Emerging Risk Factors for Stroke: What Have We Learned From Mendelian Randomization Studies?

Background and Purpose-The association of light to moderate alcohol consumption with risk of ischemic stroke remains uncertain, as are the roles of potentially mediating factors and modification by apolipoprotein E (apoE) genotype. Methods-We studied the prospective association of alcohol consumption and risk of ischemic stroke among 4410 participants free of cardiovascular disease at baseline in the Cardiovascular Health Study, a population-based cohort study of older adults from 4 US communities. Participants reported their consumption of alcoholic beverages yearly. Results-During an average follow-up period of 9.2 years, 434 cases of incident ischemic stroke occurred. Compared with long-term abstainers, the multivariate relative risks of ischemic stroke were 0.85 (95% CI, 0.63 to 1.13), 0.75 (95% CI, 0.53 to 1.06), 0.82 (95% CI, 0.51 to 1.30), and 1.03 (95% CI, 0.68 to 1.57) among consumers of 1, 1 to 6, 7 to 13, and 14 drinks per week (P quadratic trend 0.06). ApoE genotype appeared to modify the alcohol-ischemic stroke relationship (P interaction 0.08), with generally lower risks among drinkers than abstainers in apoE4-negative participants but higher risks among drinkers than abstainers among apoE4-positive participants. We could not identify candidate mediators among lipid, inflammatory, and prothrombotic factors. Conclusions-In this study of older adults, the association of alcohol use and risk of ischemic stroke was U-shaped, with modestly lower risk among consumers of 1 to 6 drinks per week. However, apoE genotype may modify this association, and even moderate alcohol intake may be associated with an increased risk of ischemic stroke among apoE4-positive older adults. (Stroke.

There is a large body of observational and laboratory evidence suggesting but not proving that increasing plasma concentrations of total homocysteine (tHcy) is a causal risk factor for atherothromboembolic ischemic stroke and other vascular events.1–9 Recent publication of the results of the landmark Vitamins in Stroke Prevention (VISP) Trial is the first evidence from a large randomized controlled trial (RCT) of the effect of lowering tHcy via folic acid–based multiple B vitamin supplementation on the incidence of “hard” clinical events, such as recurrent stroke, in patients with recent ischemic stroke.10,11 In contrast to what was expected from the epidemiological evidence, the VISP Trial did not identify a significant treatment effect of lowering tHcy by vitamin therapy on recurrent stroke, coronary events, or death, despite confirming a consistent and graded association between baseline tHcy and vascular risk (particularly the probability of stroke over time).11 Recruiting primarily from North America, VISP enrolled 3680 recent (3 to 120 days) survivors of nondisabling, noncardiogenic, ischemic stroke with baseline tHcy above the 25th percentile of the North American stroke population into a double-blind, randomized comparison of high versus low doses of a combination of 12 different vitamins, including folic acid, vitamin B12, vitamin B6, and riboflavin, which are cofactors for enzymes responsible for metabolizing homocysteine.11 After 2 years of follow-up, there was no significant difference in the cumulative incidence of the primary outcome event of recurrent cerebral infarction: 8.4% of 1814 patients who were allocated to high-dose multivitamins [including 2.5 mg of folic acid, 0.4 mg of vitamin B12, and 25 mg of vitamin B6] versus 8.1% of 1835 patients allocated to low-dose multivitamins [including 0.02 mg of folic acid, 0.006 mg of vitamin B12, 0.2 mg of vitamin B6 …

Proponents of cholesterol as a risk factor for stroke usually support their argument by citing evidence from clinical trials of the beneficial effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (“statins”) in reducing stroke risk among people with prior cardiovascular disease. Although such studies may provide some supportive evidence, causation can really only be established between a risk factor and a disease when certain criteria are met.1 These include the criteria that the association between the risk factor and the disease must be temporal and biologically plausible. Although there may be little or no debate about whether cholesterol is a biologically plausible risk factor for stroke or that high cholesterol levels precede (rather than follow) stroke, some of the other criteria are more ambiguous. These other “guidelines for causation” are discussed below: There have been numerous major prospective epidemiological studies of cholesterol and the risk of stroke. However, at best, the …

