Mutation affecting the proximal promoter of Endoglin as the origin of hereditary hemorrhagic telangiectasia type 1

Genome sequencing identify chromosome 9 inversions disrupting ENG in 2 unrelated HHT families

Hereditary hemorrhagic telangiectasia (HHT), also known as Rendu-Osler-Weber disease, is a dominant inherited vascular disorder. The clinical diagnosis is based on the Curaçao criteria and pathogenic variants in the ENG and ACVRL1 genes are responsible for most cases of HHT. Four families with a negative targeted gene panel and selected by a multidisciplinary team were selected and whole-genome sequencing was performed according to the recommendations of the French National Plan for Genomic Medicine. Structural variations were confirmed by standard molecular cytogenetic analysis (FISH). In two families with a definite diagnosis of HHT, we identified two different paracentric inversions of chromosome 9, both disrupting the ENG gene. These inversions are considered as pathogenic and causative for the HHT phenotype of the patients. This is the first time structural variations are reported to cause HHT. As such balanced events are often missed by exon-based sequencing (panel, exome), structural variations may be an under-recognized cause of HHT. Genome sequencing for the detection of these events could be suggested for patients with a definite diagnosis of HHT and in whom no causative pathogenic variant was identified.

A novel frameshift mutation of the endoglin(ENG) gene causes hereditary hemorrhagic telangiectasia in a Chinese family

PURPOSE

Hereditary hemorrhagic telangiectasia (HHT) is a dominantly inherited disorder that involves epistaxis, mucocutaneous telangiectases, and visceral arteriovenous malformations (AVMs). This study aims to investigate the genetic causes in a Chinese family with HHT.

METHODS

HHT was confirmed according to Curaçao's diagnostic criteria. Three patients diagnosed with HHT and healthy members were recruited. Whole-exome sequencing (WES) and sanger sequencing were performed to define the patient's genetically pathogenic factor.

RESULTS

The proband presented with recurrent epistaxis, hepatopulmonary arteriovenous malformation, and adenocarcinoma. A novel frameshift mutation (c.1376_1377delAC, p.H459Lfs*41) of the ENG gene was revealed in affected individuals by WES. There was no report of this variant and predicted to be highly damaging by causing truncation of the ENG protein.

CONCLUSION

We report a novel variant in the ENG gene in Chinese that extends the mutational and phenotypic spectra of the ENG gene, and also demonstrates the feasibility of WES in the application of genetic diagnosis of HHT.

Multi-organ hereditary hemorrhagic telangiectasia: A case report

BACKGROUND

Type 2 hereditary hemorrhagic telangiectasia (HHT) is a rare autosomal dominant disease and is associated with ALK1 gene mutations. Type 2 HHT patients primarily suffer from recurrent bleeding. There is currently no promising treatment.

CASE SUMMARY

A 5-year-old Chinese patient (III23) was admitted to Zhongshan Hospital for recurrent melena occurring over 2 mo. She had been experiencing epistaxis for years and had been diagnosed with idiopathic pulmonary hypertension 4 mo before presentation. Abdominal computed tomography examination showed hepatic arteriovenous malformation. Gene testing revealed a c.1121G>A mutation on the ALK1 gene. According to the international diagnostic criteria, this patient was diagnosed with HHT. In addition, 8 more family members exhibited HHT symptoms to varying degrees. Gene testing in 5 family members (2 with HHT symptoms and 3 without HHT symptoms) revealed the ALK1 c.1121G>A mutation in the 2 family members with HHT symptoms. This missense mutation results in the substitution of arginine for glutamine at amino acid position 374 (R374Q) in the conserved functional kinase domain of ALK1. Biological studies revealed that this mutation decreased the kinase activity of ALK1 and impeded the phosphorylation of its substrate Smad1. Moreover, the R374Q mutant downregulated the protein level of collagen-1, a fibrogenic factor, indicating abnormal fiber generation during vascular formation.

CONCLUSION

The R374Q mutant of ALK1 and its subsequent influence on fiber generation highly indicated its pathogenic role in this family with type 2 HHT. Detection of this gene mutation will facilitate early diagnosis of suspected type 2 HHT patients, and mechanistic studies will provide insights for future therapy.

