Meta-analysis of genome-wide association studies identifies 1q22 as a susceptibility locus for intracerebral hemorrhage.

Intracerebral hemorrhage (ICH) is the stroke subtype with the worst prognosis and has no established acute treatment. ICH is classified as lobar or nonlobar based on the location of ruptured blood vessels within the brain. These different locations also signal different underlying vascular pathologies. Heritability estimates indicate a substantial genetic contribution to risk of ICH in both locations. We report a genome-wide association study of this condition that meta-analyzed data from six studies that enrolled individuals of European ancestry. Case subjects were ascertained by neurologists blinded to genotype data and classified as lobar or nonlobar based on brain computed tomography. ICH-free control subjects were sampled from ambulatory clinics or random digit dialing. Replication of signals identified in the discovery cohort with p < 1 × 10(-6) was pursued in an independent multiethnic sample utilizing both direct and genome-wide genotyping. The discovery phase included a case cohort of 1,545 individuals (664 lobar and 881 nonlobar cases) and a control cohort of 1,481 individuals and identified two susceptibility loci: for lobar ICH, chromosomal region 12q21.1 (rs11179580, odds ratio [OR] = 1.56, p = 7.0 × 10(-8)); and for nonlobar ICH, chromosomal region 1q22 (rs2984613, OR = 1.44, p = 1.6 × 10(-8)). The replication included a case cohort of 1,681 individuals (484 lobar and 1,194 nonlobar cases) and a control cohort of 2,261 individuals and corroborated the association for 1q22 (p = 6.5 × 10(-4); meta-analysis p = 2.2 × 10(-10)) but not for 12q21.1 (p = 0.55; meta-analysis p = 2.6 × 10(-5)). These results demonstrate biological heterogeneity across ICH subtypes and highlight the importance of ascertaining ICH cases accordingly.

Integrative Mouse and Human Studies Implicate ANGPT1 and ZBTB7C as Susceptibility Genes to Ischemic Injury.

BACKGROUND AND PURPOSE: The extent of ischemic injury in response to cerebral ischemia is known to be affected by native vasculature. However, the nonvascular and dynamic vascular responses and their genetic basis are not well understood. METHODS: We performed a genome-wide association study in 235 mice from 33 inbred strains using the middle cerebral artery occlusion model. Population structure and genetic relatedness were accounted for using the efficient mixed-model association method. Human orthologs to the genes associated with the significant and suggestive single-nucleotide polymorphisms from the mouse strain survey were examined in patients with M1 occlusions admitted with signs and symptoms of acute ischemic stroke. RESULTS: We identified 4 genome-wide significant and suggestive single-nucleotide polymorphisms to be associated with infarct volume in mice (rs3694965, P=2.17×10(-7); rs31924033, P=5.61×10(-6); rs32249495, P=2.08×10(-7); and rs3677406, P=9.56×10(-6)). rs32249495, which corresponds to angiopoietin-1 (ANGPT1), was also significant in the recessive model in humans, whereas rs1944577, which corresponds to ZBTB7C, was nominally significant in both the additive and dominant genetic models in humans. ZBTB7C was shown to be upregulated in endothelial cells using both in vitro and in vivo models of ischemia. CONCLUSIONS: Genetic variations of ANGPT1 and ZBTB7C are associated with increased infarct size in both mice and humans. ZBTB7C may modulate the ischemic response via neuronal apoptosis and dynamic collateralization and, in addition to ANGPT1, may serve as potential novel targets for treatments of cerebral ischemia.

COL4A2 mutations impair COL4A1 and COL4A2 secretion and cause hemorrhagic stroke.

Collagen, type IV, alpha 1 (COL4A1) and alpha 2 (COL4A2) form heterotrimers and are abundant components of basement membranes, including those of the cerebral vasculature. COL4A1 mutations are an increasingly recognized cause of multisystem disorders, including highly penetrant cerebrovascular disease and intracerebral hemorrhage (ICH). Because COL4A1 and COL4A2 are structurally and functionally associated, we hypothesized that variants in COL4A2 would also cause ICH. We sequence COL4A2 in 96 patients with ICH and identify three rare, nonsynonymous coding variants in four patients that are not present in a cohort of 144 ICH-free individuals. All three variants change evolutionarily conserved amino acids. Using a cellular assay, we show that these putative mutations cause intracellular accumulation of COL4A1 and COL4A2 at the expense of their secretion, which supports their pathogenecity. Furthermore, we show that Col4a2 mutant mice also have completely penetrant ICH and that mutations in mouse and human lead to retention of COL4A1 and COL4A2 within the endoplasmic reticulum (ER). Importantly, two of the three putative mutations found in patients trigger ER stress and activate the unfolded protein response. The identification of putative COL4A2 mutations that might contribute to ICH in human patients provides insight into the pathogenic mechanisms of this disease. Our data suggest that COL4A2 mutations impair COL4A1 and COL4A2 secretion and can also result in cytotoxicity. Finally, our findings suggest that, collectively, mutations in COL4A1 and COL4A2 contribute to sporadic cases of ICH.

