Stroke Genetics: Discovery, Insight Into Mechanisms, and Clinical Perspectives

The Spectrum of Cerebral Small Vessel Disease: Emerging Pathophysiologic Constructs and Management Strategies

Cerebral small vessel disease (CSVD) is a spectrum of disorders that affect small arterioles, venules, cortical and leptomeningeal vessels, perivascular spaces, and the integrity of neurovascular unit, blood brain barrier, and surrounding glia and neurons. CSVD is an important cause of lacunar ischemic stroke and sporadic hemorrhagic stroke, as well as dementia-which will constitute some of the most substantive population and public health challenges over the next century. This article provides an overview of updated pathophysiologic frameworks of CSVD; discusses common and underappreciated clinical and neuroimaging manifestations of CSVD; and reviews emerging genetic risk factors linked to sporadic CSVD.

Neglected Mendelian causes of stroke in adult Chinese patients who had an ischaemic stroke or transient ischaemic attack

BACKGROUND AND PURPOSE

Multiple factors play important roles in the occurrence and prognosis of stroke. However, the roles of monogenic variants in all-cause ischaemic stroke have not been systematically investigated. We aim to identify underdiagnosed monogenic stroke in an adult ischaemic stroke/transient ischaemic attack (TIA) cohort (the Third China National Stroke Registry, CNSR-III).

METHODS

Targeted next-generation sequencing for 181 genes associated with stroke was conducted on DNA samples from 10 428 patients recruited through CNSR-III. The genetic and clinical data from electronic health records (EHRs) were reviewed for completion of the diagnostic process. We assessed the percentages of individuals with pathogenic or likely pathogenic (P/LP) variants, and the diagnostic yield of pathogenic variants in known monogenic disease genes with associated phenotypes.

RESULTS

In total, 1953 individuals harboured at least one P/LP variant out of 10 428 patients. Then, 792 (7.6%) individuals (comprising 759 individuals harbouring one P/LP variant in one gene, 29 individuals harbouring two or more P/LP variants in different genes and 4 individuals with two P/LP variants in ABCC6) were predicted to be at risk for one or more monogenic diseases based on the inheritance pattern. Finally, 230 of 792 individuals manifested a clinical phenotype in the EHR data to support the diagnosis of stroke with a monogenic cause. The most diagnosed Mendelian cause of stroke in the cohort was cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy. There were no relationships between age or family history and the incidence of first symptomatic monogenic stroke in patients.

CONCLUSION

The rate of monogenic cause of stroke was 2.2% after reviewing the clinical phenotype. Possible reasons that Mendelian causes of stroke may be missed in adult patients who had an ischaemic stroke/TIA include a late onset of stroke symptoms, combination with common vascular risks and the absence of a prominent family history.

Machine Learning-Based Etiologic Subtyping of Ischemic Stroke Using Circulating Exosomal microRNAs

Ischemic stroke is a major cause of mortality worldwide. Proper etiological subtyping of ischemic stroke is crucial for tailoring treatment strategies. This study explored the utility of circulating microRNAs encapsulated in extracellular vesicles (EV-miRNAs) to distinguish the following ischemic stroke subtypes: large artery atherosclerosis (LAA), cardioembolic stroke (CES), and small artery occlusion (SAO). Using next-generation sequencing (NGS) and machine-learning techniques, we identified differentially expressed miRNAs (DEMs) associated with each subtype. Through patient selection and diagnostic evaluation, a cohort of 70 patients with acute ischemic stroke was classified: 24 in the LAA group, 24 in the SAO group, and 22 in the CES group. Our findings revealed distinct EV-miRNA profiles among the groups, suggesting their potential as diagnostic markers. Machine-learning models, particularly logistic regression models, exhibited a high diagnostic accuracy of 92% for subtype discrimination. The collective influence of multiple miRNAs was more crucial than that of individual miRNAs. Additionally, bioinformatics analyses have elucidated the functional implications of DEMs in stroke pathophysiology, offering insights into the underlying mechanisms. Despite limitations like sample size constraints and retrospective design, our study underscores the promise of EV-miRNAs coupled with machine learning for ischemic stroke subtype classification. Further investigations are warranted to validate the clinical utility of the identified EV-miRNA biomarkers in stroke patients.