Genetics of brain arteriovenous malformations and cerebral cavernous malformations

Cerebrovascular malformations comprise abnormal development of cerebral vasculature. They can result in hemorrhagic stroke due to rupture of lesions as well as seizures and neurological defects. The most common forms of cerebrovascular malformations are brain arteriovenous malformations (bAVMs) and cerebral cavernous malformations (CCMs). They occur in both sporadic and inherited forms. Rapidly evolving molecular genetic methodologies have helped to identify causative or associated genes involved in genesis of bAVMs and CCMs. In this review, we highlight the current knowledge regarding the genetic basis of these malformations.

Endothelial cilia dysfunction in pathogenesis of hereditary hemorrhagic telangiectasia

Hereditary hemorrhagic telangiectasia (HHT) is associated with defective capillary network, leading to dilated superficial vessels and arteriovenous malformations (AVMs) in which arteries connect directly to the veins. Loss or haploinsufficiency of components of TGF-β signaling, ALK1, ENG, SMAD4, and BMP9, have been implicated in the pathogenesis AVMs. Emerging evidence suggests that the inability of endothelial cells to detect, transduce and respond to blood flow, during early development, is an underpinning of AVM pathogenesis. Therefore, components of endothelial flow detection may be instrumental in potentiating TGF-β signaling in perfused blood vessels. Here, we argue that endothelial cilium, a microtubule-based and flow-sensitive organelle, serves as a signaling hub by coupling early flow detection with potentiation of the canonical TGF-β signaling in nascent endothelial cells. Emerging evidence from animal models suggest a role for primary cilia in mediating vascular development. We reason, on recent observations, that endothelial cilia are crucial for vascular development and that embryonic loss of endothelial cilia will curtail TGF-β signaling, leading to associated defects in arteriovenous development and impaired vascular stability. Loss or dysfunction of endothelial primary cilia may be implicated in the genesis of AVMs due, in part, to inhibition of ALK1/SMAD4 signaling. We speculate that AVMs constitute part of the increasing spectrum of ciliopathy-associated vascular defects.

Distribution of Cerebrovascular Phenotypes According to Variants of the ENG and ACVRL1 Genes in Subjects with Hereditary Hemorrhagic Telangiectasia

Hereditary Hemorrhagic Telangiectasia (HHT) is an autosomal dominant disorder caused, in more than 80% of cases, by mutations of either the endoglin (ENG) or the activin A receptor-like type 1 (ACVRL1) gene. Several hundred variants have been identified in these HHT-causing genes, including deletions, missense and nonsense mutations, splice defects, duplications, and insertions. In this study, we have analyzed retrospectively collected images of magnetic resonance angiographies (MRA) of the brain of HHT patients, followed at the HHT Center of our University Hospital, and looked for the distribution of cerebrovascular phenotypes according to specific gene variants. We found that cerebrovascular malformations were heterogeneous among HHT patients, with phenotypes that ranged from classical arteriovenous malformations (AVM) to intracranial aneurysms (IA), developmental venous anomalies (DVA), and cavernous angiomas (CA). There was also wide heterogeneity among the variants of the ENG and ACVRL1 genes, which included known pathogenic variants, variants of unknown significance, variants pending classification, and variants which had not been previously reported. The percentage of patients with cerebrovascular malformations was significantly higher among subjects with ENG variants than ACVRL1 variants (25.0% vs. 13.1%, p < 0.05). The prevalence of neurovascular anomalies was different among subjects with different gene variants, with an incidence that ranged from 3.3% among subjects with the c.1231C > T, c.200G > A, or c.1120C > T missense mutations of the ACVRL1 gene, to 75.0% among subjects with the c.1435C > T missense mutation of the ACVRL1 gene. Further studies and larger sample sizes are required to confirm these findings.

Common and Rare 5′UTR Variants Altering Upstream Open Reading Frames in Cardiovascular Genomics

High-throughput sequencing (HTS) technologies are revolutionizing the research and molecular diagnosis landscape by allowing the exploration of millions of nucleotide sequences at an unprecedented scale. These technologies are of particular interest in the identification of genetic variations contributing to the risk of rare (Mendelian) and common (multifactorial) human diseases. So far, they have led to numerous successes in identifying rare disease-causing mutations in coding regions, but few in non-coding regions that include introns, untranslated (UTR), and intergenic regions. One class of neglected non-coding variations is that of 5′UTR variants that alter upstream open reading frames (upORFs) of the coding sequence (CDS) of a natural protein coding transcript. Following a brief summary of the molecular bases of the origin and functions of upORFs, we will first review known 5′UTR variations altering upORFs and causing rare cardiovascular disorders (CVDs). We will then investigate whether upORF-affecting single nucleotide polymorphisms could be good candidates for explaining association signals detected in the context of genome-wide association studies for common complex CVDs.