Burden of blood pressure-related alleles is associated with larger hematoma volume and worse outcome in intracerebral hemorrhage.

BACKGROUND AND PURPOSE: Intracerebral hemorrhage (ICH) is the acute manifestation of a progressive disease of the cerebral small vessels. The severity of this disease seems to influence not only risk of ICH but also the size of the hematoma. As the burden of high blood pressure-related alleles is associated with both hypertension-related end-organ damage and risk of ICH, we sought to determine whether this burden influences ICH baseline hematoma volume. METHODS: Prospective study in subjects of European descent with supratentorial ICH who underwent genome-wide genotyping. Forty-two single nucleotide polymorphisms associated with high blood pressure were identified from a publicly available database. A genetic risk score was constructed based on these single nucleotide polymorphisms. The score was used as the independent variable in univariate and multivariate regression models for admission ICH volume and poor clinical outcome (modified Rankin Scale, 3-6). RESULTS: A total of 323 ICH cases were enrolled in the study (135 deep and 188 lobar intracranial hematomas). The blood pressure-based genetic risk score was associated with both baseline hematoma volume and poor clinical outcome specifically in deep ICH. In multivariate regression analyses, each additional SD of the score increased mean deep ICH volume by 28% (or 2.7 mL increase; ß=0.28; SE=0.11; P=0.009) and risk of poor clinical outcome by 71% (odds ratio, 1.71; 95% confidence interval, 1.05-2.80; P=0.03). CONCLUSIONS: Increasing numbers of high blood pressure-related alleles are associated with mean baseline hematoma volume and poor clinical outcome in ICH. These findings suggest that the small vessel vasculopathy responsible for the occurrence of the hemorrhage also influences its volume.

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.

Heritability estimates identify a substantial genetic contribution to risk and outcome of intracerebral hemorrhage.

BACKGROUND AND PURPOSE: Previous studies suggest that genetic variation plays a substantial role in occurrence and evolution of intracerebral hemorrhage (ICH). Genetic contribution to disease can be determined by calculating heritability using family-based data, but such an approach is impractical for ICH because of lack of large pedigree-based studies. However, a novel analytic tool based on genome-wide data allows heritability estimation from unrelated subjects. We sought to apply this method to provide heritability estimates for ICH risk, severity, and outcome. METHODS: We analyzed genome-wide genotype data for 791 ICH cases and 876 controls, and determined heritability as the proportion of variation in phenotype attributable to captured genetic variants. Contribution to heritability was separately estimated for the APOE (encoding apolipoprotein E) gene, an established genetic risk factor, and for the rest of the genome. Analyzed phenotypes included ICH risk, admission hematoma volume, and 90-day mortality. RESULTS: ICH risk heritability was estimated at 29% (SE, 11%) for non-APOE loci and at 15% (SE, 10%) for APOE. Heritability for 90-day ICH mortality was 41% for non-APOE loci and 10% (SE, 9%) for APOE. Genetic influence on hematoma volume was also substantial: admission volume heritability was estimated at 60% (SE, 70%) for non-APOEloci and at 12% (SE, 4%) for APOE. CONCLUSIONS: Genetic variation plays a substantial role in ICH risk, outcome, and hematoma volume. Previously reported risk variants account for only a portion of inherited genetic influence on ICH pathophysiology, pointing to additional loci yet to be identified.

17q25 Locus is associated with white matter hyperintensity volume in ischemic stroke, but not with lacunar stroke status.

