Capillary malformation-arteriovenous malformation, a new clinical and genetic disorder caused by RASA1 mutations

Genetic markers and their influence on cerebrovascular malformations

Cerebrospinal vascular malformations are a group of anomalies affecting the arterial wall, the capillary arteriovenous interface, or the venous and lymphatic structures. Heritability and family studies allow identification of mutations in single genes associated with rare familial conditions causing cerebral or spinal vascular malformations, as is the case in hemorrhagic hereditary telangiectasia diseases. This article reviews the genetic and epigenetic influences increasingly reported in recent years as causal factors or triggers involved in the formation and growth of cerebromedullary vascular malformations.

The third international meeting on genetic disorders in the RAS/MAPK pathway: towards a therapeutic approach

"The Third International Meeting on Genetic Disorders in the RAS/MAPK Pathway: Towards a Therapeutic Approach" was held at the Renaissance Orlando at SeaWorld Hotel (August 2-4, 2013). Seventy-one physicians and scientists attended the meeting, and parallel meetings were held by patient advocacy groups (CFC International, Costello Syndrome Family Network, NF Network and Noonan Syndrome Foundation). Parent and patient advocates opened the meeting with a panel discussion to set the stage regarding their hopes and expectations for therapeutic advances. In keeping with the theme on therapeutic development, the sessions followed a progression from description of the phenotype and definition of therapeutic endpoints, to definition of genomic changes, to identification of therapeutic targets in the RAS/MAPK pathway, to preclinical drug development and testing, to clinical trials. These proceedings will review the major points of discussion.

Vascular Anomalies in Pediatrics

A standardized classification system allows improvements in diagnostic accuracy. Multidisciplinary vascular anomaly centers combine medical, surgical, radiologic, and pathologic expertise. This collaborative approach tailors treatment and management of vascular anomalies for affected individuals.

Genetic Variants Associated with Port-Wine Stains

Background

Port-wine stains (PWS) are capillary malformations, typically located in the dermis of the head and neck, affecting 0.3% of the population. Current theories suggest that port-wine stains are caused by somatic mutations that disrupt vascular development.

Objectives

Understanding PWS genetic determinants could provide insight into new treatments.

Methods

Our study used a custom next generation sequencing (NGS) panel and digital polymerase chain reaction to investigate genetic variants in 12 individuals with isolated port-wine stains. Importantly, affected and healthy skin tissue from the same individual were compared. A subtractive correction method was developed to eliminate background noise from NGS data. This allowed the detection of a very low level of mosaicism.

Results

A novel somatic variant GNAQ, c.547C>G, p.Arg183Gly was found in one case with 4% allele frequency. The previously reported GNAQ c.548G>A, p.Arg183Gln was confirmed in 9 of 12 cases with an allele frequency ranging from 1.73 to 7.42%. Digital polymerase chain reaction confirmed novel variants detected by next generation sequencing. Two novel somatic variants were also found in RASA1, although neither was predicted to be deleterious.

Conclusions

This is the second largest study on isolated, non-syndromic PWS. Our data suggest that GNAQ is the main genetic determinant in this condition. Moreover, isolated port-wine stains are distinct from capillary malformations seen in RASA1 disorders, which will be helpful in clinical evaluation.

Multifocal capillary malformations in an older, asymptomatic child with a novel RASA1 mutation

Multifocal capillary malformation (CM) is the cardinal feature of patients with RASA1 mutations. These CMs are ‘red flags’, signalling the possible association with an arteriovenous malformation (AVM) or an arteriovenous fistula (AVF). We report an 8‐year‐old boy who presented with > 20 CMs, who was found to have a novel mutation in the RASA1 gene. Radiological screening of children with RASA1 mutations is not standardized, and we elected to carry out baseline magnetic resonance imaging of the brain and spine in our case, which gave normal results. We discuss the recent literature and our approach in the management of such a case.

Two susceptibility loci identified for prostate cancer aggressiveness

Most men diagnosed with prostate cancer will experience indolent disease; hence, discovering genetic variants that distinguish aggressive from nonaggressive prostate cancer is of critical clinical importance for disease prevention and treatment. In a multistage, case-only genome-wide association study of 12,518 prostate cancer cases, we identify two loci associated with Gleason score, a pathological measure of disease aggressiveness: rs35148638 at 5q14.3 (RASA1, P=6.49 × 10(-9)) and rs78943174 at 3q26.31 (NAALADL2, P=4.18 × 10(-8)). In a stratified case-control analysis, the SNP at 5q14.3 appears specific for aggressive prostate cancer (P=8.85 × 10(-5)) with no association for nonaggressive prostate cancer compared with controls (P=0.57). The proximity of these loci to genes involved in vascular disease suggests potential biological mechanisms worthy of further investigation.

