RNF213 Is Associated with Intracranial Aneurysms in the French-Canadian Population

RNF213 Polymorphisms in Intracranial Artery Dissection

The ring finger protein 213 gene (RNF213) is involved in several vascular diseases, both intracranial and systemic ones. Some variants are common in the Asian population and are reported as a risk factor for moyamoya disease, intracranial stenosis and intracranial aneurysms. Among intracranial vascular diseases, both moyamoya disease and intracranial artery dissection are more prevalent in the Asian population. We performed a systematic review of the literature, aiming to assess the rate of RNF213 variants in patients with spontaneous intracranial dissections. Four papers were identified, providing data on 53 patients with intracranial artery dissection. The rate of RNF213 variants is 10/53 (18.9%) and it increases to 10/29 (34.5%), excluding patients with vertebral artery dissection. All patients had the RNF213 p.Arg4810Lys variant. RNF213 variants seems to be involved in intracranial dissections in Asian cohorts. The small number of patients, the inclusion of only patients of Asian descent and the small but non-negligible coexistence with moyamoya disease familiarity might be limiting factors, requiring further studies to confirm these preliminary findings and the embryological interpretation.

Fatal brainstem injury following proton radiation in a patient with medulloblastoma and a germline variant in RNF213

Brainstem injury occurs secondary to radiation to the posterior fossa in up to 2% of pediatric patients. It may occur after months to years after treatment. It has been associated with age less than 5 years and with comorbid conditions such as cerebrovascular disease, diabetes mellitus, and hypertension. Radiation necrosis is often symptomatic and can be fatal. A pathogenic variant in RNF213 was found in a patient who suffered fatal radiation necrosis. This mutation has been associated with moyamoya disease and may predispose to radiation necrosis.

RNF213-Related Vasculopathy: Various Systemic Vascular Diseases Involving RNF213 Gene Mutations: Review

Moyamoya disease (MMD) is a cerebrovascular disorder that is predominantly observed in women of East Asian descent, and is characterized by progressive stenosis of the internal carotid artery, beginning in early childhood, and a distinctive network of collateral vessels known as "moyamoya vessels" in the basal ganglia. Additionally, a prevalent genetic variant found in most MMD cases is the p.R4810K polymorphism of RNF213 on chromosome 17q25.3. Recent studies have revealed that RNF213 mutations are associated not only with MMD, but also with other systemic vascular disorders, including intracranial atherosclerosis and systemic vascular abnormalities such as pulmonary artery stenosis and coronary artery diseases. Therefore, the concept of "RNF213-related vasculopathy" has been proposed. This review focuses on polymorphisms in the RNF213 gene and describes a wide range of clinical and genetic phenotypes associated with RNF213-related vasculopathy. The RNF213 gene has been suggested to play an important role in the pathogenesis of vascular diseases and developing new therapies. Therefore, further research and knowledge sharing through collaboration between clinicians and researchers are required.

Association of rare RNF213 variants and intracranial aneurysm risk in a Chinese population

Background

Genetic factors play important roles in the development of intracranial aneurysm (IA). Rare RNF213 variants have been identified as being susceptible to Moyamoya disease (MMD), non-MMD intracranial artery stenosis/occlusion disease, and other vascular disorders. This study aimed to investigate the association between rare RNF213 variants and the risk of IA in a Chinese population.

Methods

We recruited 174 patients with IA for RNF213 target exome sequencing. Information on the control subjects was obtained from the 1,000 Genome Project and GeneSky in-house database. After prioritizing rare RNF213 variants, the filtered variants were confirmed by Sanger sequencing. Gene-based association analyses were performed to identify the association between variants and the disease using burden and variance component methods; that is, the weighted-sum statistic (WSS) and the sequence kernel association test (SKAT), respectively. The Student's t-test, Chi-squared test, and Fisher's exact test were used to compare the clinical characteristics between carriers and non-carriers of the RNF213 variants.

Results

After filtering, there were 14 RNF213 variants in 18 patients with IA, which were significantly associated with the disease after the gene-based association tests [minor allele frequency (MAF) <0.01, WSS P value 5.08×10^-9; SKAT P value 2.96×10^-6; SKAT-O P value 3.56×10^-8]. Significant difference was not obtained between the carriers and non-carriers of the RNF213 variants in terms of the clinical characteristics.

Conclusions

Rare RNF213 variants were associated with sporadic IA in a Chinese population. Our findings suggest that these rare RNF213 variants might have potentially important roles in IA. However, more comprehensive studies need to be conducted to confirm this association and causality.

Mystery(n) Phenotypic Presentation in Europeans: Report of Three Further Novel Missense RNF213 Variants Leading to Severe Syndromic Forms of Moyamoya Angiopathy and Literature Review

Moyamoya angiopathy (MMA) is a rare cerebral vasculopathy in some cases occurring in children. Incidence is higher in East Asia, where the heterozygous p.Arg4810Lys variant in RNF213 (Mysterin) represents the major susceptibility factor. Rare variants in RNF213 have also been found in European MMA patients with incomplete penetrance and are today a recognized susceptibility factor for other cardiovascular disorders, from extracerebral artery stenosis to hypertension. By whole exome sequencing, we identified three rare and previously unreported missense variants of RNF213 in three children with early onset of bilateral MMA, and subsequently extended clinical and radiological investigations to their carrier relatives. Substitutions all involved highly conserved residues clustered in the C-terminal region of RNF213, mainly in the E3 ligase domain. Probands showed a de novo occurring variant, p.Phe4120Leu (family A), a maternally inherited heterozygous variant, p.Ser4118Cys (family B), and a novel heterozygous variant, p.Glu4867Lys, inherited from the mother, in whom it occurred de novo (family C). Patients from families A and C experienced transient hypertransaminasemia and stenosis of extracerebral arteries. Bilateral MMA was present in the proband’s carrier grandfather from family B. The proband from family C and her carrier mother both exhibited annular figurate erythema. Our data confirm that rare heterozygous variants in RNF213 cause MMA in Europeans as well as in East Asian populations, suggesting that substitutions close to positions 4118–4122 and 4867 of RNF213 could lead to a syndromic form of MMA showing elevated aminotransferases and extracerebral vascular involvement, with the possible association of peculiar skin manifestations.

Activated leukocyte cell adhesion molecule/cluster of differentiation 166 rs10933819 (G>A) variant is associated with familial intracranial aneurysms

Rupture of intracranial aneurysms (IAs) is the most common cause of subarachnoid hemorrhage (SAH). Currently, there is sufficient evidence to indicate that inflammatory responses contribute to aneurysm rupture. Moreover, the familial occurrence of SAH suggests that genetic factors may be involved in disease susceptibility. In the present study, a clinically proven case of IA in a patient who is a heterozygous mutation carrier of the activated leukocyte cell adhesion molecule (ALCAM)/cluster of differentiation 166 (CD166) gene, is reported. Genomic DNA was extracted from two siblings diagnosed with SAH and other available family members. A variant prioritization strategy that focused on functional prediction, frequency, predicted pathogenicity, and segregation within the family was employed. Sanger sequencing was also performed on the unaffected relatives to assess the segregation of variants within the phenotype. The verified mutations were sequenced in 145 ethnicity-matched healthy individuals. Based on whole exome sequencing data obtained from three individuals, two of whom were diagnosed with IAs, the single-nucleotide variant rs10933819 was prioritized in the family. Only one variant, rs10933819 (G>A), in ALCAM co-segregated with the phenotype, and this mutation was absent in ethnicity-matched healthy individuals. Collectively, ALCAM c1382 G>A p.Gly229Val was identified, for the first time, as a pathogenic mutation in this IA pedigree.