Soluble Endoglin Stimulates Inflammatory and Angiogenic Responses in Microglia That Are Associated with Endothelial Dysfunction

Increased soluble endoglin (sENG) has been observed in human brain arteriovenous malformations (bAVMs). In addition, the overexpression of sENG in concurrence with vascular endothelial growth factor (VEGF)-A has been shown to induce dysplastic vessel formation in mouse brains. However, the underlying mechanism of sENG-induced vascular malformations is not clear. The evidence suggests the role of sENG as a pro-inflammatory modulator, and increased microglial accumulation and inflammation have been observed in bAVMs. Therefore, we hypothesized that microglia mediate sENG-induced inflammation and endothelial cell (EC) dysfunction in bAVMs. In this study, we confirmed that the presence of sENG along with VEGF-A overexpression induced dysplastic vessel formation. Remarkably, we observed increased microglial activation around dysplastic vessels with the expression of NLRP3, an inflammasome marker. We found that sENG increased the gene expression of VEGF-A, pro-inflammatory cytokines/inflammasome mediators (TNF-α, IL-6, NLRP3, ASC, Caspase-1, and IL-1β), and proteolytic enzyme (MMP-9) in BV2 microglia. The conditioned media from sENG-treated BV2 (BV2-sENG-CM) significantly increased levels of angiogenic factors (Notch-1 and TGFβ) and pERK1/2 in ECs but it decreased the level of IL-17RD, an anti-angiogenic mediator. Finally, the BV2-sENG-CM significantly increased EC migration and tube formation. Together, our study demonstrates that sENG provokes microglia to express angiogenic/inflammatory molecules which may be involved in EC dysfunction. Our study corroborates the contribution of microglia to the pathology of sENG-associated vascular malformations.

Transforming Growth Factor-β: An Agent of Change in the Tumor Microenvironment

Transforming Growth Factor-β (TGF-β) is a key regulator of embryonic development, adult tissue homeostasis, and lesion repair. In tumors, TGF-β is a potent inhibitor of early stage tumorigenesis and promotes late stage tumor progression and metastasis. Here, we review the roles of TGF-β as well as components of its signaling pathways in tumorigenesis. We will discuss how a core property of TGF-β, namely its ability to change cell differentiation, leads to the transition of epithelial cells, endothelial cells and fibroblasts to a myofibroblastoid phenotype, changes differentiation and polarization of immune cells, and induces metabolic reprogramming of cells, all of which contribute to the progression of epithelial tumors.

Non-Coding RNAs and Hereditary Hemorrhagic Telangiectasia

Non-coding RNAs (ncRNAs) are functional ribonucleic acid (RNA) species that include microRNAs (miRs), a class of short non-coding RNAs (∼21–25 nucleotides), and long non-coding RNAs (lncRNAs) consisting of more than 200 nucleotides. They regulate gene expression post-transcriptionally and are involved in a wide range of pathophysiological processes. Hereditary hemorrhagic telangiectasia (HHT) is a rare disorder inherited in an autosomal dominant fashion characterized by vascular dysplasia. Patients can develop life-threatening vascular malformations and experience severe hemorrhaging. Effective pharmacological therapies are limited. The study of ncRNAs in HHT is an emerging field with great promise. This review will explore the current literature on the involvement of ncRNAs in HHT as diagnostic and pathogenic factors.

Deciphering the vascular labyrinth: role of microRNAs and candidate gene SNPs in brain AVM development - literature review

