RASA1: variable phenotype with capillary and arteriovenous malformations

KRIT1 in vascular biology and beyond

KRIT1 is a 75 kDa scaffolding protein which regulates endothelial cell phenotype by limiting the response to inflammatory stimuli and maintaining a quiescent and stable endothelial barrier. Loss-of-function mutations in KRIT1 lead to the development of cerebral cavernous malformations (CCM), a disease marked by the formation of abnormal blood vessels which exhibit a loss of barrier function, increased endothelial proliferation, and altered gene expression. While many advances have been made in our understanding of how KRIT1, and the functionally related proteins CCM2 and PDCD10, contribute to the regulation of blood vessels and the vascular barrier, some important open questions remain. In addition, KRIT1 is widely expressed and KRIT1 and the other CCM proteins have been shown to play important roles in non-endothelial cell types and tissues, which may or may not be related to their role as pathogenic originators of CCM. In this review, we discuss some of the unsettled questions regarding the role of KRIT1 in vascular physiology and discuss recent advances that suggest this ubiquitously expressed protein may have a role beyond the endothelial cell.

Another face of RASA1: Report of familial germline variant in RASA1 with dysmorphic features

RASopathies encompass a diverse set of disorders affecting genes that encode proteins within the RAS-MAPK pathway. RASA1 mutations are the cause of an autosomal dominant disorder called capillary malformation-arteriovenous malformation type 1 (CM-AVM1). Unlike other RASopathies, facial dysmorphism has not been described in these patients. We phenotypically delineated a large family of individuals with multifocal fast-flow capillary malformations, severe lymphatic anomalies of perinatal onset, and dysmorphic features not previously described. Sequencing studies were performed on probands and related family members, confirming the segregation of dysmorphic features in affected members of a novel heterozygous variant in RASA1 (NM_002890.3:c.2366G>A, p.(Arg789Gln)). In this work, we broaden the phenotypic spectrum of CM-AVM type 1 and propose a new RASA1 variant as likely pathogenic.

Management of Pediatric Intracranial Arteriovenous Malformations

Pediatric intracranial arteriovenous malformations (AVMs) are challenging lesions managed by pediatric neurosurgeons. The high risk of hemorrhage and neurologic injury is compounded by the unique anatomy of each malformation that requires individualizing treatment options. This article reviews the current status of pediatric AVM epidemiology, pathophysiology and clinical care, with a specific focus on the rationale and methodology of surgical resection.

RASopathies for Radiologists

RASopathies are a heterogeneous group of genetic syndromes caused by germline mutations in a group of genes that encode components or regulators of the Ras/mitogen-activated protein kinase (MAPK) signaling pathway. RASopathies include neurofibromatosis type 1, Legius syndrome, Noonan syndrome, Costello syndrome, cardiofaciocutaneous syndrome, central conducting lymphatic anomaly, and capillary malformation-arteriovenous malformation syndrome. These disorders are grouped together as RASopathies based on our current understanding of the Ras/MAPK pathway. Abnormal activation of the Ras/MAPK pathway plays a major role in development of RASopathies. The individual disorders of RASopathies are rare, but collectively they are the most common genetic condition (one in 1000 newborns). Activation or dysregulation of the common Ras/MAPK pathway gives rise to overlapping clinical features of RASopathies, involving the cardiovascular, lymphatic, musculoskeletal, cutaneous, and central nervous systems. At the same time, there is much phenotypic variability in this group of disorders. Benign and malignant tumors are associated with certain disorders. Recently, many institutions have established multidisciplinary RASopathy clinics to address unique therapeutic challenges for patients with RASopathies. Medications developed for Ras/MAPK pathway-related cancer treatment may also control the clinical symptoms due to an abnormal Ras/MAPK pathway in RASopathies. Therefore, radiologists need to be aware of the concept of RASopathies to participate in multidisciplinary care. As with the clinical manifestations, imaging features of RASopathies are overlapping and at the same time diverse. As an introduction to the concept of RASopathies, the authors present major representative RASopathies, with emphasis on their imaging similarities and differences. ©RSNA, 2024 Test Your Knowledge questions for this article are available in the supplemental material.

RASopathies: Evolving Concepts in Pathogenetics, Clinical Features, and Management

RASopathies refers to the group of disorders which are caused by a mutation in various genes of the RAS/MAPK (RAT sarcoma virus/Mitogen activated protein kinase) pathway. It includes many genes with varied functions, which are responsible for cell cycle regulation. As the mutation in one gene affects the entire pathway, there are many overlapping features among the various syndromes which are included under an umbrella term "RASopathies." However, neuroectodermal involvement is a unifying feature among these syndromes, which are caused by germline mutations affecting genes along this pathway. Recently, many other RASopathies have been described to involve blood vessels, lymphatics, and immune system. Also, many cutaneous mosaic disorders have been found to have mutations in the concerned pathway. The purpose of this article is to briefly review the pathogenesis of RASopathies with cutaneous manifestations, and summarise the features that can be helpful as diagnostic clues to dermatologists. As we understand more about the pathogenesis of the pathway at the cellular level, the research on genotype-phenotype correlation and therapeutic options broadens. Targeted therapy is in the clinical and preclinical trial phase, which may brighten the future of many patients.

Defining the Functional Influence of Endothelial Cell-Expressed Oncogenic Activating Mutations on Vascular Morphogenesis and Capillary Assembly

This study sought to define key molecules and signals controlling major steps in vascular morphogenesis, and how these signals regulate pericyte recruitment and pericyte-induced basement membrane deposition. The morphogenic impact of endothelial cell (EC) expression of activating mutants of Kirsten rat sarcoma virus (kRas), mitogen-activated protein kinase 1 (Mek1), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), Akt serine/threonine kinase 1 (Akt1), Ras homolog enriched in brain (Rheb) Janus kinase 2 (Jak2), or signal transducer and activator of transcription 3 (Stat3) expression versus controls was evaluated, along with EC signaling events, pharmacologic inhibitor assays, and siRNA suppression experiments. Primary stimulators of EC lumen formation included kRas, Akt1, and Mek1, whereas PIK3CA and Akt1 stimulated a specialized type of cystic lumen formation. In contrast, the key drivers of EC sprouting behavior were Jak2, Stat3, Mek1, PIK3CA, and mammalian target of rapamycin (mTor). These conclusions are further supported by pharmacologic inhibitor and siRNA suppression experiments. EC expression of active Akt1, kRas, and PIK3CA led to markedly dysregulated lumen formation coupled to strongly inhibited pericyte recruitment and basement membrane deposition. For example, activated Akt1 expression in ECs excessively stimulated lumen formation, decreased EC sprouting behavior, and showed minimal pericyte recruitment with reduced mRNA expression of platelet-derived growth factor-BB, platelet-derived growth factor-DD, and endothelin-1, critical EC-derived factors known to stimulate pericyte invasion. The study identified key signals controlling fundamental steps in capillary morphogenesis and maturation and provided mechanistic details on why EC activating mutations induced a capillary deficiency state with abnormal lumens, impaired pericyte recruitment, and basement deposition: predisposing stimuli for the development of vascular malformations.

