Does Thrombosis Play a Causal Role in Lacunar Stroke and Cerebral Small Vessel Disease?

BACKGROUND: The importance of thromboembolism in the pathogenesis of lacunar stroke (LS), resulting from cerebral small vessel disease (cSVD), is debated, and although antiplatelets are widely used in secondary prevention after LS, there is limited trial evidence from well-subtyped patients to support this approach. We sought to evaluate whether altered anticoagulation plays a causal role in LS and cSVD using 2-sample Mendelian randomization. METHODS: From a recent genome-wide association study (n=81 190), we used 119 genetic variants associated with venous thrombosis at genome-wide significance (P<5*10-8) and with a linkage disequilibrium r2<0.001 as instrumental variables. We also used genetic associations with stroke from the GIGASTROKE consortium (62 100 ischemic stroke cases: 10 804 cardioembolic stroke, 6399 large-artery stroke, and 6811 LS). In view of the lower specificity for LS with the CT-based phenotyping mainly used in GIGASTROKE, we also used data from patients with magnetic resonance imaging-confirmed LS (n=3199). We also investigated associations with more chronic magnetic resonance imaging features of cSVD, namely, white matter hyperintensities (n=37 355) and diffusion tensor imaging metrics (n=36 533). RESULTS: Mendelian randomization analyses showed that genetic predisposition to venous thrombosis was associated with an increased odds of any ischemic stroke (odds ratio [OR], 1.19 [95% CI, 1.13-1.26]), cardioembolic stroke (OR, 1.32 [95% CI, 1.21-1.45]), and large-artery stroke (OR, 1.41 [95% CI, 1.26-1.57]) but not with LS (OR, 1.07 [95% CI, 0.99-1.17]) in GIGASTROKE. Similar results were found for magnetic resonance imaging-confirmed LS (OR, 0.94 [95% CI, 0.81-1.09]). Genetically predicted risk of venous thrombosis was not associated with imaging markers of cSVD. CONCLUSIONS: These findings suggest that altered thrombosis plays a role in the risk of cardioembolic and large-artery stroke but is not a causal risk factor for LS or imaging markers of cSVD. This raises the possibility that antithrombotic medication may be less effective in cSVD and underscores the necessity for further trials in well-subtyped cohorts with LS to evaluate the efficacy of different antithrombotic regimens in LS.

Association between APOE-ε4 allele and cognitive function is mediated by Alzheimer's disease pathology: a population-based autopsy study in an admixed sample.

BACKGROUND: Apolipoprotein E ε4 allele (APOE-ε4) is the main genetic risk factor for late-onset Alzheimer's disease (AD) and may impact cognitive function also via other neuropathological lesions. However, there is limited evidence available from diverse populations, as APOE associations with dementia seem to differ by race. Therefore, we aimed to evaluate the pathways linking APOE-ε4 to cognitive abilities through AD and non-AD neuropathology in an autopsy study with an admixed sample. METHODS: Neuropathological lesions were evaluated following international criteria using immunohistochemistry. Participants were classified into APOE-ε4 carriers (at least one ε4 allele) and non-carriers. Cognitive abilities were evaluated by the Clinical Dementia Rating Scale sum of boxes. Mediation analyses were conducted to assess the indirect association of APOE-ε4 with cognition through AD-pathology, lacunar infarcts, hyaline arteriosclerosis, cerebral amyloid angiopathy (CAA), Lewy body disease (LBD), and TAR DNA-binding protein 43 (TDP-43). RESULTS: We included 648 participants (mean age 75 ± 12 years old, mean education 4.4 ± 3.7 years, 52% women, 69% White, and 28% APOE-ε4 carriers). The association between APOE-ε4 and cognitive abilities was mediated by neurofibrillary tangles (ß = 0.88, 95% CI = 0.45; 1.38, p < 0.001) and neuritic plaques (ß = 1.36, 95% CI = 0.86; 1.96, p < 0.001). Lacunar infarcts, hyaline arteriosclerosis, CAA, LBD, and TDP-43 were not mediators in the pathway from APOE-ε4 to cognition. CONCLUSION: The association between APOE-ε4 and cognitive abilities was partially mediated by AD-pathology. On the other hand, cerebrovascular lesions and other neurodegenerative diseases did not mediate the association between APOE-ε4 and cognition.

