The Ischemic Stroke Genetics Study (ISGS) Protocol

Family History is Related to High Risk of Recurrent Events after Ischemic Stroke or Transient Ischemic Attack

OBJECTIVE

Prior data suggest paternal or sibling stroke was associated with increased risk of offspring stroke. Whether family history of cardiovascular disease (FHc) predicts risk of stroke recurrence remains unclear, we aim to determine this issue on patients with ischemic stroke (IS) or transient ischemic attack (TIA).

MATERIALS AND METHODS

This is a post hoc analysis based on the Third China National Stroke Registry III. IS/TIA patients with data of FHc status were included. FHc was defined as family history of coronary heart disease (CHD) or stroke among first-degree relatives (include parents, children, and siblings (same parents)). Cox proportional hazards regression models were performed to assess the association between FHc and recurrent events at 1 year follow-up.

RESULTS

Totally 14,208 patients with verified FHc status were included, 4,454 (31.3%) were female and the median (IQR) age was 62.0 (54.0, 70.0) years. Of these, 294 (2.1%), 726 (5.1%) and 1936 (13.6%) had family history of both CHD and stroke, family history of CHD, and family history of stroke only, respectively. Using multivariable Cox models adjusted for age, sex, and vascular risk factors, we found that patients with FHc experienced higher risk of stroke recurrence (HR=1.151, 95%CI=1.000-1.324) and combined vascular events (HR=1.186, 95%CI=1.036-1.358) at 1 year compared with those without FHc. In sensitivity analysis on patients who received primary secondary prevention treatment of antiplatelet and statins, the association persisted.

CONCLUSIONS

FHc is associated with increased risk of stroke recurrence even under primary secondary prevention treatment.

Mechanisms of Preconditioning Exercise-Induced Neurovascular Protection in Stroke

Ischemic stroke is a leading cause of death and disability. Tissue plasminogen activator is the only U.S. Food and Drug Administration approved thrombolytic therapy for ischemic stroke patients till date. However, its use is limited due to increased risk of bleeding and narrow therapeutic window. Most of the preclinically tested pharmacological agents failed to be translated to the clinic. This drives the need for alternative therapeutic approaches that not only provide enhanced neuroprotection, but also reduce the risk of stroke. Physical exercise is a sort of preconditioning that provides the body with brief ischemic episodes that can protect the body from subsequent severe ischemic attacks like stroke. Physical exercise is known to improve cardiovascular health. However, its role in providing neuroprotection in stroke is not clear. Clinical observational studies showed a correlation between regular physical exercise and reduced risk and severity of ischemic stroke and better outcomes after stroke. However, the underlying mechanisms through which prestroke exercise can reduce the stroke injury and improve the outcomes are not completely understood. The purpose of this review is to: demonstrate the impact of exercise on stroke outcomes and show the potential role of exercise in stroke prevention and recovery; uncover the underlying mechanisms through which exercise reduces the neurovascular injury and improves stroke outcomes aiming to develop novel therapeutic approaches.

Genome-Wide Association Study Meta-Analysis of Stroke in 22 000 Individuals of African Descent Identifies Novel Associations With Stroke

BACKGROUND AND PURPOSE

Stroke is a complex disease with multiple genetic and environmental risk factors. Blacks endure a nearly 2-fold greater risk of stroke and are 2× to 3× more likely to die from stroke than European Americans.

METHODS

The COMPASS (Consortium of Minority Population Genome-Wide Association Studies of Stroke) has conducted a genome-wide association meta-analysis of stroke in >22 000 individuals of African ancestry (3734 cases, 18 317 controls) from 13 cohorts.

RESULTS

In meta-analyses, we identified one single nucleotide polymorphism (rs55931441) near the HNF1A gene that reached genome-wide significance (P=4.62×10-8) and an additional 29 variants with suggestive evidence of association (P<1×10-6), representing 24 unique loci. For validation, a look-up analysis for a 100 kb region flanking the COMPASS single nucleotide polymorphism was performed in SiGN (Stroke Genetics Network) Europeans, SiGN Hispanics, and METASTROKE (Europeans). Using a stringent Bonferroni correction P value of 2.08×10-3 (0.05/24 unique loci), we were able to validate associations at the HNF1A locus in both SiGN (P=8.18×10-4) and METASTROKE (P=1.72×10-3) European populations. Overall, 16 of 24 loci showed evidence for validation across multiple populations. Previous studies have reported associations between variants in the HNF1A gene and lipids, C-reactive protein, and risk of coronary artery disease and stroke. Suggestive associations with variants in the SFXN4 and TMEM108 genes represent potential novel ischemic stroke loci.

CONCLUSIONS

These findings represent the most thorough investigation of genetic determinants of stroke in individuals of African descent, to date.

Validation of the 8-item questionnaire for verifying stroke free status with and without pictograms in three West African languages

Background

The Questionnaire for Verifying Stroke-free Status (QVSFS) has been validated in Western populations as a method for verifying stroke-free status in participants of clinical, epidemiological and genetic studies. This instrument has not been validated in low-income settings where populations have limited knowledge of stroke symptoms and literacy levels are low.

Objective

To simultaneously validate the 8-item QVSFS in 3 languages spoken in West Africa (Yoruba, Hausa and Akan) for ascertainment of stroke-free status of control subjects in SIREN.

Methods

Using a cross-sectional study design, 100 participants each from the 3 linguistic groups will be consecutively recruited from neurology and general medicine clinics of 5 tertiary referral hospitals in Nigeria and Ghana. Ascertainment of stroke status will be determined by neurologists using structured neurological examination, review of case records and neuro-imaging (Gold standard). The relative performance of QVSFS without and with pictures of stroke symptoms (pictograms) will be assessed using sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV).

Conclusion

The proposed study will provide valuable data on the performance of the QVSFS in resource-limited settings.

•

This study seeks to evaluate the performance of the 8-item QVSFS in Akan, Yoruba and Hausa for the ascertainment of stroke-free status among West Africans.

•

A line pictogram has been developed to determine its impact on the relative performance of the 8-item QVSFS.