Current guideline statements for primary and secondary prevention of cardiovascular disease (CVD) rely on estimates of absolute risk of coronary events. For example, the American Heart Association guidelines on primary prevention state that persons with ≥10% risk over 10 years of myocardial infarction (MI) or coronary death should be considered for antiplatelet therapy with aspirin.1 Similarly, the National Cholesterol Education Program Adult Treatment Panel III (ATP III) guidelines2 state that target low-density lipoprotein level should be based on projected absolute risk of future coronary events rather than on presence or absence of specific risk factors. These guidelines state that patients at high risk of MI and coronary death, defined as an absolute 10-year risk of ≥20%, should have a target low-density lipoprotein level <100 mg/dL and should receive statin therapy if needed to achieve this goal. Stroke, however, is not included as one of the outcomes contributing to these absolute risk levels. Included in the group of patients with elevated risk, moreover, are those who already have ischemic heart disease, as well as patients deemed to be “coronary heart disease (CHD) risk equivalents,” indicating those at the same elevated risk as patients with ischemic heart disease. CHD risk equivalents include patients with diabetes mellitus, those with multiple risk factors that put them at elevated risk based on calculation of their Framingham Score, and patients with “other forms of symptomatic atherosclerotic disease.” The latter group is further defined to include those with peripheral arterial disease (PAD), abdominal aortic aneurysm (AAA), and carotid artery disease. The category of “risk equivalents” in the ATP III guidelines, however, does not include the vast majority (≈80%3) of ischemic stroke patients without carotid artery disease as cause of their stroke. Ischemic stroke is therefore notably excluded from the list of outcomes contributing to …

Half of all adult deaths (and much severe disability) are caused by cardiovascular diseases, and most of these deaths involve ischemic heart disease or stroke. The Asia-Pacific region accounts for about half of the global burden of cardiovascular disease and the proportion is likely to increase during the next few decades.1,2 Smoking and elevated levels of systolic blood pressure (SBP) and total blood cholesterol are major causes of cardiovascular disease,3 yet much of our knowledge about the associations between these risk factors and cardiovascular diseases comes from studies carried out in North American and western European countries. In most Asian countries, however, the mean levels of total cholesterol are lower than those found in Western countries and the incidence of coronary heart disease (CHD) is also lower, whereas the incidence of stroke, particularly hemorrhagic stroke, is higher. Article p 3384 The Asia Pacific Cohort Studies Collaboration report in this issue of Circulation investigates the combined effects of SBP and total cholesterol on risk of cardiovascular disease in a meta-analysis of 36 cohort studies (29 conducted in Asia and 7 from Australia and New Zealand) involving 380 000 individuals.4 This meta-analysis differs from previous studies in several ways: It is the largest study from this region, involving >3000 CHD events and 4000 stroke events; individual records were available for each of the participants in each study, with cause and age of death (if applicable); and information on several thousand repeat measurements of blood pressure and cholesterol made during prolonged follow-up allowed correction for “regression dilution.” These features …

The constant release of nitric oxide (NO) is essential to maintain basal cerebrovascular tone.Oxyhaemoglobin, liberated by lysis of red blood cells after subarachnoid haemorrhage binds NO and prevents its entry into vascular smooth muscle cells.While endothelium-dependent vasoconstriction is preserved, decreased levels of NO inhibit endotheliumdependent relaxation and may cause vasospasm.S-nitrosothiols are potent vasodilators and precursors of NO.The authors' aim was to determine whether S-nitroso-N-acetylpenicillamine (SNAP), a stable S-nitrosothiol compound, could reverse vasospasm in an experimental vasospas model in rabbit.Experimental subarachnoid haemorrhage (SAH) was induced in 37 New Zealand white rabbits.The animals were divided into four groups.Control (no SAH), SAH only, SAH plus saline and SAH plus SNAP, SNAP (15 g/kg/min) or 0.09% saline (equal volume) was infused 46 hours after induction of SAH.All animals were killed by perfusion fixation 48 hours after SAH occurred.Basilar arteries were removed, sectioned and their cross sectional areas were evaluated in a blind manner, by light microscopy and by using computer assisted morphometry.Experimental SAH elicited vasospasm in all animals of SAH only and SAH plus saline group.In animals treated with SNAP, arterial narrowing was markedly attenuated without producing systemic hypotension.This widening achieved statistical significance when compared to the arteries of the SAH only and SAH plus saline group (pϽ0.01).This study indicates that the NO donor SNAP is a potentially useful drug to reverse cerebral vasospasm due to SAH.

