Muhammad Saleem Khan

Genetic risk factors for ischaemic stroke and its subtypes (the METASTROKE collaboration): a meta-analysis of genome-wide association studies.

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).

Detailed Analysis of Gene Polymorphisms Associated with Ischemic Stroke in South Asians

The burden of stroke is disproportionately high in the South Asian subcontinent with South Asian ethnicity conferring a greater risk of ischemic stroke than European ancestry regardless of country inhabited. While genes associated with stroke in European populations have been investigated, they remain largely unknown in South Asians. We conducted a comprehensive meta-analysis of known genetic polymorphisms associated with South Asian ischemic stroke, and compared effect size of the MTHFR C677T-stroke association with effect sizes predicted from homocysteine-stroke association. Electronic databases were searched up to August 2012 for published case control studies investigating genetic polymorphisms associated with ischemic stroke in South Asians. Pooled odds ratios (OR) for each gene-disease association were calculated using a random-effects model. We identified 26 studies (approximately 2529 stroke cases and 2881 controls) interrogating 33 independent genetic polymorphisms in 22 genes. Ten studies described MTHFR C677T (108 with TT genotype and 2018 with CC genotype) -homocysteine relationship and six studies (735 stroke cases and 713 controls) described homocysteine-ischemic stroke relationship. Risk association ORs were calculated for ACE I/D (OR 5.00; 95% CI, 1.17–21.37; p = 0.03), PDE4D SNP 83 (OR 2.20; 95% CI 1.21–3.99; p = 0.01), PDE4D SNP 32 (OR 1.57; 95% CI 1.01–2.45, p = 0.045) and IL10 G1082A (OR 1.44; 95% CI, 1.09–1.91, p = 0.01). Significant association was observed between elevated plasma homocysteine levels and MTHFR/677 TT genotypes in healthy South Asians (Mean difference (ΔX) 5.18 µmol/L; 95% CI 2.03–8.34: p = 0.001). Our results demonstrate that the genetic etiology of ischemic stroke in South Asians is broadly similar to the risk conferred in Europeans, although the dataset is considerably smaller and warrants the same clinical considerations for risk profiling.

Are Myocardial Infarction–Associated Single-Nucleotide Polymorphisms Associated With Ischemic Stroke?

Background and Purpose— Ischemic stroke (IS) shares many common risk factors with coronary artery disease (CAD). We hypothesized that genetic variants associated with myocardial infarction (MI) or CAD may be similarly involved in the etiology of IS. To test this hypothesis, we evaluated whether single-nucleotide polymorphisms (SNPs) at 11 different loci recently associated with MI or CAD through genome-wide association studies were associated with IS. Methods— Meta-analyses of the associations between the 11 MI-associated SNPs and IS were performed using 6865 cases and 11 395 control subjects recruited from 9 studies. SNPs were either genotyped directly or imputed; in a few cases a surrogate SNP in high linkage disequilibrium was chosen. Logistic regression was performed within each study to obtain study-specific &bgr;s and standard errors. Meta-analysis was conducted using an inverse variance weighted approach assuming a random effect model. Results— Despite having power to detect odds ratio of 1.09–1.14 for overall IS and 1.20–1.32 for major stroke subtypes, none of the SNPs were significantly associated with overall IS and/or stroke subtypes after adjusting for multiple comparisons. Conclusions— Our results suggest that the major common loci associated with MI risk do not have effects of similar magnitude on overall IS but do not preclude moderate associations restricted to specific IS subtypes. Disparate mechanisms may be critical in the development of acute ischemic coronary and cerebrovascular events.

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.

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

BackgroundStroke 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.MethodsThe 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.DiscussionWe 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.

Use of the NHS Choices website for primary care consultations: results from online and general practice surveys.

Objectives To determine the effect of using the NHS Choices website on primary care consultations in England and Wales. We examined the hypothesis that using NHS Choices may reduce the frequency of primary care consultations among young, healthy users. Design Two cross-sectional surveys of NHS Choices users. Setting Survey of NHS Choices users using an online pop-up questionnaire on the NHS Choices website and a snapshot survey of patients in six general practices in London. Participants NHS Choices website users and general practice patients. Main outcome measures For both surveys, we measured the proportion of people using NHS Choices when considering whether to consult their GP practice and on subsequent frequency of primary care consultations. Results Around 59% (n = 1559) of online and 8% (n = 125) of general practice survey respondents reported using NHS Choices in relation to their use of primary care services. Among these, 33% (n = 515) of online and 18% (n = 23) of general practice respondents reported reduced primary care consultations as a result of using NHS Choices. We estimated the equivalent capacity savings in primary care from reduced consultations as a result of using NHS Choices to be approximately £94 million per year. Conclusions NHS Choices has been shown to alter healthcare-seeking behaviour, attitudes and knowledge among its users. Using NHS Choices results in reduced demand for primary care consultations among young, healthy users for whom reduced health service use is likely to be appropriate. Reducing potentially avoidable consultations can result in considerable capacity savings in UK primary care.