Using family members to augment genetic case-control studies of a life-threatening disease

Survival bias is difficult to detect and adjust for in case-control genetic association studies but can invalidate findings when only surviving cases are studied and survival is associated with the genetic variants under study. Here, we propose a design where one genotypes genetically informative family members (such as offspring, parents, and spouses) of deceased cases and incorporates that surrogate genetic information into a retrospective maximum likelihood analysis. We show that inclusion of genotype data from first-degree relatives permits unbiased estimation of genotype association parameters. We derive closed-form maximum likelihood estimates for association parameters under the widely used log-additive and dominant association models. Our proposed design not only permits a valid analysis but also enhances statistical power by augmenting the sample with indirectly studied individuals. Gene variants associated with poor prognosis can also be identified under this design. We provide simulation results to assess performance of the methods. Copyright © 2016 John Wiley & Sons, Ltd.

Multilingual Validation of the Questionnaire for Verifying Stroke-Free Status in West Africa

BACKGROUND AND PURPOSE

The Questionnaire for Verifying Stroke-Free Status (QVSFS), a method for verifying stroke-free status in participants of clinical, epidemiological, and genetic studies, has not been validated in low-income settings where populations have limited knowledge of stroke symptoms. We aimed to validate QVSFS in 3 languages, Yoruba, Hausa and Akan, for ascertainment of stroke-free status of control subjects enrolled in an on-going stroke epidemiological study in West Africa.

METHODS

Data were collected using a cross-sectional study design where 384 participants were consecutively recruited from neurology and general medicine clinics of 5 tertiary referral hospitals in Nigeria and Ghana. Ascertainment of stroke status was by neurologists using structured neurological examination, review of case records, and neuroimaging (gold standard). Relative performance of QVSFS without and with pictures of stroke symptoms (pictograms) was assessed using sensitivity, specificity, positive predictive value, and negative predictive value.

RESULTS

The overall median age of the study participants was 54 years and 48.4% were males. Of 165 stroke cases identified by gold standard, 98% were determined to have had stroke, whereas of 219 without stroke 87% were determined to be stroke-free by QVSFS. Negative predictive value of the QVSFS across the 3 languages was 0.97 (range, 0.93-1.00), sensitivity, specificity, and positive predictive value were 0.98, 0.82, and 0.80, respectively. Agreement between the questionnaire with and without the pictogram was excellent/strong with Cohen k=0.92.

CONCLUSIONS

QVSFS is a valid tool for verifying stroke-free status across culturally diverse populations in West Africa.

Meta-Analysis of Genome-Wide Association Studies Identifies Genetic Risk Factors for Stroke in African Americans

BACKGROUND AND PURPOSE

The majority of genome-wide association studies (GWAS) of stroke have focused on European-ancestry populations; however, none has been conducted in African Americans, despite the disproportionately high burden of stroke in this population. The Consortium of Minority Population Genome-Wide Association Studies of Stroke (COMPASS) was established to identify stroke susceptibility loci in minority populations.

METHODS

Using METAL, we conducted meta-analyses of GWAS in 14 746 African Americans (1365 ischemic and 1592 total stroke cases) from COMPASS, and tested genetic variants with P<10(-6) for validation in METASTROKE, a consortium of ischemic stroke genetic studies in European-ancestry populations. We also evaluated stroke loci previously identified in European-ancestry populations.

RESULTS

The 15q21.3 locus linked with lipid levels and hypertension was associated with total stroke (rs4471613; P=3.9×10(-8)) in African Americans. Nominal associations (P<10(-6)) for total or ischemic stroke were observed for 18 variants in or near genes implicated in cell cycle/mRNA presplicing (PTPRG, CDC5L), platelet function (HPS4), blood-brain barrier permeability (CLDN17), immune response (ELTD1, WDFY4, and IL1F10-IL1RN), and histone modification (HDAC9). Two of these loci achieved nominal significance in METASTROKE: 5q35.2 (P=0.03), and 1p31.1 (P=0.018). Four of 7 previously reported ischemic stroke loci (PITX2, HDAC9, CDKN2A/CDKN2B, and ZFHX3) were nominally associated (P<0.05) with stroke in COMPASS.

CONCLUSIONS

We identified a novel genetic variant associated with total stroke in African Americans and found that ischemic stroke loci identified in European-ancestry populations may also be relevant for African Americans. Our findings support investigation of diverse populations to identify and characterize genetic risk factors, and the importance of shared genetic risk across populations.

Sequence variants on chromosome 9p21 are associated with ischemic stroke and the lipids level in Chinese Han population

BACKGROUND

Several studies have demonstrated that variants on chromosome 9p21 confer susceptibility to ischemic stroke (IS) disease. But, the results of variants' roles in Chinese IS population are blank or inconsistent.

METHODS

We performed a case-control analysis in 116 patients with IS and 118 non-IS controls of Han background to determine whether 4 single nucleotide polymorphisms were associated with IS. DNA was extracted from saliva using a magnetic nanoparticles-based method.

RESULTS

After we adjusted for clinical parameters, we found that the rs10757278-GG genotype conveyed 1.88-fold (95% confidence interval [CI], 1.1-3.1; P = .015), the rs1537378-C allele conveyed 2.0-fold (95% CI, 1.2-3.5; P = .008), and the rs1333047-TT genotype conveyed 1.64-fold (95% CI, 1.02-2.6; P = .041) increased risk of IS, respectively. In addition, there is a significant difference of the lipids level between GG genotype compared with that of AA genotype in rs10757278 (P < .05).

CONCLUSIONS

This study is the first one to demonstrate that the rs10757278-GG genotype, the rs1537378-C allele, and rs1333047-TT genotype are associated with IS in Chinese Han populations. More importantly, the variant of rs10757278 may have different degrees of influence on lipids level.

Genome-wide analysis of blood pressure variability and ischemic stroke

BACKGROUND AND PURPOSE

Visit-to-visit variability in blood pressure (vBP) is associated with ischemic stroke. We sought to determine whether such variability has genetic causes and whether genetic variants associated with BP variability are also associated with ischemic stroke.

METHODS

A Genome Wide Association Study (GWAS) for loci influencing BP variability was undertaken in 3802 individuals from the Anglo-Scandinavian Cardiac Outcome Trial (ASCOT) study, in which long-term visit-to-visit and within-visit BP measures were available. Because BP variability is strongly associated with ischemic stroke, we genotyped the sentinel single nucleotide polymorphism in an independent ischemic stroke population comprising 8624 cases and 12 722 controls and in 3900 additional (Scandinavian) participants from the ASCOT study to replicate our findings.