Lymphatic Malformations in Parkes Weber's Syndrome: Retrospective Review of 16 Cases in a Vascular Anomalies Center

INTRODUCTION

 Parkes Weber's syndrome (PWS) is a rare genetic disorder characterized by overgrowth and vascular malformations, primarily affecting the extremities. While PWS is known to be associated with arteriovenous and capillary malformations, the potential involvement of lymphatic malformations (LMs) has not been previously reported. The objective of this study is to investigate the presence of lymphatic anomalies in PWS patients and their role in the development of limb asymmetry.

MATERIALS AND METHODS

 This is a retrospective study of patients diagnosed with PWS in a Vascular Anomalies Center from 1994 to 2020. Clinical data were obtained from medical records including diagnostic imaging, lymphoscintigraphy, and genetic testing. The Institutional Review Board and Ethics Committee have approved this study.

RESULTS

 A total of 16 patients aged 18 interquartile range 14.7 years diagnosed with PWS were included (50% female). Six of the 16 patients with PWS had clinical and imaging data suggestive of LM (37.5%) and 3 of them had genetic variants in RASA1 (2/3) or KRAS (1/3). Limb asymmetry was greater in patients with isolated PWS (2.6 ± 0.8 cm) than in the PWS-lymphatic anomalies population (2 ± 0.7 cm), although not significant (p = 0.247). One in 6 patients with PWS-LM required amputation (16.6%) versus 1 in 10 in isolated PWS (10%).

CONCLUSION

 Lymphatic anomalies may be present in a significant number of patients with PWS and could have a role in limb asymmetry and outcomes. It is paramount to investigate their existence and distinguish them from true overgrowth.

Spectrum of lymphatic anomalies in patients with RASA1-related CM-AVM

BACKGROUND

Capillary malformation-arteriovenous malformation (CM-AVM) is characterized by multifocal fast-flow capillary malformations, sometimes with arteriovenous malformations/fistulas, skeletal/soft tissue overgrowth, telangiectasias, or Bier spots. Lymphatic abnormalities are infrequently reported. We describe seven patients with CM-AVM and lymphatic anomalies.

METHODS

Following IRB approval, we identified patients with CM-AVM and lymphatic anomalies seen at the Vascular Anomalies Center at Boston Children's Hospital from 2003 to 2023. We retrospectively reviewed records for clinical, genetic, laboratory, and imaging findings.

RESULTS

We found seven patients with CM-AVM and lymphatic abnormalities. Five patients were diagnosed prenatally: four with pleural effusions (including one suspected chylothorax) and one with ascites. Pleural effusions resolved after neonatal drainage in three patients and fetal thoracentesis in the fourth; however, fluid rapidly reaccumulated in this fetus causing hydrops. Ascites resolved after neonatal paracentesis, recurred at 2 months, and spontaneously resolved at 5 years; magnetic resonance lymphangiography for recurrence at age 19 years suggested a central conducting lymphatic anomaly (CCLA), and at age 20 years a right spermatic cord/scrotal lymphatic malformation (LM) was detected. Chylous pericardial effusion presented in a sixth patient at 2 months and disappeared after pericardiocentesis. A seventh patient was diagnosed with a left lower extremity LM at 16 months. Six patients underwent genetic testing, and all had RASA1 mutation. RASA1 variant was novel in three patients (c.1495delinsCTACC, c.434_451delinsA, c.2648del), previously reported in two (c.2603+1G>A, c.475_476del), and unavailable in another. Median follow-up age was 5.8 years (4 months-20 years).

CONCLUSION

CM-AVM may be associated with lymphatic anomalies, including pericardial/pleural effusions, ascites, CCLA, and LM.

Shaping the brain vasculature in development and disease in the single-cell era

The CNS critically relies on the formation and proper function of its vasculature during development, adult homeostasis and disease. Angiogenesis - the formation of new blood vessels - is highly active during brain development, enters almost complete quiescence in the healthy adult brain and is reactivated in vascular-dependent brain pathologies such as brain vascular malformations and brain tumours. Despite major advances in the understanding of the cellular and molecular mechanisms driving angiogenesis in peripheral tissues, developmental signalling pathways orchestrating angiogenic processes in the healthy and the diseased CNS remain incompletely understood. Molecular signalling pathways of the 'neurovascular link' defining common mechanisms of nerve and vessel wiring have emerged as crucial regulators of peripheral vascular growth, but their relevance for angiogenesis in brain development and disease remains largely unexplored. Here we review the current knowledge of general and CNS-specific mechanisms of angiogenesis during brain development and in brain vascular malformations and brain tumours, including how key molecular signalling pathways are reactivated in vascular-dependent diseases. We also discuss how these topics can be studied in the single-cell multi-omics era.

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.

Epidemiological study of capillary malformation among 7299 infants under 1 year of age in China

BACKGROUND

Capillary malformation (CM) is the most common vascular malformation. Large scale studies on its incidence and risk factors are limited in China.

OBJECTIVE

Our study aimed to investigate the incidence of CM in Chinese infants and to evaluate its potential risk factors.

METHODS

A cross-sectional study, including 7299 infants (aged < 1 year) were collected by a self-administered questionnaire. Independent-samples T tests or χ² tests and multivariable logistic models were used to examine the potential risk factors for CM.

RESULTS

The incidences of salmon patches and port-wine stains (PWSs) were 9.10% and 0.80%, respectively. In analyses, male sex (OR: 1.32, 95% CI: 1.12-1.55) and birth hypoxia (OR: 5.61, 95% CI: 4.39-7.16) were risk factors for salmon patches. Birth hypoxia (OR: 12.58, 95% CI: 7.26-21.79) and pregnancy-induced hypertension syndrome (PIH; OR: 3.66, 95% CI: 1.49-8.99) were associated with a higher risk of PWSs.

CONCLUSION

This epidemiological study had the largest sample size of infants with CM in the world thus far, which updated its incidence in Chinese infants and found the potential risk factors for CM.

Tandem engagement of phosphotyrosines by the dual SH2 domains of p120RasGAP

p120RasGAP is a multidomain GTPase-activating protein for Ras. The presence of two Src homology 2 domains in an SH2-SH3-SH2 module raises the possibility that p120RasGAP simultaneously binds dual phosphotyrosine residues in target proteins. One known binding partner with two proximal phosphotyrosines is p190RhoGAP, a GTPase-activating protein for Rho GTPases. Here, we present the crystal structure of the p120RasGAP SH2-SH3-SH2 module bound to a doubly tyrosine-phosphorylated p190RhoGAP peptide, revealing simultaneous phosphotyrosine recognition by the SH2 domains. The compact arrangement places the SH2 domains in close proximity resembling an SH2 domain tandem and exposed SH3 domain. Affinity measurements support synergistic binding, while solution scattering reveals that dual phosphotyrosine binding induces compaction of this region. Our studies reflect a binding mode that limits conformational flexibility within the SH2-SH3-SH2 cassette and relies on the spacing and sequence surrounding the two phosphotyrosines, potentially representing a selectivity mechanism for downstream signaling events.