Background: Brain arteriovenous malformations (AVMs) are a relatively infrequent vascular pathology of unknown etiology that, despite their rarity, cause the highest number of hemorrhagic strokes under the age of 30 years. They pose a challenge to all forms of treatment due to their variable morphology, location, size, and, last but not least, evolving nature. MicroRNAs (miRNAs) are non-coding RNA strands that may suppress the expression of target genes by binding completely or partially to their complementary sequences. Single nucleotide polymorphisms (SNPs), as the name implies, are variations in a single nucleotide in the DNA, usually found in the non-coding segments. Although the majority of SNPs are harmless, some located in the proximity of candidate genes may result in altered expression or function of these genes and cause diseases or affect how different pathologies react to treatment. The roles miRNAs and certain SNPs play in the development and growth of AVMs are currently uncertain, yet progress in deciphering the minutiae of this pathology is already visible. Methods and Results: We performed an electronic Medline (PubMed, PubMed Central) and Google Academic exploration using permutations of the terms: "arteriovenous malformations," "single nucleotide polymorphisms," "microRNA," "non-coding RNA," and "genetic mutations." The findings were then divided into two categories, namely the miRNAs and the candidate gene SNPs associated with AVMs respectively. 6 miRNAs and 12 candidate gene SNPs were identified and discussed. Conclusions: The following literature review focuses on the discoveries made in ascertaining the different implications of miRNAs and candidate gene SNPs in the formation and evolution of brain AVMs, as well as highlighting the possible directions of future research and biological treatment. Abbreviations: ACVRL1/ALK1: activin receptor-like kinase 1; Akt: protein kinase B; ANGPTL4: angiopoietin-like 4; ANRIL: antisense noncoding RNA in the INK4 locus; AVM: arteriovenous malformation; AVM-BEC: arteriovenous malformation brain endothelial cell; BRCA1: breast cancer type 1 susceptibility protein; CCS: case-control study; CDKN2A/B: cyclin-dependent kinase inhibitor 2A/B; CLTC: clathrin heavy chain; DNA: deoxyribonucleic acid; ERK: extracellular signal-regulated kinase; GPR124: probable G-protein coupled receptor 124; GWAS: genome-wide association study; HHT: hereditary hemorrhagic telangiectasia; HIF1A: hypoxia-inducible factor 1A; IA: intracranial aneurysm; ICH: intracranial hemorrhage; Id-1: inhibitor of DNA-binding protein A; IL-17: interleukin 17; MAP4K3: mitogen-activated protein kinase kinase kinase kinase 3; miRNA: microRNA; MMP: matrix metalloproteinase; NFkB: nuclear factor kappa-light-chain of activated B cells; NOTCH: neurogenic locus notch homolog; p38MAPK: p38 mitogen-activated protein kinase; PI3K: phosphoinositide 3-kinase; RBBP8: retinoblastoma-binding protein 8; RNA: ribonucleic acid; SNAI1: Snail Family Transcriptional Repressor 1; SNP: single nucleotide polymorphism; SOX-17: SRY-related HMG-box; TGF-β: transformation growth factor β; TGFR: transformation growth factor receptor; TIMP-4, tissue inhibitor of metalloproteinase 4; TSP-1: thrombospondin-1; UTR: untranslated region; VEGF: Vascular Endothelial Growth Factor; VSMC: vascular smooth muscle cell; Wnt1: Wnt family member 1.

Genetics of vascular malformation and therapeutic implications

PURPOSE OF REVIEW

Vascular malformations (VaMs) are a consequence of disrupted morphogenesis that may involve arterial, capillary, venous, or lymphatic endothelium alone or in a combination. VaMs can have serious health impacts, leading to life-threatening conditions sometimes. Genetic mutations affecting proliferation, migration, adhesion, differentiation, and survival of endothelial cells, as well as integrity of extracellular matrix are believed to be the pathogenesis of these disorders. Here, we present an updated review of genetic mutations and potential therapeutic targets for VaMs.

RECENT FINDINGS

Increased number of genetic mutations have been discovered in vascular anomalies via targeted deep sequencing. When a genetic defect is identified, it often presents in only a small percentage of cells within the malformation. In addition, mutations within the same gene may result in different clinical phenotypes. Management of VaMs can be challenging depending on the severity and functional impairment associated. There are no standard treatment algorithms available to date for VaMs, therefore the disorder has significant unmet clinical needs. Currently, the focus of therapeutic development is to target constitutively activated intracellular signaling pathways resulted from genetic mutations.

SUMMARY

Knowledge about the genetic mutations and altered signaling pathways related to VaMs have improved our understanding about the pathogenesis of vascular anomalies and provided insights to the development of new targeted therapies.