RESULTS

The ASCOT discovery GWAS identified a cluster of 17 correlated single nucleotide polymorphisms within the NLGN1 gene (3q26.31) associated with BP variability. The strongest association was with rs976683 (P=1.4×10(-8)). Conditional analysis of rs976683 provided no evidence of additional independent associations at the locus. Analysis of rs976683 in patients with ischemic stroke found no association for overall stroke (odds ratio, 1.02; 95% CI, 0.97-1.07; P=0.52) or its subtypes: cardioembolic (odds ratio, 1.07; 95% CI, 0.97-1.16; P=0.17), large vessel disease (odds ratio, 0.98; 95% CI, 0.89-1.07; P=0.60), and small vessel disease (odds ratio, 1.07; 95% CI, 0.97-1.17; P=0.19). No evidence for association was found between rs976683 and BP variability in the additional (Scandinavian) ASCOT participants (P=0.18).

CONCLUSIONS

We identified a cluster of single nucleotide polymorphisms at the NLGN1 locus showing significant association with BP variability. Follow-up analyses did not support an association with risk of ischemic stroke and its subtypes.

TREM2 in neurodegeneration: evidence for association of the p.R47H variant with frontotemporal dementia and Parkinson's disease

BACKGROUND

A rare variant in the Triggering Receptor Expressed on Myeloid cells 2 (TREM2) gene has been reported to be a genetic risk factor for Alzheimer's disease by two independent groups (Odds ratio between 2.9-4.5). Given the key role of TREM2 in the effective phagocytosis of apoptotic neuronal cells by microglia, we hypothesized that dysfunction of TREM2 may play a more generalized role in neurodegeneration. With this in mind we set out to assess the genetic association of the Alzheimer's disease-related risk variant in TREM2 (rs75932628, p.R47H) with other related neurodegenerative disorders.

RESULTS

The study included 609 patients with frontotemporal dementia, 765 with amyotrophic lateral sclerosis, 1493 with Parkinson's disease, 772 with progressive supranuclear palsy, 448 with ischemic stroke and 1957 controls subjects free of neurodegenerative disease. A significant association was observed for the TREM2 p.R47H substitution in susceptibility to frontotemporal dementia (OR = 5.06; p-value = 0.001) and Parkinson's disease (OR = 2.67; p-value = 0.026), while no evidence of association with risk of amyotrophic lateral sclerosis, progressive supranuclear palsy or ischemic stroke was observed.

CONCLUSIONS

Our results suggest that the TREM2 p.R47H substitution is a risk factor for frontotemporal dementia and Parkinson's disease in addition to Alzheimer's disease. These findings suggest a more general role for TREM2 dysfunction in neurodegeneration, which could be related to its role in the immune response.

Common variants within oxidative phosphorylation genes influence risk of ischemic stroke and intracerebral hemorrhage

BACKGROUND AND PURPOSE

Previous studies demonstrated association between mitochondrial DNA variants and ischemic stroke (IS). We investigated whether variants within a larger set of oxidative phosphorylation (OXPHOS) genes encoded by both autosomal and mitochondrial DNA were associated with risk of IS and, based on our results, extended our investigation to intracerebral hemorrhage (ICH).

METHODS

This association study used a discovery cohort of 1643 individuals, a validation cohort of 2432 individuals for IS, and an extension cohort of 1476 individuals for ICH. Gene-set enrichment analysis was performed on all structural OXPHOS genes, as well as genes contributing to individual respiratory complexes. Gene-sets passing gene-set enrichment analysis were tested by constructing genetic scores using common variants residing within each gene. Associations between each variant and IS that emerged in the discovery cohort were examined in validation and extension cohorts.

RESULTS

IS was associated with genetic risk scores in OXPHOS as a whole (odds ratio [OR], 1.17; P=0.008) and complex I (OR, 1.06; P=0.050). Among IS subtypes, small vessel stroke showed association with OXPHOS (OR, 1.16; P=0.007), complex I (OR, 1.13; P=0.027), and complex IV (OR, 1.14; P=0.018). To further explore this small vessel association, we extended our analysis to ICH, revealing association between deep hemispheric ICH and complex IV (OR, 1.08; P=0.008).

CONCLUSIONS

This pathway analysis demonstrates association between common genetic variants within OXPHOS genes and stroke. The associations for small vessel stroke and deep ICH suggest that genetic variation in OXPHOS influences small vessel pathobiology. Further studies are needed to identify culprit genetic variants and assess their functional consequences.

Genetic variants associated with myocardial infarction in the PSMA6 gene and Chr9p21 are also associated with ischaemic stroke

BACKGROUND

Ischaemic stroke shares common traditional risk factors with coronary artery disease (CAD) and myocardial infarction (MI). This study evaluated whether genetic risk factors for CAD and MI also affect susceptibility to ischaemic stroke in Caucasians and African Americans.

METHODS

Included in the study were a Caucasian series (713 ischaemic stroke patients, 708 controls) and a small African American series (166 ischaemic stroke patients, 117 controls). Twenty single-nucleotide polymorphisms (SNPs) previously shown to be associated with CAD or MI were genotyped and assessed for association with ischaemic stroke and ischaemic stroke subtypes using odds ratios (ORs) from multivariable logistic regression models.

RESULTS

In Caucasians, four SNPs on chromosome 9p21 were significantly associated with risk of cardioembolic stroke, the strongest of which was rs1333040 (OR 1.55, P = 0.0007); similar but weaker trends were observed for small vessel stroke, with no associations observed regarding large vessel stroke. Chromosome 9p21 SNPs were also associated with risk of ischaemic stroke in African Americans (rs1333040, OR 0.65, P = 0.023; rs1333042, OR 0.55, P = 0.070; rs2383207, OR 0.55, P = 0.070). The PSMA6 SNP rs1048990 on chromosome 14q13 was associated with overall ischaemic stroke in both Caucasians (OR 0.80, P = 0.036) and African Americans (OR 0.31, P = 0.020).

CONCLUSIONS

Our results provide evidence that chromosome 9p21 variants are associated with cardioembolic ischaemic stroke in Caucasians and with overall ischaemic stroke in African Americans. The PSMA6 variant rs1048990 also appears to affect susceptibility to ischaemic stroke in both populations. These findings require validation, particularly the preliminary findings regarding African Americans given the small size of that series.