Whole-genome sequencing identifies variants in ANK1, LRRN1, HAS1, and other genes and regulatory regions for stroke in type 1 diabetes

Individuals with type 1 diabetes (T1D) carry a markedly increased risk of stroke, with distinct clinical and neuroimaging characteristics as compared to those without diabetes. Using whole-exome or whole-genome sequencing of 1,051 individuals with T1D, we aimed to find rare and low-frequency genomic variants associated with stroke in T1D. We analysed the genome comprehensively with single-variant analyses, gene aggregate analyses, and aggregate analyses on genomic windows, enhancers and promoters. In addition, we attempted replication in T1D using a genome-wide association study (N = 3,945) and direct genotyping (N = 3,263), and in the general population from the large-scale population-wide FinnGen project and UK Biobank summary statistics. We identified a rare missense variant on SREBF1 exome-wide significantly associated with stroke (rs114001633, p.Pro227Leu, p-value = 7.30 × 10-8), which replicated for hemorrhagic stroke in T1D. Using gene aggregate analysis, we identified exome-wide significant genes: ANK1 and LRRN1 displayed replication evidence in T1D, and LRRN1, HAS1 and UACA in the general population (UK Biobank). Furthermore, we performed sliding-window analyses and identified 14 genome-wide significant windows for stroke on 4q33-34.1, of which two replicated in T1D, and a suggestive genomic window on LINC01500, which replicated in T1D. Finally, we identified a suggestively stroke-associated TRPM2-AS promoter (p-value = 5.78 × 10-6) with borderline significant replication in T1D, which we validated with an in vitro cell-based assay. Due to the rarity of the identified genetic variants, future replication of the genomic regions represented here is required with sequencing of individuals with T1D. Nevertheless, we here report the first genome-wide analysis on stroke in individuals with diabetes.

Stroke genetics and how it Informs novel drug discovery

INTRODUCTION

Stroke is one of the main causes of death and disability worldwide. Nevertheless, despite the global burden of this disease, our understanding is limited and there is still a lack of highly efficient etiopathology-based treatment. It is partly due to the complexity and heterogenicity of the disease. It is estimated that around one-third of ischemic stroke is heritable, emphasizing the importance of genetic factors identification and targeting for therapeutic purposes.

AREAS COVERED

In this review, the authors provide an overview of the current knowledge of stroke genetics and its value in diagnostics, personalized treatment, and prognostication.

EXPERT OPINION

As the scale of genetic testing increases and the cost decreases, integration of genetic data into clinical practice is inevitable, enabling assessing individual risk, providing personalized prognostic models and identifying new therapeutic targets and biomarkers. Although expanding stroke genetics data provides different diagnostics and treatment perspectives, there are some limitations and challenges to face. One of them is the threat of health disparities as non-European populations are underrepresented in genetic datasets. Finally, a deeper understanding of underlying mechanisms of potential targets is still lacking, delaying the application of novel therapies into routine clinical practice.

Cerebral Small Vessel Disease, Hypertension, and Vascular Contributions to Cognitive Impairment and Dementia

Hypertension-associated cerebral small vessel disease is a common finding in older people. Strongly associated with age and hypertension, small vessel disease is found at autopsy in over 50% of people aged ≥65 years, with a spectrum of clinical manifestations. It is the main cause of lacunar stroke and a major source of vascular contributions to cognitive impairment and dementia. The brain areas affected are subcortical and periventricular white matter and deep gray nuclei. Neuropathological sequelae are diffuse white matter lesions (seen as white matter hyperintensities on T2-weighted magnetic resonance imaging), small ischemic foci (lacunes or microinfarcts), and less commonly, subcortical microhemorrhages. The most common form of cerebral small vessel disease is concentric, fibrotic thickening of small penetrating arteries (up to 300 microns outer diameter) termed arteriolosclerosis. Less common forms are small artery atheroma and lipohyalinosis (the lesions described by C. Miller Fisher adjacent to lacunes). Other microvascular lesions that are not reviewed here include cerebral amyloid angiopathy and venous collagenosis. Here, we review the epidemiology, neuropathology, clinical management, genetics, preclinical models, and pathogenesis of hypertensive small vessel disease. Knowledge gaps include initiating factors, molecular pathogenesis, relationships between arterial pathology and tissue damage, possible reversibility, pharmacological targets, and molecular biomarkers. Progress is anticipated from multicell transcriptomic and proteomic profiling, novel experimental models and further target-finding and interventional clinical studies.