Causal Effect of the 25-Hydroxyvitamin D Concentration on Cerebral Small Vessel Disease: A Mendelian Randomization Study.

BACKGROUND: Previous observational studies reported that a lower serum 25-hydroxyvitamin D [25(OH)D] concentration is associated with a higher burden of cerebral small vessel disease (cSVD). The causality of this association is uncertain, but it would be clinically important, given that 25(OH)D can be a target for intervention. We tried to examine the causal effect of 25(OH)D concentration on cSVD-related phenotypes using a Mendelian randomization approach. METHODS: Genetic instruments for each serum 25(OH)D concentration and cSVD-related phenotypes (lacunar stroke, white matter hyperintensity, cerebral microbleeds, and perivascular spaces) were derived from large-scale genome-wide association studies. We performed 2-sample Mendelian randomization analyses with multiple post hoc sensitivity analyses. A bidirectional Mendelian randomization approach was also used to explore the possibility of reverse causation. RESULTS: We failed to find any significant causal effect of 25(OH)D concentration on cSVD-related phenotypes (odds ratio [95% CI], 1.00 [0.87-1.16], 1.01 [0.96-1.07], 1.06 [0.85-1.33], 1.00 [0.97-1.03], 1.02 [0.99-1.04], 1.01 [0.99-1.04] for lacunar stroke, white matter hyperintensity, cerebral microbleeds, and white matter, basal ganglia, hippocampal perivascular spaces, respectively). These results were reproduced in the sensitivity analyses accounting for genetic pleiotropy. Conversely, when we examined the effects of cSVD phenotypes on 25(OH)D concentration, cerebral microbleeds were negatively associated with 25(OH)D concentration (0.94 [0.92-0.96]). CONCLUSIONS: Given the adequate statistical power (>0.8) of the analyses, our findings suggest that the previously reported association between 25(OH)D concentration and cSVD phenotypes might not be causal and partly attributed to reverse causation.

Human blood metabolites and lacunar stroke: A Mendelian randomization study.

BACKGROUND: Lacunar stroke accounts for a quarter of all strokes, but little is known about the underlying pathological mechanisms. Analysis of serum metabolites may allow better understanding of the underlying biological processes. Mendelian randomization (MR) can provide information on the causality of associations. AIMS: To identify causal relationships between serum metabolites and lacunar stroke. METHODS: We applied a two-sample MR analysis to evaluate relationships between 486 serum metabolites and lacunar stroke. The inverse-variance weighted (IVW) method was used to estimate the causal relationship of the exposure on the outcome, while sensitivity analyses were performed using MR-Egger, weighted median, and MR-PRESSO to eliminate the pleiotropy. We also performed a metabolic pathway analysis to identify potential metabolic pathways. RESULTS: We identified 15 known (8 risk and 7 protective) and 14 unknown serum metabolites associated with lacunar stroke. Among the known risk metabolites, two were lipids (1-linoleoylglycerophosphoethanolamine and dihomo-linolenate (20:3n3 or n6)), five amino acids (kynurenine, isobutyrylcarnitine, aspartate, trans-4-hydroxyproline, and 3-methyl-2-oxovalerate), and one peptide (ADSGEGDFXAEGGGVR). The known protective metabolites included four lipids (4-androsten-3beta,17beta-diol disulfate 1, 1-palmitoleoylglycerophosphocholine, adrenate (22:4n6), and glycodeoxycholate), one amino acid (methionine), and two exogenous metabolites (homostachydrine and 2-methoxyacetaminophen sulfate). Metabolic pathway analysis identified several pathways that might be involved in the disease. CONCLUSION: We identified eight risk and seven protective human serum metabolites associated with lacunar stroke. Isobutyrylcarnitine was positively associated with an increased risk of lacunar stroke. In addition, 3-methyl-2-oxovalerate and aspartate may be involved in the disease pathogenesis through metabolic pathways.