Polymorphisms of genes in nitric oxide-forming pathway associated with ischemic stroke in Chinese Han population

AIM

To investigate the association of polymorphisms in four critical genes implicated in the NO-forming pathway with ischemic stroke (IS) in a Chinese Han population.

METHODS

DNA samples of 558 IS patients and 557 healthy controls from Chinese Han population were genotyped using the Taqman(TM) 7900HT Sequence Detection System. Six SNPs (rs841, rs1049255, rs2297518, rs1799983, rs2020744, rs4673) of the 4 related genes (eNOS, iNOS, GCH1, and CYBA) in the NO forming pathway were analyzed using the SPSS 13.0 software package for Windows.

RESULTS

One SNP located in the intron of GCH1 (rs841) was associated with IS independent of the traditional cardiovascular risk factors in co-dominant and dominant models (P=0.003, q=0.027; P=0.00006, q=0.0108; respectively). Moreover, the combination of rs1049255 CC+CT and rs841 GA+AA genotypes was associated with significantly higher risk for IS after adjustments (OR=1.73, 95% CI: 1.27-2.35, P<0.0001, q<0.0001).

CONCLUSION

The data suggest that genetic variants within the NO-forming pathway alter susceptibility to IS in Chinese Han population. Replication of the present results in other independent cohorts is warranted.

Genomic risk profiling of ischemic stroke: results of an international genome-wide association meta-analysis

INTRODUCTION

Familial aggregation of ischemic stroke derives from shared genetic and environmental factors. We present a meta-analysis of genome-wide association scans (GWAS) from 3 cohorts to identify the contribution of common variants to ischemic stroke risk.

METHODS

This study involved 1464 ischemic stroke cases and 1932 controls. Cases were genotyped using the Illumina 610 or 660 genotyping arrays; controls, with Illumina HumanHap 550Kv1 or 550Kv3 genotyping arrays. Imputation was performed with the 1000 Genomes European ancestry haplotypes (August 2010 release) as a reference. A total of 5,156,597 single-nucleotide polymorphisms (SNPs) were incorporated into the fixed effects meta-analysis. All SNPs associated with ischemic stroke (P<1×10(-5)) were incorporated into a multivariate risk profile model.

RESULTS

No SNP reached genome-wide significance for ischemic stroke (P<5×10(-8)). Secondary analysis identified a significant cumulative effect for age at onset of stroke (first versus fifth quintile of cumulative profiles based on SNPs associated with late onset, ß = 14.77 [10.85,18.68], P = 5.5×10(-12)), as well as a strong effect showing increased risk across samples with a high propensity for stroke among samples with enriched counts of suggestive risk alleles (P<5×10(-6)). Risk profile scores based only on genomic information offered little incremental prediction.

DISCUSSION

There is little evidence of a common genetic variant contributing to moderate risk of ischemic stroke. Quintiles based on genetic loading of alleles associated with a younger age at onset of ischemic stroke revealed a significant difference in age at onset between those in the upper and lower quintiles. Using common variants from GWAS and imputation, genomic profiling remains inferior to family history of stroke for defining risk. Inclusion of genomic (rare variant) information may be required to improve clinical risk profiling.

Effect modification by population dietary folate on the association between MTHFR genotype, homocysteine, and stroke risk: a meta-analysis of genetic studies and randomised trials

BACKGROUND

The MTHFR 677C→T polymorphism has been associated with raised homocysteine concentration and increased risk of stroke. A previous overview showed that the effects were greatest in regions with low dietary folate consumption, but differentiation between the effect of folate and small-study bias was difficult. A meta-analysis of randomised trials of homocysteine-lowering interventions showed no reduction in coronary heart disease events or stroke, but the trials were generally set in populations with high folate consumption. We aimed to reduce the effect of small-study bias and investigate whether folate status modifies the association between MTHFR 677C→T and stroke in a genetic analysis and meta-analysis of randomised controlled trials.

METHODS

We established a collaboration of genetic studies consisting of 237 datasets including 59,995 individuals with data for homocysteine and 20,885 stroke events. We compared the genetic findings with a meta-analysis of 13 randomised trials of homocysteine-lowering treatments and stroke risk (45,549 individuals, 2314 stroke events, 269 transient ischaemic attacks).

FINDINGS

The effect of the MTHFR 677C→T variant on homocysteine concentration was larger in low folate regions (Asia; difference between individuals with TT versus CC genotype, 3·12 μmol/L, 95% CI 2·23 to 4·01) than in areas with folate fortification (America, Australia, and New Zealand, high; 0·13 μmol/L, -0·85 to 1·11). The odds ratio (OR) for stroke was also higher in Asia (1·68, 95% CI 1·44 to 1·97) than in America, Australia, and New Zealand, high (1·03, 0·84 to 1·25). Most randomised trials took place in regions with high or increasing population folate concentrations. The summary relative risk (RR) of stroke in trials of homocysteine-lowering interventions (0·94, 95% CI 0·85 to 1·04) was similar to that predicted for the same extent of homocysteine reduction in large genetic studies in populations with similar folate status (predicted RR 1·00, 95% CI 0·90 to 1·11). Although the predicted effect of homocysteine reduction from large genetic studies in low folate regions (Asia) was larger (RR 0·78, 95% CI 0·68 to 0·90), no trial has evaluated the effect of lowering of homocysteine on stroke risk exclusively in a low folate region.

INTERPRETATION

In regions with increasing levels or established policies of population folate supplementation, evidence from genetic studies and randomised trials is concordant in suggesting an absence of benefit from lowering of homocysteine for prevention of stroke. Further large-scale genetic studies of the association between MTHFR 677C→T and stroke in low folate settings are needed to distinguish effect modification by folate from small-study bias. If future randomised trials of homocysteine-lowering interventions for stroke prevention are undertaken, they should take place in regions with low folate consumption.

FUNDING

Full funding sources listed at end of paper (see Acknowledgments).

Bio-Repository of DNA in stroke (BRAINS): a study protocol

Background

Stroke is one of the commonest causes of mortality in the world and anticipated to be an increasing burden to the developing world. Stroke has a genetic basis and identifying those genes may not only help us define the mechanisms that cause stroke but also identify novel therapeutic targets. However, large scale highly phenotyped DNA repositories are required in order for this to be achieved.