Brain arteriovenous malformation in hereditary hemorrhagic telangiectasia: Recent advances in cellular and molecular mechanisms

Hereditary hemorrhagic telangiectasia (HHT) is a genetic disorder characterized by vessel dilatation, such as telangiectasia in skin and mucosa and arteriovenous malformations (AVM) in internal organs such as the gastrointestinal tract, lungs, and brain. AVMs are fragile and tortuous vascular anomalies that directly connect arteries and veins, bypassing healthy capillaries. Mutations in transforming growth factor β (TGFβ) signaling pathway components, such as ENG (ENDOGLIN), ACVRL1 (ALK1), and SMAD4 (SMAD4) genes, account for most of HHT cases. 10-20% of HHT patients develop brain AVMs (bAVMs), which can lead to vessel wall rupture and intracranial hemorrhages. Though the main mutations are known, mechanisms leading to AVM formation are unclear, partially due to lack of animal models. Recent mouse models allowed significant advances in our understanding of AVMs. Endothelial-specific deletion of either Acvrl1, Eng or Smad4 is sufficient to induce AVMs, identifying endothelial cells (ECs) as primary targets of BMP signaling to promote vascular integrity. Loss of ALK1/ENG/SMAD4 signaling is associated with NOTCH signaling defects and abnormal arteriovenous EC differentiation. Moreover, cumulative evidence suggests that AVMs originate from venous ECs with defective flow-migration coupling and excessive proliferation. Mutant ECs show an increase of PI3K/AKT signaling and inhibitors of this signaling pathway rescue AVMs in HHT mouse models, revealing new therapeutic avenues. In this review, we will summarize recent advances and current knowledge of mechanisms controlling the pathogenesis of bAVMs, and discuss unresolved questions.

Three Cases of Familial Moyamoya Disease with RASA1 Mutations-A Case Report

OBJECTIVE

The prevalence of moyamoya disease (MMD) is relatively high in East Asia, whereas the susceptibility genes of MMD have not been identified.

METHODS

Here, we reported 3 patients diagnosed with MMD from 1 single family, including a 53-year-old mother (case 1) and her 32-year-old and 29-year-old daughters (cases 2 and 3). The younger daughter was diagnosed with cerebral hemorrhage. Computed tomographic angiogram showed the typical signs of MMD in 3 patients.

RESULTS

Clinical whole-exome sequencing was performed in 3 daughters of case 1, and RASA1 mutations in chr5: 87,376,389 and NM_002890.2: c.2012-4C > T were determined to have the strongest correlation with MMD. RASA1 mutations were verified in case 1, husband of case 1 and the descendant of case 3 by using Sanger sequencing.

CONCLUSIONS

According to the findings of literature review, this is the first study indicating the association between RASA1 mutations and MMD.

Sudden death caused by ruptured brain arteriovenous malformation in an adolescent with autism spectrum disorder

Brain arteriovenous malformations (bAVMs) are infrequent disorders in the pediatric population. The rupture of a bAVM is a clinical emergency often followed by death. Autism spectrum disorder shares a number of symptoms with AVM malformation; this may impede antemortem diagnosis. An 11-year-old boy with autism spectrum disorder (ASD) without other medical history died suddenly. Initially, choking on a peanut butter sandwich was suspected; autopsy did not demonstrate aspiration, but identified a ruptured right cerebellar AVM, with the characteristic tortuous vessels. The histology on the lesion confirmed the presence of arterialized veins and showed gliotic tissue and hemosiderin-laden macrophages, consistent with prior bleeding. BAVM pathogenesis is unknown; congenital disease may have several mechanisms including genetic predisposition and familial risk factors; development de novo may occur after hemorrhagic intracranial events such as surgical intervention and head trauma. ASD may present with overlapping symptoms of bAVM and may also interfere with expressing subtle neurologic symptoms to caretakers. ASD and AVM are rarely reported in association.

The Genetics of Vascular Birthmarks

One in ten infants are born with a vascular birthmark each year. Some vascular birthmarks, such as infantile hemangiomas, are common, while vascular malformations, such as capillary, lymphatic, venous, and arteriovenous malformations, are less so. Diagnosing uncommon vascular birthmarks can be challenging, given the phenotypic heterogeneity and overlap amongst these lesions. Both sporadic and germline variants have been detected in various genes associated with vascular birthmarks. Identification of these genetic variants offers insight into both diagnosis and underlying molecular pathways and can be fundamental in the discovery of novel therapeutic approaches. The PIK3/AKT/mTOR and RAS/MEK/ERK signaling pathways, which mediate cell growth and angiogenesis, are activated secondary to genetic variations in vascular malformations. Somatic variants in TEK (TIE2) and PIK3CA cause venous malformations. Variants in PIK3CA also cause lymphatic malformations as well as a number of overgrowth syndromes associated with vascular anomalies. Variants in GNAQ and GNA11 have been identified in both so-called "congenital" hemangiomas and capillary malformations. RASA1 and EPHB4 variants are associated with capillary malformation-arteriovenous malformation syndrome. This review discusses the genetics of vascular birthmarks including the various phenotypes, genetic variants, pathogenesis, associated syndromes, and new diagnostic techniques.

Endothelial k-RasV12 Expression Induces Capillary Deficiency Attributable to Marked Tube Network Expansion Coupled to Reduced Pericytes and Basement Membranes

OBJECTIVE

We sought to determine how endothelial cell (EC) expression of the activating k-Ras (kirsten rat sarcoma 2 viral oncogene homolog) mutation, k-RasV12, affects their ability to form lumens and tubes and interact with pericytes during capillary assembly Approach and Results: Using defined bioassays where human ECs undergo observable tubulogenesis, sprouting behavior, pericyte recruitment to EC-lined tubes, and pericyte-induced EC basement membrane deposition, we assessed the impact of EC k-RasV12 expression on these critical processes that are necessary for proper capillary network formation. This mutation, which is frequently seen in human ECs within brain arteriovenous malformations, was found to markedly accentuate EC lumen formation mechanisms, with strongly accelerated intracellular vacuole formation, vacuole fusion, and lumen expansion and with reduced sprouting behavior, leading to excessively widened tube networks compared with control ECs. These abnormal tubes demonstrate strong reductions in pericyte recruitment and pericyte-induced EC basement membranes compared with controls, with deficiencies in fibronectin, collagen type IV, and perlecan deposition. Analyses of signaling during tube formation from these k-RasV12 ECs reveals strong enhancement of Src (Src proto-oncogene, non-receptor tyrosine kinase), Pak2 (P21 [RAC1 (Rac family small GTPase 1)] activated kinase 2), b-Raf (v-raf murine sarcoma viral oncogene homolog B1), Erk (extracellular signal-related kinase), and Akt (AK strain transforming) activation and increased expression of PKCε (protein kinase C epsilon), MT1-MMP (membrane-type 1 matrix metalloproteinase), acetylated tubulin and CDCP1 (CUB domain-containing protein 1; most are known EC lumen regulators). Pharmacological blockade of MT1-MMP, Src, Pak, Raf, Mek (mitogen-activated protein kinase) kinases, Cdc42 (cell division cycle 42)/Rac1, and Notch markedly interferes with lumen and tube formation from these ECs.