BACKGROUND AND PURPOSE: Recently, a novel locus at 17q25 was associated with white matter hyperintensities (WMH) on MRI in stroke-free individuals. We aimed to replicate the association with WMH volume (WMHV) in patients with ischemic stroke. If the association acts by promoting a small vessel arteriopathy, it might be expected to also associate with lacunar stroke. METHODS: We quantified WMH on MRI in the stroke-free hemisphere of 2588 ischemic stroke cases. Association between WMHV and 6 single-nucleotide polymorphisms at chromosome 17q25 was assessed by linear regression. These single-nucleotide polymorphisms were also investigated for association with lacunar stroke in 1854 cases and 51 939 stroke-free controls from METASTROKE. Meta-analyses with previous reports and a genetic risk score approach were applied to identify other novel WMHV risk variants and uncover shared genetic contributions to WMHV in community participants without stroke and ischemic stroke. RESULTS: Single-nucleotide polymorphisms at 17q25 were associated with WMHV in ischemic stroke, the most significant being rs9894383 (P=0.0006). In contrast, there was no association between any single-nucleotide polymorphism and lacunar stroke. A genetic risk score analysis revealed further genetic components to WMHV shared between community participants without stroke and ischemic stroke. CONCLUSIONS: This study provides support for an association between the 17q25 locus and WMH. In contrast, it is not associated with lacunar stroke, suggesting that the association does not act by promoting small-vessel arteriopathy or the same arteriopathy responsible for lacunar infarction.

Apolipoprotein E genotype is associated with CT angiography spot sign in lobar intracerebral hemorrhage.

BACKGROUND AND PURPOSE: The CT angiography (CTA) spot sign predicts hematoma expansion and poor outcome in patients with primary intracerebral hemorrhage (ICH). The biological underpinnings of the spot sign remain poorly understood; it may be that the underlying vasculopathy influences its presence. Therefore, we conducted a study to identify genetic predictors of the spot sign. METHODS: In an ongoing prospective cohort study, we analyzed 371 patients with CTA and genetic data available. CTAs were reviewed for the spot sign by 2 experienced readers, blinded to clinical data, according to validated criteria. Analyses were stratified by ICH location. RESULTS: In multivariate analysis, patients on warfarin were more likely to have a spot sign regardless of ICH location (OR, 3.85; 95% CI, 1.33-11.13 in deep ICH and OR, 2.86; 95% CI, 1.33-6.13 in lobar ICH). Apolipoprotein E ε2, but not ε4, was associated with the presence of a spot sign in lobar ICH (OR, 2.09; 95% CI, 1.05-4.19). There was no effect for ε2 or ε4 in deep ICH. CONCLUSIONS: Patients with ICH on warfarin are more likely to present with a spot sign regardless of ICH location. Among patients with lobar ICH, those who possess the apolipoprotein E ε2 allele are more likely to have a spot sign. Given the established relationship between apolipoprotein E ε2 and vasculopathic changes in cerebral amyloid angiopathy, our findings suggest that both hemostatic factors and vessel pathology influence spot sign presence.

Predicting hematoma expansion after primary intracerebral hemorrhage.

IMPORTANCE: Many clinical trials focus on restricting hematoma expansion following acute intracerebral hemorrhage (ICH), but selecting those patients at highest risk of hematoma expansion is challenging. OBJECTIVE: To develop a prediction score for hematoma expansion in patients with primary ICH. DESIGN, SETTING, AND PARTICIPANTS: Prospective cohort study at 2 urban academic medical centers among patients having primary ICH with available baseline and follow-up computed tomography for volumetric analysis (817 patients in the development cohort and 195 patients in the independent validation cohort). MAIN OUTCOMES AND MEASURES: Hematoma expansion was assessed using semiautomated software and was defined as more than 6 mL or 33% growth. Covariates were tested for association with hematoma expansion using univariate and multivariable logistic regression. A 9-point prediction score was derived based on the regression estimates and was subsequently tested in the independent validation cohort. RESULTS: Hematoma expansion occurred in 156 patients (19.1%). In multivariable analysis, predictors of expansion were as follows: warfarin sodium use, the computed tomography angiography spot sign, and shorter time to computed tomography (≤ 6 vs >6 hours) (P < .001 for all), as well as baseline ICH volume (<30 [reference], 30-60 [P = .03], and >60 [P = .005] mL). The incidence of hematoma expansion steadily increased with higher scores. In the independent validation cohort (n = 195), our prediction score performed well and showed strong association with hematoma expansion (odds ratio, 4.59; P < .001 for a high vs low score). The C statistics for the score were 0.72 for the development cohort and 0.77 for the independent validation cohort. CONCLUSIONS AND RELEVANCE: A 9-point prediction score for hematoma expansion was developed and independently validated. The results open a path for individualized treatment and trial design in ICH aimed at patients at highest risk of hematoma expansion with maximum potential for therapeutic benefit.

