RNA-Sequencing Highlights Inflammation and Impaired Integrity of the Vascular Wall in Brain Arteriovenous Malformations

Background and Purpose—

Interventional treatment of unruptured brain arteriovenous malformations (BAVMs) has become increasingly controversial. Because medical therapy is still lacking, we aimed to obtain insight into the disease mechanisms implicated in BAVMs and to identify potential targets for medical treatment to prevent rupture of a BAVM.

Methods—

We used next-generation RNA sequencing to identify differential expression on a transcriptome-wide level comparing tissue samples of 12 BAVMs to 16 intracranial control arteries. We identified differentially expressed genes by negative binominal generalized log-linear regression (false discovery rate corrected P <0.05). We selected 10 genes for validation using droplet digital polymerase chain reaction. We performed functional pathway analysis accounting for potential gene-length bias, to establish enhancement of biological pathways involved in BAVMs. We further assessed which Gene Ontology terms were enriched.

Results—

We found 736 upregulated genes in BAVMs including genes implicated in the cytoskeletal machinery and cell-migration and genes encoding for inflammatory cytokines and secretory products of neutrophils and macrophages. Furthermore, we found 498 genes downregulated including genes implicated in extracellular matrix composition, the binary angiopoietin-TIE system, and TGF (transforming growth factor)-β signaling. We confirmed the differential expression of top 10 ranked genes. Functional pathway analysis showed enrichment of the protein digestion and absorption pathway (false discovery rate-adjusted P =1.70×10 −2 ). We identified 47 enriched Gene Ontology terms (false discovery rate-adjusted P <0.05) implicated in cytoskeleton network, cell-migration, endoplasmic reticulum, transmembrane transport, and extracellular matrix composition.

Conclusions—

Our genome-wide RNA-sequencing study points to involvement of inflammatory mediators, loss of cerebrovascular quiescence, and impaired integrity of the vascular wall in the pathophysiology of BAVMs. Our study may lend support to potential receptivity of BAVMs to medical therapeutics, including those promoting vessel maturation, and anti-inflammatory and immune-modifying drugs.

Risk Factors for Intracranial Aneurysm Rupture: A Systematic Review

BACKGROUND

Intracranial aneurysm rupture prediction is poor, with only a few risk factors for rupture identified and used in clinical practice.

OBJECTIVE

To provide an overview of all the risk factors (including genetic, molecular, morphological, and hemodynamic factors) that have potential for use in clinical practice.

METHODS

We systematically searched PubMed and EMBASE and focused on factors that can be easily assessed in clinical practice, might be used for rupture prediction in clinical practice, and/or are potential targets for further research. Studies were categorized according to methodological quality, and a meta-analysis was performed, if possible.

RESULTS

We included 102 studies describing 144 risk factors that fulfilled predefined criteria. There was strong evidence for the morphological factors irregular shape (studied in 4 prospective cohort studies of high-quality, pooled odds ratio [OR] of 4.8 [95% confidence interval 2.7-8.7]), aspect ratio (pooled OR 10.2 [4.3-24.6]), size ratio, bottleneck factor, and height-to-width ratio to increase rupture risk. Moderate level of evidence was found for presence of contact with the perianeurysmal environment (pooled OR 3.5 [1.4-8.4]), unbalanced nature of this contact (pooled OR 17.8 [8.3-38.5]), volume-to-ostium ratio, and direction of the aneurysm dome (pooled OR 1.5 [1.2-1.9]).

CONCLUSION

Irregular aneurysm shape was identified as a risk factor with potential for use in clinical practice. The risk factors aspect ratio, size ratio, bottleneck factor, height-to-width ratio, contact with the perianeurysmal environment, volume-to-ostium ratio, and dome-direction should first be confirmed in multivariate analysis and incorporated in prediction models.

Assessment of the Most Optimal Control Tissue for Intracranial Aneurysm Gene Expression Studies

