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1.  Shared genetic susceptibility to ischemic stroke and coronary artery disease – a genome-wide analysis of common variants 
Summary
Background and Purpose
Ischemic stroke (IS) and coronary artery disease (CAD) share several risk factors and each have a substantial heritability. We conducted a genome-wide analysis to evaluate the extent of shared genetic determination of the two diseases.
Methods
Genome-wide association data were obtained from the METASTROKE, CARDIoGRAM, and C4D consortia. We first analyzed common variants reaching a nominal threshold of significance (p<0.01) for CAD for their association with IS and vice versa. We then examined specific overlap across phenotypes for variants that reached a high threshold of significance. Finally, we conducted a joint meta-analysis on the combined phenotype of IS or CAD. Corresponding analyses were performed restricted to the 2,167 individuals with the ischemic large artery stroke (LAS) subtype.
Results
Common variants associated with CAD at p<0.01 were associated with a significant excess risk for IS and for LAS and vice versa. Among the 42 known genome-wide significant loci for CAD, three and five loci were significantly associated with IS and LAS, respectively. In the joint meta-analyses, 15 loci passed genome-wide significance (p<5×10-8) for the combined phenotype of IS or CAD and 17 loci passed genome-wide significance for LAS or CAD. Since these loci had prior evidence for genome-wide significance for CAD we specifically analyzed the respective signals for IS and LAS and found evidence for association at chr12q24/SH2B3 (pIS=1.62×10-07) and ABO (pIS =2.6×10-4) as well as at HDAC9 (pLAS=2.32×10-12), 9p21 (pLAS =3.70×10-6), RAI1-PEMT-RASD1 (pLAS =2.69×10-5), EDNRA (pLAS =7.29×10-4), and CYP17A1-CNNM2-NT5C2 (pLAS =4.9×10-4).
Conclusions
Our results demonstrate substantial overlap in the genetic risk of ischemic stroke and particularly the large artery stroke subtype with coronary artery disease.
doi:10.1161/STROKEAHA.113.002707
PMCID: PMC4112102  PMID: 24262325
2.  Comparison of Statistical and Clinical Predictions of Functional Outcome after Ischemic Stroke 
PLoS ONE  2014;9(10):e110189.
Background
To determine whether the predictions of functional outcome after ischemic stroke made at the bedside using a doctor’s clinical experience were more or less accurate than the predictions made by clinical prediction models (CPMs).
Methods and Findings
A prospective cohort study of nine hundred and thirty one ischemic stroke patients recruited consecutively at the outpatient, inpatient and emergency departments of the Western General Hospital, Edinburgh between 2002 and 2005. Doctors made informal predictions of six month functional outcome on the Oxford Handicap Scale (OHS). Patients were followed up at six months with a validated postal questionnaire. For each patient we calculated the absolute predicted risk of death or dependence (OHS≥3) using five previously described CPMs. The specificity of a doctor’s informal predictions of OHS≥3 at six months was good 0.96 (95% CI: 0.94 to 0.97) and similar to CPMs (range 0.94 to 0.96); however the sensitivity of both informal clinical predictions 0.44 (95% CI: 0.39 to 0.49) and clinical prediction models (range 0.38 to 0.45) was poor. The prediction of the level of disability after stroke was similar for informal clinical predictions (ordinal c-statistic 0.74 with 95% CI 0.72 to 0.76) and CPMs (range 0.69 to 0.75). No patient or clinician characteristic affected the accuracy of informal predictions, though predictions were more accurate in outpatients.
Conclusions
CPMs are at least as good as informal clinical predictions in discriminating between good and bad functional outcome after ischemic stroke. The place of these models in clinical practice has yet to be determined.
doi:10.1371/journal.pone.0110189
PMCID: PMC4192583  PMID: 25299053
3.  Stroke Genetics Network (SiGN) Study: Design and rationale for a genome-wide association study of ischemic stroke subtypes 
Background and Purpose
Meta-analyses of extant genome-wide data illustrate the need to focus on subtypes of ischemic stroke for gene discovery. The NINDS Stroke Genetics Network (SiGN) contributes substantially to meta-analyses that focus on specific subtypes of stroke.
Methods
The NINDS Stroke Genetics Network (SiGN) includes ischemic stroke cases from 24 Genetic Research Centers (GRCs), 13 from the US and 11 from Europe. Investigators harmonize ischemic stroke phenotyping using the web-based Causative Classification of Stroke (CCS) system, with data entered by trained and certified adjudicators at participating GRCs. Through the Center for Inherited Diseases Research (CIDR), SiGN plans to genotype 10,296 carefully phenotyped stroke cases using genome-wide SNP arrays, and add to these another 4,253 previously genotyped cases for a total of 14,549 cases. To maximize power for subtype analyses, the study allocates genotyping resources almost exclusively to cases. Publicly available studies provide most of the control genotypes. CIDR-generated genotypes and corresponding phenotypic data will be shared with the scientific community through dbGaP, and brain MRI studies will be centrally archived.
Conclusions
The SiGN consortium, with its emphasis on careful and standardized phenotyping of ischemic stroke and stroke subtypes, provides an unprecedented opportunity to uncover genetic determinants of ischemic stroke.