Novel signaling axis of FHOD1-RNF213-Col1α/Col3α in the pathogenesis of hypertension-induced tunica media thickening

Hypertension-induced tunica media thickening (TMT) is the most important fundamental for the subsequent complications like stroke and cardiovascular diseases. Pathogenically, TMT originates from both vascular smooth muscle cells (VSMCs) hypertrophy due to synthesizing more amount of intracellular contractile proteins and excess secretion of extracellular matrix. However, what key molecules are involved in the pathogenesis of TMT is unknown. We hypothesize that formin homology 2 domain-containing protein 1 (FHOD1), an amply expressed mediator for assembly of thin actin filament in VSMCs, is a key regulator for the pathogenesis of TMT. In this study, we found that FHOD1 expression and its phosphorylation/activation were both upregulated in the arteries of three kinds of hypertensive rats. Ang-II induced actin filament formation and hypertrophy through activation and upregulation of FHOD1 in VSMCs. Active FHOD1-mediated actin filament assembly and secretions of collagen-1α/collagen-3α played crucial roles in Ang-II-induced VSMCs hypertrophy in vitro and hypertensive TMT in vivo. Proteomics demonstrated that activated FL-FHOD1 or its C-terminal diaphanous-autoregulatory domain significantly upregulated RNF213 (ring finger protein 213), a 591-kDa cytosolic E3 ubiquitin ligase with its loss-of-functional mutations being a susceptibility gene for Moyamoya disease which has prominent tunica media thinning in both intracranial and systemic arteries. Mechanistically, activated FHOD1 upregulated its downstream effector RNF213 independently of its classical pathway of decreasing G-actin/F-actin ratio, transcription, and translation, but dependently on its C-terminus-mediated stabilization of RNF213 protein. FHOD1-RNF213 signaling dramatically promoted collagen-1α/collagen-3α syntheses in VSMCs. Our results discovered a novel signaling axis of FHOD1-RNF213-collagen-1α/collagen-3α and its key role in the pathogenesis of hypertensive TMT.

Unraveling Mechanisms of Cryptogenic Stroke at the Genetic Level: A Systematic Literature Review

Background A substantial proportion of ischemic strokes remain cryptogenic, which has important implications for secondary prevention. Identifying genetic variants related to mechanisms of stroke causes may provide a chance to clarify the actual causes of cryptogenic strokes. Methods and Results In a 2-step process, 2 investigators independently and systematically screened studies that reported genetic variants in regard to stroke causes that were published between January 1991 and April 2021. Studies on monogenetic disorders, investigation of vascular risk factors as the primary end point, reviews, meta-analyses, and studies not written in English were excluded. We extracted information on study types, ancestries, corresponding single nucleotide polymorphisms, and sample and effect sizes. There were 937 studies screened, and 233 were eligible. We identified 35 single nucleotide polymorphisms and allele variants that were associated with an overlap between cryptogenic strokes and another defined cause. Conclusions Associations of single variants with an overlap between cryptogenic stroke and another defined cause were limited to a few polymorphisms. A limitation of all studies is a low granularity of clinical data, which is of major importance in a complex disease such as stroke. Deep phenotyping is in supposed contradiction with large sample sizes but needed for genome-wide analyses. Future studies should attempt to address this restriction to advance the promising approach of elucidating the cause of stroke at the genetic level. Especially in a highly heterogenous disease such as ischemic stroke, genetics are promising to establish a personalized approach in diagnostics and treatment in the sense of precision medicine.

Association between genetic predisposition and disease burden of stroke in China: a genetic epidemiological study

Background

Stroke ranks second worldwide and first in China as a leading cause of death and disability. It has a polygenic architecture and is influenced by environmental and lifestyle factors. However, it remains unknown as to whether and how much the genetic predisposition of stroke is associated with disease burden.

Methods

Allele frequency from the whole genome sequencing data in the Chinese Millionome Database of 141,418 individuals and trait-specific polygenic risk score models were applied to estimate the provincial genetic predisposition to stroke, stroke-related risk factors and stroke-related drug response. Disease burden including mortality, disability-adjusted life years (DALYs), years of life lost(YLLs), years lived with disability (YLDs) and prevalence in China was collected from the Global Burden Disease study. The association between stroke genetic predisposition and the epidemiological burden was assessed and then quantified in both regression-based models and machine learning-based models at a provincial resolution.