Novel Multifaceted Roles for RNF213 Protein

Ring Finger Protein 213 (RNF213), also known as Mysterin, is the major susceptibility factor for Moyamoya Arteriopathy (MA), a progressive cerebrovascular disorder that often leads to brain stroke in adults and children. Although several rare RNF213 polymorphisms have been reported, no major susceptibility variant has been identified to date in Caucasian patients, thus frustrating the attempts to identify putative therapeutic targets for MA treatment. For these reasons, the investigation of novel biochemical functions, substrates and unknown partners of RNF213 will help to unravel the pathogenic mechanisms of MA and will facilitate variant interpretations in a diagnostic context in the future. The aim of the present review is to discuss novel perspectives regarding emerging RNF213 roles in light of recent literature updates and dissect their relevance for understanding MA and for the design of future research studies. Since its identification, RNF213 involvement in angiogenesis and vasculogenesis has strengthened, together with its role in inflammatory signals and proliferation pathways. Most recent studies have been increasingly focused on its relevance in antimicrobial activity and lipid metabolism, highlighting new intriguing perspectives. The last area could suggest the main role of RNF213 in the proteasome pathway, thus reinforcing the hypotheses already previously formulated that depict the protein as an important regulator of the stability of client proteins involved in angiogenesis. We believe that the novel evidence reviewed here may contribute to untangling the complex and still obscure pathogenesis of MA that is reflected in the lack of therapies able to slow down or halt disease progression and severity.

RNF213-Associated Vascular Disease: A Concept Unifying Various Vasculopathies

The ring finger protein 213 gene (RNF213) encodes a 590 kDa protein that is thought to be involved in angiogenesis. This gene was first recognized as a vasculopathy-susceptibility locus through genome-wide association studies undertaken in a Japanese population, demonstrating that heterozygotes for RNF213 p.Arg4810Lys (c.14429G>A, rs112735431) had a greatly increased risk of moyamoya disease. The association of RNF213 p.Arg4810Lys as a susceptibility variant of moyamoya disease was reproduced in Korean and Chinese individuals and, later, in Caucasians. Variants of the RNF213 gene have been linked to a number of vascular diseases such as moyamoya disease, intracranial major artery stenosis, pulmonary arterial hypertension, and peripheral pulmonary artery stenosis, and have also been associated with co-occurrent diseases and vascular disease in different organs. Based on the findings that we have reported to date, our paper proposes a new concept of “RNF213-associated vascular disease” to unify these conditions with the aim of capturing patients with multiple diseases but with a common genetic background. This concept will be highly desirable for clarifying all of the diseases in the RNF213-associated vascular disease category by means of global epidemiological investigations because of the possibility of such diseases appearing asymptomatically in some patients.

Moyamoya Disease Susceptibility Gene RNF213 Regulates Endothelial Barrier Function

BACKGROUND

Variants in the ring finger protein 213 (RNF213) gene are known to be associated with increased predisposition to cerebrovascular diseases development. Genomic studies have identified RNF213 as a major risk factor of Moyamoya disease in East Asian descendants. However, little is known about the RNF213 (ring finger protein 213) biological functions or its associated pathogenic mechanisms underlying Moyamoya disease.

METHODS

To investigate RNF213 loss-of-function effect in endothelial cell, stable RNF213-deficient human cerebral endothelial cells were generated using the CRISPR-Cas9 genome editing technology.

RESULTS

In vitro assays, using RNF213 knockout brain endothelial cells, showed clear morphological changes and increased blood-brain barrier permeability. Downregulation and delocalization of essential interendothelial junction proteins involved in the blood-brain barrier maintenance, such as PECAM-1 (platelet endothelial cell adhesion molecule-1), was also observed. Brain endothelial RNF213-deficient cells also showed an abnormal potential to transmigration of leukocytes and secreted high amounts of proinflammatory cytokines.

CONCLUSIONS

Taken together, these results indicate that RNF213 could be a key regulator of cerebral endothelium integrity, whose disruption could be an early pathological mechanism leading to Moyamoya disease. This study also further reinforces the importance of blood-brain barrier integrity in the development of Moyamoya disease and other RNF213-associated diseases.

PPIL4 is essential for brain angiogenesis and implicated in intracranial aneurysms in humans

Intracranial aneurysm (IA) rupture leads to subarachnoid hemorrhage, a sudden-onset disease that often causes death or severe disability. Although genome-wide association studies have identified common genetic variants that increase IA risk moderately, the contribution of variants with large effect remains poorly defined. Using whole-exome sequencing, we identified significant enrichment of rare, deleterious mutations in PPIL4, encoding peptidyl-prolyl cis-trans isomerase-like 4, in both familial and index IA cases. Ppil4 depletion in vertebrate models causes intracerebral hemorrhage, defects in cerebrovascular morphology and impaired Wnt signaling. Wild-type, but not IA-mutant, PPIL4 potentiates Wnt signaling by binding JMJD6, a known angiogenesis regulator and Wnt activator. These findings identify a novel PPIL4-dependent Wnt signaling mechanism involved in brain-specific angiogenesis and maintenance of cerebrovascular integrity and implicate PPIL4 gene mutations in the pathogenesis of IA.

Whole Exome Sequencing in Patients with Phenotypically Associated Familial Intracranial Aneurysm

Objective

Familial intracranial aneurysms (FIAs) are found in approximately 6%–20% of patients with intracranial aneurysms (IAs), suggesting that genetic predisposition likely plays a role in its pathogenesis. The aim of this study was to identify possible IA-associated variants using whole exome sequencing (WES) in selected Korean families with FIA.

Materials and Methods

Among the 26 families in our institutional database with two or more IA-affected first-degree relatives, three families that were genetically enriched (multiple, early onset, or common site involvement within the families) for IA were selected for WES. Filtering strategies, including a family-based approach and knowledge-based prioritization, were applied to derive possible IA-associated variants from the families. A chromosomal microarray was performed to detect relatively large chromosomal abnormalities.

Results

Thirteen individuals from the three families were sequenced, of whom seven had IAs. We noted three rare, potentially deleterious variants (PLOD3 c.1315G>A, NTM c.968C>T, and CHST14 c.58C>T), which are the most promising candidates among the 11 potential IA-associated variants considering gene-phenotype relationships, gene function, co-segregation, and variant pathogenicity. Microarray analysis did not reveal any significant copy number variants in the families.

Conclusion

Using WES, we found that rare, potentially deleterious variants in PLOD3, NTM, and CHST14 genes are likely responsible for the subsets of FIAs in a cohort of Korean families.

