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.

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.

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.

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.

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.

Abstract TMP84: A Prediction Score for Hematoma Expansion Following Acute Intracerebral Hemorrhage

Purpose: Hematoma expansion (HE) following acute intracerebral hemorrhage (ICH) is common and associated with poor outcome. Ongoing clinical trials therefore focus on restricting HE. In order to provide treatment options to the patients at highest risk of HE, we aimed to develop a prediction score for HE.

Methods: We performed a prospective cohort study of consecutive primary ICH patients presenting to a single center over a 12-year period, with available baseline and follow-up CTs. HE was assessed using semi-automated software and defined as 6 mL or 33% growth. Our cohort was randomly divided in a 2/3 development and 1/3 validation cohort. Uni- and multivariate logistic regression was performed to assess clinical and neuroimaging covariates for relationship with HE. A prediction model was derived based on regression estimates, and this model was subsequently tested in the validation cohort.

Results: 817 ICH patients were included: 544 in the development cohort and 273 in the validation cohort. Overall, HE occurred in 156 patients (19%). In multivariate analysis, warfarin use (OR 2.09 [95%CI 1.24-3.52], p = 0.006), shorter time to CT (≤6 vs. >6 hours; OR 2.14 [95%CI 1.18-3.90], p = 0.013), baseline ICH volume (<30, 30-60, >60 mL; OR 1.90 [95%CI 1.01-3.55], p = 0.045), and the CT angiography spot sign (OR 3.59 [95%CI 1.77-7.29], p = 0.0004) were predictive of HE. The derived prediction score (0-9) showed a linear relation with the probability of HE and mortality (at discharge and 90 days), in both the development and the validation cohorts. The probability of HE in the validation cohort was 0%, 10%, 39%, and 54% for categorized scores 0, 1-3, 4-6, and 7-9, respectively. The c statistics were 0.69 for the development cohort and 0.78 for the validation cohort.

Conclusion: Warfarin use, presentation within 6 hours after ICH, larger ICH volumes at baseline, and the CT angiography spot sign are independent predictors of HE and mortality. Based on these findings, we developed a prediction score for HE. Since no therapy has demonstrated benefit in a randomized trial, our results open a path for individualized treatment and trial design in ICH, aimed at patients at highest risk of HE.

Abstract 118: Burden of Blood Pressure-Related Alleles is Associated with Larger Hematoma Volume and Worse Outcome in Intracerebral Hemorrhage

Purpose: Intracerebral hemorrhage (ICH) is the acute manifestation of a progressive disease of the cerebral small vessels. The severity of this disease appears to influence not only risk of ICH, but also the size of the hematoma. As the burden of high blood pressure(BP)-associated alleles is associated with hypertension-related end-organ damage, we sought to determine if this burden influences ICH admission hematoma volume (AHV).

Methods: Prospective study undertaken in 441 ICH patients of European ancestry (210 deep and 231 lobar intracranial hematomas). Forty-three single-nucleotide polymorphisms (SNPs) known to be associated with high BP were genotyped in Illumina610-Quad. Single-SNP association analyses with AHV were performed using linear regression. Subsequently, a genetic risk score was calculated as the sum of the products generated by multiplying, at each of the 43 loci, the number risk alleles times the reported effect of that allele on BP. The score was utilized as the independent variable of univariate and multivariate regression models for 2 outcomes: AHV and poor clinical outcome (modified Rankin Scale 3-6). Principal components analysis was utilized to account for population structure.

Results: Individually assessed, no single SNP was associated with AHV. In univariate linear regression, the genetic risk score was associated with AHV in all (deep and lobar) and deep locations (Figure 1), but not in lobar hemorrhages.

In multivariate regression analyses, each additional standard deviation of the genetic risk score increased mean deep AHV by 21% (or 2.7-milliliter increase, beta=0.21, standard error=0.08, p=0.01) and risk poor clinical outcome by 55% (odds ratio=1.55, 95% confidence interval 1.05-2.28, p=0.03). No significant associations were observed when considering all (deep and lobar) and lobar hemorrhages.

Conclusion: In deep ICH, increasing numbers of high BP-related alleles are associated with larger AHV and poor clinical outcome.