Methods

The proposed Bio-Repository of DNA in Stroke (BRAINS) will recruit all subtypes of stroke as well as controls from two different continents, Europe and Asia. Subjects recruited from the UK will include stroke patients of European ancestry as well as British South Asians. Stroke subjects from South Asia will be recruited from India and Sri Lanka. South Asian cases will also have control subjects recruited.

Discussion

We describe a study protocol to establish a large and highly characterized stroke biobank in those of European and South Asian descent. With different ethnic populations being recruited, BRAINS has the ability to compare and contrast genetic risk factors between those of differing ancestral descent as well as those who migrate into different environments.

White matter hyperintensity volume is increased in small vessel stroke subtypes

OBJECTIVE

White matter hyperintensity (WMH) may be a marker of an underlying cerebral microangiopathy. Therefore, we hypothesized that WMH would be most severe in patients with lacunar stroke and intracerebral hemorrhage (ICH), 2 types of stroke in which cerebral small vessel (SV) changes are pathophysiologically relevant.

METHODS

We determined WMH volume (WMHV) in cohorts of prospectively ascertained patients with acute ischemic stroke (AIS) (Massachusetts General Hospital [MGH], n = 628, and the Ischemic Stroke Genetics Study [ISGS], n = 263) and ICH (MGH, n = 122).

RESULTS

Median WMHV was 7.5 cm³ (interquartile range 3.4-14.7 cm³) in the MGH AIS cohort (mean age 65 ± 15 years). MGH patients with larger WMHV were more likely to have lacunar stroke compared with cardioembolic (odds ratio [OR] = 1.87 per SD normally transformed WMHV), large artery (OR = 2.25), undetermined (OR = 1.87), or other (OR = 1.85) stroke subtypes (p < 0.03). These associations were replicated in the ISGS cohort (p = 0.03). In a separate analysis, greater WMHV was seen in ICH compared with lacunar stroke (OR = 1.2, p < 0.02) and in ICH compared with all ischemic stroke subtypes combined (OR = 1.34, p < 0.007).

CONCLUSIONS

Greater WMH burden was associated with SV stroke compared with other ischemic stroke subtypes and, even more strongly, with ICH. These data, from 2 independent samples, support the model that increasing WMHV is a marker of more severe cerebral SV disease and provide further evidence for links between the biology of WMH and SV stroke.

Common mitochondrial sequence variants in ischemic stroke

OBJECTIVE

Rare mitochondrial mutations cause neurologic disease, including ischemic stroke and MRI white matter changes. We investigated whether common mitochondrial genetic variants influence risk of sporadic ischemic stroke and, in patients with stroke, the volume of white matter hyperintensity (WMHV).

METHODS

In this multicenter, mitochondrial genome-wide association study (GWAS), 2284 ischemic stroke cases and 1728 controls from the International Stroke Genetics Consortium were genotyped for 64 mitochondrial single nucleotide polymorphisms (SNPs). Imputation resulted in 144 SNPs, which were tested in each cohort and in meta-analysis for ischemic stroke association. A genetic score of all mitochondrial variants was also tested in association with ischemic stroke.

RESULTS

No individual SNP reached adjusted significance in meta-analysis. A genetic score comprised of the summation of contributions from individual variants across the mitochondrial genome showed association with ischemic stroke in meta-analysis (odds ratio [OR] = 1.13, p < 0.0001) with minimal heterogeneity (I(2) = 0.00). This ischemic stroke score was robust to permutation, and was also associated with WMHV in 792 nested case individuals with ischemic stroke (p = 0.037).

INTERPRETATION

In this mitochondrial GWAS of ischemic stroke, a genetic score comprised of the sum of all common variants in the mitochondrial genome showed association with ischemic stroke. In an independent analysis of a related trait, this same score correlated with WMHV in stroke cases. Despite this aggregate association, no individual variant reached significance. Substantially larger studies will be required to identify precise sequence variants influencing cerebrovascular disease.

Principal-component analysis for assessment of population stratification in mitochondrial medical genetics

Although inherited mitochondrial genetic variation can cause human disease, no validated methods exist for control of confounding due to mitochondrial population stratification (PS). We sought to identify a reliable method for PS assessment in mitochondrial medical genetics. We analyzed mitochondrial SNP data from 1513 European American individuals concomitantly genotyped with the use of a previously validated panel of 144 mitochondrial markers as well as the Affymetrix 6.0 (n = 432), Illumina 610-Quad (n = 458), or Illumina 660 (n = 623) platforms. Additional analyses were performed in 938 participants in the Human Genome Diversity Panel (HGDP) (Illumina 650). We compared the following methods for controlling for PS: haplogroup-stratified analyses, mitochondrial principal-component analysis (PCA), and combined autosomal-mitochondrial PCA. We computed mitochondrial genomic inflation factors (mtGIFs) and test statistics for simulated case-control and continuous phenotypes (10,000 simulations each) with varying degrees of correlation with mitochondrial ancestry. Results were then compared across adjustment methods. We also calculated power for discovery of true associations under each method, using a simulation approach. Mitochondrial PCA recapitulated haplogroup information, but haplogroup-stratified analyses were inferior to mitochondrial PCA in controlling for PS. Correlation between nuclear and mitochondrial principal components (PCs) was very limited. Adjustment for nuclear PCs had no effect on mitochondrial analysis of simulated phenotypes. Mitochondrial PCA performed with the use of data from commercially available genome-wide arrays correlated strongly with PCA performed with the use of an exhaustive mitochondrial marker panel. Finally, we demonstrate, through simulation, no loss in power for detection of true associations with the use of mitochondrial PCA.

Candidate gene polymorphisms for ischemic stroke

BACKGROUND AND PURPOSE

Ischemic stroke (IS) is a multifactorial disorder with strong evidence from twin, family, and animal model studies suggesting a genetic influence on risk and prognosis. Several candidate genes for IS have been proposed, but few have been replicated. We investigated the contribution of 67 candidate genes (369 single nucleotide polymorphisms [SNPs]) on the risk of IS in a North American population of European descent.

METHODS

Two independent studies were performed. In the first, 342 SNPs from 52 candidate genes were genotyped in 307 IS cases and 324 control subjects. The SNPs significantly associated with IS were tested for replication in another cohort of 583 IS cases and 270 control subjects. In the second study, 212 SNPs from 62 candidate genes were analyzed in 710 IS cases with subtyping available and 3751 control subjects.