RNF213 c.14576G>A Is Associated with Intracranial Internal Carotid Artery Saccular Aneurysms

A mutation in RNF213 (c.14576G>A), a gene associated with moyamoya disease (>80%), plays a role in terminal internal carotid artery (ICA) stenosis (>15%) (ICS). Studies on RNF213 and cerebral aneurysms (AN), which did not focus on the site of origin or morphology, could not elucidate the relationship between the two. However, a report suggested a relationship between RNF213 and AN in French-Canadians. Here, we investigated the relationship between ICA saccular aneurysm (ICA-AN) and RNF213. We analyzed RNF213 expression in subjects with ICA-AN and atherosclerotic ICS. Cases with a family history of moyamoya disease were excluded. AN smaller than 4 mm were confirmed as AN only by surgical or angiographic findings. RNF213 was detected in 12.2% of patients with ICA-AN and 13.6% of patients with ICS; patients with ICA-AN and ICS had a similar risk of RNF213 mutation expression (odds ratio, 0.884; 95% confidence interval, 0.199-3.91; p = 0.871). The relationship between ICA-AN and RNF213 (c.14576G>A) was not correlated with the location of the ICA and bifurcation, presence of rupture, or multiplicity. When the etiology and location of AN were more restricted, the incidence of RNF213 mutations in ICA-AN was higher than that reported in previous studies. Our results suggest that strict maternal vessel selection and pathological selection of AN morphology may reveal an association between genetic mutations and ICA-AN development. The results of this study may form a basis for further research on systemic vascular diseases, in which the RNF213 (c.14576G>A) mutation has been implicated.

The Genetic Basis of Moyamoya Disease

Moyamoya disease (MMD) is a rare cerebrovascular disease characterized by progressive spontaneous bilateral occlusion of the intracranial internal cerebral arteries (ICA) and their major branches with compensatory capillary collaterals resembling a “puff of smoke” (Japanese: Moyamoya) on cerebral angiography. These pathological alterations of the vessels are called Moyamoya arteriopathy or vasculopathy and a further distinction is made between primary and secondary MMD. Clinical presentation depends on age and population, with hemorrhage and ischemic infarcts in particular leading to severe neurological dysfunction or even death. Although the diagnostic suspicion can be posed by MRA or CTA, cerebral angiography is mandatory for diagnostic confirmation. Since no therapy to limit the stenotic lesions or the development of a collateral network is available, the only treatment established so far is surgical revascularization. The pathophysiology still remains unknown. Due to the early age of onset, familial cases and the variable incidence rate between different ethnic groups, the focus was put on genetic aspects early on. Several genetic risk loci as well as individual risk genes have been reported; however, few of them could be replicated in independent series. Linkage studies revealed linkage to the 17q25 locus. Multiple studies on the association of SNPs and MMD have been conducted, mainly focussing on the endothelium, smooth muscle cells, cytokines and growth factors. A variant of the RNF213 gene was shown to be strongly associated with MMD with a founder effect in the East Asian population. Although it is unknown how mutations in the RNF213 gene, encoding for a ubiquitously expressed 591 kDa cytosolic protein, lead to clinical features of MMD, RNF213 has been confirmed as a susceptibility gene in several studies with a gene dosage-dependent clinical phenotype, allowing preventive screening and possibly the  development of new therapeutic approaches. This review focuses on the genetic basis of primary MMD only.

Genetics of Intracranial Aneurysms

Rupture of an intracranial aneurysm leads to aneurysmal subarachnoid hemorrhage, a severe type of stroke which is, in part, driven by genetic variation. In the past 10 years, genetic studies of IA have boosted the number of known genetic risk factors and improved our understanding of the disease. In this review, we provide an overview of the current status of the field and highlight the latest findings of family based, sequencing, and genome-wide association studies. We further describe opportunities of genetic analyses for understanding, prevention, and treatment of the disease.

Rare Neurovascular Diseases in Korea: Classification and Related Genetic Variants

Rare neurovascular diseases (RNVDs) have not been well-recognized in Korea. They involve the central nervous system and greatly affect the patients' lives. However, these diseases are difficult to diagnose and treat due to their rarity and incurability. We established a list of RNVDs by referring to the previous literature and databases worldwide to better understand the diseases and their current management status. We categorized 68 RNVDs based on their pathophysiology and clinical manifestations and estimated the prevalence of each disease in Korea. Recent advances in genetic, molecular, and developmental research have enabled further understanding of these RNVDs. Herein, we review each disease, while considering its classification based on updated pathologic mechanisms, and discuss the management status of RNVD in Korea.

A Rare Variant of ANK3 Is Associated With Intracranial Aneurysm

Intracranial aneurysm (IA) is a cerebrovascular disorder in which abnormal dilation of a blood vessel results from weakening of the blood vessel wall. The aneurysm may rupture, leading to subarachnoid hemorrhage with severe outcomes. This study was conducted to identify the genetic factors involved in the etiology of IA. Whole-exome sequencing was performed in three IA-aggregate families to identify candidate variants. Further association studies of candidate variants were performed among sporadic cases and controls. Bioinformatic analysis was used to predict the functions of candidate genes and variants. Twenty variants were identified after whole-exome sequencing, among which eight were selected for replicative association studies. ANK3 c.4403G>A (p.R1468H) was significantly associated with IA (odds ratio 4.77; 95% confidence interval 1.94–11.67; p-value = 0.00019). Amino acid R1468 in ANK3 was predicted to be located in the spectrin-binding domain of ankyrin-G and may regulate the migration of vascular endothelial cells and affect cell–cell junctions. Therefore, the variation p.R1468H may cause weakening of the artery walls, thereby accelerating the formation of IA. Thus, ANK3 is a candidate gene highly related to IA.

Mutations of RNF213 are responsible for sporadic cerebral cavernous malformation and lead to a mulberry-like cluster in zebrafish

Although familial forms of cerebral cavernous malformation are mainly attributed to three CCM genes (KRIT1, CCM2 and PDCD10), no mutation is identified in sporadic cerebral cavernous malformation cases with a unique lesion, indicating additional genes for sporadic cerebral cavernous malformation. To screen the candidate genes, we conducted whole exome sequencing in 31 sporadic cerebral cavernous malformation patients and 32 healthy controls, and identified 5 affected individuals carrying 6 heterozygous deleterious mutations in RNF213 but no RNF213 mutation in healthy individuals. To further confirm RNF213 was associated with cerebral cavernous malformation, we generated rnf213a homozygous knockout zebrafish and found mutation of rnf213a in zebrafish led to a mulberry-like cluster of disordered-flow vascular channels which was reminiscent of human cerebral cavernous malformation. In addition, we revealed kbtbd7 and anxa6 were significantly downregulated due to rnf213a mutation through transcriptomic sequencing and RT-qPCR analysis. Based on the mulberry-like phenotype partly rescued by mRNA of kbtbd7 as well as anxa6, we suggested that rnf213a promoted mulberry-like cluster via downregulation of kbtbd7 and anxa6. Altogether, we firstly demonstrate RNF213is a novel candidate gene for sporadic cerebral cavernous malformation and the mutation of rnf213a is responsible for the mulberry-like cluster in zebrafish.

Development and Validation of a Nomogram to Predict the Individual Future Stroke Risk for Adult Patients With Moyamoya Disease: A Multicenter Retrospective Cohort Study in China

Background: Studies exploring the predictive performance of major risk factors associated with future stroke events are insufficient, and a useful tool to predict individual risk is not available. Therefore, personalized advice for preventing future stroke in patients with moyamoya disease (MMD) cannot provide evidence-based recommendations. The aim of this study was to develop a novel nomogram with reliable validity to predict the individual risk of future stroke for adult MMD patients.