Quantifying the risk of heart disease following acute ischaemic stroke: a meta-analysis of over 50 000 participants

Objective Following an acute stroke, there is a high risk of recurrence. However, the leading cause of mortality following a stroke is due to coronary artery disease (CAD) and myocardial infarction (MI) but that risk has not been robustly quantified. We sought to reliably quantify the risk of ischaemic heart disease (IHD) in patients presenting with acute ischaemic stroke (AIS) in the absence of a known cardiac history. Setting A meta-analysis study. PubMed, MEDLINE, EMBASE and Google Scholar were searched for potential studies up to October 2015. Included studies reported an acute cerebral ischaemic event and followed for CAD or MI within 1 year in patients without known IHD. Using arcsine transformed proportions for meta-analysis, studies were combined using a generic inverse variance random-effects model to calculate the pooled standardised mean difference and 95% CIs. These were interpreted as the percentage prevalence of CAD or incidence of MI following AIS. Results 17 studies with 4869 patients with AIS demonstrated a mean average of asymptomatic CAD in 52%. Anatomical methods of CAD detection revealed a prevalence of asymptomatic ≥50% coronary stenosis in 32% (95% CI 19% to 47%; p<0.00001). 8 studies with 47229 patients with ischaemic stroke revealed an overall risk of MI in the year following stroke of 3% (95% CI 1% to 5%; p<0.00001) despite the absence of any cardiac history. Conclusions One-third of patients with ischaemic stroke with no cardiac history have more than 50% coronary stenosis and 3% are at risk of developing MI within a year. Our findings provide a reliable quantitative measure of the risk of IHD following AIS in patients with no cardiac history.

Estimating Weight of Patients With Acute Stroke When Dosing for Thrombolysis.

Background and Purpose— Estimating patient weight forms an important part of emergency ischemic stroke management guiding the dose of alteplase (tissue-type plasminogen activator). Weighing patients with stroke can be logistically challenging and time consuming, potentially delaying treatment times. We aimed to assess the reliability of approximating weight to determine recombinant tissue-type plasminogen activator dose and whether potential inaccurate dosing affected patient outcomes. Methods— Two hundred forty-two consecutive patients were studied at a large tertiary stroke center. Estimated and actual measured weight, alteplase dose, and pre-and post-modified Rankin Scale/National Institute of Health Stroke Scale outcome were recorded for each patient. Results— Clinicians significantly underestimated weights by 1.13 kg (range, −43 to +18 kg; SD, 7.14; P<0.05). The difference between estimated and actual weight proved to be greatest in the heaviest third of patients (−4.51 kg; SD, 8.35; P<0.001), resulting in 19.7% of patients receiving a deviation of at least 10% from the recommended recombinant tissue-type plasminogen activator dose. On average, the heaviest third of patients received an underdose of 0.04 mg/kg and were found to have a greater baseline National Institute of Health Stroke Scale on admission (P<0.001). National Institute of Health Stroke Scale improvement by day 7 or on discharge was significantly reduced in patients weighing >78 kg (National Institute of Health Stroke Scale score difference of 4.0 points, P<0.05) than in lighter individuals. Conclusions— Clinicians are poor at approximating the weights of patients with stroke in the acute setting, especially when patients lie at the extremes of weight. Beds capable of weighing patients should be mandated in emergency rooms for patients with acute stroke.

Towards the genetic basis of cerebral venous thrombosis - The BEAST Consortium: A study protocol

Introduction Cerebral venous thrombosis (CVT) is a rare cerebrovascular condition accounting for <1% of all stroke cases and mainly affects young adults. Its genetic aetiology is not clearly elucidated. Methods and analysis To better understand the genetic basis of CVT, we have established an international biobank of CVT cases, Biorepository to Establish the Aetiology of Sinovenous Thrombosis (BEAST) which aims to recruit highly phenotyped cases initially of European descent and later from other populations. To date we have recruited 745 CVT cases from 12 research centres. As an initial step, the consortium plans to undertake a genome-wide association analysis of CVT using the Illumina Infinium HumanCoreExome BeadChip to assess the association and impact of common and low-frequency genetic variants on CVT risk by using a case–control study design. Replication will be performed to confirm putative findings. Furthermore, we aim to identify interactions of genetic variants with several environmental and comorbidity factors which will likely contribute to improve the understanding of the biological mechanisms underlying this complex disease. Ethics and dissemination BEAST meets all ethical standards set by local institutional review boards for each of the participating sites. The research outcomes will be published in international peer-reviewed open-access journals with high impact and visibility. The results will be presented at national and international meetings to highlight the contributions into improving the understanding of the mechanisms underlying this uncommon but important disease. This international DNA repository will become an important resource for investigators in the field of haematological and vascular disorders.

Knowledge of blood pressure in a UK general public population

Little is known about the general public’s understanding of the role of blood pressure (BP) in contributing to heart disease and stroke. This study aimed to gain a wider understanding of the knowledge and awareness of BP in a selected London population. As part of a stroke awareness campaign, members of the public were offered BP testing and were asked about their knowledge and awareness of BP. Descriptive statistics were employed to explore knowledge and awareness of BP. χ2-test was run to explore the difference between knowledge and awareness of BP, and whether there was a difference in BP readings in normotensive and hypertensive participants. A total of 1019 participants (males 295; mean age 54 years, range 16–92) were recruited with a mean BP of 130/77 mm Hg. Over half (52%) of the total population was unable to correctly estimate an acceptable range of BP, and of that group 28% had a systolic BP (SBP) >140 mm Hg. Of the 31% self-reporting hypertension and on medication, over a quarter (27%) did not know the range for acceptable BP. A third were poorly controlled with a SBP >140 mm Hg. Mean SBP in the hypertensive participants who correctly estimated ‘acceptable BP’ was 3 mm Hg lower (147 mm Hg) than those who guessed incorrectly (150 mm Hg) (P<0.04). There remains a lack of understanding of BP in the general public population with individuals having little knowledge of an acceptable BP range. Hypertensive patients demonstrate a particularly poor understanding of BP. This study suggests that good knowledge of BP influences BP control in a hypertensive population and has important public health implications.