doi:10.1161/STROKEAHA.113.001857
PMCID: PMC4056331  PMID: 24021684
ischemic stroke; genetics; genomics
4.  A Multi-Ethnic Meta-Analysis of Genome-Wide Association Studies in Over 100,000 Subjects Identifies 23 Fibrinogen-Associated Loci but no Strong Evidence of a Causal Association between Circulating Fibrinogen and Cardiovascular Disease 
Sabater-Lleal, Maria | Huang, Jie | Chasman, Daniel | Naitza, Silvia | Dehghan, Abbas | Johnson, Andrew D | Teumer, Alexander | Reiner, Alex P | Folkersen, Lasse | Basu, Saonli | Rudnicka, Alicja R | Trompet, Stella | Mälarstig, Anders | Baumert, Jens | Bis, Joshua C. | Guo, Xiuqing | Hottenga, Jouke J | Shin, So-Youn | Lopez, Lorna M | Lahti, Jari | Tanaka, Toshiko | Yanek, Lisa R | Oudot-Mellakh, Tiphaine | Wilson, James F | Navarro, Pau | Huffman, Jennifer E | Zemunik, Tatijana | Redline, Susan | Mehra, Reena | Pulanic, Drazen | Rudan, Igor | Wright, Alan F | Kolcic, Ivana | Polasek, Ozren | Wild, Sarah H | Campbell, Harry | Curb, J David | Wallace, Robert | Liu, Simin | Eaton, Charles B. | Becker, Diane M. | Becker, Lewis C. | Bandinelli, Stefania | Räikkönen, Katri | Widen, Elisabeth | Palotie, Aarno | Fornage, Myriam | Green, David | Gross, Myron | Davies, Gail | Harris, Sarah E | Liewald, David C | Starr, John M | Williams, Frances M.K. | Grant, P.J. | Spector, Timothy D. | Strawbridge, Rona J | Silveira, Angela | Sennblad, Bengt | Rivadeneira, Fernando | Uitterlinden, Andre G | Franco, Oscar H | Hofman, Albert | van Dongen, Jenny | Willemsen, G | Boomsma, Dorret I | Yao, Jie | Jenny, Nancy Swords | Haritunians, Talin | McKnight, Barbara | Lumley, Thomas | Taylor, Kent D | Rotter, Jerome I | Psaty, Bruce M | Peters, Annette | Gieger, Christian | Illig, Thomas | Grotevendt, Anne | Homuth, Georg | Völzke, Henry | Kocher, Thomas | Goel, Anuj | Franzosi, Maria Grazia | Seedorf, Udo | Clarke, Robert | Steri, Maristella | Tarasov, Kirill V | Sanna, Serena | Schlessinger, David | Stott, David J | Sattar, Naveed | Buckley, Brendan M | Rumley, Ann | Lowe, Gordon D | McArdle, Wendy L | Chen, Ming-Huei | Tofler, Geoffrey H | Song, Jaejoon | Boerwinkle, Eric | Folsom, Aaron R. | Rose, Lynda M. | Franco-Cereceda, Anders | Teichert, Martina | Ikram, M Arfan | Mosley, Thomas H | Bevan, Steve | Dichgans, Martin | Rothwell, Peter M. | Sudlow, Cathie L M | Hopewell, Jemma C. | Chambers, John C. | Saleheen, Danish | Kooner, Jaspal S. | Danesh, John | Nelson, Christopher P | Erdmann, Jeanette | Reilly, Muredach P. | Kathiresan, Sekar | Schunkert, Heribert | Morange, Pierre-Emmanuel | Ferrucci, Luigi | Eriksson, Johan G | Jacobs, David | Deary, Ian J | Soranzo, Nicole | Witteman, Jacqueline CM | de Geus, Eco JC | Tracy, Russell P. | Hayward, Caroline | Koenig, Wolfgang | Cucca, Francesco | Jukema, J Wouter | Eriksson, Per | Seshadri, Sudha | Markus, Hugh S. | Watkins, Hugh | Samani, Nilesh J | Wallaschofski, Henri | Smith, Nicholas L. | Tregouet, David | Ridker, Paul M. | Tang, Weihong | Strachan, David P. | Hamsten, Anders | O’Donnell, Christopher J.
Circulation  2013;128(12):10.1161/CIRCULATIONAHA.113.002251.
Background
Estimates of the heritability of plasma fibrinogen concentration, an established predictor of cardiovascular disease (CVD), range from 34 to 50%. Genetic variants so far identified by genome-wide association (GWA) studies only explain a small proportion (< 2%) of its variation.
Methods and Results
We conducted a meta-analysis of 28 GWA studies, including more than 90,000 subjects of European ancestry, the first GWA meta-analysis of fibrinogen levels in 7 African Americans studies totaling 8,289 samples, and a GWA study in Hispanic-Americans totaling 1,366 samples. Evaluation for association of SNPs with clinical outcomes included a total of 40,695 cases and 85,582 controls for coronary artery disease (CAD), 4,752 cases and 24,030 controls for stroke, and 3,208 cases and 46,167 controls for venous thromboembolism (VTE). Overall, we identified 24 genome-wide significant (P<5×10−8) independent signals in 23 loci, including 15 novel associations, together accounting for 3.7% of plasma fibrinogen variation. Gene-set enrichment analysis highlighted key roles in fibrinogen regulation for the three structural fibrinogen genes and pathways related to inflammation, adipocytokines and thyrotrophin-releasing hormone signaling. Whereas lead SNPs in a few loci were significantly associated with CAD, the combined effect of all 24 fibrinogen-associated lead SNPs was not significant for CAD, stroke or VTE.
Conclusion
We identify 23 robustly associated fibrinogen loci, 15 of which are new. Clinical outcome analysis of these loci does not support a causal relationship between circulating levels of fibrinogen and CAD, stroke or VTE.
doi:10.1161/CIRCULATIONAHA.113.002251
PMCID: PMC3842025  PMID: 23969696
Fibrinogen; cardiovascular disease; genome-wide association study
5.  APOE associations with severe CAA-associated vasculopathic changes – collaborative meta-analysis 
Objectives
Cerebral amyloid angiopathy (CAA) is associated with lobar intracerebral haemorrhage (ICH). While only the ε4 allele of the apolipoprotein E gene (APOE) is associated with the presence of CAA, both APOE-ε4 and ε2 are associated with lobar ICH. The generally accepted explanation is that APOE-ε4 promotes vascular amyloid deposition, while APOE-ε2 promotes progression to severe CAA with associated vasculopathic changes that cause vessel rupture and ICH. We assessed the evidence for these allele-specific effects.
Methods
We systematically identified published studies with data on APOE genotype and histopathological assessment of post-mortem brains for CAA severity. We obtained unpublished data from these for meta-analyses of the effects of ε4-containing (ε4+) and ε2-containing (ε2+) genotypes on progression to severe CAA.
Results
Of six eligible studies (543 eligible participants), data were available from five (497 participants, 353 with CAA). Meta-analyses showed a possible association of ε4+ genotypes with severe CAA (ε4+ versus ε4-: severe versus mild/moderate CAA, odds ratio [OR] 2.5, 95% confidence interval [CI] 1.4 to 4.5, p=0.002; severe versus moderate CAA, OR 1.7, 95%CI 0.9 to 3.1, p=0.11). For ε2+ versus ε2-genotypes, there was no significant association, but the very small number of participants with ε2+ genotypes (22) precluded reliable estimates.
Conclusions
We found a possible association of severe CAA with APOE-ε4 but not APOE-ε2. However, our findings do not exclude a biologically meaningful association between APOE-ε2 and severe CAA. Further work is needed to elucidate fully the allele-specific associations of APOE with CAA and their mechanisms.
doi:10.1136/jnnp-2013-306485
PMCID: PMC4018226  PMID: 24163429
Cerebral Amyloid Angiopathy; Apolipoproteins E; Cerebral Hemorrhage; Systematic Review
6.  Meta-analysis in more than 17,900 cases of ischemic stroke reveals a novel association at 12q24.12 
Neurology  2014;83(8):678-685.