Background and Purpose- Finding adequate control tissue for intracranial aneurysm (IA) pathophysiological studies, including gene expression studies, can be challenging. We compared gene expression profiles of superficial temporal, cortical, and circle of Willis (CoW) arteries and IA in search of the most optimal control tissue for future experiments. Methods- We compared RNA-sequencing data of IA samples and of superficial temporal, cortical, and CoW artery samples using Pearson correlation, Euclidean distance, and principal component analysis. We used the Mann-Whitney U test for comparison of Pearson correlation coefficients and Euclidean distances, to assess which control tissue is most similar to IA in terms of gene expression. Other unrelated tissues were used as negative controls. Results- The cortical and the CoW arteries were more similar to IA in terms of gene expression than the superficial temporal artery. This was based on Pearson correlation (+0.023 [90% CI, 0.017/0.029; P=1.9E-09] for the cortical artery and +0.034 [90% CI, 0.028/0.040; P=6.0E-15] for the CoW artery compared with the superficial temporal artery), Euclidean distance (-25.71 [90% CI, -31.54/-20.02; P=1.9E-11] for the cortical artery and -38.09 [90% CI, -44.08/-32.19; P<2.2E-16] for the CoW artery compared with the superficial temporal artery) and principal component analysis. In all analyses, the unrelated tissues formed separate groups compared with IA and the 3 control arteries. Conclusions- The cortical arteries and the CoW arteries are better controls for gene expression studies on IA than the superficial temporal artery. This probably relates to differences in anatomy of these tissues, such as the presence of an external elastic lamina in the extracranial vasculature and absence in the intracranial vasculature, because IAs, cortical arteries, and CoW arteries are all intracranial while the superficial temporal artery is extracranial. Since CoW arteries can only be obtained postmortem, cortical arteries are preferred over CoW arteries.

Gadolinium Enhancement of the Aneurysm Wall in Unruptured Intracranial Aneurysms Is Associated with an Increased Risk of Aneurysm Instability: A Follow-Up Study

BACKGROUND AND PURPOSE

Previous studies have suggested that gadolinium enhancement of the wall of unruptured intracranial aneurysms on MR imaging may reflect aneurysm wall instability. However, all previous studies were cross-sectional. In this longitudinal study, we investigated whether aneurysm wall enhancement is associated with an increased risk of aneurysm instability.

MATERIALS AND METHODS

We included all patients 18 years of age or older with ≥1 unruptured aneurysm from the University Medical Center Utrecht, the Netherlands, who were included in 2 previous studies with either 3T or 7T aneurysm wall MR imaging and for whom it was decided not to treat the aneurysm but to monitor it with follow-up imaging. We investigated the risk of growth or rupture during follow-up of aneurysms with and without gadolinium enhancement of the aneurysm wall at baseline and calculated the risk difference between the 2 groups with corresponding 95% confidence intervals.

RESULTS

We included 57 patients with 65 unruptured intracranial aneurysms. After a median follow-up of 27 months (interquartile range, 20-31 months), growth (n = 2) or rupture (n = 2) was observed in 4 of 19 aneurysms (21%; 95% CI, 6%-54%) with wall enhancement and in zero of 46 aneurysms (0%; 95% CI, 0%-8%) without enhancement (risk difference, 21%; 95% CI, 3%-39%).

CONCLUSIONS

Gadolinium enhancement of the aneurysm wall on MR imaging is associated with an increased risk of aneurysm instability. The absence of wall enhancement makes it unlikely that the aneurysm will grow or rupture in the short term. Larger studies are needed to investigate whether aneurysm wall enhancement is an independent predictor of aneurysm instability.

Quantification of Intracranial Aneurysm Volume Pulsation with 7T MRI

BACKGROUND AND PURPOSE

Aneurysm volume pulsation is a potential predictor of intracranial aneurysm rupture. We evaluated whether 7T MR imaging can quantify aneurysm volume pulsation.

MATERIALS AND METHODS

In Stage I of the study, 10 unruptured aneurysms in 9 patients were studied using a high-resolution (0.6-mm, isotropic) 3D gradient-echo sequence with cardiac gating. Semiautomatic segmentation was used to measure aneurysm volume (in cubic millimeters) per cardiac phase. Aneurysm pulsation was defined as the relative increase in volume between the phase with the smallest volume and the phase with the largest volume. The accuracy and precision of the measured volume pulsations were addressed by digital phantom simulations and a repeat image analysis. In Stage II, the imaging protocol was optimized and 9 patients with 9 aneurysms were studied with and without administration of a contrast agent.

RESULTS

The mean aneurysm pulsation in Stage I was 8% ± 7% (range, 2%-27%), with a mean volume change of 15 ± 14 mm³ (range, 3-51 mm³). The mean difference in volume change for the repeat image analysis was 2 ± 6 mm³. The artifactual volume pulsations measured with the digital phantom simulations were of the same magnitude as the volume pulsations observed in the patient data, even after protocol optimization in Stage II.

CONCLUSIONS

Volume pulsation quantification with the current imaging protocol on 7T MR imaging is not accurate due to multiple imaging artifacts. Future studies should always include aneurysm-specific accuracy analysis.