Introduction: Low density lipoprotein cholesterol (LDL-C) is an established causal factor for coronary heart disease (CHD) and ischemic stroke. A positive linear association between LDL-C and risk of CHD or ischemic stroke was reported from western populations but among Japanese the evidence still insufficient especially on the risk of ischemic stroke. This study used a longitudinal data from the Aichi Worker’s Cohort Study to explore the associations of LDL-C levels with the incidence of CHD, and stroke subtypes. Methods: Pooled data of 6325 adults (5001 men and 1324 women) who responded to the second (2002) and third (2007) wave surveys of the study were used for the current analysis. Propensity scores for LDL-C categories were generated using multinomial logistic regression that included age, sex, smoking, alcohol drinking, physical activity, body mass index, high-density lipoprotein cholesterol, triglycerides, history of diabetes and hypertension, antihypertensive medication, taking dyslipidemia medication and survey year. Hazard ratios (HRs) and the 95% confidence intervals (95% CIs) were estimated from inverse probability weighted (IPW) cox proportional hazards model for LDL-C categories associations with risks of CHD, stroke and its subtypes, and CVD. We also used restricted cubic spline to examine the possible nonlinear relationship. Results: During a median of 14 years of follow-up, 73 strokes (40 ischemic stroke, 30 hemorrhagic stroke and 3 unknown) and 60 CHD were observed. In comparison with LDL-C &lt; 120 mg/ dl, LDL-C ≥160 mg/dl was significantly associated with the increased risk of CVD (HR 1.79, 95% CI: 1.12-2.86) and CHD (HR 3.82, 95% CI: 1.80-8.06), but not with stroke (HR 1.05, 95% CI: 0.54-2.06), hemorrhagic stroke (HR 0.47, 95% CI: 0.13-1.67) or ischemic stroke (HR 1.56, 95% CI: 0.66-3.68). The results of restricted cubic spline analysis showed that the risks of CVD and CHD gradually increased from LDL-C of 120 mg/dl. On the other hand, the risk of ischemic stroke was flat until around LDL-C of 160 mg/dl and then increased afterward. The risk of hemorrhagic stroke was flat from LDL-C of 120 mg/dl or above, but showed an increased risk trend towards lower levels of LDL-C. Conclusions: Based on this recent, long-term prospective study among middle-aged Japanese workers and by applying the IPW method to adjust for several confounding variables, we found that LDL-C was linearly and positively associated with CHD incidence while higher LDL-C levels tended to be at an increased risk of ischemic stroke, though non-significant.

Effects of Genetic Variants on Stroke Risk.

Alcohol consumption and risk of stroke and coronary heart disease among Japanese women: The Japan Public Health Center-based prospective study

AimsPCSK9 genetic variants that have large effects on low-density lipoprotein cholesterol (LDL-C) and coronary heart disease (CHD) have prompted the development of therapeutic PCSK9-inhibition. However, there is limited evidence that PCSK9 variants are associated with ischaemic stroke (IS).Methods and resultsAssociations of the loss-of-function PCSK9 genetic variant (rs11591147; R46L), and five additional PCSK9 variants, with IS and IS subtypes (cardioembolic, large vessel, and small vessel) were estimated in a meta-analysis involving 10 307 IS cases and 19 326 controls of European ancestry. They were then compared with the associations of these variants with LDL-C levels (in up to 172 970 individuals) and CHD (in up to 60 801 CHD cases and 123 504 controls). The rs11591147 T allele was associated with 0.5 mmol/L lower LDL-C level (P = 9 × 10−143) and 23% lower CHD risk [odds ratio (OR): 0.77, 95% confidence interval (CI): 0.69–0.87, P = 7 × 10−6]. However, it was not associated with risk of IS (OR: 1.04, 95% CI: 0.84–1.28, P = 0.74) or IS subtypes. Information from additional PCSK9 variants also indicated consistently weaker effects on IS than on CHD.ConclusionPCSK9 genetic variants that confer life-long lower PCSK9 and LDL-C levels appear to have significantly weaker, if any, associations with risk of IS than with risk of CHD. By contrast, similar proportional reductions in risks of IS and CHD have been observed in randomized trials of therapeutic PCSK9-inhibition. These findings have implications for our understanding of when Mendelian randomization can be relied upon to predict the effects of therapeutic interventions.