Objectives:
To perform a genome-wide association study (GWAS) using the Immunochip array in 3,420 cases of ischemic stroke and 6,821 controls, followed by a meta-analysis with data from more than 14,000 additional ischemic stroke cases.
Methods:
Using the Immunochip, we genotyped 3,420 ischemic stroke cases and 6,821 controls. After imputation we meta-analyzed the results with imputed GWAS data from 3,548 cases and 5,972 controls recruited from the ischemic stroke WTCCC2 study, and with summary statistics from a further 8,480 cases and 56,032 controls in the METASTROKE consortium. A final in silico “look-up” of 2 single nucleotide polymorphisms in 2,522 cases and 1,899 controls was performed. Associations were also examined in 1,088 cases with intracerebral hemorrhage and 1,102 controls.
Results:
In an overall analysis of 17,970 cases of ischemic stroke and 70,764 controls, we identified a novel association on chromosome 12q24 (rs10744777, odds ratio [OR] 1.10 [1.07–1.13], p = 7.12 × 10−11) with ischemic stroke. The association was with all ischemic stroke rather than an individual stroke subtype, with similar effect sizes seen in different stroke subtypes. There was no association with intracerebral hemorrhage (OR 1.03 [0.90–1.17], p = 0.695).
Conclusion:
Our results show, for the first time, a genetic risk locus associated with ischemic stroke as a whole, rather than in a subtype-specific manner. This finding was not associated with intracerebral hemorrhage.
doi:10.1212/WNL.0000000000000707
PMCID: PMC4150131  PMID: 25031287
7.  A Novel MMP12 Locus Is Associated with Large Artery Atherosclerotic Stroke Using a Genome-Wide Age-at-Onset Informed Approach 
PLoS Genetics  2014;10(7):e1004469.
Genome-wide association studies (GWAS) have begun to identify the common genetic component to ischaemic stroke (IS). However, IS has considerable phenotypic heterogeneity. Where clinical covariates explain a large fraction of disease risk, covariate informed designs can increase power to detect associations. As prevalence rates in IS are markedly affected by age, and younger onset cases may have higher genetic predisposition, we investigated whether an age-at-onset informed approach could detect novel associations with IS and its subtypes; cardioembolic (CE), large artery atherosclerosis (LAA) and small vessel disease (SVD) in 6,778 cases of European ancestry and 12,095 ancestry-matched controls. Regression analysis to identify SNP associations was performed on posterior liabilities after conditioning on age-at-onset and affection status. We sought further evidence of an association with LAA in 1,881 cases and 50,817 controls, and examined mRNA expression levels of the nearby genes in atherosclerotic carotid artery plaques. Secondly, we performed permutation analyses to evaluate the extent to which age-at-onset informed analysis improves significance for novel loci. We identified a novel association with an MMP12 locus in LAA (rs660599; p = 2.5×10−7), with independent replication in a second population (p = 0.0048, OR(95% CI) = 1.18(1.05–1.32); meta-analysis p = 2.6×10−8). The nearby gene, MMP12, was significantly overexpressed in carotid plaques compared to atherosclerosis-free control arteries (p = 1.2×10−15; fold change = 335.6). Permutation analyses demonstrated improved significance for associations when accounting for age-at-onset in all four stroke phenotypes (p<0.001). Our results show that a covariate-informed design, by adjusting for age-at-onset of stroke, can detect variants not identified by conventional GWAS.
Author Summary
Ischaemic stroke places an enormous burden on global healthcare. However, the disease processes that lead to stroke are not fully understood. Genome-wide association studies have recently established that common genetic variants can increase risk of ischaemic stroke and its subtypes. In this study, we aimed to identify novel genetic associations with ischaemic stroke and its subtypes by addressing the fact that younger onset cases may have a stronger genetic component, and using this information in our analyses. We identify a novel genetic variant on chromosome 11 (rs660599), which is associated with increased risk of large artery stroke. We also show that mRNA expression of the nearest gene (MMP12) is higher in arteries with the disease process underlying large artery stroke (atherosclerosis). Finally, we evaluate our novel analysis approach, and show that our method is likely to identify further associations with ischaemic stroke.
doi:10.1371/journal.pgen.1004469
PMCID: PMC4117446  PMID: 25078452
8.  17q25 Locus Is Associated With White Matter Hyperintensity Volume in Ischemic Stroke, But Not With Lacunar Stroke Status 
Background and Purpose
Recently, a novel locus at 17q25 was associated with white matter hyperintensities (WMH) on MRI in stroke-free individuals. We aimed to replicate the association with WMH volume (WMHV) in patients with ischemic stroke. If the association acts by promoting a small vessel arteriopathy, it might be expected to also associate with lacunar stroke.
Methods
We quantified WMH on MRI in the stroke-free hemisphere of 2588 ischemic stroke cases. Association between WMHV and 6 single-nucleotide polymorphisms at chromosome 17q25 was assessed by linear regression. These single-nucleotide polymorphisms were also investigated for association with lacunar stroke in 1854 cases and 51 939 stroke-free controls from METASTROKE. Meta-analyses with previous reports and a genetic risk score approach were applied to identify other novel WMHV risk variants and uncover shared genetic contributions to WMHV in community participants without stroke and ischemic stroke.
Results
Single-nucleotide polymorphisms at 17q25 were associated with WMHV in ischemic stroke, the most significant being rs9894383 (P=0.0006). In contrast, there was no association between any single-nucleotide polymorphism and lacunar stroke. A genetic risk score analysis revealed further genetic components to WMHV shared between community participants without stroke and ischemic stroke.
Conclusions
This study provides support for an association between the 17q25 locus and WMH. In contrast, it is not associated with lacunar stroke, suggesting that the association does not act by promoting small-vessel arteriopathy or the same arteriopathy responsible for lacunar infarction.
doi:10.1161/STROKEAHA.113.679936
PMCID: PMC3771337  PMID: 23674528
genetics; Genome-wide Association Study; leukoaraiosis; small-vessel disease; stroke
9.  Formal and informal prediction of recurrent stroke and myocardial infarction after stroke: a systematic review and evaluation of clinical prediction models in a new cohort 
BMC Medicine  2014;12:58.
Background
The objective of this study was to: (1) systematically review the reporting and methods used in the development of clinical prediction models for recurrent stroke or myocardial infarction (MI) after ischemic stroke; (2) to meta-analyze their external performance; and (3) to compare clinical prediction models to informal clinicians’ prediction in the Edinburgh Stroke Study (ESS).