Systematic screening in hereditary hemorrhagic telangiectasia: a review

PURPOSE OF REVIEW

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant inherited disease characterized by telangiectasia and arteriovenous malformations (AVMs). To date, five genetic types of HHT and one combined juvenile polyposis syndrome and HHT are known. Clinical and genetic screening of patients suspected with HHT is recommended to confirm the diagnosis and to prevent complications associated with HHT. The aim of this article is to give an overview of the evidence and to formulate a recommendation for clinicians concerning screening for HHT.

RECENT FINDINGS

Complications of HHT such as stroke, brain abscess and intracranial hemorrhage are caused by pulmonary and cerebral AVMs (CAVMs) and can often be prevented by screening and treatment when possible. Screening and treatment of these AVMs will result in an increased life expectancy comparable with that of the general population as opposed to unscreened and untreated HHT patients.

SUMMARY

Screening of HHT patients and their first-degree relatives is recommended to prevent severe complications including stroke, brain abscess and intracranial hemorrhage.

Characterization of a family mutation in the 5' untranslated region of the endoglin gene causative of hereditary hemorrhagic telangiectasia

Hereditary hemorrhagic telangiectasia (HHT) is a vascular disease characterized by nose and gastrointestinal bleeding, telangiectases in skin and mucosa, and arteriovenous malformations in major internal organs. Most patients carry a mutation in the coding region of the endoglin (ENG) or activin A receptor type II-1 (ACVRL1) gene. Nonetheless, in around 15% of patients, sequencing analysis and duplication/deletion tests fail to pinpoint mutations in the coding regions of these genes. In these cases, it has been shown that sequencing of the 5’-untranslated region (5’UTR) of ENG may be useful to identify novel mutations in the ENG non-coding region. Here we report the genetic characterization and functional analysis of the heterozygous mutation c.-142A>T in the 5’UTR region of ENG found in a family with several members affected by HHT. This variant gives rise to a new initiation codon of the protein that involves the change in its open reading frame. Transfection studies in monkey cells using endoglin expression vectors demonstrated that c-142A>T mutation results in a clear reduction in the levels of the endoglin protein. These results support the inclusion of the 5’UTR of ENG in the standard genetic testing for HHT to increase its sensitivity.

Genome sequencing reveals a deep intronic splicing ACVRL1 mutation hotspot in Hereditary Haemorrhagic Telangiectasia

Introduction

Hereditary haemorrhagic telangiectasia (HHT) is a genetically heterogeneous disorder caused by mutations in the genes ENG, ACVRL1, and SMAD4. Yet the genetic cause remains unknown for some families even after exhaustive exome analysis. We hypothesised that non-coding regions of the known HHT genes may harbour variants that disrupt splicing in these cases.

Methods

DNA from 35 individuals with clinical findings of HHT and 2 healthy controls from 13 families underwent whole genome sequencing. Additionally, 87 unrelated cases suspected to have HHT were evaluated using a custom designed next-generation sequencing panel to capture the coding and non-coding regions of ENG, ACVRL1 and SMAD4. Individuals from both groups had tested negative previously for a mutation in the coding region of known HHT genes. Samples were sequenced on a HiSeq2500 instrument and data were analysed to identify novel and rare variants.

Results

Eight cases had a novel non-coding ACVRL1 variant that disrupted splicing. One family had an ACVRL1intron 9:chromosome 3 translocation, the first reported case of a translocation causing HHT. The other seven cases had a variant located within a ~300 bp CT-rich ‘hotspot’ region of ACVRL1intron 9 that disrupted splicing.

Conclusions

Despite the difficulty of interpreting deep intronic variants, our study highlights the importance of non-coding regions in the disease mechanism of HHT, particularly the CT-rich hotspot region of ACVRL1intron 9. The addition of this region to HHT molecular diagnostic testing algorithms will improve clinical sensitivity.

Hereditary hemorrhagic telangiectasia: diagnosis and management from the hematologist's perspective

Hereditary hemorrhagic telangiectasia (HHT), also known as Osler-Weber-Rendu syndrome, is an autosomal dominant disorder that causes abnormal blood vessel formation. The diagnosis of hereditary hemorrhagic telangiectasia is clinical, based on the Curaçao criteria. Genetic mutations that have been identified include ENG, ACVRL1/ALK1, and MADH4/SMAD4, among others. Patients with HHT may have telangiectasias and arteriovenous malformations in various organs and suffer from many complications including bleeding, anemia, iron deficiency, and high-output heart failure. Families with the same mutation exhibit considerable phenotypic variation. Optimal treatment is best delivered via a multidisciplinary approach with appropriate diagnosis, screening and local and/or systemic management of lesions. Anti-angiogenic agents such as bevacizumab have emerged as a promising systemic therapy in reducing bleeding complications but are not curative. Other pharmacological agents include iron supplementation, antifibrinolytics and hormonal treatment. This review discusses the biology of HHT, management issues that face the practising hematologist, and considerations of future directions in HHT treatment.