Intracranial Aneurysm–Associated Single-Nucleotide Polymorphisms Alter Regulatory DNA in the Human Circle of Willis

Background and Purpose—

Genome-wide association studies significantly link intracranial aneurysm (IA) to single-nucleotide polymorphisms (SNPs) in 6 genomic loci. To gain insight into the relevance of these IA-associated SNPs, we aimed to identify regulatory regions and analyze overall gene expression in the human circle of Willis (CoW), on which these aneurysms develop.

Methods—

We performed chromatin immunoprecipitation and sequencing for histone modifications H3K4me1 and H3K27ac to identify regulatory regions, including distal enhancers and active promoters, in postmortem specimens of the human CoW. These experiments were complemented with RNA sequencing on the same specimens. We determined whether these regulatory regions overlap with IA-associated SNPs, using computational methods. By combining our results with publicly available data, we investigated the effect of IA-associated SNPs on the newly identified regulatory regions and linked them to potential target genes.

Results—

We find that IA-associated SNPs are significantly enriched in CoW regulatory regions. Some of the IA-associated SNPs that overlap with a regulatory region are likely to alter transcription factor binding, and in proximity to these regulatory regions are 102 genes that are expressed in the CoW. In addition, gene expression in the CoW is enriched for genes related to cell adhesion and the extracellular matrix.

Conclusions—

CoW regulatory regions link IA-associated SNPs to genes with a potential role in the development of IAs. Our data refine previous predictions on SNPs associated with IA and provide a substantial resource from which candidates for follow-up studies can be prioritized.

RNA Sequencing Analysis of Intracranial Aneurysm Walls Reveals Involvement of Lysosomes and Immunoglobulins in Rupture

BACKGROUND AND PURPOSE

Analyzing genes involved in development and rupture of intracranial aneurysms can enhance knowledge about the pathogenesis of aneurysms, and identify new treatment strategies. We compared gene expression between ruptured and unruptured aneurysms and control intracranial arteries.

METHODS

We determined expression levels with RNA sequencing. Applying a multivariate negative binomial model, we identified genes that were differentially expressed between 44 aneurysms and 16 control arteries, and between 22 ruptured and 21 unruptured aneurysms. The differential expression of 8 relevant and highly significant genes was validated using digital polymerase chain reaction. Pathway analysis was used to identify enriched pathways. We also analyzed genes with an extreme pattern of differential expression: only expressed in 1 condition without any expression in the other.

RESULTS

We found 229 differentially expressed genes in aneurysms versus controls and 1489 in ruptured versus unruptured aneurysms. The differential expression of all 8 genes selected for digital polymerase chain reaction validation was confirmed. Extracellular matrix pathways were enriched in aneurysms versus controls, whereas pathways involved in immune response and the lysosome pathway were enriched in ruptured versus unruptured aneurysms. Immunoglobulin genes were expressed in aneurysms, but showed no expression in controls.

CONCLUSIONS

For rupture of intracranial aneurysms, we identified the lysosome pathway as a new pathway and found further evidence for the role of the immune response. Our results also point toward a role for immunoglobulins in the pathogenesis of aneurysms. Immune-modifying drugs are, therefore, interesting candidate treatment strategies in the prevention of aneurysm development and rupture.

Thinner Regions of Intracranial Aneurysm Wall Correlate with Regions of Higher Wall Shear Stress: A 7T MRI Study

BACKGROUND AND PURPOSE

Both hemodynamics and aneurysm wall thickness are important parameters in aneurysm pathophysiology. Our aim was to develop a method for semi-quantitative wall thickness assessment on in vivo 7T MR images of intracranial aneurysms for studying the relation between apparent aneurysm wall thickness and wall shear stress.

MATERIALS AND METHODS

Wall thickness was analyzed in 11 unruptured aneurysms in 9 patients who underwent 7T MR imaging with a TSE-based vessel wall sequence (0.8-mm isotropic resolution). A custom analysis program determined the in vivo aneurysm wall intensities, which were normalized to the signal of nearby brain tissue and were used as measures of apparent wall thickness. Spatial wall thickness variation was determined as the interquartile range in apparent wall thickness (the middle 50% of the apparent wall thickness range). Wall shear stress was determined by using phase-contrast MR imaging (0.5-mm isotropic resolution). We performed visual and statistical comparisons (Pearson correlation) to study the relation between wall thickness and wall shear stress.

RESULTS

3D colored apparent wall thickness maps of the aneurysms showed spatial apparent wall thickness variation, which ranged from 0.07 to 0.53, with a mean variation of 0.22 (a variation of 1.0 roughly means a wall thickness variation of 1 voxel [0.8 mm]). In all aneurysms, apparent wall thickness was inversely related to wall shear stress (mean correlation coefficient, -0.35; P < .05).