Methods
We searched Medline, EMBASE, reference lists and forward citations of relevant articles from 1980 to 19 April 2013. We included articles which developed multivariable clinical prediction models for the prediction of recurrent stroke and/or MI following ischemic stroke. We extracted information to assess aspects of model development as well as metrics of performance to determine predictive ability. Model quality was assessed against a pre-defined set of criteria. We used random-effects meta-analysis to pool performance metrics.
Results
We identified twelve model development studies and eleven evaluation studies. Investigators often did not report effective sample size, regression coefficients, handling of missing data; typically categorized continuous predictors; and used data dependent methods to build models. A meta-analysis of the area under the receiver operating characteristic curve (AUROCC) was possible for the Essen Stroke Risk Score (ESRS) and for the Stroke Prognosis Instrument II (SPI-II); the pooled AUROCCs were 0.60 (95% CI 0.59 to 0.62) and 0.62 (95% CI 0.60 to 0.64), respectively. An evaluation among minor stroke patients in the ESS demonstrated that clinicians discriminated poorly between those with and those without recurrent events and that this was similar to clinical prediction models.
Conclusions
The available models for recurrent stroke discriminate poorly between patients with and without a recurrent stroke or MI after stroke. Models had a similar discrimination to informal clinicians' predictions. Formal prediction may be improved by addressing commonly encountered methodological problems.
doi:10.1186/1741-7015-12-58
PMCID: PMC4022243  PMID: 24708686
Systematic review; Meta-analysis; Stroke; Prediction; Statistical modelling; Evaluation; Development
10.  Epidemiology of stroke and its subtypes in Chinese vs white populations 
Neurology  2013;81(3):264-272.
Objective:
We aimed to systematically assess the evidence for differences in the incidence of stroke and distribution of its subtypes in Chinese compared with white populations.
Methods:
We comprehensively sought studies conducted since 1990 in Chinese populations of 1) first-ever stroke incidence (community-based studies only), and 2) pathologic types/subtypes of stroke (hospital- or community-based studies of first-ever or recurrent strokes). We identified community-based studies in white populations from a recent systematic review. For each study, we calculated age-standardized stroke incidence and the proportions of each pathologic type and ischemic subtype, using random-effects meta-analysis to pool proportions of stroke types/subtypes in Chinese and in white populations.
Results:
Age-standardized annual first-ever stroke incidence in community-based studies was higher among Chinese than white populations (for ages 45–74 years, range 205–584 vs 170–335 per 100,000, respectively). Intracerebral hemorrhage accounted for a larger, more variable proportion of strokes in China than Taiwan (range 27%–51% vs 17%–28%), in Chinese community-based than hospital-based studies (27%–51% vs 17%–30%), and in community-based Chinese than white studies (pooled proportion 33% vs 12%). Although the overall proportion of lacunar ischemic stroke appeared higher in Chinese than white populations, variable study methodologies precluded reliable comparisons.
Conclusions:
There is good evidence for a slightly higher overall stroke incidence and higher proportion of intracerebral hemorrhage in Chinese vs white populations, but no clear evidence for different distributions of ischemic stroke subtypes. Studies using comparable, population-based case ascertainment and similar classification methods are needed to address this.
doi:10.1212/WNL.0b013e31829bfde3
PMCID: PMC3770160  PMID: 23858408
11.  Ischaemic stroke is associated with the ABO locus: the Euroclot study 
Annals of neurology  2013;73(1):16-31.
Objectives
End-stage coagulation and the structure/function of fibrin are implicated in the pathogenesis of ischaemic stroke. We explored whether genetic variants associated with end-stage coagulation in healthy volunteers account for the genetic predisposition to ischemic stroke and examined their influence on stroke subtype.
Methods
Common genetic variants identified through genome-wide association studies of coagulation factors and fibrin structure/function in healthy twins (n=2,100 Stage 1) were examined in ischemic stroke (n=4,200 cases) using 2 independent samples of European ancestry (Stage 2). A third clinical collection having stroke subtyping (total 8,900 cases 55,000 controls) was used for replication (Stage 3).
Results
Stage 1 identified 524 SNPs from 23 LD blocks having significant association (p<5 ×10-8) with one or more coagulation/fibrin phenotypes. Most striking associations included SNP rs5985 with factor XIII activity (p=2.6×10-186), rs10665 with FVII (p = 2.4×10-47) and rs505922 in the ABO gene with both von Willebrand Factor (vWF p=4.7×10-57) and factor VIII (p=1.2×10-36). In Stage 2, the 23 independent SNPs were examined in stroke cases/non-cases using MORGAM and WTCCC2 collections. SNP rs505922 was nominally associated with ischaemic stroke, odds ratio = 0.94 (95% confidence intervals, 0.88-0.99), p=0.023. Independent replication in Meta-Stroke confirmed the rs505922 association with stroke, beta=0.066 (0.02) p = 0.001, a finding specific to large vessel and cardioembolic stroke (p = 0.001 and p = <0.001 respectively) but not seen with small vessel stroke (p=0.811).
Interpretation
ABO gene variants are associated with large vessel and cardioembolic stroke but not small vessel disease. This work sheds light on the different pathogenic mechanisms underpinning stroke subtype.
doi:10.1002/ana.23838
PMCID: PMC3582024  PMID: 23381943
GWAS; thrombosis; stroke; coagulation factor; stroke subtype
12.  Statistical evaluation of surrogate endpoints: a systematic review 
Trials  2013;14(Suppl 1):P73.
doi:10.1186/1745-6215-14-S1-P73
PMCID: PMC3980768
13.  Common variants at 6p21.1 are associated with large artery atherosclerotic stroke 
Nature genetics  2012;44(10):10.1038/ng.2397.
Genome-wide association studies (GWAS) have not consistently detected replicable genetic risk factors for ischemic stroke, potentially due to etiological heterogeneity of this trait. We performed GWAS of ischemic stroke and a major ischemic stroke subtype (large artery atherosclerosis, LAA) using 1,162 ischemic stroke cases (including 421 LAA cases) and 1,244 population controls from Australia. Evidence for a genetic influence on ischemic stroke risk was detected, but this influence was higher and more significant for the LAA subtype. We identified a new LAA susceptibility locus on chromosome 6p21.1 (rs556621: odds ratio (OR) = 1.62, P = 3.9 × 10−8) and replicated this association in 1,715 LAA cases and 52,695 population controls from 10 independent population cohorts (meta-analysis replication OR = 1.15, P = 3.9 × 10−4; discovery and replication combined OR = 1.21, P = 4.7 × 10−8). This study identifies a genetic risk locus for LAA and shows how analyzing etiological subtypes may better identify genetic risk alleles for ischemic stroke.