Exome-based gene panel analysis in a cohort of acute juvenile ischemic stroke patients:relevance of NOTCH3 and GLA variants.

BACKGROUND: Genetic variants are considered to have a crucial impact on the occurrence of ischemic stroke. In clinical routine, the diagnostic value of next-generation sequencing (NGS) in the medical clarification of acute juvenile stroke has not been investigated so far. MATERIAL AND METHODS: We analyzed an exome-based gene panel of 349 genes in 172 clinically well-characterized patients with magnetic resonance imaging (MRI)-proven, juvenile (age ≤ 55 years), ischemic stroke admitted to a single comprehensive stroke center. RESULTS: Monogenetic diseases causing ischemic stroke were observed in five patients (2.9%): In three patients with lacunar stroke (1.7%), we identified pathogenic variants in NOTCH3 causing cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Hence, CADASIL was identified at a frequency of 12.5% in the lacunar stroke subgroup. Further, in two male patients (1.2%) suffering from lacunar and cardioembolic stroke, pathogenic variants in GLA causing Fabry's disease were present. Additionally, genetic variants in monogenetic diseases lacking impact on stroke occurrence, variants of unclear significance (VUS) in monogenetic diseases, and (cardiovascular-) risk genes in ischemic stroke were observed in a total of 15 patients (15.7%). CONCLUSION: Genetic screening for Fabry's disease in cardioembolic and lacunar stroke as well as CADASIL in lacunar stroke might be beneficial in routine medical work-up of acute juvenile ischemic stroke.

Clinical features and pathogenicity assessment in patients with HTRA1-autosomal dominant disease.

BACKGROUND: Heterozygous mutations in HTRA1 were recently found to cause autosomal dominant cerebral small vessel disease (CSVD), and it was named HTRA1-autosomal dominant disease (AD-HTRA1) in the consensus recommendations of the European Academy of Neurology. This study aimed to investigate the clinical features of a mutation in HTRA1 and the effect of HTRA1 mutation on white matter hyperintensity (WMH). METHODS: A proband's brain magnetic resonance imaging (MRI) showed multiple lacunar infarctions and multiple WMH in the lateral ventricle, external capsule, frontal lobe and corpus callosum. The proband and family members were tested for CSVD-related genes by next-generation sequencing and the clinical data of the patients were collected. The published literature on AD-HTRA1 was collected, and the clinical characteristics and pathogenicity of the patients were summarized. Combined Annotation Dependent Depletion (CADD) is a tool for scoring the deleteriousness of single-nucleotide variants and insertion/deletion variants in the human genome. The relationship between the degree of WMH and the pathogenicity of the mutation was further analyzed. RESULT: It was found that the proband and her family members had a heterozygous missense mutation of c.854C > T (p.P285L) in the 4 exon of HTRA1 gene. A retrospective analysis of 5 families with c.854C > T mutation found that the patients had an early age of onset, cognitive impairment was more common, and alopecia and spondylosis could be combined at the same time. By univariate analysis, the severity of WMH was found to be significantly associated with the mutated CADD score (p < 0.05, Spearman's rho = 0.266). CONCLUSION: The clinical manifestations of AD-HTRA1 with mutation site c.854C > T (p.P285L) are similar to CARASIL, and brain MRI are mainly moderate or severe WMH and lacunar infarction (LI). WMH are affected by mutation sites. Therefore, our pathogenicity score for mutations can predict the severity of WMH.

Association of Vascular Risk Factors and Genetic Factors With Penetrance of Variants Causing Monogenic Stroke.