CONCLUSIONS

Overall, this novel work demonstrates that EC expression of k-RasV12 disrupts capillary assembly due to markedly excessive lumen formation coupled with strongly reduced pericyte recruitment and basement membrane deposition, which are critical pathogenic features predisposing the vasculature to develop arteriovenous malformations.

The RASopathies: from pathogenetics to therapeutics

The RASopathies are a group of disorders caused by a germline mutation in one of the genes encoding a component of the RAS/MAPK pathway. These disorders, including neurofibromatosis type 1, Noonan syndrome, cardiofaciocutaneous syndrome, Costello syndrome and Legius syndrome, among others, have overlapping clinical features due to RAS/MAPK dysfunction. Although several of the RASopathies are very rare, collectively, these disorders are relatively common. In this Review, we discuss the pathogenesis of the RASopathy-associated genetic variants and the knowledge gained about RAS/MAPK signaling that resulted from studying RASopathies. We also describe the cell and animal models of the RASopathies and explore emerging RASopathy genes. Preclinical and clinical experiences with targeted agents as therapeutics for RASopathies are also discussed. Finally, we review how the recently developed drugs targeting RAS/MAPK-driven malignancies, such as inhibitors of RAS activation, direct RAS inhibitors and RAS/MAPK pathway inhibitors, might be leveraged for patients with RASopathies.

RASopathies: Dermatologists’ viewpoints

Ras/mitogen-activated protein kinase pathway dysregulation results in a group of disorders, collectively termed as RASopathies. Neurofibromatosis type 1, Noonan syndrome, Noonan syndrome with multiple lentigines, Noonan syndrome/loose anagen hair, Legius syndrome, Costello syndrome, cardio-facio-cutaneous syndrome and capillary malformation-arteriovenous malformation are the well-recognized RASopathies. These are characterized by multi-organ tumours and hamartomas. Some other features in common are facial dysmorphism, skeletal abnormalities, congenital heart disease, neurocognitive abnormalities and risk of various solid-organ and haematological malignancies. Some of the RASopathies are heterogeneous, caused by several gene mutations resulting in variations in phenotypes and severity ranging from mild to fatal. Significant phenotypic overlaps among different disorders, often makes it difficult to pinpoint a clinical diagnosis. Specific cutaneous manifestations are present in some of the RASopathies and are often the earliest clinical signs/symptoms. Hence, dermatologists contribute significantly as primary care physicians by identifying disorder-specific cutaneous lesions. However, diagnostic work-up and management of these disorders are often multidisciplinary. Confirmation of diagnosis is possible only by genetic mapping in each case. Genetic counseling of the patients and the affected families is an important component of the management. The aim of this review is description of cutaneous manifestations of RASopathies in the background of multi-system involvement to enable dermatologists a comprehensive and logical approach to work up and diagnose such patients in the absence of facility for specific molecular testing.

Identification of the circ_PRKDC/miR-20a-3p/RASA1 axis in regulating HaCaT keratinocyte migration

Migration of keratinocytes plays a crucial role in the re-epithelialization phase during wound healing. Circular RNA (circRNA) protein kinase, DNA-activated, catalytic subunit (circ_PRKDC, hsa_circ_0084443) has been identified as a regulator of keratinocyte migration. However, the molecular basis governing it remains unclear. The levels of circ_PRKDC, microRNA (miR)-20a-3p, and RAS p21 protein activator 1 (RASA1) were assessed by quantitative real-time PCR (qRT-PCR) or western blot. Subcellular localization, Actinomycin D, and Ribonuclease (RNase) R assays were performed to characterise circ_PRKDC. Cell migration was gauged by transwell and wound-healing assays. A direct relationship between miR-20a-3p and circ_PRKDC or RASA1 was verified by dual-luciferase reporter and RNA pull-down assays. Circ_PRKDC expression was reduced in wound skin during wound healing. Circ_PRKDC modulated migration of HaCaT keratinocytes. Mechanistically, circ_PRKDC directly targeted miR-20a-3p. The regulation of circ_PRKDC on HaCaT keratinocyte migration was mediated by miR-20a-3p. RASA1 was identified as a direct and functional target of miR-20a-3p, and miR-20a-3p-mediated inhibition of RASA1 impacted HaCaT keratinocyte migration. Circ_PRKDC acted as a post-transcriptional modulator of RASA1 expression through miR-20a-3p. Moreover, circ_PRKDC modulated migration of HaCaT keratinocytes by RASA1. Our findings demonstrated a novel molecular basis, the miR-20a-3p/RASA1 axis, for the regulation of circ_PRKDC on HaCaT keratinocyte migration.

Down-regulated placental miR-21 contributes to preeclampsia through targeting RASA1

Human placenta was obtained from early onset preeclampsia, late onset preeclampsia, and their gestational age-matched normal pregnancy. Using RT-qPCR, western blot, and immunohistochemistry, it was demonstrated that miR-21 expressions were significantly decreased in preeclampsia while RASA1 were increased. Suppression of miR-21 in placental HTR-8/SVneo cells, remarkably upregulated RASA1, decreased proliferation, inhibited invasion, and promoted apoptosis of trophoblast cells, while overexpression of miR-21 alleviated these effects. Dual-luciferase reporter assays revealed RASA1 to be a direct target of miR-21 in trophoblast cells. miR-21 may serve key roles in the development of preeclampsia by targeting RASA1.

Genetic Basis and Therapies for Vascular Anomalies

Vascular and lymphatic malformations represent a challenge for clinicians. The identification of inherited and somatic mutations in important signaling pathways, including the PI3K (phosphoinositide 3-kinase)/AKT (protein kinase B)/mTOR (mammalian target of rapamycin), RAS (rat sarcoma)/RAF (rapidly accelerated fibrosarcoma)/MEK (mitogen-activated protein kinase kinase)/ERK (extracellular signal-regulated kinases), HGF (hepatocyte growth factor)/c-Met (hepatocyte growth factor receptor), and VEGF (vascular endothelial growth factor) A/VEGFR (vascular endothelial growth factor receptor) 2 cascades has led to the evaluation of tailored strategies with preexisting cancer drugs that interfere with these signaling pathways. The era of theranostics has started for the treatment of vascular anomalies. Registration: URL: https://www.clinicaltrialsregister.eu; Unique identifier: 2015-001703-32.