Functional analysis of a novel ENG variant in a patient with hereditary hemorrhagic telangiectasia (HHT) identifies a new Sp1 binding-site

Hereditary Hemorrhagic Telangiectasia (HHT) is a rare disease, with an autosomal dominant inheritance and a worldwide incidence of about 1: 5000 individuals. In >80% of patients, HHT is caused by mutations in either ENG or ACVRL1, which code for ENDOGLIN and Activin A Receptor Type II-Like Kinase 1 (ALK1), belonging to the TGF-β/BMP signalling pathway. Typical HHT clinical features are mucocutaneous telangiectases, arteriovenous malformations, spontaneous and recurrent epistaxis, as well as gastrointestinal bleedings. An additional, but less frequent, clinical manifestation in some HHT patients is the presence of Pulmonary Arterial Hypertension (PAH). The aim of this work is to describe the functional role of a novel ENG intronic variant found in a patient affected by both HHT and PAH, in order to assess whether it has a pathogenic role. We proved that the variant lies in a novel binding-site for the transcription factor Sp1, known to be involved in the regulation of ENG and ACVRL1 transcription. We confirmed a pathogenic role for this intronic variant, as it significantly reduces ENG transcription by affecting this novel Sp1 binding-site.

Videodermoscopy and doppler-ultrasound in spider naevi: towards a new classification?

INTRODUCTION

Spider naevi (SN) are considered a subtype of telangiectasias, currently classified as low-flow vascular malformations.

OBJECTIVE

To describe the videodermoscopy and Doppler-ultrasound (US) features of a large group of SN.

MATERIAL AND METHODS

A retrospective study of cases of SN collected at our Dermatology department during the period between June 2015 and June 2017 was performed. Clinical images, dermoscopic, videodermoscopic and Doppler-US files were reviewed. For each case, the age of the patient, time since onset, size and dermoscopic pattern of the lesions were recorded. The presence of pulsatility was also evaluated visually on the videodermoscopy.

RESULTS

Two hundred and thirty-three SN in 189 patients were included. The mean age was 39.5 years (range: 10-76 years). Mean size of the lesions was 4.1 ± 2.0 mm. We described three dermoscopic patterns: network, star and looping. Older age, longer time since onset and larger size were found associated with higher frequency of the looping and star patterns compared to that of network pattern (P < 0.01). Pulsatility during videodermoscopy was found in 88 patients (37%). This pulsatility phenomenon was more commonly associated with the looping pattern (64.7%) than star- (40.3%) or network-like patterns (29.9%) (P < 0.001). In Doppler-US studies, a high-flow with arterial biphasic waveform was found.

CONCLUSIONS

In the light of the results, we support that SN could be reconsidered in upcoming classifications as lesions closer to the group of high-flow arteriovenous malformations.

Deregulated TGF-β/BMP Signaling in Vascular Malformations

Correct organization of the vascular tree requires the balanced activities of several signaling pathways that regulate tubulogenesis and vascular branching, elongation, and pruning. When this balance is lost, the vessels can be malformed and fragile, and they can lose arteriovenous differentiation. In this review, we concentrate on the transforming growth factor (TGF)-β/bone morphogenetic protein (BMP) pathway, which is one of the most important and complex signaling systems in vascular development. Inactivation of these pathways can lead to altered vascular organization in the embryo. In addition, many vascular malformations are related to deregulation of TGF-β/BMP signaling. Here, we focus on two of the most studied vascular malformations that are induced by deregulation of TGF-β/BMP signaling: hereditary hemorrhagic telangiectasia (HHT) and cerebral cavernous malformation (CCM). The first of these is related to loss-of-function mutation of the TGF-β/BMP receptor complex and the second to increased signaling sensitivity to TGF-β/BMP. In this review, we discuss the potential therapeutic targets against these vascular malformations identified so far, as well as their basis in general mechanisms of vascular development and stability.