APOE ε variants increase risk of warfarin-related intracerebral hemorrhage.

OBJECTIVE: We aimed to assess the effect of APOE ε variants on warfarin-related intracerebral hemorrhage (wICH), evaluated their predictive power, and tested for interaction with warfarin in causing wICH. METHODS: This was a prospective, 2-stage (discovery and replication), case-control study. wICH was classified as lobar or nonlobar based on the location of the hematoma. Controls were sampled from ambulatory clinics (discovery) and random digit dialing (replication). APOE ε variants were directly genotyped. A case-control design and logistic regression analysis were utilized to test for association between APOE ε and wICH. A case-only design and logistic regression analysis were utilized to test for interaction between APOE ε and warfarin. Receiver operating characteristic curves were implemented to evaluate predictive power. RESULTS: The discovery stage included 319 wICHs (44% lobar) and 355 controls. APOE ε2 was associated with lobar (odds ratio [OR] 2.46; p < 0.001) and nonlobar wICH (OR 1.67; p = 0.04), whereas ε4 was associated with lobar (OR 2.09; p < 0.001) but not nonlobar wICH (p = 0.35). The replication stage (63 wICHs and 1,030 controls) confirmed the association with ε2 (p = 0.03) and ε4 (p = 0.003) for lobar but not for nonlobar wICH (p > 0.20). Genotyping information on APOE ε variants significantly improved case/control discrimination of lobar wICH (C statistic 0.80). No statistical interaction between warfarin and APOE was found (p > 0.20). CONCLUSIONS: APOE ε variants constitute strong risk factors for lobar wICH. APOE exerts its effect independently of warfarin, although power limitations render this absence of interaction preliminary. Evaluation of the predictive ability of APOE in cohort studies is warranted.

TOMM40 in Cerebral Amyloid Angiopathy Related Intracerebral Hemorrhage: Comparative Genetic Analysis with Alzheimer's Disease.

Cerebral amyloid angiopathy (CAA) related intracerebral hemorrhage (ICH) is a devastating form of stroke with no known therapies. Clinical, neuropathological, and genetic studies have suggested both overlap and divergence between the pathogenesis of CAA and the biologically related condition of Alzheimer's disease (AD). Among the genetic loci associated with AD are APOE and TOMM40, a gene in close proximity to APOE. We investigate here whether variants within TOMM40 are associated with CAA-related ICH and CAA neuropathology. Using cohorts from the Massachusetts General Hospital (MGH) and the Alzheimer's Disease Neuroimaging Initiative (ADNI), we designed a comparative analysis of high-density SNP genotype data for CAA-related ICH and AD. APOE ε4 was associated with CAA-related ICH and AD, while APOE ε2 was protective in AD but a risk factor for CAA. A total of 14 SNPs within TOMM40 were associated with AD (p < 0.05 after multiple testing correction), but not CAA-related ICH (all p > 0.20); as a result, all AD-associated SNPs within TOMM40 showed heterogeneity of effect in CAA-related ICH (BD p < 0.001). Analysis of CAA neuropathology in the Religious Orders Study (ROS) and Rush Memory and Aging Project (MAP), however, found that neuritic plaque, diffuse plaque burden, and vascular amyloid burden associated with all TOMM40 SNPs (p < 0.02). These results suggest that alterations in TOMM40 can promote vascular as well as plaque amyloid deposition, but not the full pathogenic pathway leading to CAA-related ICH.

Genome-wide association study identifies a variant in HDAC9 associated with large vessel ischemic stroke.

Genetic factors have been implicated in stroke risk, but few replicated associations have been reported. We conducted a genome-wide association study (GWAS) for ischemic stroke and its subtypes in 3,548 affected individuals and 5,972 controls, all of European ancestry. Replication of potential signals was performed in 5,859 affected individuals and 6,281 controls. We replicated previous associations for cardioembolic stroke near PITX2 and ZFHX3 and for large vessel stroke at a 9p21 locus. We identified a new association for large vessel stroke within HDAC9 (encoding histone deacetylase 9) on chromosome 7p21.1 (including further replication in an additional 735 affected individuals and 28,583 controls) (rs11984041; combined P = 1.87 × 10(-11); odds ratio (OR) = 1.42, 95% confidence interval (CI) = 1.28-1.57). All four loci exhibited evidence for heterogeneity of effect across the stroke subtypes, with some and possibly all affecting risk for only one subtype. This suggests distinct genetic architectures for different stroke subtypes.