Importance: It is uncertain whether typical variants causing monogenic stroke are associated with cerebrovascular disease in the general population and why the phenotype of these variants varies so widely. Objective: To determine the frequency of pathogenic variants in the 3 most common monogenic cerebral small vessel diseases (cSVD) and their associations with prevalent and incident stroke and dementia. Design, Setting, and Participants: This cohort study is a multicenter population-based study of data from UK Biobank participants recruited in 2006 through 2010, with the latest follow-up in September 2021. A total of 9.2 million individuals aged 40 to 69 years who lived in the United Kingdom were invited to join UK Biobank, of whom 5.5% participated in the baseline assessment. Participants eligible for our study (n = 454 756, excluding 48 569 with incomplete data) had whole-exome sequencing and available data pertaining to lacunar stroke-related diseases, namely stroke, dementia, migraine, and epilepsy. Exposures: NOTCH3, HTRA1, and COL4A1/2 pathogenic variants in monogenic stroke; Framingham cardiovascular risk; and ischemic stroke polygenic risk. Main Outcomes and Measures: Primary outcomes were prevalent and incident stroke and dementia. Odds ratios (ORs) and hazard ratios (HRs) were adjusted for age, sex, ethnicity, exome sequencing batch, and top 10 genetic principal components. Results: Of the 454 756 participants (208 027 [45.8%] men; mean [SD] age, 56.5 [8.1] years), 973 participants carried NOTCH3 variants, 546 carried HTRA1 variants, and 336 carried COL4A1/2 variants. Variant carriers were at least 66% more likely to have had stroke. NOTCH3 carriers had increased vascular dementia risk (OR, 5.42; 95% CI, 3.11-8.74), HTRA1 carriers an increased all-cause dementia risk (OR, 2.17; 95% CI, 1.28-3.41), and COL4A1/2 carriers an increased intracerebral hemorrhage risk (OR, 3.56; 95% CI, 1.34-7.53). NOTCH3 variants were associated with incident ischemic stroke and vascular dementia. NOTCH3 and HTRA1 variants were associated with magnetic resonance imaging markers of cSVD. Cardiovascular risk burden was associated with increased stroke risk in NOTCH3 and HTRA1 carriers. Variant location was also associated with risk. Conclusions and Relevance: In this cohort study, pathogenic variants associated with rare monogenic stroke were more common than expected in the general population and associated with stroke and dementia. Cardiovascular risk burden is associated with the penetrance of such variants. Our results support the hypothesis that cardiovascular risk factor control may improve disease prognosis in individuals with monogenic cSVD variants. This lays the foundation for future studies to evaluate the effect of early identification before symptom onset on mitigating stroke and dementia risk.

Identification of novel proteins for lacunar stroke by integrating genome-wide association data and human brain proteomes.

BACKGROUND: Previous genome-wide association studies (GWAS) have identified numerous risk genes for lacunar stroke, but it is challenging to decipher how they confer risk for the disease. We employed an integrative analytical pipeline to efficiently transform genetic associations to identify novel proteins for lacunar stroke. METHODS: We systematically integrated lacunar stroke genome-wide association study (GWAS) (N=7338) with human brain proteomes (N=376) to perform proteome-wide association studies (PWAS), Mendelian randomization (MR), and Bayesian colocalization. We also used an independent human brain proteomic dataset (N=152) to annotate the new genes. RESULTS: We found that the protein abundance of seven genes (ICA1L, CAND2, ALDH2, MADD, MRVI1, CSPG4, and PTPN11) in the brain was associated with lacunar stroke. These seven genes were mainly expressed on the surface of glutamatergic neurons, GABAergic neurons, and astrocytes. Three genes (ICA1L, CAND2, ALDH2) were causal in lacunar stroke (P < 0.05/proteins identified for PWAS; posterior probability of hypothesis 4 ≥ 75 % for Bayesian colocalization), and they were linked with lacunar stroke in confirmatory PWAS and independent MR. We also found that ICA1L is related to lacunar stroke at the brain transcriptome level. CONCLUSIONS: Our present proteomic findings have identified ICA1L, CAND2, and ALDH2 as compelling genes that may give key hints for future functional research and possible therapeutic targets for lacunar stroke.

Genetic basis of lacunar stroke: a pooled analysis of individual patient data and genome-wide association studies.