Findings

Among the 30 administrative divisions in China, the genetic predisposition of stroke was characterized by a north-higher-than-south gradient (p < 0.0001). Genetic predisposition to stroke, blood pressure, body mass index, and alcohol use were strongly intercorrelated (rho >0.6; p < 0.05 after Bonferroni correction for each comparison). Genetic risk imposed an independent effect of approximately 1-6% on mortality, DALYs and YLLs.

Interpretation

The distribution pattern of stroke genetic predisposition is different at a macroscopic level, and it subtly but significantly impacts the epidemiological burden. Further research is warranted to identify the detailed aetiology and potential translation into public health measures.

Funding

Beijing Municipal Science and Technology Commission (Z191100006619106), CAMS Innovation Fund for Medical Sciences (CAMS-I2M, 2023-I2M-1-001), the National High Level Hospital Clinical Research Funding (2022-GSP-GG-17), National Natural Science Foundation of China (32000398, 32171441 to X.J.), Natural Science Foundation of Guangdong Province, China (2017A030306026 to X.J.), and National Key R&D Program of China (2022YFC2502402).

Association between HSPA8 Gene Variants and Ischemic Stroke: A Pilot Study Providing Additional Evidence for the Role of Heat Shock Proteins in Disease Pathogenesis

HSPA8 is involved in many stroke-associated cellular processes, playing a pivotal role in the protein quality control system. Here we report the results of the pilot study aimed at determining whether HSPA8 SNPs are linked to the risk of ischemic stroke (IS). DNA samples from 2139 Russians (888 IS patients and 1251 healthy controls) were genotyped for tagSNPs (rs1461496, rs10892958, and rs1136141) in the HSPA8 gene using probe-based PCR. SNP rs10892958 of HSPA8 was associated with an increased risk (risk allele G) of IS in smokers (OR = 1.37; 95% CI = 1.07-1.77; p = 0.01) and patients with low fruit and vegetable consumption (OR = 1.36; 95% CI = 1.14-1.63; p = 0.002). SNP rs1136141 of HSPA8 was also associated with an increased risk of IS (risk allele A) exclusively in smokers (OR = 1.68; 95% CI = 1.23-2.28; p = 0.0007) and in patients with a low fruit and vegetable intake (OR = 1.29; 95% CI = 1.05-1.60; p = 0.04). Sex-stratified analysis revealed an association of rs10892958 HSPA8 with an increased risk of IS in males (risk allele G; OR = 1.30; 95% CI = 1.05-1.61; p = 0.01). Thus, SNPs rs10892958 and rs1136141 in the HSPA8 gene represent novel genetic markers of IS.

The Future of Ischemic Stroke Diagnosis and a Review of Underrecognized Ischemic Stroke Etiologies

Accurate ischemic stroke etiologic determination and diagnosis form the foundation of excellent cerebrovascular care as from it stems initiation of the appropriate secondary prevention strategy as well as appropriate patient education regarding specific risk factors for that subtype. Recurrent stroke rates are highest among those patients who receive an incorrect initial stroke diagnosis. Patient distrust and patient reported depression are also higher. The cause of the ischemic stroke also informs predicted patient outcomes and the anticipated recovery trajectory. Finally, determining the accurate cause of the ischemic stroke provides the patient the opportunity to enroll in appropriate research studies studying mechanism, or targeting treatment approaches for that particular disease process. Advances in ischemic stroke research, imaging techniques, biomarkers, and the ability to rapidly perform genetic sequencing over the past decade have shown that classifying patients into large etiologic buckets may not always be appropriate and may represent one reason why some patients are labeled as cryptogenic, or for whom an underlying etiology is never found. Aside from the more traditional stroke mechanisms, there is new research emerging regarding clinical findings that are not normative, but the contributions to ischemic stroke are unclear. In this article, we first review the essential steps to accurate ischemic stroke etiologic classification and then transition to a discussion of embolic stroke of undetermined source (ESUS) and other new entities that have been postulated as causal in ischemic stroke (i.e., genetics and subclinical atherosclerosis). We also discuss the limitations that are inherent in the current ischemic stroke diagnostic algorithms and finally review the most recent studies regarding more uncommon diagnoses and the future of stroke diagnostics and classification.