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.

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; β=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.

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.

Abstract 104: APOE Genotype Is Associated With CT Angiography Spot Sign In Lobar Intracerebral Hemorrhage

Purpose: The presence of active contrast extravasation following CT angiography (CTA), the spot sign, predicts the development of hematoma expansion and poor clinical outcome in patients with primary intracerebral hemorrhage (ICH). The biological underpinnings of the spot sign remain poorly understood, and there are no established risk factors for its presence. We conducted a prospective cohort study to identify determinants of the CTA spot sign.

Materials and Methods: We performed a prospective cohort study of consecutive patients presenting to a single center with primary ICH over an 11-year period. Patients were included in this analysis if they underwent CT and CTA at presentation and consented to participation in genetic studies. CTAs were reviewed by two experienced readers, blinded to clinical data, according to previously published validated criteria. Due to its established association with lobar ICH volume, APOE genotype, as well as common clinical covariates, were analyzed for association with spot sign presence. Analyses were stratified by deep, lobar and probable / definite cerebral amyloid angiopathy (CAA) related ICH (by Boston criteria).

Results: Of 372 patients, 151 had deep, 198 had lobar and 23 had mixed ICH. We identified at least 1 spot sign in 96 of 372 patients (25.8%). 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, p-value 0.013) in deep ICH, OR 2.86 (95% CI 1.33-6.13, p-value 0.007) in lobar ICH and OR 6.65 (95% CI 1.34-32.99, p-value 0.020) in the subset meeting criteria for CAA-related ICH. APOE ε2, but not ε4, was associated with spot sign in lobar ICH (OR 2.09 [95% CI 1.05-4.19], p = 0.036) and CAA-related ICH (OR 2.07 [95% CI 1.24-3.46], p-value 0.005). There was no effect for ε2 or ε4 in deep ICH. ( Table 1 )

Conclusion: Patients on warfarin at the time of ICH are more likely to have a spot sign at presentation, regardless of the location of the ICH. Among patients with lobar ICH, those who possess the APOE ε2 allele are more likely to have a spot sign. Given the established relationship between APOE ε2 and vasculopathic changes in CAA, our findings suggest that both hemostatic factors and vessel pathology influence spot sign presence and risk of prolonged bleeding in ICH.

Abstract 103: Genetic Markers for Hypertension and Body Mass Index are also Associated with Risk of Intracerebral Hemorrhage

Background: Genetic variation plays a substantial role in risk of intracerebral hemorrhage (ICH). Because a number of genetic variants associated with Hypertension (HTN) and Body Mass Index (BMI) have already been identified, and both HTN and BMI influence risk of ICH, we sought to determine whether the cumulative burden of HT and BMI genes increases risk of ICH.

Objective: To test the hypothesis that increasing numbers of risk alleles for HTN and high BMI produce additive increments in ICH risk.

Methods: Prospective study of consecutive individuals with ICH admitted to the Massachusetts General Hospital between 2004 and 2009, and gender- and age-matched controls. Fourteen SNPs associated with HTN and 42 with high BMI were identified (p-values <5x10E-8) from previous reports and genotyped in our cohort using Illumina 610-QuadBead. Genetic markers unavailable on this platform were imputed. Association analysis for each marker was completed using logistic regression under additive effects model, with gender and age as covariates. The combined effect on ICH of genetic variants for HTN and high BMI was evaluated using a score-based approach. The score for a given individual was calculated as the beta from the regression analysis for each marker, multiplied by the number of risk alleles carried by that subject. The resulting quintile-based score and ICH case-status were the independent and dependent variables, respectively, of a logistic regression model that had gender and age as covariates. Bonferroni-corrected p-values < 0.5/12 = 0.004 were considered significant.

Results: A total of 661 subjects were included: 392 cases (186 deep, 194 lobar, 12 multifocal) and 269 controls; mean age 73±9, males 341 (52%). Increasing burdens of risk alleles were associated with increasing risk of ICH in both lobar and deep locations ( Table ).

Conclusion: Higher values of a genetic score of HTN and high BMI risk alleles were associated with an increased risk of ICH. This association was more pronounced for deep ICH.

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.