BACKGROUND: The genetic basis of lacunar stroke is poorly understood, with a single locus on 16q24 identified to date. We sought to identify novel associations and provide mechanistic insights into the disease. METHODS: We did a pooled analysis of data from newly recruited patients with an MRI-confirmed diagnosis of lacunar stroke and existing genome-wide association studies (GWAS). Patients were recruited from hospitals in the UK as part of the UK DNA Lacunar Stroke studies 1 and 2 and from collaborators within the International Stroke Genetics Consortium. Cases and controls were stratified by ancestry and two meta-analyses were done: a European ancestry analysis, and a transethnic analysis that included all ancestry groups. We also did a multi-trait analysis of GWAS, in a joint analysis with a study of cerebral white matter hyperintensities (an aetiologically related radiological trait), to find additional genetic associations. We did a transcriptome-wide association study (TWAS) to detect genes for which expression is associated with lacunar stroke; identified significantly enriched pathways using multi-marker analysis of genomic annotation; and evaluated cardiovascular risk factors causally associated with the disease using mendelian randomisation. FINDINGS: Our meta-analysis comprised studies from Europe, the USA, and Australia, including 7338 cases and 254 798 controls, of which 2987 cases (matched with 29 540 controls) were confirmed using MRI. Five loci (ICA1L-WDR12-CARF-NBEAL1, ULK4, SPI1-SLC39A13-PSMC3-RAPSN, ZCCHC14, ZBTB14-EPB41L3) were found to be associated with lacunar stroke in the European or transethnic meta-analyses. A further seven loci (SLC25A44-PMF1-BGLAP, LOX-ZNF474-LOC100505841, FOXF2-FOXQ1, VTA1-GPR126, SH3PXD2A, HTRA1-ARMS2, COL4A2) were found to be associated in the multi-trait analysis with cerebral white matter hyperintensities (n=42 310). Two of the identified loci contain genes (COL4A2 and HTRA1) that are involved in monogenic lacunar stroke. The TWAS identified associations between the expression of six genes (SCL25A44, ULK4, CARF, FAM117B, ICA1L, NBEAL1) and lacunar stroke. Pathway analyses implicated disruption of the extracellular matrix, phosphatidylinositol 5 phosphate binding, and roundabout binding (false discovery rate <0·05). Mendelian randomisation analyses identified positive associations of elevated blood pressure, history of smoking, and type 2 diabetes with lacunar stroke. INTERPRETATION: Lacunar stroke has a substantial heritable component, with 12 loci now identified that could represent future treatment targets. These loci provide insights into lacunar stroke pathogenesis, highlighting disruption of the vascular extracellular matrix (COL4A2, LOX, SH3PXD2A, GPR126, HTRA1), pericyte differentiation (FOXF2, GPR126), TGF-ß signalling (HTRA1), and myelination (ULK4, GPR126) in disease risk. FUNDING: British Heart Foundation.

Alternate approach to stroke phenotyping identifies a genetic risk locus for small vessel stroke.

Ischemic stroke (IS), caused by obstruction of cerebral blood flow, is one of the leading causes of death. While neurologists agree on delineation of IS into three subtypes (cardioembolic stroke (CES), large artery stroke (LAS), and small vessel stroke (SVS)), several subtyping systems exist. The most commonly used systems are TOAST (Trial of Org 10172 in Acute Stroke Treatment) and CCS (Causative Classification System for Stroke), but agreement is only moderate. We have compared two approaches to combining the existing subtyping systems for a phenotype suited for a genome-wide association study (GWAS). We used the NINDS Stroke Genetics Network dataset (SiGN, 11,477 cases with CCS and TOAST subtypes and 28,026 controls). We defined two new phenotypes: the intersect, for which an individual must be assigned the same subtype by CCS and TOAST; and the union, for which an individual must be assigned a subtype by either CCS or TOAST. The union yields the largest sample size while the intersect yields a phenotype with less potential misclassification. We performed GWAS for all subtypes, using the original subtyping systems, the intersect, and the union as phenotypes. In each subtype, heritability was higher for the intersect compared with the other phenotypes. We observed stronger effects at known IS variants with the intersect compared with the other phenotypes. With the intersect, we identify rs10029218:G>A as an associated variant with SVS. We conclude that this approach increases the likelihood to detect genetic associations in ischemic stroke.

mtDNA Copy Number Contributes to All-Cause Mortality of Lacunar Infarct in a Chinese Prospective Stroke Population.