RESULTS

None of the candidate genes (SNPs) were significantly associated with IS risk independent of known stroke risk factors after correction for multiple hypotheses testing.

CONCLUSIONS

These results are consistent with previous meta-analyses that demonstrate an absence of genetic association of variants in plausible candidate genes with IS risk. Our study suggests that the effect of the investigated SNPs may be weak or restricted to specific populations or IS subtypes.

Prestroke physical activity and early functional status after stroke

BACKGROUND

The importance of physical activity as a modifiable risk factor for stroke in particular and cardiovascular disease in general is well documented. The effect of exercise on stroke severity and stroke outcomes is less clear. This study aimed to assess that effect.

METHODS

Data collected for patients enrolled in the Ischemic Stroke Genetics Study were reviewed for prestroke self-reported levels of activity and four measures of stroke outcome assessed at enrollment and approximately 3 months after enrollment. Logistic regression was used to assess the association between physical activity and stroke outcomes, unadjusted and adjusted for patient characteristics.

RESULTS

A total of 673 patients were enrolled; 50.5% reported aerobic physical activity less than once a week, 28.5% reported aerobic physical activity one to three times weekly, and 21% reported aerobic physical activity four times a week or more. Patients with moderate and high levels of physical activity were more likely to have higher Barthel Index (BI) scores at enrollment. A similar association was detected for exercise and good outcomes for the Oxford Handicap Scale (OHS). After 3 months of follow-up, moderate activity was still associated with a high BI score. No significant association was detected for activity and the OHS or Glasgow Outcome Scale at follow-up after adjustment for patient characteristics.

CONCLUSIONS

Higher levels of self-reported prestroke physical activity may be associated with functional advantages after stroke. Our findings should be seen as exploratory, requiring confirmation, ideally in a longitudinal study of exercise in an older population.

Whole genome approaches in ischemic stroke

BACKGROUND AND PURPOSE

The field of ischemic stroke genetics is moving beyond candidate gene studies into the realm of genomewide association studies. Such studies have resulted in discoveries in diverse, complex disorders.

METHODS

The author conducted an informal qualitative review of peer-reviewed medical literature.

RESULTS

The power of genomewide association studies to confirm prior associations and establish new ones is illustrated by recent work focusing on type 2 diabetes mellitus. A pilot genomewide association study of ischemic stroke failed to identify a single gene of major effect.

CONCLUSIONS

Follow-up studies with substantially greater statistical power are essential and are being planned by the Wellcome Trust and others.

Whole genome analyses suggest ischemic stroke and heart disease share an association with polymorphisms on chromosome 9p21

BACKGROUND AND PURPOSE

Recently independent studies reported an association between coronary heart disease and single-nucleotide polymorphisms (SNPs) located at chromosome 9p21, near CDKN2A and CDKN2B genes. Given that stroke is a common complication after myocardial infarction, we investigated if the same SNPs were associated with ischemic stroke in our population.

METHODS

We recently initiated a whole genome analysis of ischemic stroke and published the first stage of a case control study using >400,000 SNPs from Illumina Infinium Human-1 and HumanHap300 assays. We focused on SNPs recently associated with heart disease by Helgadottir and colleagues and SNPs from the same haplotype block.

RESULTS

In analyses both unadjusted and adjusted for stroke risk factors, significant associations with ischemic stroke were observed for SNPs from the same haplotype block previously associated with myocardial infarction. Significant association was also seen between disease and haplotypes involving these SNPs, both with and without adjustment for stroke risk factors (odd ratios: 1.01 to 2.65).

CONCLUSIONS

These data are important for 3 reasons: first, they suggest a genetic association for stroke; second, they suggest that this association shares pathogenic mechanisms with heart disease and diabetes; and third, they illustrate, that public release of data can facilitate rapid risk locus discovery.

Structural genomic variation in ischemic stroke

Technological advances in molecular genetics allow rapid and sensitive identification of genomic copy number variants (CNVs). This, in turn, has sparked interest in the function such variation may play in disease. While a role for copy number mutations as a cause of Mendelian disorders is well established, it is unclear whether CNVs may affect risk for common complex disorders. We sought to investigate whether CNVs may modulate risk for ischemic stroke (IS) and to provide a catalog of CNVs in patients with this disorder by analyzing copy number metrics produced as a part of our previous genome-wide single-nucleotide polymorphism (SNP)-based association study of ischemic stroke in a North American white population. We examined CNVs in 263 patients with ischemic stroke (IS). Each identified CNV was compared with changes identified in 275 neurologically normal controls. Our analysis identified 247 CNVs, corresponding to 187 insertions (76%; 135 heterozygous; 25 homozygous duplications or triplications; 2 heterosomic) and 60 deletions (24%; 40 heterozygous deletions; 3 homozygous deletions; 14 heterosomic deletions). Most alterations (81%) were the same as, or overlapped with, previously reported CNVs. We report here the first genome-wide analysis of CNVs in IS patients. In summary, our study did not detect any common genomic structural variation unequivocally linked to IS, although we cannot exclude that smaller CNVs or CNVs in genomic regions poorly covered by this methodology may confer risk for IS. The application of genome-wide SNP arrays now facilitates the evaluation of structural changes through the entire genome as part of a genome-wide genetic association study.

Impact of restricting enrollment in stroke genetics research to adults able to provide informed consent

BACKGROUND AND PURPOSE

The extent of potential consent bias in observational studies elucidating genetic and environmental contributions to ischemic stroke is largely unknown. The purpose of this study was to assess differences in stroke cohort characteristics between those who provided informed consent and those whose enrollment was authorized by surrogate decision makers.

METHODS

The Ischemic Stroke Genetics Study (ISGS) is a prospective, 5-center, case-control study of first-ever ischemic stroke. Demographic, clinical, and stroke characteristics were compared between cases enrolled by self versus by surrogate. Data from one site that limits enrollment only to those able to self-consent were also analyzed to compare those who enrolled with those not able to consent.

RESULTS

Overall, 10% (54 of 517) were enrolled using surrogate authorization. Self-consented and surrogate-authorized cases did not differ significantly in age, sex, or conventional risk factors. Surrogate-authorized cases had significantly more severe stroke deficits, larger infarcts, and infarcts localizing to left supratentorial regions. Similarly, at the site restricting enrollment, stroke severity and characteristics differed between self-consented individuals and those otherwise eligible but unable to provide consent.

