disease have typically been determined by screening families for the segregation of genetic variants with the disease trait in affected, but not unaffected, individuals. However, instances of intrafamilial etiological heterogeneity, where pathogenic variants in a culprit gene are not shared among all affected family members, continue to emerge and confound gene-discovery and genetic counselling efforts. Discordant intrafamilial cases lacking a mutation shared by other affected family members are described as disease phenocopies. This description often results in an over-simplified acceptance of an environmental cause of disease in the phenocopy cases, while the role of intrafamilial genetic heterogeneity, shared de novo mutations or epigenetic aberrations in such families is often ignored. On a related note, it is now evident that the same disease-associated variant can be present in individuals exhibiting clinically distinct phenotypes, thereby genetically uniting seemingly unrelated syndromes to form a spectrum of disease. Herein, we discuss the intricacies of determining complex degenerative disease aetiology and suggest alternative mechanisms of disease transmission that may account for the apparent missing heritability of disease.
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Affiliation(s)
- Jessica L Lowry
- The Ken and Ruth Davee Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Éanna B Ryan
- The Ken and Ruth Davee Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.,Northwestern University Interdepartmental Neuroscience Program, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Y Taylan Esengul
- The Ken and Ruth Davee Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Nailah Siddique
- The Ken and Ruth Davee Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Teepu Siddique
- The Ken and Ruth Davee Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.,Northwestern University Interdepartmental Neuroscience Program, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.,Department of Cell and Developmental Biology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.,Department of Pathology Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
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