The study aimed to investigate the relationship between mtDNA copy number and the risk of all-cause mortality in stroke. One thousand four hundred eighty-four stroke patients were documented including 273 deaths (127 thrombosis, 52 lacunar, 94 hemorrhage). Patients in the third quartile had the lowest mortality rates in overall stroke and the three subtypes. The lowest quartile of mtDNA copy number (Q1 < 85.85) indicated an increased risk of all-cause mortality in stroke patients (adjusted HR, 1.52; 95% CI, 1.08-2.14; p = 0.017). In the subtype analysis, the risk of all-cause mortality appeared only in lacunar infarct, and the patients in the Q1 (< 87.76) and Q4 (> 150.61) mtDNA copy number groups showed significantly higher risks of HRs (Q1, adjusted HR, 3.87, 95% CI, 1.52-9.83; Q4, adjusted HR, 3.08, 95% CI, 1.16-8.18). Stroke patients with lacunar infarct in mtDNA copy number < 87.76 or > 150.61 were at a high risk of poor outcomes in all-cause mortality.

How common are single gene mutations as a cause for lacunar stroke? A targeted gene panel study.

OBJECTIVES: To determine the frequency of rare and pertinent disease-causing variants in small vessel disease (SVD)-associated genes (such as NOTCH3, HTRA1, COL4A1, COL4A2, FOXC1, TREX1, and GLA) in cerebral SVD, we performed targeted gene sequencing in 950 patients with younger-onset apparently sporadic SVD stroke using a targeted sequencing panel. METHODS: We designed a high-throughput sequencing panel to identify variants in 15 genes (7 known SVD genes, 8 SVD-related disorder genes). The panel was used to screen a population of 950 patients with younger-onset (≤70 years) MRI-confirmed SVD stroke, recruited from stroke centers across the United Kingdom. Variants were filtered according to their frequency in control databases, predicted effect, presence in curated variant lists, and combined annotation dependent depletion scores. Whole genome sequencing and genotyping were performed on a subset of patients to provide a direct comparison of techniques. The frequency of known disease-causing and pertinent variants of uncertain significance was calculated. RESULTS: We identified previously reported variants in 14 patients (8 cysteine-changing NOTCH3 variants in 11 patients, 2 HTRA1 variants in 2 patients, and 1 missense COL4A1 variant in 1 patient). In addition, we identified 29 variants of uncertain significance in 32 patients. CONCLUSION: Rare monogenic variants account for about 1.5% of younger onset lacunar stroke. Most are cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy variants, but the second most common gene affected is HTRA1. A high-throughput sequencing technology platform is an efficient, reliable method to screen for such mutations.

Association of COL4A2 Gene Polymorphisms with Lacunar Stroke in Xinjiang Han Populations.

Recent studies have shown that variants in the COL4A2 genes are associated with sporadic cerebral small vessel disease. The aim of the study was to investigate the relationship between COL4A2 gene polymorphisms and lacunar stroke in Xinjiang Han populations. The improved multiple ligase detection reaction (iMLDR) method was used to analyze the genotypes of seven single-nucleotide polymorphisms (SNPs) in the COL4A2 gene (rs3803230, rs391859, rs4103, rs445348, rs76425569, rs7990383, rs9515185) in a case-control study of 406 lacunar stroke patients and 425 controls. The GG genotype of rs3803230 (adjusted OR = 1.303, 95% CI = 1.146-1.480, P < 0.001) and the GA/AA genotype of rs76425569 (adjusted OR = 1.744, 95% CI = 1.306-2.329, P < 0.001) showed significant increases in the risk of lacunar stroke. The G-A haplotype of rs3803230-rs76425569 carried a significant increase in the risk of lacunar stroke (OR = 1.616, 95% CI = 1.292-2.022, P < 0.001). Hypertension stratification analyses demonstrated that the GA/AA genotype of rs76425569 was significantly associated with lacunar stroke in the hypertensive group (adjusted OR = 1.316, 95% CI = 1.083-1.598, P = 0.006). In the non-hypertensive group, the GG genotype of rs3803230 (adjusted OR = 1.584, 95% CI = 1.257-1.997, P < 0.001) and GA/AA genotype of rs76425569 were significantly associated with lacunar stroke (adjusted OR = 1.312, 95% CI = 1.054-1.635, P = 0.015). The TT genotype of rs4103 was significantly associated with lacunar stroke in the non-hypertensive group (adjusted OR = 1.355, 95% CI = 1.152-1.594, P < 0.001). This study demonstrates that the COL4A2 gene could play a role in the pathogenesis of lacunar stroke in the Han population of China.