RASopathies: from germline mutations to somatic and multigenic diseases

The RAS-RAF-MEK-ERK signaling pathway is vital for different cellular mechanisms including cell proliferation, differentiation and apoptosis. This importance is highlighted by the high prevalence of mutations in RAS or related proteins of the pathway in cancers. More recently, development abnormalities have been linked to various germline mutations in this pathway and called RASopathies. Interestingly, rare disorders such as RAS-associated leukoproliferative diseases and histiocytosis have also been recently linked to multiple mutations in the same pathway, sometimes with the same mutation. This review will focus on germline RASopathies and rare somatic RASopathies and focus on how gain-of-function mutations in the same pathway can lead to various diseases.

Uterine Arteriovenous Malformation: A Pictorial Review of Diagnosis and Management

Uterine arteriovenous malformation (UAVM) is a rare condition and is classified as either congenital or acquired UAVM. Patients with UAVMs usually experience miscarriages or recurrent menorrhagia. Ultrasound is used for the initial estimation of UAVMs. Computed tomography and magnetic resonance imaging are noninvasive and valuable methods that provide good compatibility with digital subtraction angiography to support the diagnosis and treatment of UAVM. Timely diagnosis is crucial to provide appropriate treatment for alleviating complications. This article presents a pictorial and literature review of the current evidence of the diagnosis and management of UAVM.

Computational fluid dynamics modeling aiding surgical planning in a toddler with Parkes Weber syndrome

Parkes Weber syndrome is a fast-flow and slow-flow vascular anomaly with limb overgrowth that can lead to congestive heart failure and limb ischemia. Current management strategies have focused on symptom management with focal embolization. A pediatric case with early onset heart failure is reported. We discuss the use of computational fluid dynamics (CFD) modeling to guide a surgical management strategy in a toddler with an MAP2K1 mutation.

Prenatal features, associated co-morbidities and clinical course of agenesis of the ductus venosus in the current era

OBJECTIVES

Agenesis of the ductus venosus (ADV) has been associated with additional anomalies in up to 83% of cases. We sought to investigate characteristics, co-morbidities and outcomes of ADV in the current era. We hypothesized that rates of cardiac and non-cardiac diagnoses and survival would be higher, due to advances in genetic testing, prenatal diagnosis and surveillance.

METHODS

A retrospective series of cases diagnosed at our institution from 2007 to 2018 were identified by searching our database. Cardiac and obstetric charts were reviewed for cardiac and extra-cardiac anomalies, genetic results and outcomes.

RESULTS

Fourteen cases were diagnosed at a mean gestational age of 23.9 weeks (range 13-33). All had associated genetic, cardiac or extra-cardiac anomalies. Eight (57%) had cardiac anomalies and one other developed cardiomyopathy by 6 months. Extra-cardiac anomalies were present in 93% (13/14) and genetic diagnoses made in 75% (6/8) of those tested. Cardiac output Z-scores were >2 in 60% (6/10) prior to delivery. Two had hydrops, there was one intra-uterine death, 13 live-births and two neonatal deaths.

CONCLUSION

Our cohort had more associated diagnoses and a lower mortality than previously reported. In our experience, high output occurs frequently, however with a relatively low risk of hydrops and intrauterine death.

Capillary malformation-arteriovenous malformation syndrome: a multicentre study

BACKGROUND

Capillary malformation-arteriovenous malformation (CM-AVM) syndrome is a rare syndrome with characteristic skin lesions that are associated with fast-flow vascular malformations (FFVMs) in one-third of patients. Few case series have been described, and none in Spain.

AIM

To identify the prevalence of dermatological parameters, FFVMs and associated features in a large series of patients with CM-AVM.

METHODS

We conducted an observational study of patients with CM-AVM syndrome diagnosed in 15 Spanish hospitals over 3 years. The main clinical, radiological, genetic findings and associated diseases were analysed.

RESULTS

In total, 64 patients were assessed. In 26.5% of cases, the diagnosis was incidental. In 75% of patients, there was one significantly larger macule, which we termed the 'herald patch'. FFVMs were detected in 34% of the patients, with 30% located on the skin, 7.8% in the brain and in 1.5% in the spine. There was a positive family history in 65% of the 64 patients. Genetic analysis was performed for RASA1 mutations in 57 patients, of whom 42 (73%) had a positive result. All 4 patients tested for EPHB4 mutations had a positive result. No tumour lesions were detected in the series, except for five infantile haemangiomas.

CONCLUSIONS

Our data on clinical lesions, associated FFVM, family history and genetics are similar to those previously published in the literature. An extensive data analysis failed to demonstrate any statistically significant association between the presence of an FFVM and any clinical, familial or genetic parameter that could predict its onset, although a link between the presence of a herald patch on the midline face and the presence of a brain FFVM was observed. We did not detect any genotype-phenotype correlation.

Endothelial sprouting, proliferation, or senescence: tipping the balance from physiology to pathology

Therapeutic modulation of vascular cell proliferation and migration is essential for the effective inhibition of angiogenesis in cancer or its induction in cardiovascular disease. The general view is that an increase in vascular growth factor levels or mitogenic stimulation is beneficial for angiogenesis, since it leads to an increase in both endothelial proliferation and sprouting. However, several recent studies showed that an increase in mitogenic stimuli can also lead to the arrest of angiogenesis. This is due to the existence of intrinsic signaling feedback loops and cell cycle checkpoints that work in synchrony to maintain a balance between endothelial proliferation and sprouting. This balance is tightly and effectively regulated during tissue growth and is often deregulated or impaired in disease. Most therapeutic strategies used so far to promote vascular growth simply increase mitogenic stimuli, without taking into account its deleterious effects on this balance and on vascular cells. Here, we review the main findings on the mechanisms controlling physiological vascular sprouting, proliferation, and senescence and how those mechanisms are often deregulated in acquired or congenital cardiovascular disease leading to a diverse range of pathologies. We also discuss alternative approaches to increase the effectiveness of pro-angiogenic therapies in cardiovascular regenerative medicine.

Genetics of vascular anomalies

Vascular anomalies are developmental defects of the vasculature and encompass a variety of disorders. The identification of genes mutated in the different malformations provides insight into the etiopathogenic mechanisms and the specific roles the associated proteins play in vascular development and maintenance. A few familial forms of vascular anomalies exist, but most cases occur sporadically. It is becoming evident that somatic mosaicism plays a major role in the formation of vascular lesions. The use of Next Generating Sequencing for high throughput and "deep" screening of both blood and lesional DNA and RNA has been instrumental in detecting such low frequency somatic changes. The number of novel causative mutations identified for many vascular anomalies has soared within a 10-year period. The discovery of such genes aided in unraveling a holistic overview of the pathogenic mechanisms, by which in vitro and in vivo models could be generated, and opening the doors to development of more effective treatments that do not address just symptoms. Moreover, as many mutations and the implicated signaling pathways are shared with cancers, current oncological therapies could potentially be repurposed for the treatment of vascular anomalies.