Methods: This study included 450 patients from seven medical centers between January 2013 and December 2018. Follow-ups were performed via clinical visits and/or telephone interviews from initial discharge to December 2019. The cohort was randomly assigned to a training set (2/3, n = 300) for nomogram development and a test set (1/3, n = 150) for external validation. The Kaplan-Meier analyses and receiver operating characteristic (ROC) curves were applied to assess the clinical benefits of this nomogram.

Results: Diabetes mellitus, a family history of MMD, a past history of stroke or transient ischemic attack, clinical manifestation, and treatment were identified as major risk factors via the least absolute shrinkage and selection operator (LASSO) method. A nomogram including these predictors was established via a multivariate Cox regression model, which displayed excellent discrimination [Harrell's concordance index (C-index), 0.85; 95% confidence interval (CI): 0.75–0.96] and calibration. In the external validation, the nomogram was found to have good discrimination (C-index, 0.81; 95% CI: 0.68–0.94) and calibration. In the subgroup analysis, this predictive nomogram also showed great performance in both ischemic-type (C-index, 0.90; 95% CI: 0.77–1.00) and hemorrhagic-type MMD (C-index, 0.72; 95% CI: 0.61–0.83). Furthermore, the nomogram was shown to have potential in clinical practice through Kaplan-Meier analyses and ROC curves.

Conclusions: We developed a novel nomogram incorporating several clinical characteristics with relatively good accuracy, which may have considerable potential for evaluating individual future stroke risk and providing useful management recommendations for adult patients with MMD in clinical practice.

Peptidomic profiling of cerebrospinal fluid from patients with intracranial saccular aneurysms

Intracranial saccular aneurysms (ISA) represent 90%-95% of all intracranial aneurysm cases, characterizing abnormal pockets at arterial branch points. Ruptures lead to subarachnoid hemorrhages (SAH) and poor prognoses. We applied mass spectrometry-based peptidomics to investigate the peptidome of twelve cerebrospinal fluid (CSF) samples collected from eleven patients diagnosed with ISA. For peptide profile analyses, participants were classified into: 1) ruptured intracranial saccular aneurysms (RIA), 2) unruptured intracranial saccular aneurysms (UIA), and late-ruptured intracranial saccular aneurysms (LRIA). Altogether, a total of 2199 peptides were detected by both Mascot and Peaks software, from which 484 (22.0%) were unique peptides. All unique peptides presented conserved chains, domains, regions of protein modulation and/or post-translational modification sites related to human diseases. Gene Ontology (GO) analyses of peptide precursor proteins showed that 42% are involved in binding, 56% in cellular anatomical entities, and 39% in intercellular signaling molecules. Unique peptides identified in patients diagnosed with RIA have a larger molecular weight and a distinctive developmental process compared to UIA and LRIA (P ≤ 0.05). Continued investigations will allow the characterization of the biological and clinical significance of the peptides identified in the present study, as well as identify prototypes for peptide-based pharmacological therapies to treat ISA. SIGNIFICANCE.

RNF213 rare variants and cerebral arteriovenous malformation in a Chinese population

OBJECTIVE

Cerebral arteriovenous malformation (AVM) is characterised by an abnormal tangle of arteries and veins, the rupture of which is a significant portion of the morbidity and mortality cases, especially in young populations. However, the exact risk factors and pathophysiologic mechanisms of AVM remain poorly understood. RNF213 variants have been identified as obvious susceptible factors of several cerebrovascular disorders, such as Moyamoya disease and intracranial aneurysms. Thus, this study aimed to determine whether there is an association between RNF213 rare variants and AVM.

METHODS

The AVM group included 22 patients with AVM. The control group included 1007 samples from the GeneSky in-house database and 208 samples from the 1000 Genome Project of Chinese Han Population. Genomic DNA samples were extracted from the peripheral blood of the AVM patients, and targeted exome sequencing of RNF213 was performed to assess the existence of low-frequency or rare variants. Sanger sequencing was performed to validate the identified variants. Logistic regression analysis was performed to calculate the odds ratios (ORs) and 95 % confidence intervals (CIs) of the candidate variants and risk of AVM. Statistical analyses were performed using SPSS version 21.0.

RESULTS

The RNF213 c.10997T>C variant (amino acid mutation p.M3666T, NM_001256071) was observed in two AVM patients after filtration. It was significantly associated with AVM in the Chinese population (ORs, 10.30 and 25.08; 95 %; CIs, 1.38-77.10 and 4.34-144.90 compared with 1000 Genome Project of Chinese Han Population and GeneSky in-house database, respectively).

CONCLUSION

Rare variants of RNF213 are associated with AVM in the Chinese population, suggesting the important role of RNF213 in AVM. Further studies are needed to verify these findings.

Pericyte Ontogeny: The Use of Chimeras to Track a Cell Lineage of Diverse Germ Line Origins

The goal of lineage tracing is to understand body formation over time by discovering which cells are the progeny of a specific, identified, ancestral progenitor. Subsidiary questions include unequivocal identification of what they have become, how many descendants develop, whether they live or die, and where they are located in the tissue or body at the end of the window examined. A classical approach in experimental embryology, lineage tracing continues to be used in developmental biology and stem cell and cancer research, wherever cellular potential and behavior need to be studied in multiple dimensions, of which one is time. Each technical approach has its advantages and drawbacks. This chapter, with some previously unpublished data, will concentrate nonexclusively on the use of interspecies chimeras to explore the origins of perivascular (or mural) cells, of which those adjacent to the vascular endothelium are termed pericytes for this purpose. These studies laid the groundwork for our understanding that pericytes derive from progenitor mesenchymal pools of multiple origins in the vertebrate embryo, some of which persist into adulthood. The results obtained through xenografting, like in the methodology described here, complement those obtained through genetic lineage-tracing techniques within a given species.

Genome-wide association study of intracranial aneurysms identifies 17 risk loci and genetic overlap with clinical risk factors

Rupture of an intracranial aneurysm leads to subarachnoid hemorrhage, a severe type of stroke. To discover new risk loci and the genetic architecture of intracranial aneurysms, we performed a cross-ancestry, genome-wide association study in 10,754 cases and 306,882 controls of European and East Asian ancestry. We discovered 17 risk loci, 11 of which are new. We reveal a polygenic architecture and explain over half of the disease heritability. We show a high genetic correlation between ruptured and unruptured intracranial aneurysms. We also find a suggestive role for endothelial cells by using gene mapping and heritability enrichment. Drug-target enrichment shows pleiotropy between intracranial aneurysms and antiepileptic and sex hormone drugs, providing insights into intracranial aneurysm pathophysiology. Finally, genetic risks for smoking and high blood pressure, the two main clinical risk factors, play important roles in intracranial aneurysm risk, and drive most of the genetic correlation between intracranial aneurysms and other cerebrovascular traits.