CONCLUSIONS

Failure to permit surrogate authorization in genetic studies of ischemic stroke may skew enrollment toward less severe strokes caused by smaller infarcts. This potential consent bias may undermine the ability to identify genetic determinants of risk and severity and suggests that surrogate enrollment in these studies can be ethically justifiable.

Association of integrin alpha2 gene variants with ischemic stroke

Genetic variants in the gene encoding integrin alpha2 (ITGA2) have been reported to be associated with an increased risk for ischemic stroke. The purpose of this study was to investigate the association between haplotype-tagging single-nucleotide polymorphisms (tSNPs) in ITGA2 and risk of ischemic stroke in a collection of North American stroke cases and controls. The study included 484 cases and 263 controls. Thirteen tSNPs were genotyped. Association tests at and across each tSNP were performed, including haplotype association analysis. Secondary analyses considered stroke subtypes on the basis of Trial of Org 10172 in Acute Stroke Treatment (TOAST) criteria. We observed significant association between tSNP rs3756541 (additive model, odds ratio (OR), 1.49; 95% confidence interval (CI), 1.11 to 2.04; P=0.009) and disease and a trend toward association at rs2303124 (recessive model, OR, 1.56; 95% CI, 1.05 to 2.33; P=0.03). These associations remained significant in the haplotype analyses. The associated tSNPs did not distinguish stroke etiology after application of TOAST criteria. Our results suggest that genetic variability within ITGA2 may confer risk for ischemic stroke independent of conventional risk factors. These results provide additional support for a role for platelet receptor genes in the pathogenesis of ischemic stroke of diverse subtypes.

Sex differences in stroke evaluations in the Ischemic Stroke Genetics Study

BACKGROUND

Epidemiologic studies suggest sex differences in evaluation of patients presenting with ischemic stroke. Sex differences in stroke evaluation could lead to sex differences in the validity of diagnosing ischemic stroke subtypes. This study assessed sex differences in the Ischemic Stroke Genetics Study (ISGS).

METHODS

The ISGS is a prospective case-control genetic association study of patients with first-ever ischemic stroke at 5 US tertiary stroke centers. The diagnostic tests performed as part of medical care were recorded for each enrolled patient.

RESULTS

A total of 505 patients were enrolled; 45% (229 of 505) were women and 55% (276 of 505) were men. Mean age at time of stroke was greater for women (66.6 v 61.9 years; P = .001). Frequency of brain computed tomography was 92% (254 of 276) for men and 90% (206 of 229) for women (P = .42). Magnetic resonance imaging was completed in 84% (232 of 276) of men and 83% (191 of 229) of women (P = .91). Frequency of electrocardiography was 91% (252 of 276) for men and 90% (206 of 229) for women (P = .60). Echocardiography was done in 74% (203 of 276) of men and 79% (180 of 229) of women (P = .19). Cervical arterial imaging occurred in 91% (208 of 229) of women and 86% (237 of 276) of men (P = .09). Intracranial vascular imaging was performed in 75% (207 of 276) of men and 79% (181 of 229) of women (P = .28).

CONCLUSIONS

Our findings suggest no significant sex differences in the extent to which major diagnostic tests were performed in patients in ISGS. Dedicated tertiary stroke centers may reduce the sex bias in stroke evaluation that has been identified by previous studies.

Sex differences in stroke severity, symptoms, and deficits after first-ever ischemic stroke

OBJECTIVE

The purpose of the study was to assess whether there were sex differences in stroke severity, infarct characteristics, symptoms, or the symptoms-deficit relationship at the time of acute stroke presentation.

METHODS

In a prospective study of 505 patients with first-ever ischemic stroke (the Ischemic Stroke Genetics Study), stroke subtype was centrally adjudicated and infarcts were characterized by imaging. Deficits were assessed by National Institutes of Health Stroke Scale (NIHSS) and stroke symptoms were assessed using a structured interview. Kappa statistics were generated to assess agreement between the NIHSS and the structured interview, and a Chi square test was used to assess agreement between the NIHSS and the structured interview by sex.

RESULTS

In all, 276 patients (55%) were men and 229 (45%) were women. Ages ranged from 19 to 94 years (median, 65 years). The mean (+/-SD) NIHSS score of 3.8 (+/-4.5) for men and 4.3 (+/-5.2) for women was similar (P = .15). No sex difference was observed for the symptoms of numbness, visual deficits, or language. Weakness occurred in a greater proportion of women (69%) than men (59%) (P = .03). Stroke subtype did not differ significantly between sexes (P = .79). Infarct size and location were similar for each sex. The association between symptoms and neurologic deficits did not differ by sex.

CONCLUSIONS

We found no sex difference in stroke severity, stroke subtype, or infarct size and location in patients with incident ischemic stroke. A greater proportion of women presented with weakness; however, similar proportions of men and women presented with other traditional stroke symptoms.

A genome-wide genotyping study in patients with ischaemic stroke: initial analysis and data release

BACKGROUND

Despite evidence of a genetic role in stroke, the identification of common genetic risk factors for this devastating disorder remains problematic. We aimed to identify any common genetic variability exerting a moderate to large effect on risk of ischaemic stroke, and to generate publicly available genome-wide genotype data to facilitate others doing the same.

METHODS

We applied a genome-wide high-density single-nucleotide-polymorphism (SNP) genotyping approach to a cohort of samples with and without ischaemic stroke (n=278 and 275, respectively), and did an association analysis adjusted for known confounders in a final cohort of 249 cases and 268 controls. More than 400,000 unique SNPs were assayed.

FINDINGS

We produced more than 200 million genotypes in 553 unique participants. The raw genotypes of all the controls have been posted publicly in a previous study of Parkinson's disease. From this effort, results of genotype and allele association tests have been publicly posted for 88% of stroke patients who provided proper consent for public release. Preliminary analysis of these data did not reveal any single locus conferring a large effect on risk for ischaemic stroke.

INTERPRETATION

The data generated here comprise the first phase of a genome-wide association analysis in patients with stroke. Release of phase I results generated in these publicly available samples from each consenting individual makes this dataset a valuable resource for data-mining and augmentation.