Pathophysiology of Lacunar Stroke: History's Mysteries and Modern Interpretations.

Since the term "lacune" was adopted in the 1800s to describe infarctions from cerebral small vessels, their underlying pathophysiological basis remained obscure until the 1960s when Charles Miller Fisher performed several autopsy studies of stroke patients. He observed that the vessels displayed segmental arteriolar disorganization that was associated with vessel enlargement, hemorrhage, and fibrinoid deposition. He coined the term "lipohyalinosis" to describe the microvascular mechanism that engenders small subcortical infarcts in the absence of a compelling embolic source. Since Fisher's early descriptions of lipohyalinosis and lacunar stroke (LS), there have been many advancements in the understanding of this disease process. Herein, we review lipohyalinosis as it relates to modern concepts of cerebral small vessel disease (cSVD). We discuss clinical classifications of LS as well as radiographic definitions based on modern neuroimaging techniques. We provide a broad and comprehensive overview of LS pathophysiology both at the vessel and parenchymal levels. We also comment on the role of biomarkers, the possibility of systemic disease processes, and advancements in the genetics of cSVD. Lastly, we assess preclinical models that can aid in studying LS disease pathogenesis. Enhanced understanding of this highly prevalent disease will allow for the identification of novel therapeutic targets capable of mitigating disease sequelae.

Serum alkaline phosphatase level is correlated with the incidence of cerebral small vessel disease.

BACKGROUND: Vascular calcification is one of the mechanisms underlying the pathogenesis of cerebral small vessel disease (CSVD). Whether higher levels of serum alkaline phosphatase (ALP), a predictor of vascular calcification, are independently associated with CSVD remains inconclusive. PURPOSE: The present study explored the link between levels of circulating ALP and CSVD in a Chinese population. METHODS: A total of 568 participants were recruited from the healthcare center at the affiliated Zhongshan Hospital of Dalian University and the Fifth People Hospital of Dalian between January 2010 and December 2016. The subjects were divided into three groups based on the infarct and severity of white matter hyper-intensities (WMH) as categorized by brain magnetic resonance imaging (MRI) analysis and Fazekas rating scales: no/mild cerebral WMH (nm-WMH); moderate-to-severe WMH (MS-WMH); and silent lacunar infarct (SLI). The subjects were also divided into three tertiles based on circulating levels of ALP: ≤64, 65-105 and ≥106 (IU/L). Information regarding the risk factors, such as coronary artery disease, diabetes mellitus, hypertension and serum ALP level, C-reactive protein, homocysteine (HCY), and other laboratory results, were collected. The associations of ALP with WMH and SLI were evaluated using logistic regression analysis. RESULTS: After adjustment for vascular risk factors, subjects with MS-WMH and SLI were more likely to have ALP levels ≥106 IU/L than ≤64 IU/L. The mean circulating level of ALP was substantially increased in patients with MS-WMH or SLI compared with patients with nm-WMH. The multivariate model revealed that this significant difference remained when MS-WMH or SLI was added to the model, after adjustment for confounding factors. CONCLUSION: The circulating level of ALP was positively correlated with a high risk of silent lacunar infarct and white matter hyperintensity; important indicators of small vessel disease.

Genetic variation in PLEKHG1 is associated with white matter hyperintensities (n = 11,226).