Association of single nucleotide polymorphisms of MTHFR, TCN2, RNF213 with susceptibility to hypertension and blood pressure

Methylenetetrahydrofolate reductase gene (MTHFR), transcobalaminII (TCN2) and ring finger protein 213 (RNF213) are related to homocysteine (Hcy) level and are of great significance for hypertension. We aimed to evaluate the associations of MTHFR (rs1801133, rs1801131, rs9651118), TCN2 (rs117353193) and RNF213 (rs9916351) with hypertension and blood pressure (BP). A total of 953 patients with hypertension and 1103 controls were enrolled. Genotyping was performed by Taqman. Logistic regression analysis indicated that A allele of TCN2 rs117353193 under the dominant model had a significantly protective effect (P=0.045) after adjustment, which showed that AA+GA genotype has a lower risk than GG. Additionally, the average diastolic BP (DBP) (P=0.044) and mean arterial pressure (MAP) (P=0.035) levels were significantly different between genotypes of RNF213 rs9916351. Further pairwise comparison showed that the average systolic BP (SBP) level of the TT genotype carriers were significantly higher than in CC (P=0.024), and the average DBP and MAP levels of the TT genotype carriers were higher than in CT (P=0.044, P=0.012, respectively) and CC (P=0.048, P=0.010, respectively). In the recessive model, the average SBP (P=0.043), DBP (P=0.018) and MAP (P=0.017) levels with the TT genotype carriers were significantly higher than in CT+CC. Multiple linear regression analysis suggested that RNF213 rs9916351 in the recessive model had significant effects on SBP (P=0.025), DBP (P=0.017) and MAP (P=0.010) as a risk factor. However, no associations were observed between MTHFR and hypertension. TCN2 rs117353193 might serve as a protective factor in hypertension, and RNF213 rs9916351 might be a risk factor that is linked to increase BP level in Northeast Chinese population.

Comprehensive investigation of RNF213 nonsynonymous variants associated with intracranial artery stenosis

Intracranial artery stenosis (ICAS) is the most common cause of ischemic stroke worldwide. RNF213 single nucleotide variant c.14429G > A (p.Arg4810Lys, rs112735431) was recently reported to be associated with ICAS in East Asians. However, the disease susceptibility of other RNF213 variants has not been clarified. This study comprehensively investigated ICAS-associated RNF213 variants in a pool of 168 Japanese ICAS patients and 1,194 control subjects. We found 138 nonsynonymous germline variants by target resequencing of all coding exons in RNF213. Association study between ICAS patients and control subjects revealed that only p.Arg4810Lys had significant association with ICAS (P = 1.5 × 10^-28, odds ratio = 29.3, 95% confidence interval 15.31-56.2 [dominant model]). Fourteen of 138 variants were rare variants detected in ICAS patients not harboring p.Arg4810Lys variant. Two of these rare variants (p.Cys118Arg and p.Leu2356Phe) consistent with variants previously reported in moyamoya disease patients characterized by stenosis of intracranial artery and association with RNF213, and three rare variants (p.Ser193Gly, p.Val1817Leu, and p.Asp3329Tyr) were found neither in control subjects and Single Nucleotide Polymorphism Database. The present findings may improve our understanding of the genetic background of intracranial artery stenosis.

Exome sequencing in 38 patients with intracranial aneurysms and subarachnoid hemorrhage

Objective

Genetic risk factors for unruptured intracranial aneurysms (UIA) and aneurysmal subarachnoid hemorrhage (aSAH) are poorly understood. We aimed to verify recently reported risk genes and to identify novel sequence variants involved in the etiology of UIA/aSAH.

Methods

We performed exome sequencing (ES) in 35 unrelated individuals and 3 family members, each with a history of UIA and/or aSAH. We searched for sequence variants with minor allele frequency (MAF) ≤ 5% in the reported risk genes ADAMTS15, ANGPTL6, ARHGEF17, LOXL2, PCNT, RNF213, THSD1 and TMEM132B. To identify novel putative risk genes we looked for unknown (MAF = 0) variants shared by the three relatives.

Results

We identified 20 variants with MAF ≤ 5% in 18 individuals: 9 variants in PCNT (9 patients), 4 in RNF213 (3 patients), 3 in THSD1 (6 patients), 2 in ANGPTL6 (3 patients), 1 in ADAMTS15 (1 patient) and 1 in TMEM132B (1 patient). In the affected family, prioritization of shared sequence variants yielded five novel putative risk genes. Based on predicted pathogenicity of identified variants, population genetics data and a high functional relevance for vascular biology, EDIL3 was selected as top candidate and screened in additional 37 individuals with UIA and/or aSAH: a further very rare EDIL3 sequence variant in two unrelated sporadic patients was identified.

Conclusions

Our data support a role of sequence variants in PCNT, RNF213 and THSD1 as susceptibility factors for cerebrovascular disease. The documented function in vascular wall integrity, the crucial localization of affected amino acids and gene/variant association tests suggest EDIL3 as a further valid candidate disease gene for UIA/aSAH.

Electronic supplementary material

The online version of this article (10.1007/s00415-020-09865-6) contains supplementary material, which is available to authorized users.

Distribution of Intracranial Major Artery Stenosis/Occlusion According to RNF213 Polymorphisms

Intracranial major artery stenosis/occlusion (ICASO) is the major cause of ischemic stroke. Recent studies have suggested that variants of RNF213, a susceptibility gene for moyamoya disease (MMD), are also related to non-MMD ICASO. Regarding the predominant involvement of steno-occlusion on anterior circulation in MMD, we hypothesized that the ICASO distribution pattern (anterior/posterior) in non-MMD may differ according to RNF213 variants. This study analyzed 1024 consecutive Korean subjects without MMD who underwent computed tomography angiography (CTA) or magnetic resonance angiography (MRA). We evaluated four single nucleotide polymorphisms (SNPs) in the exon region of RNF213: 4448G > A (rs148731719), 4810G > A (rs112735431), 4863G > A (rs760732823), and 4950G > A (rs371441113). Associations between RNF213 variants and anterior/posterior ICASO were examined using multivariate logistic regression analysis. Anterior ICASO was present in 23.0% of study subjects, and posterior ICASO was present in 8.2%. The GA genotype of RNF213 4810G > A (adjusted odds ratio (AOR) [95% confidence interval (CI)], 2.39 [1.14–4.87] compared to GG; p = 0.018) and GA genotype of RNF213 4950G > A (AOR [95% CI], 1.71 [1.11–2.63] compared to GG; p = 0.015) were more frequent in subjects with anterior ICASO. The genotype frequency of RNF213 4863G > A differed significantly according to the presence of posterior ICASO. Further investigations of the functional and biological roles of RNF213 will improve our understanding of the pathomechanisms of ICASO and cerebrovascular disease.

Exome sequencing reveals a novel variant in NFX1 causing intracranial aneurysm in a Chinese family

BACKGROUND

Genetic risk factors play an important role in the pathogenesis of familial intracranial aneurysms (FIAs); however, the molecular mechanisms remain largely unknown.

OBJECTIVE

To investigate potential FIA-causing genetic variants by rare variant interrogation and a family-based genomics approach in a large family with an extensive multigenerational pedigree with FIAs.

METHOD

Exome sequencing (ES) was performed in a dominant likely family with intracranial aneurysms (IAs). Variants were analyzed by an in-house developed pipeline and prioritized using various filtering strategies, including population frequency, variant type, and predicted variant pathogenicity. Sanger sequencing was also performed to evaluate the segregation of the variants with the phenotype.