Overgrowth syndromes with vascular anomalies

Overgrowth syndromes with vascular anomalies encompass entities with a vascular anomaly as the predominant feature vs those syndromes with predominant somatic overgrowth and a vascular anomaly as a more minor component. The focus of this article is to categorize these syndromes phenotypically, including updated clinical criteria, radiologic features, evaluation, management issues, pathophysiology, and genetic information. A literature review was conducted in PubMed using key words "overgrowth syndromes and vascular anomalies" as well as specific literature reviews for each entity and supportive genetic information (e.g., somatic mosaicism). Additional searches in OMIM and Gene Reviews were conducted for each syndrome. Disease entities were categorized by predominant clinical features, known genetic information, and putative affected signaling pathway. Overgrowth syndromes with vascular anomalies are a heterogeneous group of disorders, often with variable clinical expression, due to germline or somatic mutations. Overgrowth can be focal (e.g., macrocephaly) or generalized, often asymmetrically (and/or mosaically) distributed. All germ layers may be affected, and the abnormalities may be progressive. Patients with overgrowth syndromes may be at an increased risk for malignancies. Practitioners should be attentive to patients having syndromes with overgrowth and vascular defects. These patients require proactive evaluation, referral to appropriate specialists, and in some cases, early monitoring for potential malignancies. Progress in identifying vascular anomaly-related overgrowth syndromes and their genetic etiology has been robust in the past decade and is contributing to genetically based prenatal diagnosis and new therapies targeting the putative causative genetic mutations.

Heredity of port-wine stains: investigation of families without a RASA1 mutation

Background: The prevalence of capillary malformations, also known as port-wine stains (PWS), is 0.3%. Familial segregation can occur. The capillary malformation–arteriovenous malformation (CM-AVM) phenotype is caused by mutations in the RASA1 gene. In PWS familial cases, the inheritance is considered to be autosomal dominant with variable penetrance. Objective: Investigation of the heredity of PWS among patients who attended the vascular anomaly section at the Department of Dermatology in Malmoe, Southern Sweden, between 1993 and 2004 and to study the involvement of the RASA1 gene in patients with a positive family history of PWS. Subjects and methods: A total of 254 patients were examined and given a questionnaire regarding family history of PWS. The first group of 175 patients (109 females and 66 males) reported a negative family history. The other group of 65 patients (46 females and 19 males) reported a positive family history (50% parents or brothers and sisters). Results: The heredity of PWS was 27% (65/240). Twenty-one patients with a positive family history and relatives had no CM-AVM phenotype for mutations in the RASA1 gene. Conclusion: PWS may have a stronger heredity component than it was reported earlier and inheritance should be considered when counseling a patient. RASA1 mutations do not explain the PWS in our patients.

Relapsing fetal bilateral hydrothorax, an isolated expression of a vein of Galen aneurysmal malformation

We report a case of bilateral fetal hydrothorax presenting at 20 weeks of pregnancy, spontaneously resolving at 22 weeks and severely relapsing at 28 weeks in a fetus with normal karyotype. The cause was a high-output heart failure caused by vein of Galen malformation.

Clinical spectrum of capillary malformation-arteriovenous malformation syndrome presenting to a pediatric dermatology practice: a retrospective study

Capillary malformation-arteriovenous malformation syndrome (CM-AVM) is an autosomal dominant disorder caused by RASA1 mutations. The prevalence and phenotypic spectrum are unknown. Evaluation of patients with multiple CMs is challenging because associated AVMs can be life threatening. The objective of this study was to describe the clinical characteristics of children presenting with features of CM-AVM to an academic pediatric dermatology practice. After institutional review board approval was received, a retrospective chart review was performed of patients presenting between 2009 and 2012 with features of CM-AVM. We report nine cases. Presenting symptoms ranged from extensive vascular stains and cardiac failure to CMs noted incidentally during routine skin examination. All demonstrated multiple CMs, two had Parkes Weber syndrome, and two had multiple infantile hemangiomas. Seven patients had family histories of multiple CMs; three had family histories of large, atypical CMs. Six had personal or family histories of AVMs. Genetic evaluation was recommended for all and was pursued by six families; four RASA1 mutations were identified, including one de novo. Consultations with neurology, cardiology, and orthopedics were recommended. Most patients (89%) have not required treatment to date. CM-AVM is an underrecognized condition with a wide clinical spectrum that often presents in childhood. Further evaluation may be indicated in patients with multiple CMs. This study is limited by its small and retrospective nature.