OBJECTIVE: To identify novel genetic associations with white matter hyperintensities (WMH). METHODS: We performed a genome-wide association meta-analysis of WMH volumes in 11,226 individuals, including 8,429 population-based individuals from UK Biobank and 2,797 stroke patients. Replication of novel loci was performed in an independent dataset of 1,202 individuals. In all studies, WMH were quantified using validated automated or semi-automated methods. Imputation was to either the Haplotype Reference Consortium or 1,000 Genomes Phase 3 panels. RESULTS: We identified a locus at genome-wide significance in an intron of PLEKHG1 (rs275350, ß [SE] = 0.071 [0.013]; p = 1.6 × 10-8), a Rho guanine nucleotide exchange factor that is involved in reorientation of cells in the vascular endothelium. This association was validated in an independent sample (overall p value, 2.4 × 10-9). The same single nucleotide polymorphism was associated with all ischemic stroke (odds ratio [OR] [95% confidence interval (CI)] 1.07 [1.03-1.12], p = 0.00051), most strongly with the small vessel subtype (OR [95% CI] 1.09 [1.00-1.19], p = 0.044). Previous associations at 17q25 and 2p16 reached genome-wide significance in this analysis (rs3744020; ß [SE] = 0.106 [0.016]; p = 1.2 × 10-11 and rs7596872; ß [SE] = 0.143 [0.021]; p = 3.4 × 10-12). All identified associations with WMH to date explained 1.16% of the trait variance in UK Biobank, equivalent to 6.4% of the narrow-sense heritability. CONCLUSIONS: Genetic variation in PLEKHG1 is associated with WMH and ischemic stroke, most strongly with the small vessel subtype, suggesting it acts by promoting small vessel arteriopathy.

The role of clinical and neuroimaging features in the diagnosis of CADASIL.

BACKGROUND: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common familial cerebral small vessel disease, caused by NOTCH3 gene mutations. The aim of our study was to identify clinical and neuroradiological features which would be useful in identifying which patients presenting with lacunar stroke and TIA are likely to have CADASIL. METHODS: Patients with lacunar stroke or TIA were included in the present study. For each patient, demographic and clinical data were collected. MRI images were centrally analysed for the presence of lacunar infarcts, microbleeds, temporal lobe involvement, global atrophy and white matter hyperintensities. RESULTS: 128 patients (mean age 56.3 ± 12.4 years) were included. A NOTCH3 mutation was found in 12.5% of them. A family history of stroke, the presence of dementia and external capsule lesions on MRI were the only features significantly associated with the diagnosis of CADASIL. Although thalamic, temporal pole gliosis and severe white matter hyperintensities were less specific for CADASIL diagnosis, the combination of a number of these factors together with familial history for stroke result in a higher positive predictive value and specificity. CONCLUSIONS: A careful familial history collection and neuroradiological assessment can identify patients in whom NOTCH3 genetic testing has a higher yield.

Advances in Understanding the Pathophysiology of Lacunar Stroke: A Review.

Importance: Stroke is the second leading cause of death in the world, and nearly one-third of ischemic strokes are lacunar strokes (LSs) or small subcortical infarcts. Although smaller in size, they create large problems, leaving many patients with intellectual and physical disabilities. Because there are limitations in understanding the underlying pathophysiology of LS, the development of novel therapies has been slow. Observations: When the term lacune was described in the 1800s, its underlying pathophysiological basis was obscure. In the 1960s, C. Miller Fisher, MD, performed autopsy studies that showed that vessels supplying lacunes displayed segmental arteriolar disorganization, characterized by vessel enlargement, hemorrhage, and fibrinoid deposition. For these pathologic changes, he coined the term lipohyalinosis. Since that time, few attempts have been made to reconcile this pathologic description with modern mechanisms of cerebral small vessel disease (CSVD). During the past 6 years, progress has been made in understanding the clinical mechanisms, imaging characteristics, and genetic basis of LS. Conclusions and Relevance: Questions persist regarding the order of events related to the initiation and progression of CSVD, how LS is related to other sequelae of CSVD, and whether LS is part of a systemic disease process. The relative roles of aging, oxidative stress, mechanical stress, genetic predisposition, and other vascular risk factors should be further studied, especially in the era of widespread antihypertensive use. Although understanding of endothelial dysfunction has increased, future work on the role of media and adventitial dysfunction should be explored. Recent advances in mapping the brain vasculome may generate new hypotheses. The investigation of new therapeutic targets, aimed at reversing CSVD processes and promoting neural repair after LS, depends upon further understanding these basic mechanisms.