doi:10.1038/ng.2397
PMCID: PMC3651583  PMID: 22941190
14.  Genetic risk factors for ischaemic stroke and its subtypes (the METASTROKE Collaboration): a meta-analysis of genome-wide association studies 
Traylor, Matthew | Farrall, Martin | Holliday, Elizabeth G | Sudlow, Cathie | Hopewell, Jemma C | Cheng, Yu-Ching | Fornage, Myriam | Ikram, M Arfan | Malik, Rainer | Bevan, Steve | Thorsteinsdottir, Unnur | Nalls, Mike A | Longstreth, WT | Wiggins, Kerri L | Yadav, Sunaina | Parati, Eugenio A | DeStefano, Anita L | Worrall, Bradford B | Kittner, Steven J | Khan, Muhammad Saleem | Reiner, Alex P | Helgadottir, Anna | Achterberg, Sefanja | Fernandez-Cadenas, Israel | Abboud, Sherine | Schmidt, Reinhold | Walters, Matthew | Chen, Wei-Min | Ringelstein, E Bernd | O'Donnell, Martin | Ho, Weang Kee | Pera, Joanna | Lemmens, Robin | Norrving, Bo | Higgins, Peter | Benn, Marianne | Sale, Michele | Kuhlenbäumer, Gregor | Doney, Alexander S F | Vicente, Astrid M | Delavaran, Hossein | Algra, Ale | Davies, Gail | Oliveira, Sofia A | Palmer, Colin N A | Deary, Ian | Schmidt, Helena | Pandolfo, Massimo | Montaner, Joan | Carty, Cara | de Bakker, Paul I W | Kostulas, Konstantinos | Ferro, Jose M | van Zuydam, Natalie R | Valdimarsson, Einar | Nordestgaard, Børge G | Lindgren, Arne | Thijs, Vincent | Slowik, Agnieszka | Saleheen, Danish | Paré, Guillaume | Berger, Klaus | Thorleifsson, Gudmar | Hofman, Albert | Mosley, Thomas H | Mitchell, Braxton D | Furie, Karen | Clarke, Robert | Levi, Christopher | Seshadri, Sudha | Gschwendtner, Andreas | Boncoraglio, Giorgio B | Sharma, Pankaj | Bis, Joshua C | Gretarsdottir, Solveig | Psaty, Bruce M | Rothwell, Peter M | Rosand, Jonathan | Meschia, James F | Stefansson, Kari | Dichgans, Martin | Markus, Hugh S
Lancet Neurology  2012;11(11):951-962.
Summary
Background
Various genome-wide association studies (GWAS) have been done in ischaemic stroke, identifying a few loci associated with the disease, but sample sizes have been 3500 cases or less. We established the METASTROKE collaboration with the aim of validating associations from previous GWAS and identifying novel genetic associations through meta-analysis of GWAS datasets for ischaemic stroke and its subtypes.
Methods
We meta-analysed data from 15 ischaemic stroke cohorts with a total of 12 389 individuals with ischaemic stroke and 62 004 controls, all of European ancestry. For the associations reaching genome-wide significance in METASTROKE, we did a further analysis, conditioning on the lead single nucleotide polymorphism in every associated region. Replication of novel suggestive signals was done in 13 347 cases and 29 083 controls.
Findings
We verified previous associations for cardioembolic stroke near PITX2 (p=2·8×10−16) and ZFHX3 (p=2·28×10−8), and for large-vessel stroke at a 9p21 locus (p=3·32×10−5) and HDAC9 (p=2·03×10−12). Additionally, we verified that all associations were subtype specific. Conditional analysis in the three regions for which the associations reached genome-wide significance (PITX2, ZFHX3, and HDAC9) indicated that all the signal in each region could be attributed to one risk haplotype. We also identified 12 potentially novel loci at p<5×10−6. However, we were unable to replicate any of these novel associations in the replication cohort.
Interpretation
Our results show that, although genetic variants can be detected in patients with ischaemic stroke when compared with controls, all associations we were able to confirm are specific to a stroke subtype. This finding has two implications. First, to maximise success of genetic studies in ischaemic stroke, detailed stroke subtyping is required. Second, different genetic pathophysiological mechanisms seem to be associated with different stroke subtypes.
Funding
Wellcome Trust, UK Medical Research Council (MRC), Australian National and Medical Health Research Council, National Institutes of Health (NIH) including National Heart, Lung and Blood Institute (NHLBI), the National Institute on Aging (NIA), the National Human Genome Research Institute (NHGRI), and the National Institute of Neurological Disorders and Stroke (NINDS).
doi:10.1016/S1474-4422(12)70234-X
PMCID: PMC3490334  PMID: 23041239
15.  Lack of Association of White Matter Lesions with Ipsilateral Carotid Artery Stenosis 
Background
White matter lesions (WML) are commonly seen on brain MRI and are generally considered a marker of tissue damage from cerebral small vessel disease. WML are associated with increasing age and vascular risk factors, but their precise cause is unknown. A role for carotid artery atherothromboemboli has been suggested. If this is the case, more WML would be expected ipsilateral to increasing degrees of carotid stenosis.
Methods
We recruited patients with ischaemic stroke from two large, separate prospective stroke studies, assessed with brain MRI and carotid Doppler ultrasound. We scored hemispheric WML visually in periventricular and deep locations. We assessed the association between carotid stenosis asymmetry and WML asymmetry, and vice versa. Further, we assessed the association between carotid stenosis and ipsilateral WML, before and after adjusting for vascular risk factors, and tested associations between ipsilateral and contralateral stenoses and WML.
Results
We recruited 247 (Study 1) and 253 (Study 2) patients. In Study 1 and Study 2, 36 (15%) and 29 (11%) patients had ≥50% carotid stenosis, and 27 (11%) and 15 (6%) had ≥70% stenosis, respectively. Carotid stenosis was asymmetric in 28 (11%) and 26 (10%) patients and WML were asymmetric in 22 (9%) and 11 (4%) patients in Study 1 and Study 2, respectively. We found no association between carotid stenosis and ipsilateral WML score, before or after adjusting for vascular risk factors or sidedness, but WML were strongly associated with increasing age (p < 0.001).
Conclusion
In two large cohorts of ischaemic stroke patients, we found no association between carotid stenosis and ipsi- or contralateral WML. There is now substantial evidence that atherothromboemboli are unlikely to cause most WML or other forms of cerebral small vessel lesions. Future studies should focus on determining what causes the intrinsic small vessel pathological changes that appear to underlie most WML.
doi:10.1159/000336762
PMCID: PMC4067711  PMID: 22433285
Leukoaraiosis; White matter lesions; Aetiology; Carotid stenosis; Atheroma; Thromboembolism; Magnetic resonance imaging
16.  The association of circulating inflammatory markers with recurrent vascular events after stroke: a prospective cohort study 
Background
Inflammatory markers may be associated with recurrent vascular events after stroke. We aimed to: (1) determine the association between interleukin-6, C-reactive protein, fibrinogen and white cell count and recurrent vascular events after stroke, and (2) compare the association between circulating inflammatory markers and the risk of death from vascular versus non-vascular causes.