Cerebral small vessel disease: Recent advances and future directions

Cerebral small vessel disease (SVD) causes lacunar stroke and intracerebral hemorrhage, and is the most common pathology underlying vascular cognitive impairment. Increasingly, the importance of other clinical features of SVD is being recognized including motor impairment, (vascular) parkinsonism, impaired balance, falls, and behavioral symptoms, such as depression, apathy, and personality change. Epidemiological data show a high prevalence of the characteristic magnetic resonance imaging (MRI) features of white matter hyperintensities and lacunar infarcts in community studies, and recent data suggest that it is also a major health burden in low- and middle-income countries. In this review, we cover advances in diagnosis, imaging, clinical presentations, pathogenesis, and treatment.The two most common pathologies underlying SVD are arteriolosclerosis caused by aging, hypertension, and other conventional vascular risk factors, and cerebral amyloid angiopathy (CAA) caused by vascular deposition of β-amyloid. We discuss the revised Boston criteria of CAA based on MRI features, which have been recently validated. Imaging is providing important insights into pathogenesis, including improved detection of tissue damage using diffusion tensor imaging (DTI) leading to its use to monitor progression and surrogate endpoints in clinical trials. Advanced MRI techniques can demonstrate functional or dynamic abnormalities of the blood vessels, while the high spatial resolution provided by ultrahigh field MRI at 7 T allows imaging of individual perforating arteries for the first time, and the measurement of flow velocity and pulsatility within these arteries. DTI and structural network analysis have highlighted the importance of network disruption in mediating the effect of different SVD pathologies in causing a number of symptoms, including cognitive impairment, apathy, and gait disturbance.Despite the public health importance of SVD, there are few proven treatments. We review the evidence for primary prevention, and recent data showing how intensive blood pressure lowering reduces white matter hyperintensities (WMH) progression and delays the onset of cognitive impairment. There are few treatments for secondary prevention, but a number of trials are currently evaluating novel treatment approaches. Recent advances have implicated molecular processes related to endothelial dysfunction, nitric oxide synthesis, blood-brain barrier integrity, maintenance and repair of the extracellular matrix, and inflammation. Novel treatment approaches are being developed to a number of these targets. Finally, we highlight the importance of large International collaborative initiatives in SVD to address important research questions and cover a number which have recently been established.

Applications of Extracellular Vesicles in Nervous System Disorders: An Overview of Recent Advances

Diseases affecting the brain and spinal cord fall under the umbrella term "central nervous system disease". Most medications used to treat or prevent chronic diseases of the central nervous system cannot cross the blood-brain barrier (BBB) and hence cannot reach their intended target. Exosomes facilitate cellular material movement and signal transmission. Exosomes can pass the blood-brain barrier because of their tiny size, high delivery efficiency, minimal immunogenicity, and good biocompatibility. They enter brain endothelial cells via normal endocytosis and reverse endocytosis. Exosome bioengineering may be a method to produce consistent and repeatable isolation for clinical usage. Because of their tiny size, stable composition, non-immunogenicity, non-toxicity, and capacity to carry a wide range of substances, exosomes are indispensable transporters for targeted drug administration. Bioengineering has the potential to improve these aspects of exosomes significantly. Future research into exosome vectors must focus on redesigning the membrane to produce vesicles with targeting abilities to increase exosome targeting. To better understand exosomes and their potential as therapeutic vectors for central nervous system diseases, this article explores their basic biological properties, engineering modifications, and promising applications.

Exosomes as CNS Drug Delivery Tools and Their Applications

Central nervous system (CNS) diseases threaten the health of people all over the world. However, due to the structural and functional particularities of the brain and spinal cord, CNS-targeted drug development is rather challenging. Exosomes are small cellular vesicles with lipid bilayers that can be secreted by almost all cells and play important roles in intercellular communication. The advantages of low immunogenicity, the ability to cross the blood-brain barrier, and the flexibility of drug encapsulation make them stand out among CNS drug delivery tools. Herein, we reviewed the research on exosomes in CNS drug delivery over the past decade and outlined the impact of the drug loading mode, administration route, and engineered modification on CNS targeting. Finally, we highlighted the problems and prospects of exosomes as CNS drug delivery tools.