CONCLUSIONS

A method was developed to measure the wall thickness semi-quantitatively, by using 7T MR imaging. An inverse correlation between wall shear stress and apparent wall thickness was determined. In future studies, this noninvasive method can be used to assess spatial wall thickness variation in relation to pathophysiologic processes such as aneurysm growth and rupture.

Lessons learned from whole exome sequencing in multiplex families affected by a complex genetic disorder, intracranial aneurysm

Genetic risk factors for intracranial aneurysm (IA) are not yet fully understood. Genomewide association studies have been successful at identifying common variants; however, the role of rare variation in IA susceptibility has not been fully explored. In this study, we report the use of whole exome sequencing (WES) in seven densely-affected families (45 individuals) recruited as part of the Familial Intracranial Aneurysm study. WES variants were prioritized by functional prediction, frequency, predicted pathogenicity, and segregation within families. Using these criteria, 68 variants in 68 genes were prioritized across the seven families. Of the genes that were expressed in IA tissue, one gene (TMEM132B) was differentially expressed in aneurysmal samples (n=44) as compared to control samples (n=16) (false discovery rate adjusted p-value=0.023). We demonstrate that sequencing of densely affected families permits exploration of the role of rare variants in a relatively common disease such as IA, although there are important study design considerations for applying sequencing to complex disorders. In this study, we explore methods of WES variant prioritization, including the incorporation of unaffected individuals, multipoint linkage analysis, biological pathway information, and transcriptome profiling. Further studies are needed to validate and characterize the set of variants and genes identified in this study.

Genetic risk load according to the site of intracranial aneurysms

OBJECTIVE

We investigated whether risk alleles of single nucleotide polymorphisms associated with intracranial aneurysm (IA) are enriched in patients with familial IA, IA located at the middle cerebral artery (MCA), or IA rupture at a younger age.

METHODS

In this case-only study, we calculated genetic risk scores (GRS) for 973 Dutch and 718 Finnish patients with IA by summing effect size-weighted risk allele counts of 7 single nucleotide polymorphisms associated with IAs previously identified through genome-wide association studies. We tested the GRS for association with presence of familial IA or IA at the MCA using logistic regression, and with age at time of IA rupture using linear regression. We also calculated odds ratios with 95% confidence intervals for the proportion of patients with each characteristic in the highest compared with the lowest GRS tertile.

RESULTS

GRS were higher in IA at the MCA in the Dutch (p = 2.5 × 10(-4)), Finnish (p = 0.039), and combined cohort (p = 4.9 × 10(-5)). GRS were not associated with familial IA in the Dutch (p = 0.34), Finnish (p = 0.45), and combined cohort (p = 0.98), or with age at time of IA rupture in the Dutch (p = 0.28), Finnish (p = 0.86), and combined cohort (p = 0.45). In the combined cohort, odds ratios were 0.89 (0.67-1.20) for familial IA, 1.03 (0.79-1.34) for lower age, and 1.54 (1.20-1.98) for MCA aneurysms.

CONCLUSIONS

Our findings suggest that genetic risk factors have a larger role in the development of IA at the MCA than at other sites, and that genetic heterogeneity should be considered in future genetic studies.

The Association Between Genetic Risk Factors and the Size of Intracranial Aneurysms at Time of Rupture

BACKGROUND:

Genetic risk factors for intracranial aneurysms may influence the size of aneurysms.

OBJECTIVE:

To assess the association between genetic risk factors and the size of aneurysms at the time of rupture.

METHODS:

Genotypes of 7 independent single-nucleotide polymorphisms (SNPs) of the 6 genetic risk loci identified in genome-wide association studies of patients with intracranial aneurysms were obtained from 700 Dutch patients with an aneurysmal subarachnoid hemorrhage (1997-2007) previously genotyped in the genome-wide association studies; 255 additional Dutch patients with an aneurysmal subarachnoid hemorrhage (2007-2011) were genotyped for these SNPs. Aneurysms were measured on computerized tomography angiography or digital subtraction angiography. The mean aneurysm size (with standard error) was compared between patients with and without a genetic risk factor by the use of linear regression. The association between SNPs and size was assessed for single SNPs and for the combined effect of SNPs by using a weighted genetic risk score.

RESULTS:

Single SNPs showed no association with aneurysm size, nor did the genetic risk score.