Little is known about the association of the TIMD4 (T-cell immunoglobulin and mucin domain 4 gene)-HAVCR1 (hepatitis A virus cellular receptor 1) variants and lipid metabolism, the risk of coronary heart disease (CHD) and ischemic stroke (IS). The present study aimed to determine the TIMD4-HAVCR1 variants, their haplotypes and gene–environment interactions on serum lipid levels, the risk of CHD and IS, and the lipid-lowering efficacy of atorvastatin in a southern Chinese Han population. Genotypes of three variants in 622 controls, 579 CHD, and 546 IS patients were determined by the Snapshot technology. Atorvastatin calcium tablet (20 mg/day) was given in 724 hyperlipidemic patients for 8 weeks after genotyping. The rs12522248 genotypic and allelic frequencies were different between controls and patients, and were associated with the risk of CHD and IS. The rs1501908G-rs12522248T-rs2036402T haplotype was associated with an increased risk of CHD; the G-C-T haplotype was associated with lower risk of CHD; and the C-C-C haplotype was associated with an increased risk of IS. Variants and their haplotypes in controls were associated with triglyceride (rs1501908), low-density lipoprotein cholesterol (LDL-C, rs1501908, G-T-T), high-density lipoprotein cholesterol (HDL-C, rs12522248, C-C-C) and the ratio of total cholesterol (TC) to HDL-C (C-C-C). Interactions of rs1501908- and rs2036402-alcohol (HDL-C); rs1501908- and rs12522248-high body mass index (hBMI, ≥24 kg/m2; TC); and TIMD4-HAVCR1 variants-atorvastatin on several lipid parameters were detected. Interactions of rs12522248TC/CC-hBMI, G-T-T-, and C-C-C-smoking on the risk of CHD; and C-C-C-smoking, C-C-C-, and G-C-T-hBMI on the risk of IS were also observed. These findings suggest that the TIMD4-HAVCR1 variants may be the genetic risk factors for CHD and IS.

Stroke is a complex disease, with both genetic and environmental factors having a role in its pathogenesis. A review of past studies shows some evidence of genetic influences in the development of stroke. This is supported by studies of cardiovascular disease, which indicate major genetic influences at several levels including the development of risk factors. New approaches to phenotypic classifications, patient ascertainment, and genetic analysis will stimulate research into the role of genetics in cerebrovascular disease.

63 - Alcohol, Beer, and Ischemic Stroke

This study aimed to assess the association of the tribbles pseudokinase 1 (TRIB1) and transcriptional repressor GATA binding 1 (TRPS1) single nucleotide polymorphisms (SNPs) and the gene-gene (G × G) and gene-environment (G × E) interactions with serum lipid levels, the risk of coronary heart disease (CHD) and ischemic stroke (IS) in the Guangxi Han population. Genotyping of the rs2954029, rs2980880, rs10808546, rs231150, rs2737229 and rs10505248 SNPs was performed in 625 controls and 1146 unrelated patients (CHD, 593 and IS, 553). The genotypic and allelic frequencies of some SNPs were different between controls and patients (CHD, rs2954029 and rs231150; IS, rs2954029 and rs2980880; P < 0.05-0.01). Two SNPs were associated with increased risk of CHD (rs2954029 and rs231150) and IS (rs2954029) in different genetic models. Several SNPs in controls were associated with total cholesterol (rs2954029, rs2980880 and rs2737229), triglyceride (rs2954029 and rs10808546), low-density lipoprotein cholesterol (rs2954029), high-density lipoprotein cholesterol (rs2980880 and rs231150) and apolipoprotein A1 (rs2737229) levels. The rs2954029TA/AA-age (>60 year) interaction increased the risk of CHD, whereas the rs10808546CT/TT-drinking interaction decreased the risk of IS. The rs2954029A-rs2980880C-rs10808546C haplotype was associated with increased risk of CHD and IS. The rs2954029A-rs2980880T-rs10808546C haplotype was associated with increased risk of CHD. The rs2954029-rs231150 interactions had an increased risk of both CHD and IS. These results suggest that several TRIB1 and TRPS1 SNPs were associated with dyslipidemia and increased risk of CHD and IS in our study population. The G × G and G × E interactions on serum lipid levels, and the risk of CHD and IS were also observed.

Advances in Neurocardiology: Focus on Atrial Fibrillation.