Overgrowth syndromes and new therapies

Overgrowth syndromes represent a diverse group of disorders with overlapping features. Interdisciplinary management by a team of experts in vascular anomalies is crucial for establishing the correct diagnosis and optimizing outcomes for these patients. Unique management considerations include increased risk for thrombosis and in some cases, cancer. In recent years, research has demonstrated that these disorders are primarily caused by somatic mutations in growth pathways, particularly the PI3K-mTOR pathway. This improved understanding had led to promising new therapies for this group of patients.

Periosteal new bone formation in Klippel-Trénaunay syndrome: a case report

BACKGROUND

Klippel-Trénaunay syndrome (KTS) is a complex congenital vascular disorder, typically accompanied by port-wine stains, varicose veins, and limb hypertrophy. This paper reports a rare and unusual clinical condition of periosteal reaction in a pediatric case of KTS. Although periosteal new bone formation is not rare in children, as is KTS, their dual occurrence or the presentation of the former due to KTS has not been previously documented. Our objective in this study is to highlight the potential association between periosteal new bone formation and KTS, as well as to help physicians consider this association when bone neoplasm has been ruled out.

CASE PRESENTATION

A 7-year old girl, initially presented with a persistent mild swelling in her left shank, with no abnormalities in the X-ray of the tibiofibular. However, after a few consults and examinations, 7 weeks later, a 17 cm-long periosteal new bone formation along the left tibia and diffused dilated vessels in the left shank were revealed by the radiological examination. Not knowing the true nature of the fast-growing lesion in a typical case of KTS was worrying. Therefore, a core needle biopsy was performed. The test demonstrated a possible parosteal hemangioma. Following further investigation through an excisional biopsy, and a pathological analysis, hyperplasia of the bone tissues with no tumor cells was revealed. Thereafter, an elastic stocking treatment was prescribed. During the first two-year follow-up, recurrence of the mass or sign of progression of KTS was not observed.

CONCLUSIONS

Periosteal new bone formation is a potential manifestation of KTS. Based on the conclusive pathological results of the excisional biopsy, invasive examinations and surgeries could be avoided in future KTS-subperiosteal lesion manifestations.

De novo intracranial arteriovenous malformation development after endovascular treatment for a pial arteriovenous fistula in capillary malformation-arteriovenous malformation syndrome

Capillary malformation-arteriovenous malformation (CM-AVM) syndrome is a newly described entity characterized by autosomal dominantly inherited multifocal capillary malformations caused by RASA1 mutations (CM-AVM1) or EPHB4 mutations (CM-AVM2). Concurrent high-flow vascular anomalies in the brain are often present in the form of intracranial AVM or arteriovenous fistula (AVF). These high-flow lesions are often identified at or soon after birth because of the characteristic unique capillary malformations or a systemic disorder due to a high-flow shunt, such as respiratory distress or heart failure. However, de novo intracranial AVMs have not been reported in patients with CM-AVM syndrome. Herein, we report the case of a six-year-old boy with CM-AVM1 who had been treated for an intracranial pial arteriovenous fistula approximately five years previously, in whom a de novo intracranial AVM was identified on a follow-up angiographic study. To the best of our knowledge, this report is the first to document a de novo intracranial AVM in a patient with CM-AVM. We recommend careful neuroimaging follow-up even if initial neuroimaging screening is negative because of the risk of de novo AVM development.

Emerging importance of molecular pathogenesis of vascular malformations in clinical practice and classifications

Vascular malformations occur during early vascular development resulting in abnormally formed vessels that can manifest as arterial, venous, capillary or lymphatic lesions, or in combination, and include local tissue overdevelopment. Vascular malformations are largely caused by sporadic somatic gene mutations. This article aims to review and discuss current molecular signaling pathways and therapeutic targets for vascular malformations and to classify vascular malformations according to the molecular pathways involved. A literature review was performed using Embase and Medline. Different MeSH terms were combined for the search strategy, with the aim of encompassing all studies describing the classification, pathogenesis, and treatment of vascular malformations. Major pathways involved in the pathogenesis of vascular malformations are vascular endothelial growth factor (VEGF), Ras/Raf/MEK/ERK, angiopoietin-TIE2, transforming growth factor beta (TGF-β), and PI3K/AKT/mTOR. These pathways are involved in controlling cellular growth, apoptosis, differentiation, and proliferation, and play a central role in endothelial cell signaling and angiogenesis. Many vascular malformations share similar aberrant molecular signaling pathways with cancers and inflammatory disorders. Therefore, selective anticancer agents and immunosuppressants may be beneficial in treating vascular malformations of specific mutations. The current classification systems of vascular malformations, including the International Society of the Study of Vascular Anomalies (ISSVA) classification, are primarily observational and clinical, and are not based on the molecular pathways involved in the pathogenesis of the condition. Several molecular pathways with potential therapeutic targets have been demonstrated to contribute to the development of various vascular anomalies. Classifying vascular malformations based on their molecular pathogenesis may improve treatment by determining the underlying nature of the condition and their potential therapeutic target.

Microcephaly-capillary malformation syndrome: the newly reported cases

Microcephaly-capillary malformation syndrome (MICCAP: OMIM 614261) is a severe monogenic disorder inherited in an autosomal recessive manner caused by mutations in the STAMBP gene. There are less than 20 published cases of the syndrome to date. The paper reports three new cases of rare MICCAP syndrome. The cause of the disorder was confirmed in three affected individuals from two unrelated families by pedigree analysis, biochemical analysis, RFLP analysis and automated Sanger sequencing. The two brothers were homozygous for the potentially pathogenic STAMBP gene variant c.188A>G (p.Tyr63Cys). Clinical phenotype of the girl from the second family resulted from the combination of two genetic disorders: galactosemia caused by the compound heterozygosity for the pathogenic GALT gene variants (c.563A>G and c.855G>T), and MICCAP caused by the STAMBP gene variants (c.204-5c>g and с.668_669delCA), one of which originated de novo. The prevalence of microcephaly-capillary malformation syndrome in Russia is evaluated, it is one per 120,000 people (CI: 1/356 724–1/62 691). The carrier frequency is one per 173 people. The target STAMBP gene analysis makes the genetic confirmation of the MICCAP syndrome quicklier. When determining the tactics of diagnosis and therapy in each particular case, the possibility of combination of two rare genetic disorders in one patient should be considered.

Histopathological hallmarks of cutaneous lesions of capillary malformation-arteriovenous malformation syndrome

IMPORTANCE

Capillary malformation-arteriovenous malformation (CM-AVM) syndrome is a recently described syndrome with distinctive cutaneous lesions. Very little is known about the histopathology of these lesions.

OBJECTIVE

The purpose of the study was to evaluate the histopathological characteristics of the pink macules of the CM-AVM syndrome and to investigate if these pink macules could be classified as capillary malformations or arteriovenous malformations based on their histopathological features.