IL1RN VNTR polymorphism in ischemic stroke: analysis in 3 populations

BACKGROUND AND PURPOSE

Genetic factors influence risk for ischemic stroke and likely do so at multiple steps in the pathogenic process. Variants in genes related to inflammation contribute to risk of stroke. The purpose of this study was to confirm our earlier finding of an association between allele 2 of a variable number tandem repeat of the IL-1 receptor antagonist gene (IL1RN) and cerebrovascular disease.

METHODS

An association study of the variable number tandem repeat genotype with ischemic stroke and stroke subtypes was performed on samples from a North American study of affected sibling pairs concordant for ischemic stroke and 2 North American cohorts of prospectively ascertained ischemic stroke cases and unrelated controls. DNA analysis was performed on cases and controls, stratified by race.

RESULTS

After adjustment for age, sex, and stroke risk factors, the odds ratio for association of allele 2 and ischemic stroke was 2.80 (95% confidence interval, 1.29 to 6.11; P=0.03) for the white participants. The effect of allele 2 of IL1RN on stroke risk most closely fits a recessive genetic model (P=0.009). For the smaller sample of nonwhite participants, the results were not significant.

CONCLUSIONS

Allele 2 of IL1RN, present in nearly one-quarter of stroke patients, may contribute to genetic risk for ischemic stroke and confirm the previously identified association with cerebrovascular disease. These results are driven by the association in the white participants. Further exploration in a larger nonwhite sample is warranted.

Family history of stroke and severity of neurologic deficit after stroke

BACKGROUND

A family history of stroke is an independent risk factor for stroke.

OBJECTIVE

To assess whether severity of neurologic deficit after stroke is associated with a family history of stroke.

METHODS

The Ischemic Stroke Genetics Study, a five-center study of first-ever symptomatic ischemic stroke, assessed case subjects prospectively for a family history of stroke-affected first-degree relatives. Certified adjudicators used the NIH Stroke Scale (NIHSS) to determine the severity of neurologic deficit.

RESULTS

A total of 505 case subjects were enrolled (median age, 65 years; 55% male), with 81% enrolled within 1 week of onset of symptoms. A sibling history of stroke was associated with more severe stroke. The odds of an NIHSS score of 5 or higher were 2.0 times greater for cases with a sibling history of stroke compared with cases with no sibling history (95% CI, 1.0 to 3.9). An association of family history of stroke in parents or children with stroke severity was not detected.

CONCLUSIONS

A sibling history of stroke increased the likelihood of a more severe stroke in the case subjects, independent of age, sex, and other potential confounding factors. Other family history characteristics were not associated with stroke severity.

Lessons from adult stroke trials

Before designing epidemiologic, genetic, or treatment trials in pediatric stroke, we should learn from adult trials which preceded. Adult trialists state that there is a need for improved animal models to mimic human disease. Dose-response curves with blinded outcome measures would improve preclinical data. Functional and histologic outcome measures would improve the animal model. In regard to human Phase 2 medication trials, safety, delivery, end points, and surrogate markers are necessary. The detection of biologic activity can be defined in Phase 2B trials. For Phase 3 trials, the experiment needs to be simple with global outcome measures as end points. New statistical designs such as futility analysis may improve and streamline trials in both adults and children. Clinical trials are a long process, and care needs to be incorporated at every step. Why is there a propensity of failed studies for acute ischemic stroke in adults? The reasons include (a) the animal model fails us, (b) the Phase 2 trials are ineffective in defining dose, and (c) the Phase 3 trials are poorly done. Because clinical trials, more often than not, fail to give positive (effective treatment) results, it seems reasonable to attempt to learn from others' past experiences before initiating pediatric stroke trials.

Phosphodiesterase 4D and 5-lipoxygenase activating protein in ischemic stroke

Risk for ischemic stroke is mediated by both environmental and genetic factors. Although several environmental exposures have been implicated, relatively little is known about the genetic basis of predisposition to this disease. Recent studies in Iceland identified risk polymorphisms in two putative candidate genes for ischemic stroke: phosphodiesterase 4D (PDE4D) and 5-lipoxygenase activating protein (ALOX5AP). A collection of North American sibling pairs concordant for ischemic stroke and two cohorts of prospectively ascertained North American ischemic stroke cases and control subjects were used for evaluation of PDE4D and ALOX5AP. Although no evidence supported linkage of ischemic stroke with either of the two candidate genes, single-nucleotide polymorphisms and haplotypic associations were observed between PDE4D and ischemic stroke. There was no evidence of association between variants of ALOX5AP and ischemic stroke. These data suggest that common variants in PDE4D may contribute to the genetic risk for ischemic stroke in multiple populations.

Genetics of cerebrovascular disorders

Physicians must be able to recognize stroke caused by a mendelian or mitochondrial disorder. Some genetic disorders such as sickle cell anemia and Fabry disease have proven disease-specific treatments, whereas others have no effective treatment, including cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Proper diagnosis of a genetic disorder has prognostic value and prevents patient exposure to unnecessary and potentially harmful therapeutic agents and diagnostic tests. This article reviews the clinical and genetic features of some mendellan and mitochondrial disorders associated with ischemic stroke, hemorrhagic stroke, and cerebrovascular malformations.

Is there a genetic basis for pediatric stroke?

PURPOSE OF REVIEW Childhood: stroke is more common than brain tumor, but because there is a wide spectrum in terms of etiology and most centers see only a few cases every year, there have been few large studies of genetic and environmental risk factors until recently. This review focuses on the clinical and radiologic methodology required to distinguish phenotypes in patients, and it focuses on the available data on genetic predisposition.

RECENT FINDINGS

A number of conditions with Mendelian inheritance (eg, sickle cell disease) predispose to childhood stroke, but the search for epistatic polymorphisms that explain why some but not all of these patients are affected has been hampered by our poor understanding of the pathophysiology. Emergency vascular imaging, including arteriography and venography, will almost certainly assist with the description of stroke subtypes with different genetic predisposition in these patients and in the important group of children who were completely healthy before their stroke. Environmental exposure (eg, to infection, hypoxemia, and vitamins) may play a crucial role in modifying genetic expression and must be described carefully in prospective studies.

SUMMARY

Now that much of the work on classifying stroke subtypes in children has been undertaken, international collaboration is likely to lead to identification of the genetic and environmental risk factors, and thus to primary and secondary prevention.