Methods and Results
We prospectively recruited patients with acute stroke (n=817) and followed them for up to 4 years for the occurrence of: fatal or non-fatal recurrent stroke, myocardial infarction or fatal vascular events, and death from any cause (n=159). The delay to assessment was a median of 10 days. The adjusted incidence of the outcome cluster ‘recurrent stroke, myocardial infarction or vascular death’ after stroke was significantly higher with higher levels of interleukin 6 (75th to 25th centile: hazard ratio [HR] 1.56, 95 % CI 1.37 to 1.77), C-reactive protein (75th to 25th centile HR 1·08, 95% CI 1·04 to 1·11) and fibrinogen (75th to 25th centile HR 1.45, 95% CI 1.24 to 1.72). The associations between inflammatory markers and death were stronger than with recurrent vascular events. The associations of inflammatory markers with vascular and non-vascular deaths were similar.
Conclusions
Though inflammatory markers were associated with an increased risk of recurrent vascular events and vascular death after stroke, they were also associated with non-vascular causes of death, suggesting that inflammatory markers do not play a causal role specifically in the generation of recurrent vascular events after stroke. Future studies of the prediction of recurrent vascular events after stroke should concentrate on clinical variables, or different blood markers.
doi:10.1161/STROKEAHA.110.588954
PMCID: PMC3016514  PMID: 21127302
Inflammation; stroke; prognosis
18.  Improving adherence to medication in stroke survivors (IAMSS): a randomised controlled trial: study protocol 
BMC Neurology  2010;10:15.
Background
Adherence to therapies is a primary determinant of treatment success, yet the World Health Organisation estimate that only 50% of patients who suffer from chronic diseases adhere to treatment recommendations. In a previous project, we found that 30% of stroke patients reported sub-optimal medication adherence, and this was associated with younger age, greater cognitive impairment, lower perceptions of medication benefits and higher specific concerns about medication. We now wish to pilot a brief intervention aimed at (a) helping patients establish a better medication-taking routine, and (b) eliciting and modifying any erroneous beliefs regarding their medication and their stroke.
Methods/Design
Thirty patients will be allocated to a brief intervention (2 sessions) and 30 to treatment as usual. The primary outcome will be adherence measured over 3 months using Medication Event Monitoring System (MEMS) pill containers which electronically record openings. Secondary outcomes will include self reported adherence and blood pressure.
Discussion
This study shall also assess uptake/attrition, feasibility, ease of understanding and acceptability of this complex intervention.
Trial Registration
Current Controlled Trials ISRCTN38274953
doi:10.1186/1471-2377-10-15
PMCID: PMC2838838  PMID: 20181255
19.  Associations of Clinical Stroke Misclassification (‘Clinical-Imaging Dissociation’) in Acute Ischemic Stroke 
Background
Up to 20% of lacunar infarcts are clinically misdiagnosed as cortical infarcts and vice versa. The reasons for this discrepancy are unclear. We assessed clinical and imaging features which might explain this ‘clinical-imaging dissociation’ (C-ID).
Methods
Patients with an acute stroke syndrome (cortical or lacunar) underwent magnetic resonance imaging including diffusion-weighted imaging (DWI). We recorded DWI-positive infarcts and proximity to cortex for small subcortical infarcts. We examined factors associated with C-ID.
Results
137 patients with a mild cortical or lacunar syndrome had an acute ischemic lesion on DWI. Of these, 21/93 (23%) with a cortical syndrome had an acute lacunar infarct and 7/44 (16%) with a lacunar syndrome had an acute cortical infarct. From 72 patients with an acute lacunar infarct on DWI, lesion proximity to cortex (odds ratio (OR) 14.5, 95% confidence interval (CI) 1.61–130.1), left hemisphere location (OR 8.95, 95% CI 1.23–64.99) and diabetes (OR 17.1, 95% CI 1.49–196.16) predicted C-ID. On multivariate analysis of all 137 patients, C-ID was associated with diabetes (OR 7.12, 95% CI 1.86–27.2).
Conclusions
C-ID occurs in a fifth of patients with mild stroke. Lacunar infarcts lying close to cortex are more likely to cause cortical symptoms. Diabetes is associated with any clinical-imaging mismatch. Stroke misclassification which can arise with clinical classification alone should be minimized in research by verification with high-sensitivity imaging.
doi:10.1159/000286342
PMCID: PMC4067720  PMID: 20173323
Acute ischemic stroke; Stroke subtype; Infarction; Acute stroke imaging; Diffusion-weighted imaging
20.  Inflammatory Markers and Poor Outcome after Stroke: A Prospective Cohort Study and Systematic Review of Interleukin-6 
PLoS Medicine  2009;6(9):e1000145.
In a prospective cohort study of patient outcomes following stroke, William Whiteley and colleagues find that markers of inflammatory response are associated with poor outcomes. However, addition of these markers to existing prognostic models does not improve outcome prediction.
Background
The objective of this study was to determine whether: (a) markers of acute inflammation (white cell count, glucose, interleukin-6, C-reactive protein, and fibrinogen) are associated with poor outcome after stroke and (b) the addition of markers to previously validated prognostic models improves prediction of poor outcome.
Methods and Findings
We prospectively recruited patients between 2002 and 2005. Clinicians assessed patients and drew blood for inflammatory markers. Patients were followed up by postal questionnaire for poor outcome (a score of>2 on the modified Rankin Scale) and death through the General Register Office (Scotland) at 6 mo. We performed a systematic review of the literature and meta-analysis of the association between interleukin-6 and poor outcome after stroke to place our study in the context of previous research. We recruited 844 patients; mortality data were available in 844 (100%) and functional outcome in 750 (89%). After appropriate adjustment, the odds ratios for the association of markers and poor outcome (comparing the upper and the lower third) were interleukin-6, 3.1 (95% CI: 1.9–5.0); C-reactive protein, 1.9 (95% CI: 1.2–3.1); fibrinogen, 1.5 (95% CI: 1.0–2.36); white cell count, 2.1 (95% CI: 1.3–3.4); and glucose 1.3 (95% CI: 0.8–2.1). The results for interleukin-6 were similar to other studies. However, the addition of inflammatory marker levels to validated prognostic models did not materially improve model discrimination, calibration, or reclassification for prediction of poor outcome after stroke.