DESIGN-SETTINGS-PARTICIPANTS

We conducted a retrospective multicenter study involving eight hospitals in Spain. Fifteen biopsies from pink macules of the CM-AVM syndrome were analysed and compared with five biopsies of diverse capillary malformations and three stage I arteriovenous malformations.

RESULTS

Pink macules' biopsies of the CM-AVM syndrome showed similar features including a high vascular density encompassing capillaries and numerous thick-walled arterioles mainly located in the superficial dermis, a predominance of elongated over round vessels, scarce or absent erythrocytes within the lumina and discrete perivascular inflammation. CMs were characterized by an increased number of capillary-type vessels mostly rounded and located in the upper dermis. AVMs were composed by highly increased numbers of vessels with a branching pattern involving the full thickness of the dermis, without erythrocytes within the lumina. Wilms tumour 1 protein was positive in the endothelial cells both in pink macules of the CM-AVM and in arteriovenous malformations.

CONCLUSIONS AND RELEVANCE

Pink macules of the CM-AVM syndrome seem to be different from capillary malformations. Our results suggest that histologically and immunohistochemically they are closer to incipient arteriovenous malformations than to capillary malformations. A deepened knowledge about the nature of these skin lesions will contribute to the better understanding of capillary malformation-arteriovenous malformation syndrome, and will open the possibility of new and more specific treatments in the future.

Role of colour-Doppler high-frequency ultrasonography in capillary malformation-arteriovenous malformation syndrome: a case series

High-frequency ultrasonography (HFUS) represents a useful adjunct for dermatologists in the diagnosis of capillary malformation-arteriovenous malformation (CM-AVM) syndrome. We present a paediatric case series of 6 patients with confirmed RASA1 gene mutation in whom HFUS demonstrated AVM beneath cutaneous CM-like lesions greater than 1.5 cm.

Advancing RAS/RASopathy therapies: An NCI-sponsored intramural and extramural collaboration for the study of RASopathies

RASopathies caused by germline pathogenic variants in genes that encode RAS pathway proteins. These disorders include neurofibromatosis type 1 (NF1), Noonan syndrome (NS), cardiofaciocutaneous syndrome (CFC), and Costello syndrome (CS), and others. RASopathies are characterized by heterogenous manifestations, including congenital heart disease, failure to thrive, and increased risk of cancers. Previous work led by the NCI Pediatric Oncology Branch has altered the natural course of one of the key manifestations of the RASopathy NF1. Through the conduct of a longitudinal cohort study and early phase clinical trials, the MEK inhibitor selumetinib was identified as the first active therapy for the NF1-related peripheral nerve sheath tumors called plexiform neurofibromas (PNs). As a result, selumetinib was granted breakthrough therapy designation by the FDA for the treatment of PN. Other RASopathy manifestations may also benefit from RAS targeted therapies. The overall goal of Advancing RAS/RASopathy Therapies (ART), a new NCI initiative, is to develop effective therapies and prevention strategies for the clinical manifestations of the non-NF1 RASopathies and for tumors characterized by somatic RAS mutations. This report reflects discussions from a February 2019 initiation meeting for this project, which had broad international collaboration from basic and clinical researchers and patient advocates.

Crystal structures of p120RasGAP N-terminal SH2 domain in its apo form and in complex with a p190RhoGAP phosphotyrosine peptide

The Rho and Ras pathways play vital roles in cell growth, division and motility. Cross-talk between the pathways amplifies their roles in cell proliferation and motility and its dysregulation is involved in disease pathogenesis. One important interaction for cross-talk occurs between p120RasGAP (RASA1), a GTPase activating protein (GAP) for Ras, and p190RhoGAP (p190RhoGAP-A, ARHGAP35), a GAP for Rho. The binding of these proteins is primarily mediated by two SH2 domains within p120RasGAP engaging phosphorylated tyrosines of p190RhoGAP, of which the best studied is pTyr-1105. To better understand the interaction between p120RasGAP and p190RhoGAP, we determined the 1.75 Å X-ray crystal structure of the N-terminal SH2 domain of p120RasGAP in the unliganded form, and its 1.6 Å co-crystal structure in complex with a synthesized phosphotyrosine peptide, EEENI(p-Tyr)SVPHDST, corresponding to residues 1100–1112 of p190RhoGAP. We find that the N-terminal SH2 domain of p120RhoGAP has the characteristic SH2 fold encompassing a central beta-sheet flanked by two alpha-helices, and that peptide binding stabilizes specific conformations of the βE-βF loop and arginine residues R212 and R231. Site-directed mutagenesis and native gel shifts confirm phosphotyrosine binding through the conserved FLVR motif arginine residue R207, and isothermal titration calorimetry finds a dissociation constant of 0.3 ± 0.1 μM between the phosphopeptide and SH2 domain. These results demonstrate that the major interaction between two important GAP proteins, p120RasGAP and p190RhoGAP, is mediated by a canonical SH2-pTyr interaction.

Activation of Ras in the Vascular Endothelium Induces Brain Vascular Malformations and Hemorrhagic Stroke

Cerebrovascular malformations (CVMs) affect approximately 3% of the population, risking hemorrhagic stroke, seizures, and neurological deficits. Recently Ras mutations have been identified in a majority of brain arterio-venous malformations. We generated an endothelial-specific, inducible HRAS^V12 mouse model, which results in dilated, proliferative blood vessels in the brain, blood-brain barrier breakdown, intracerebral hemorrhage, and rapid lethality. Organoid morphogenesis models revealed abnormal cessation of proliferation, abnormalities in expression of tip and stalk genes, and a failure to properly form elongating tubes. These defects were influenced by both hyperactive PI-3' kinase signaling and altered TGF-β signaling. Several phenotypic changes predicted by the in vitro morphogenesis analysis were validated in the mouse model. These data provide a model of brain vascular malformations induced by mutant Ras and reveal insights into intersecting molecular mechanisms in the pathogenesis of brain vascular malformations.

Capillary Malformation-Arteriovenous Malformation Combined Alagille Syndrome in a Patient With Double Gene Variations of RASA1 and NOTCH2

Background: Capillary malformation–arteriovenous malformation (CM-AVM) is an autosomal dominant disorder characterized by CMs, often in association with fast-flow vascular malformations. Alagille syndrome is an autosomal dominant multisystem disorder, usually involving hepatic, cardiac, ophthalmic, skeletal, or renal dysplasia. The combination of CM-AVM and Alagille syndrome in a patient presenting serious vascular malformations in the liver and heart has never been reported. Here, we report the case of a 20-month-old infant presenting these two diseases.

Case presentation: The patient manifested port-wine stains, congenital heart disease, cholestasis with abnormal morphology, and vascular anomalies. Color Doppler (B-mode) ultrasonography, and radiological imaging including computed tomography (CT) with enhanced three-dimensional (3D) reconstruction and angiography, revealed a type II Abernethy malformation in the hepatic portal vein. The left hepatic lobe was enlarged showing dilation of the portal vein and the left artery. Whole exome sequencing (WES) identified a paternally inherited RASA1 heterozygous pathogenic variant p.(Ser219Ter) causing CM-AVM and a de novo NOTCH2 heterozygous variant p.(Met2042Thr) associated with Alagille syndrome.