CONCLUSION:

The 6 genetic risk loci have no major influence on the size of aneurysms at the time of rupture. Because these risk loci explain no more than 5% of the genetic risk, other genetic factors for intracranial aneurysms may influence aneurysm size and thereby proneness to rupture.

Regional differences in incidence and patient characteristics of moyamoya disease: a systematic review

BACKGROUND AND PURPOSE

Moyamoya disease (MMD) is a rare cause of stroke, initially described in Japan. In other countries, incidences and presenting symptoms may differ from those in Japan. The literature on regional differences in incidence and patient characteristics of MMD was systematically reviewed.

METHODS

Medline, EMBASE and CINAHL were searched for population based studies on MMD published between January 1969 and January 2011. From studies that met predefined inclusion criteria, information was extracted on incidence and patient characteristics. Incidences with corresponding 95% CIs if possible were calculated and descriptive statistics for patient characteristics were used.

RESULTS

8 studies were included: three from Japan, one each from Taiwan and China and three from the USA. Incidences per 100 000 patient years ranged in Japan from 0.35 to 0.94 (95% CI 0.69 to 1.19), in the USA from 0.05 (-0.04 to 0.12) in Iowa to 0.17 (-0.06 to 0.40) in Hawaii and were 0.41 (0.28 to 0.54) in Nanjing, China and 0.02 (0.003 to 0.04) in Taiwan. Female to male ratio ranged from 1.1 (0.9 to 1.5) in Nanjing to 2.8 (1.2 to 6.1) in Iowa. Proportions with intracerebral haemorrhage as the initial presentation were 56% in China, 52% in Taiwan, 29% in Hawaii, 21% in Japan and 10% in Iowa. Patients with childhood onset presented most often with ischaemia (>75%) in all regions.

CONCLUSIONS

MMD incidence was higher in Japan and China than in Taiwan and North America and presenting symptoms showed regional differences, which are thus far unexplained. Population based data on MMD in Europe are lacking.

Lower incidence of cytomegalovirus infection with everolimus versus mycophenolate mofetil in de novo cardiac transplant recipients: a randomized, multicenter study

Cytomegalovirus (CMV) is a major cause of infectious complications following cardiac transplantation, severely affecting short- and long-term outcomes. A 12-month, multicenter, randomized, open-label study in de novo cardiac transplant patients was undertaken to compare the efficacy, renal function, and safety of everolimus plus reduced cyclosporine versus mycophenolate mofetil (MMF) plus standard cyclosporine (ClinicalTrials.gov NCT00150046). CMV-specific data was prospectively collected on infections, laboratory evidence, CMV syndrome, and CMV disease. In total, 176 patients were randomized (everolimus 92; MMF 84). Use of CMV prophylaxis was similar between groups (everolimus 20.8%; MMF 24.0%). Patients in the everolimus arm had a significantly lower incidence of any CMV event (8.8% versus 32.5% with MMF, P<0.001), CMV infection as an adverse event (4.4% versus 16.9%, P=0.011), laboratory evidence of CMV (antigenemia 7.7% versus 27.7%, P<0.001; polymerase chain reaction assay 2.2% versus 12.0%, P=0.015), and CMV syndrome (1.1% versus 8.4%, P=0.028). In the donor (D)+/recipient (R)+and D-/R+ subgroups, even after adjusting for use of prophylaxis, the CMV event rate remained significantly lower with everolimus than with MMF (P=0.0015 and P=0.0381, respectively). In conclusion, de novo cardiac transplant recipients experienced lower rates of CMV infection, CMV syndrome, or organ involvement on an everolimus-based immunosuppressant regimen compared with MMF.

Clinical significance of internal thoracic artery morphometry and inter-ethnic differences

The internal thoracic artery (ITA) is used extensively for coronary revascularisation. Clinical observations suggest an inter-ethnic difference in ITA morphometry between Indians and whites presenting for coronary artery bypass surgery. However, accurate morphometric data comparing these ethnic groups were not available. This study analyses the morphometry of the left and right ITAs in 60 cadavers (43 blacks, 9 whites, 8 Indians). The lengths of the arteries were measured and the external diameters were recorded at the origin of the 1st, 4th and 6th costal cartilages. Significant differences in length and diameter on the right and left sides between ethnic groups were demonstrated. In particular, these differences were marked between the white and Indian groups. Clinically, these differences can be so marked that in some instances the left ITA in Indian patients is so small at the distal point of take-down as to be unsuitable for use as an arterial conduit. This is one of the reasons that has prompted the use of the ITA as a composite graft. Our study appears to be the first to highlight this inter-ethnic difference and to support the clinical impression.