Conclusions
Raised levels of markers of the acute inflammatory response after stroke are associated with poor outcomes. However, the addition of these markers to a previously validated stroke prognostic model did not improve the prediction of poor outcome. Whether inflammatory markers are useful in prediction of recurrent stroke or other vascular events is a separate question, which requires further study.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Every year, 15 million people have a stroke. In the US alone, someone has a stroke every 40 seconds and someone dies from a stroke every 3–4 minutes. Stroke occurs when the blood supply to the brain is suddenly interrupted by a blood clot blocking a blood vessel in the brain (ischemic stroke, the commonest type of stroke) or by a blood vessel in the brain bursting (hemorrhagic stroke). Deprived of the oxygen normally carried to them by the blood, the brain cells near the blockage die. The symptoms of stroke depend on which part of the brain is damaged but include sudden weakness or paralysis along one side of the body, vision loss in one or both eyes, and confusion or trouble speaking or understanding speech. Anyone experiencing these symptoms should seek medical assistance immediately because prompt treatment can limit the damage to the brain. Risk factors for stroke include age (three-quarters of strokes occur in people over 65 years old), high blood pressure, and heart disease.
Why Was This Study Done?
Many people are left with permanent disabilities after a stroke. An accurate way to predict the likely long-term outcome (prognosis) for individual patients would help clinicians manage their patients and help relatives and patients come to terms with their changed circumstances. Clinicians can get some idea of their patients' likely outcomes by assessing six simple clinical variables. These include the ability to lift both arms and awareness of the present situation. But could the inclusion of additional variables improve the predictive power of this simple prognostic model? There is some evidence that high levels in the blood of inflammatory markers (for example, interleukin-6 and C-reactive protein) are associated with poor outcomes after stroke—inflammation is the body's response to infection and to damage. In this prospective cohort study, the researchers investigate whether inflammatory markers are associated with poor outcome after stroke and whether the addition of these markers to the six-variable prognostic model improves its predictive power. Prospective cohort studies enroll a group of participants and follow their subsequent progress.
What Did the Researchers Do and Find?
The researchers recruited 844 patients who had had a stroke (mainly mild ischemic strokes) in Edinburgh. Each patient was assessed soon after the stroke by a clinician and blood was taken for the measurement of inflammatory markers. Six months after the stroke, the patient or their relatives completed a postal questionnaire that assessed their progress. Information about patient deaths was obtained from the General Register Office for Scotland. Dependency on others for the activities of daily life or dying was recorded as a poor outcome. In their statistical analysis of these data, the researchers found that raised levels of several inflammatory markers increased the likelihood of a poor outcome. For example, after allowing for age and other factors, individuals with interleukin-6 levels in the upper third of the measured range were three times as likely to have a poor outcome as patients with interleukin-6 levels in the bottom third of the range. A systematic search of the literature revealed that previous studies that had looked at the potential association between interleukin-6 levels and outcome after stroke had found similar results. Finally, the researchers found that the addition of inflammatory marker levels to the six-variable prognostic model did not substantially improve its ability to predict outcome after stroke for this cohort of patients.
What Do These Findings Mean?
These findings provide additional support for the idea that increased levels of inflammatory markers are associated with a poor outcome after stroke. However, because patients with infections were not excluded from the study, infection may be responsible for part of the observed association. Importantly, these findings also show that although the inclusion of inflammatory markers in the six variable prognostic model slightly improves its ability to predict outcome, the magnitude of this improvement is too small to warrant the use of these markers in routine practice. Whether the measurement of inflammatory markers might be useful in the prediction of recurrent stroke—at least a quarter of people who survive a stroke will have another one within 5 years—requires further study.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000145.
This study is further discussed in a PLoS Medicine Perspective by Len Kritharides
The US National Institute of Neurological Disorders and Stroke provides information about all aspects of stroke (in English and Spanish); the Know Stroke site provides educational materials about stroke prevention, treatment, and rehabilitation (in English and Spanish)
The Internet Stroke Center provides detailed information about stroke for patients, families and health professionals (in English and Spanish)
The UK National Health Service also provides information for patients and their families about stroke (in several languages)
MedlinePlus provides links to further resources and advice about stroke (in English and Spanish)
The six simple variable model for prediction of death or disability after stroke is available here: http://dcnapp1.dcn.ed.ac.uk/scope/
doi:10.1371/journal.pmed.1000145
PMCID: PMC2730573  PMID: 19901973
21.  Effects of apolipoprotein E genotype on outcome after ischaemic stroke, intracerebral haemorrhage and subarachnoid haemorrhage 
Background:
Rodent models of acute ischaemic stroke and head injury suggest that apolipoprotein E genotype (APOE) influences neuronal repair, regeneration and survival after brain injury. Possession of an APOE ε4 allele is associated with poor outcome after head injury in clinical studies. APOE might therefore influence outcome after acute stroke in humans.
Methods:
We comprehensively sought, identified, assessed and performed meta-analyses of studies reporting on the association between APOE and the combined outcome of death or dependency, or death alone, several months after ischaemic stroke (IS), intracerebral haemorrhage (ICH) or subarachnoid haemorrhage (SAH).
Results:
Our main analyses included data from 9 studies in a total of 2262 patients (1453 IS, 199 ICH, 610 SAH). Overall, ε4+ genotypes were not significantly associated with risk of death or dependency several months after stroke. However, there was significant heterogeneity between studies, and between the three pathological types of stroke. ε4+ genotypes were associated with increased death or dependency after SAH (RR 1.40, 95% CI 1.06 to 1.84), with a trend toward a similar association with ICH (RR 1.38, 95% CI 0.99 to 1.92), but not IS (RR 0.98, 95% CI 0.85 to 1.12). Results were similar for death alone.
Conclusions:
APOE may differentially affect outcome after the three main pathological types of stroke. Further, large studies are needed to confirm or refute these findings, and to assess the possibility of an interaction between the effects of APOE and age.
doi:10.1136/jnnp.2006.097543
PMCID: PMC2077401  PMID: 16926234
22.  Comparing risks of death and recurrent vascular events between lacunar and non-lacunar infarction 
Brain : a journal of neurology  2005;128(Pt 11):2507-2517.