RESULTS

Based on the ES data obtained from five individuals from a family with 7/21 living members affected with IAs, a total of 14 variants were prioritized as candidate variants. Familial segregation analysis revealed that NFX1 c.2519T>C (p.Leu840Pro) segregated in accordance with Mendelian expectations with the phenotype within the family-that is, present in all IA-affected cases and absent from all unaffected members of the second generation. This missense variant is absent from public databases (1000genome, ExAC, gnomAD, ESP5400), and has damaging predictions by bioinformatics tools (Gerp ++ score = 5.88, CADD score = 16.43, MutationTaster score = 1, LRT score = 0). In addition, 840Leu in NFX1 is robustly conserved in mammals and maps in a region before the RING-type zinc finger domain.

CONCLUSION

NFX1 c.2519T>C (p.Leu840Pro) may contribute to the pathogenetics of a subset of FIAs.

Familial Intracranial Aneurysm in Newfoundland: Clinical and Genetic Analysis

Objective:

Intracranial aneurysm (IA) is an expansion of the weakened arterial wall that is often asymptomatic until rupture, resulting in subarachnoid hemorrhage. Here we describe the high prevalence of familial IA in a cohort of Newfoundland ancestry. We began to investigate the genetic etiology of IA in affected family members, as the inheritance of this disease is poorly understood.

Methods:

Whole exome sequencing was completed for a cohort of 12 affected individuals from two multiplex families with a strong family history of IA. A filtering strategy was implemented to identify rare, shared variants. Filtered variants were prioritized based on validation by Sanger sequencing and segregation within the families.

Results:

In family R1352, six variants passed filtering; while in family R1256, 68 variants remained, so further filtering was pursued. Following validation by Sanger sequencing, top candidates were investigated in a set of population controls, namely,C4orf6c.A1G (p.M1V) andSPDYE4c.C103T (p.P35S). Neither was detected in 100 Newfoundland control samples.

Conclusion:

Rare and potentially deleterious variants were identified in both families, though incomplete segregation was identified for all filtered variants. Alternate methods of variant prioritization and broader considerations regarding the interplay of genetic and environmental factors are necessary in future studies of this disease.

Genetic architecture and adaptations of Nunavik Inuit

The Canadian Inuit have a distinct population background that may entail particular implications for the health of its individuals. However, the number of genetic studies examining this Inuit population is limited, and much remains to be discovered in regard to its genetic characteristics. In this study, we generated whole-exome sequences and genomewide genotypes for 170 Nunavik Inuit, a small and isolated founder population of Canadian Arctic indigenous people. Our study revealed the genetic background of Nunavik Inuit to be distinct from any known present-day population. The majority of Nunavik Inuit show little evidence of gene flow from European or present-day Native American peoples, and Inuit living around Hudson Bay are genetically distinct from those around Ungava Bay. We also inferred that Nunavik Inuit have a small effective population size of 3,000 and likely split from Greenlandic Inuit ∼10.5 kya. Nunavik Inuit went through a bottleneck at approximately the same time and might have admixed with a population related to the Paleo-Eskimos. Our study highlights population-specific genomic signatures in coding regions that show adaptations unique to Nunavik Inuit, particularly in pathways involving fatty acid metabolism and cellular adhesion (CPNE7, ICAM5, STAT2, and RAF1). Subsequent analyses in selection footprints and the risk of intracranial aneurysms (IAs) in Nunavik Inuit revealed an exonic variant under weak negative selection to be significantly associated with IA (rs77470587; P = 4.6 × 10^-8).

Genetic basis of intracranial aneurysm formation and rupture: clinical implications in the postgenomic era

OBJECTIVE

Despite the prevalence and impact of intracranial aneurysms (IAs), the molecular basis of their pathogenesis remains largely unknown. Moreover, there is a dearth of clinically validated biomarkers to efficiently screen patients with IAs and prognosticate risk for rupture. The aim of this study was to survey the literature to systematically identify the spectrum of genetic aberrations that have been identified in IA formation and risk of rupture.

METHODS

A literature search was performed using the Medical Subject Headings (MeSH) system of databases including PubMed, EMBASE, and Google Scholar. Relevant studies that reported on genetic analyses of IAs, rupture risk, and long-term outcomes were included in the qualitative analysis.

RESULTS

A total of 114 studies were reviewed and 65 were included in the qualitative synthesis. There are several well-established mendelian syndromes that confer risk to IAs, with variable frequency. Linkage analyses, genome-wide association studies, candidate gene studies, and exome sequencing identify several recurrent polymorphic variants at candidate loci, and genes associated with the risk of aneurysm formation and rupture, including ANRIL (CDKN2B-AS1, 9p21), ARGHEF17 (11q13), ELN (7q11), SERPINA3 (14q32), and SOX17 (8q11). In addition, polymorphisms in eNOS/NOS3 (7q36) may serve as predictive markers for outcomes following intracranial aneurysm rupture. Genetic aberrations identified to date converge on posited molecular mechanisms involved in vascular remodeling, with strong implications for an associated immune-mediated inflammatory response.

CONCLUSIONS

Comprehensive studies of IA formation and rupture have identified candidate risk variants and loci; however, further genome-wide analyses are needed to identify high-confidence genetic aberrations. The literature supports a role for several risk loci in aneurysm formation and rupture with putative candidate genes. A thorough understanding of the genetic basis governing risk of IA development and the resultant aneurysmal subarachnoid hemorrhage may aid in screening, clinical management, and risk stratification of these patients, and it may also enable identification of putative mechanisms for future drug development.

Rare and Low-Frequency Variants in RNF213 Confer Susceptibility to Moyamoya Syndrome Associated with Hyperthyroidism

BACKGROUND

Moyamoya syndrome (MMS), distinguished from definite moyamoya disease (MMD), is characterized by moyamoya vasculopathy thought to develop secondary to underlying conditions (e.g., hyperthyroidism). Recent studies have shown that a proportion of East Asian (EAS) patients with MMS possess the p.R4810K variant of RNF213 (rs112735431), the foremost susceptibility variant among EAS patients with MMD. We evaluated the association between hyperthyroidism-associated MMS (hMMS) and sequence variants in RNF213.

METHODS

We performed next-generation sequencing of RNF213 in 15 patients with hMMS. Candidate coding variants for the association analysis were defined by allelic frequencies of <1%, based on the p.R4810K frequency in the Japanese population. The association with hMMS was tested using a collapsing method, and 260 unrelated EAS women from the 1000 Genomes Project served as population-based controls.

RESULTS

All patients were female, reflecting female predominance in both moyamoya and hyperthyroid conditions. Five candidate missense variants in RNF213 were identified in 8 of 15 patients (53.3%): p.C118R, p.R4062Q, and p.R4810K as heterozygous; and p.A3468V and p.S3986N as compound heterozygous with p.R4810K. Among 260 EAS female controls, 36 (13.8%) had putatively functional variants. All identified variants were missense variants and were significantly overrepresented among patients compared with EAS controls (permuted P = 0.00010; odds ratio = 7.03; 95% confidence interval, 2.09-24.3).