Conclusion: This is the first case of combined CM-AVM and Alagille syndrome presenting serious liver and heart abnormalities diagnosed using imaging technology and WES. The patient harbored variants in two genes: RASA1 and NOTCH2, which rarely contribute to aberrant vascular development. This report highlights the value of accurately diagnosing similar diseases and guiding therapy using genetic testing combined with careful clinical examinations.

Using Drosophila Models and Tools to Understand the Mechanisms of Novel Human Cancer Driver Gene Function

The formation, overgrowth and metastasis of tumors comprise a complex series of cellular and molecular events resulting from the combined effects of a variety of aberrant signaling pathways, mutations, and epigenetic alterations. Modeling this complexity in vivo requires multiple genes to be manipulated simultaneously, which is technically challenging. Here, we analyze how Drosophila research can further contribute to identifying pathways and elucidating mechanisms underlying novel cancer driver (risk) genes associated with tumor growth and metastasis in humans.

Klippel-Trenaunay-Weber Syndrome with Atypical Presentation of Cerebral Cavernous Angioma: A Case Report and Literature Review

BACKGROUND

Klippel-Trenaunay-Weber syndrome (KTWS) is a rare syndrome characterized by the triad of cutaneous hemangiomas, venous varicosities, and osseous-soft tissue hypertrophy of the affected limb. Clinical manifestations, genetic testing, and radiologic imaging are the key steps in diagnosing this syndrome.

CASE DESCRIPTION

An 18-month-old boy was brought for follow-up brain magnetic resonance imaging (MRI) with a history of right lower limb hypertrophy, cutaneous varicosities, and hemangiomas diagnosed at birth. A baseline MRI at 12 months revealed multiple hemorrhagic lesions within the cerebrum, the largest in the right temporal lobe, which was treated surgically at the age of 18 months because of its rapid growth. This is the youngest patient with KTWS treated surgically for intracranial hemangiomas.

CONCLUSION

KTWS is a rare disease with a wide range of manifestations. Multisystemic evaluation of this group of patients should be performed to identify cavernous hemangiomas at the early stage of life and adequately treat them in the future. Treatment of KTWS patients with cavernous hemangiomas should not be different from the treatment of patients with any other hemangiomas, and surgical intervention should be considered on a case-to-case bases.

Ras-Specific GTPase-Activating Proteins-Structures, Mechanisms, and Interactions

Ras-specific GTPase-activating proteins (RasGAPs) down-regulate the biological activity of Ras proteins by accelerating their intrinsic rate of GTP hydrolysis, basically by a transition state stabilizing mechanism. Oncogenic Ras is commonly not sensitive to RasGAPs caused by interference of mutants with the electronic or steric requirements of the transition state, resulting in up-regulation of activated Ras in respective cells. RasGAPs are modular proteins containing a helical catalytic RasGAP module surrounded by smaller domains that are frequently involved in the subcellular localization or contributing to regulatory features of their host proteins. In this review, we summarize current knowledge about RasGAP structure, mechanism, regulation, and dual-substrate specificity and discuss in some detail neurofibromin, one of the most important negative Ras regulators in cellular growth control and neuronal function.

EphrinB2-EphB4-RASA1 Signaling in Human Cerebrovascular Development and Disease

Recent whole exome sequencing studies in humans have provided novel insight into the importance of the ephrinB2-EphB4-RASA1 signaling axis in cerebrovascular development, corroborating and extending previous work in model systems. Here, we aim to review the human cerebrovascular phenotypes associated with ephrinB2-EphB4-RASA1 mutations, including those recently discovered in Vein of Galen malformation: the most common and severe brain arteriovenous malformation in neonates. We will also discuss emerging paradigms of the molecular and cellular pathophysiology of disease-causing ephrinB2-EphB4-RASA1 mutations, including the potential role of somatic mosaicism. These observations have potential diagnostic and therapeutic implications for patients with rare congenital cerebrovascular diseases and their families.

Phenotype of CM-AVM2 caused by variants in EPHB4: how much overlap with hereditary hemorrhagic telangiectasia (HHT)?

PURPOSE

EPHB4 variants were recently reported to cause capillary malformation-arteriovenous malformation 2 (CM-AVM2). CM-AVM2 mimics RASA1-related CM-AVM1 and hereditary hemorrhagic telangiectasia (HHT), as clinical features include capillary malformations (CMs), telangiectasia, and arteriovenous malformations (AVMs). Epistaxis, another clinical feature that overlaps with HHT, was reported in several cases. Based on the clinical overlap of CM-AVM2 and HHT, we hypothesized that patients considered clinically suspicious for HHT with no variant detected in an HHT gene (ENG, ACVRL1, or SMAD4) may have an EPHB4 variant.

METHODS

Exome sequencing or a next-generation sequencing panel including EPHB4 was performed on individuals with previously negative molecular genetic testing for the HHT genes and/or RASA1.

RESULTS

An EPHB4 variant was identified in ten unrelated cases. Seven cases had a pathogenic EPHB4 variant, including one with mosaicism. Three cases had an EPHB4 variant of uncertain significance. The majority had epistaxis (6/10 cases) and telangiectasia (8/10 cases), as well as CMs. Two of ten cases had a central nervous system AVM.

CONCLUSIONS

Our results emphasize the importance of considering CM-AVM2 as part of the clinical differential for HHT and other vascular malformation syndromes. Yet, these cases highlight significant differences in the cutaneous presentations of CM-AVM2 versus HHT.

DDX24 Mutations Associated With Malformations of Major Vessels to the Viscera

Vascular malformations present diagnostic and treatment challenges. In particular, malformations of vessels to the viscera are often diagnosed late or incorrectly due to the insidious onset and deep location of the disease. Therefore, a better knowledge of the genetic mutations underlying such diseases is needed. Here, we evaluated a four-generation family carrying vascular malformations of major vessels that affect multiple organs, which we named "multiorgan venous and lymphatic defect" (MOVLD) syndrome. Genetic analyses identified an association between a mutation in DEAD-box helicase 24 (DDX24), a gene for which the function is largely unknown, and MOVLD. Next, we screened 161 patients with sporadic vascular malformations of similar phenotype to our MOVLD family and found the same mutation or one of the two additional DDX24 mutations in 26 cases. Structural modeling revealed that two of the mutations are located within the adenosine triphosphate-binding domain of DDX24. Knockdown of DDX24 expression in endothelial cells resulted in elevated migration and tube formation. Transcriptomic analysis linked DDX24 to vascular system-related functions. Conclusion: Our results provide a link between DDX24 and vascular malformation and indicate a crucial role for DDX24 in endothelial cell functions; these findings create an opportunity for genetic diagnosis and therapeutic targeting of malformations of vessels to the viscera.