Summary
Differences in prognosis of lacunar and non-lacunar infarction patients might support distinct arterial pathological processes underlying these two subtypes of ischaemic stroke. We did a systematic review in which we identified cohort studies with ischaemic stroke subtype-specific follow-up data on death, recurrent stroke and/or myocardial infarction (MI). We calculated risks of death and recurrent stroke at 1 month, 1-12 months and 1-5 years, as well as risks of MI and cardiac death. We compared non-lacunar with lacunar infarction, using study-specific and summary odds ratios. We also compared the pattern of recurrent stroke subtypes after lacunar and non-lacunar infarction. One month odds of death and of recurrent stroke were significantly greater following non-lacunar than lacunar infarction, but the difference decreased thereafter (one month mortality: OR 3.81, 95% CI 2.77 to 5.23; 1-12 month mortality: OR 2.32, 95% CI 1.74 to 3.08; 1-5 year mortality: OR 1.77, 95% CI 1.28 to 2.45; one month stroke recurrence OR 2.11, 95% CI 1.20 to 3.69; 1-12 month stroke recurrence OR 1.24, 95% CI 0.85 to 1.83; 1-5 year stroke recurrence OR 1.61, 95% CI 0.96 to 2.70). Recurrent strokes were more likely to be lacunar if the index event was lacunar. Few studies reported on the risk of MI, but we found no significant difference in risk of cardiac death in non-lacunar versus lacunar infarction. Thus, although early mortality and stroke recurrence risk are higher among non-lacunar than lacunar infarct patients, the risks appear not to differ in the longer term and the risks of cardiac outcomes are similar, although data are limited. There is some evidence that recurrent ischaemic stroke subtypes breed true. These results provide limited support for a distinct arterial pathology underlying lacunar infarction.
doi:10.1093/brain/awh636
PMCID: PMC2577181  PMID: 16195245
lacunar infarction; prognosis; outcome; recurrent stroke; death
23.  Does Apolipoprotein E Genotype Influence the Risk of Ischemic Stroke, Intracerebral Hemorrhage, or Subarachnoid Hemorrhage? 
Background and Purpose
Apolipoprotein E genotype (APOE) is associated with cholesterol metabolism, ischemic heart disease, and cerebral amyloid angiopathy, and so may affect risk of both ischemic and hemorrhagic stroke.
Methods
We comprehensively sought and identified studies of the association of apoE with ischemic stroke (IS), intracerebral hemorrhage (ICH), and subarachnoid hemorrhage (SAH). We did meta-analyses to assess the evidence for an association between APOE and the various pathological types and subtypes of stroke, and assessed the effects of several methodological criteria.
Results
We analyzed data from 31 eligible studies (26 IS, 8 ICH, and 3 SAH) in 5961 cases and 17 965 controls. ∊4 allele-containing (∊4+) genotypes were significantly associated with IS (odds ratio [OR], 1.11; 95% CI, 1.01 to 1.22) and SAH (OR, 1.42; 95% CI, 1.01 to 1.99) and nonsignificantly with ICH (OR, 1.16; 95% CI, 0.93 to 1.44), whereas ∊2+ genotypes were associated with ICH (OR, 1.32; 95% CI, 1.01 to 1.74). Associations appeared stronger with ∊4+ genotypes for large artery compared with other IS subtypes and for Asian compared with white populations, and with ∊2+ genotypes for lobar compared with deep hemorrhages. However, we found no association between ∊4+ genotypes and IS when we analyzed only larger studies (>200 cases; OR, 0.99; 95% CI, 0.88 to 1.11) or studies without control selection bias (OR, 0.99; 95% CI, 0.85 to 1.17).
Conclusions
Publication and selection biases make existing studies of APOE and stroke unreliable. Further, very large, methodologically rigorous studies are needed.
doi:10.1161/01.STR.0000199065.12908.62
PMCID: PMC2577180  PMID: 16385096
apolipoproteins E; genetics; meta-analysis; stroke
24.  Are Lacunar Strokes Really Different? 
Background and Purpose
Differences in risk factors between lacunar and nonlacunar infarcts might support a distinct arterial pathological process underlying lacunar infarction.
Methods
We did a systematic review of studies comparing risk factors in patients with lacunar versus nonlacunar infarction. For each risk factor, we calculated study-specific and pooled relative risks (RRs) for lacunar versus nonlacunar infarction.
Results
A total of 16 of 28 studies included risk factors in their ischemic stroke subtype definitions. Hypertension and diabetes appeared commoner among patients with lacunar versus nonlacunar infarction. However, analyses confined to studies using risk factor-free ischemic subtype definitions found only a marginal excess of hypertension with lacunar versus nonlacunar infarction (RR, 1.11; 95% CI, 1.04 to 1.19) and no difference for diabetes (RR, 0.95; 95% CI, 0.83 to 1.09). Atrial fibrillation and carotid stenosis were associated more with nonlacunar than lacunar infarction but less so when only studies using risk factor-free classifications were considered. Otherwise, there was no evidence of differences in risk factor profiles.
Conclusions
Risk factor-free ischemic stroke subtype classification methods should be used for comparing risk factor profiles between lacunar and nonlacunar subtypes.
doi:10.1161/01.STR.0000157949.34986.30
PMCID: PMC2577185  PMID: 15761206
lacunar infarction; meta-analysis; risk factors; stroke
25.  Association Between Apolipoprotein E Genotype and Carotid Intima-Media Thickness May Suggest a Specific Effect on Large Artery Atherothrombotic Stroke 
Background and Purpose
Apolipoprotein E genotype (APOE) influences cholesterol levels and ischemic heart disease. Although there is no convincing overall association with ischemic stroke, APOE may influence large artery (atherothrombotic) stroke, for which carotid intima-media thickness (CIMT) is an informative intermediate phenotype. We therefore performed a systematic review and meta-analysis of the association between APOE and CIMT.
Methods
We sought all published studies assessing the association between APOE and CIMT. From each study, we extracted available data on study methods, subjects’ characteristics, and mean (and standard deviation) CIMT for each genotype or genotype group. We calculated study-specific and random effects pooled differences in mean CIMT between genotype groups, and assessed heterogeneity between studies and predefined subgroups using I2 and χ2 statistics.
Results
Meta-analysis of 22 published studies (30 879 subjects) showed a significant association between APOE and CIMT (pooled mean difference ε4-versus ε2-allele containing genotypes 46 μm, 95% CI 29 to 62, P<0.00001). We found evidence of small study (mainly publication) bias, with a diminished (but still highly statistically significant) association in studies of >1000 subjects (pooled mean difference 17 μm, 95% CI 12 to 23, P<0.00001). The association was larger among high vascular risk and eastern Asian populations, but this may simply reflect the smaller size of these studies.
Conclusion
Our results show a clear association of APOE with CIMT, even though publication bias means that this is overestimated by the published literature. These findings suggest the possibility of a specific association with large artery ischemic stroke.
doi:10.1161/STROKEAHA.107.488866
PMCID: PMC2577179  PMID: 18063831
apolipoprotein E; association; carotid intimal medial thickness; genetics; meta-analysis

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