CONCLUSIONS

Rare and low-frequency missense variants in RNF213 confer susceptibility to both MMD and hMMS. This finding indicates that susceptibility variants in RNF213 may require additional clinical factors with an effect equivalent to hyperthyroidism in order to develop moyamoya vasculopathy.

DNA Methylation Analysis Identifies Differentially Methylated Sites Associated with Early-Onset Intracranial Atherosclerotic Stenosis

Aim: Studies have suggested that genetic and environmental factors do not account for all risks and mechanisms of intracranial atherosclerotic stenosis (ICAS). DNA methylation may play a role in the progression of ICAS.

Methods: DNA methylation profiles of peripheral blood leucocytes from 7 patients with early-onset ICAS and 7 perfectly matched controls were interrogated for the first time using the Illumina Infinium Human MethylationEPIC BeadChip. Afterward, functional analysis for differentially methylated genes was conducted. In addition, pyrosequencing verification was performed in an independent cohort comprising 21 patients with earlyonset ICAS and 21 age- and gender-matched controls.

Results: A total of 318 cytosine-phosphate-guanine sites were found to be differentially methylated based on the established standards. Functional analysis annotated differentially methylated sites to atherosclerosis-related processes and pathways, such as the negative regulation of hydrolase activity (GO 0051346), type II diabetes mellitus (KEGG hsa04930), and the insulin signaling pathway (KEGG hsa04910). In addition, a differentially methylated site was also validated, cg22443212 in gene Rnf213, which showed significant hypermethylation in patients with early-onset ICAS compared with controls 59.56% (49.77%, 88.55%) vs. 44.65% (25.07%, 53.21%), respectively; P = 0.010). Receiver operating characteristic curve analysis showed that the area under the curve value of cg22443212 was 0.744 (95% confidence interval, 0.586–0.866; P = 0.002).

Conclusions: We revealed that altered DNA methylation may play a role in the occurrence and development of ICAS. These results provided new epigenetic insights into ICAS.

Intracranial Aneurysms: Pathology, Genetics, and Molecular Mechanisms

Intracranial aneurysms (IA) are local dilatations in cerebral arteries that predominantly affect the circle of Willis. Occurring in approximately 2-5% of adults, these weakened areas are susceptible to rupture, leading to subarachnoid hemorrhage (SAH), a type of hemorrhagic stroke. Due to its early age of onset and poor prognosis, SAH accounts for > 25% of years lost for all stroke victims under the age of 65. In this review, we describe the cerebrovascular pathology associated with intracranial aneurysms. To understand IA genetics, we summarize syndromes with elevated incidence, genome-wide association studies (GWAS), whole exome studies on IA-affected families, and recent research that established definitive roles for Thsd1 (Thrombospondin Type 1 Domain Containing Protein 1) and Sox17 (SRY-box 17) in IA using genetically engineered mouse models. Lastly, we discuss the underlying molecular mechanisms of IA, including defects in vascular endothelial and smooth muscle cells caused by dysfunction in mechanotransduction, Thsd1/FAK (Focal Adhesion Kinase) signaling, and the Transforming Growth Factor β (TGF-β) pathway. As illustrated by THSD1 research, cell adhesion may play a significant role in IA.

Dietary patterns among French-speaking men residing in Montreal, Canada

The purpose of this study was to describe dietary patterns among 1636 French-speaking men residing in Montreal, Canada and to assess sociodemographic and lifestyle characteristics of men adhering to the dietary patterns identified. Participants were population controls from the Prostate Cancer and Environment Study, a case-control study conducted between 2006 and 2011 in Montreal. Information on diet was collected using a food frequency questionnaire, and principal component analysis, a data-driven method and a posteriori method, was used to identify dietary patterns. Three dietary patterns were identified; Healthy, Modified Western – Salty and Modified Western - Sweet patterns accounted for 7.0%, 5.4%, and 3.2% of the variance, respectively. The Healthy pattern was characterized by consumption of fruits, vegetables, vegetable soup, chicken, fish and seafood, cheese, rice, yogurt, and wine. The Modified Western – Salty pattern included high loadings for beef, pork, chicken, hot-dogs or sausages, cold cuts, bacon, barbecue cooking, meat slightly blackened, potatoes, pasta with tomato sauce, pizza, pastries, dark carbonated soft drinks, ice cream, and white bread. The third pattern, labelled as Modified Western - Sweet, had high loadings of cookies, muffins, cakes, pastries, pies, ice cream, fruits and vegetables. In multivariate analyses, the Healthy pattern was positively associated with higher income and education, moderate recreational physical activity and less heavy smoking, and inversely associated with French ancestry. The Modified Western – Salty pattern was positively associated with French, other European, and Latino ancestries, and with married and common-law relationships. Finally, the Modified Western – Sweet pattern was more common among men of French ancestry and users of vitamin/mineral supplements. The Healthy pattern has been frequently observed in other Western populations, but the other two are described for the first time in a study population of men.

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First study of data-driven dietary patterns focussing on men only in Montreal.

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3 dietary patterns: Healthy, Modified Western –Salty, and Modified Western –Sweet.

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The Modified Western – Salty and Modified Western – Sweet patterns are novel.

RNF213 Variant Diversity Predisposes Distinct Populations to Dissimilar Cerebrovascular Diseases

In recent years, the ring finger protein 213 gene (RNF213) has gradually attracted attention, mainly because it has been found that RNF213 c.14429 G>A is associated with moyamoya disease (MMD) in East Asian populations. Recent studies have revealed that RFN213 is not only associated with MMD but is also connected with intracranial major artery stenosis/occlusion (ICASO) and intracranial aneurysm (IA). However, only the relationship between RNF213 c.14429 G>A and ICASO has been confirmed, and whether RNF213 has other mutations related to ICASO remains unclear. RNF213 and IA are currently only confirmed to be correlated in French-Canadian Population and no correlation has been found in the Japanese population. This review summarizes the advances in the associations between RNF213 and different cerebrovascular diseases and highlights that variant diversity of RNF213 may predispose distinct populations to dissimilar cerebrovascular diseases.

The Genetic Landscape of Cerebral Steno-Occlusive Arteriopathy and Stroke in Sickle Cell Anemia

Sickle cell disease (SCD) is one of the most common autosomal recessive diseases in humans, occurring at a frequency of 1 in 365 African-American and 1 in 50 sub-Saharan African births. Despite progress in managing complications of SCD, these remain a major health burden worldwide. Stroke is a common and serious complication of SCD, most often associated with steno-occlusive cerebral arteriopathy, but little is known about its pathogenesis. Transcranial Doppler ultrasonography is currently the only predictive test for future development of stroke in patients with sickle cell anemia and is used to guide preventative treatment. However, transcranial Doppler ultrasonography does not identify all patients at increased risk for stroke, and progressive arteriopathy may occur despite preventative treatment. While sibling studies have shown a strong genetic contribution to the development of steno-occlusive arteriopathy (SOA) in SCD, the only genome-wide association study compared a relatively small cohort of 177 patients with stroke to 335 patients with no history of stroke. This single study detected variants in only 2 genes, ENPP1 and GOLGB1, and only one of these was confirmed in a subsequent independent study. Thus, the underlying genes and pathogenesis of SOA in SCD remain poorly understood, greatly limiting the ability to develop more effective preventive therapies. Dissecting the molecular causes of stroke in SCD will provide valuable information that can be used to better prevent stroke, stratify risk of SOA, and optimize personalized medicine approaches.

Rho Guanine Nucleotide Exchange Factor ARHGEF17 Is a Risk Gene for Intracranial Aneurysms

BACKGROUND

Intracranial aneurysm (IA) is usually a late-onset disease, affecting 1% to 3% of the general population and leading to life-threatening subarachnoid hemorrhage. Genetic susceptibility has been implicated in IAs, but the causative genes remain elusive.

METHODS

We performed next-generation sequencing in a discovery cohort of 20 Chinese IA patients. Bioinformatics filters were exploited to search for candidate deleterious variants with rare and low allele frequency. We further examined the candidate variants in a multiethnic sample collection of 86 whole exome sequenced unsolved familial IA cases from 3 previously published studies.

RESULTS

We identified that the low-frequency variant c.4394C>A_p.Ala1465Asp (rs2298808) of ARHGEF17 was significantly associated with IA in our Chinese discovery cohort (P=7.3×10-4; odds ratio=7.34). It was subsequently replicated in Japanese familial IA patients (P=0.039; odds ratio=4.00; 95% confidence interval=0.832-14.8) and was associated with IA in the large Chinese sample collection comprising 832 sporadic IA-affected and 599 control individuals (P=0.041; odds ratio=1.51; 95% confidence interval=1.02-Inf). When combining the sequencing data of all familial IA patients from 4 different ethnicities (ie, Chinese, Japanese, European American, and French-Canadian), we identified a significantly increased mutation burden for ARHGEF17 (21/106 versus 11/306; P=8.1×10-7; odds ratio=6.6; 95% confidence interval=2.9-15.8) in cases as compared with controls. In zebrafish, arhgef17 was highly expressed in the brain blood vessel. arhgef17 knockdown caused blood extravasation in the brain region. Endothelial lesions were identified exclusively on cerebral blood vessels in the arhgef17-deficient zebrafish.

CONCLUSIONS

Our results provide compelling evidence that ARHGEF17 is a risk gene for IA.

Novel and recurrent RNF213 variants in Japanese pediatric patients with moyamoya disease

Moyamoya disease is a progressive steno-occlusive condition of the main intracranial arteries that results in the compensatory formation of fragile moyamoya vessels at the base of the brain. RNF213 is the most significant susceptibility gene and is often found with the p.Arg4810Lys founder variant in East Asian patients. We identified three putatively deleterious variants of this gene from three pediatric patients: two were novel, and one was a recurrent missense variant previously reported in other pediatric patients.

Rare Coding Variants in ANGPTL6 Are Associated with Familial Forms of Intracranial Aneurysm

Intracranial aneurysms (IAs) are acquired cerebrovascular abnormalities characterized by localized dilation and wall thinning in intracranial arteries, possibly leading to subarachnoid hemorrhage and severe outcome in case of rupture. Here, we identified one rare nonsense variant (c.1378A>T) in the last exon of ANGPTL6 (Angiopoietin-Like 6)-which encodes a circulating pro-angiogenic factor mainly secreted from the liver-shared by the four tested affected members of a large pedigree with multiple IA-affected case subjects. We showed a 50% reduction of ANGPTL6 serum concentration in individuals heterozygous for the c.1378A>T allele (p.Lys460Ter) compared to relatives homozygous for the normal allele, probably due to the non-secretion of the truncated protein produced by the c.1378A>T transcripts. Sequencing ANGPTL6 in a series of 94 additional index case subjects with familial IA identified three other rare coding variants in five case subjects. Overall, we detected a significant enrichment (p = 0.023) in rare coding variants within this gene among the 95 index case subjects with familial IA, compared to a reference population of 404 individuals with French ancestry. Among the 6 recruited families, 12 out of 13 (92%) individuals carrying IA also carry such variants in ANGPTL6, versus 15 out of 41 (37%) unaffected ones. We observed a higher rate of individuals with a history of high blood pressure among affected versus healthy individuals carrying ANGPTL6 variants, suggesting that ANGPTL6 could trigger cerebrovascular lesions when combined with other risk factors such as hypertension. Altogether, our results indicate that rare coding variants in ANGPTL6 are causally related to familial forms of IA.

The Role of RNF213 4810G>A and 4950G>A Variants in Patients with Moyamoya Disease in Korea

Although a founder variant of RNF213 4810G>A is a major genetic risk factor for moyamoya disease (MMD) in East Asians, the frequency and disease susceptibility of RNF213 variants remain largely unknown. This study investigated the mutation analysis of RNF213 (4448, 4810, 4863, and 4950) between Korean MMD and healthy controls. We performed a polymerase chain reaction-restriction fragment length polymorphism analysis. To identify the association between RNF213 gene polymorphisms and MMD disease, we performed statistical analyses such as multivariable logistic regression and Fisher’s exact test. Genetic data from 117 MMD patients were analyzed and compared with 253 healthy controls. We assessed and compared single nucleotide polymorphisms of RNF213 (4448, 4810, 4863, and 4950) between MMD and control groups. We performed genome-wide association studies to investigate the genetic pathophysiology of MMD. Among the RNF213 variants (4448G>A, 4810G>A, 4863G>A, and 4950G>A), RNF213 4810G>A and 4950G>A variants were more frequent in MMD patients. In a subgroup analysis, the RNF213 4810G>A was more frequent in moyamoya disease, and the comparison with GG+AA genotype was also significantly different in moyamoya patients. These results confirm that RNF213 4810G>A and RNF213 4950G>A were more frequent in MMD patients. We have confirmed that RNF213 4810G>A and 4950G>A are strongly associated with Korean MMD in children and adults as well as for the ischemic and hemorrhagic types.

Rare RNF213 variants in the C-terminal region encompassing the RING-finger domain are associated with moyamoya angiopathy in Caucasians

Moyamoya angiopathy (MMA) is a cerebral angiopathy affecting the terminal part of internal carotid arteries. Its prevalence is 10 times higher in Japan and Korea than in Europe. In East Asian countries, moyamoya is strongly associated to the R4810K variant in the RNF213 gene that encodes for a protein containing a RING-finger and two AAA+ domains. This variant has never been detected in Caucasian MMA patients, but several rare RNF213 variants have been reported in Caucasian cases. Using a collapsing test based on exome data from 68 European MMA probands and 573 ethnically matched controls, we showed a significant association between rare missense RNF213 variants and MMA in European patients (odds ratio (OR)=2.24, 95% confidence interval (CI)=(1.19-4.11), P=0.01). Variants specific to cases had higher pathogenicity predictive scores (median of 24.2 in cases versus 9.4 in controls, P=0.029) and preferentially clustered in a C-terminal hotspot encompassing the RING-finger domain of RNF213 (P<10^-3). This association was even stronger when restricting the analysis to childhood-onset and familial cases (OR=4.54, 95% CI=(1.80-11.34), P=1.1 × 10^-3). All clinically affected relatives who were genotyped were carriers. However, the need for additional factors to develop MMA is strongly suggested by the fact that only 25% of mutation carrier relatives were clinically affected.