Histopathologic and ultrasound characteristics of cutaneous capillary malformations in a patient with capillary malformation-arteriovenous malformation syndrome

Capillary malformation-arteriovenous malformation (CM-AVM) syndrome is an autosomal dominant disorder caused by mutations in RASA1. Multifocal, small, round-to-oval, pinkish-to-red cutaneous capillary malformations are seen in more than 90% of people with RASA1 mutations. These RASA1-associated cutaneous capillary malformations (CMs) can accompany internal or cutaneous arteriovenous malformation (AVM) or arteriovenous fistula to constitute CM-AVM syndrome. The cutaneous capillary malformations in CM-AVM syndrome are unusual in that some lesions have high-flow characteristics (according to Doppler or a white halo). We describe the histopathologic and corresponding ultrasound and Doppler findings in a CM from a patient with clinical CM-AVM syndrome and show that an arterial component is not present in the dermis or the most superficial portions of the subcutaneous fat but that there is ultrasound evidence that an AVM resides in the underlying adipose tissue.

A shower of second hit events as the cause of multifocal renal cell carcinoma in tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a genetic disorder characterized by seizures and tumor formation in multiple organs, mainly in the brain, skin, kidney, lung and heart. Renal cell carcinoma (RCC) occurs in ∼3% of TSC patients, and typically develops at age <50. Here we describe genetic findings in two TSC patients with multiple renal tumors, each of whom had the germline mutation TSC2 p.R905Q. The first (female) TSC patient had a left followed by a right nephrectomy at ages 24 and 27. Both kidneys showed multifocal TSC-associated papillary RCC (PRCC). Targeted, next-generation sequencing (NGS) analysis of TSC2 in five tumors (four from the left kidney, one from the right) showed loss of heterozygosity in one tumor, and four different TSC2 point mutations (p.E1351*, p.R1032*, p.R1713H, c.4178_4179delCT) in the other four samples. Only one of the 11 other tumors available from this patient had one of the TSC2 second hit mutations identified. Whole-exome analysis of the five tumors identified a very small number of additional mutated genes, with an average of 3.4 nonsilent coding, somatic mutations per tumor, none of which were seen in >1 tumor. The second (male) TSC patient had bilateral partial nephrectomies (both at age 36), with similar findings of multifocal PRCC. NGS analysis of TSC2 in two of these tumors identified a second hit mutation c.2355+1G>T in one sample that was not seen in other tumors. In conclusion, we report the first detailed genetic analysis of RCCs in TSC patients. Molecular studies indicate that tumors developed independently due to various second hit events, suggesting that these patients experienced a 'shower' of second hit mutations in TSC2 during kidney development leading to this severe phenotype.

An infiltrative angioarchitectural variant of arteriovenous malformation of temporalis

Vascular anomalies of the head and neck region pose a certain diagnostic and therapeutic paradox. Management of arteriovenous malformations (AVM) is a challenge owing to the presence of abnormal vascular communications and high recurrence. We report a case of a 19-year-old male patient, who presented with diffuse swelling in the right temporal region. Magnetic Resonance Angiography (MRA) suggested it to be an AVM in the temporalis muscle, having afferents in the ascending pharyngeal artery, with cavernous angioma. Surgical excision of the lesion was carried out under carotid control. Histopathology of the excised specimen utilizing special stains confirmed the presence of AVM. An absence of distinct nidus concomitant along with the exuberant proliferation of capillaries between the muscle fibres suggested it be an infiltrative angioarchitectural variant. The present case highlights significance of diagnosing AVM in temporalis muscle which is a rare occurrence in head and neck region. Also, the importance of ruling out other closely resembling vascular diathesis, both non neoplastic and malignant is discussed.

Capillary malformation-arteriovenous malformation syndrome with spinal involvement

Capillary malformation-arteriovenous malformation (CM-AVM) is a recently identified autosomal dominant disorder. Arteriovenous lesions have been reported in the brain, limbs, and face. We report a 7-year-old patient with CM-AVM with spinal AVM, which is a rarely reported association.

Genetics of hemangiomas, vascular malformations, and primary lymphedema

With improved genetic testing and genomic sequencing, abnormalities are increasingly being identified in affected or germline tissues in DNA of patients with vascular tumors, vascular malformations, and lymphedema. Recognition of the genetics of vascular anomalies should help clinicians make more specific diagnoses, anticipate diagnosis-specific morbidities, provide better genetic counseling, and have a better understanding of the pathogenesis of these anomalies. Growing pharmacologic options, including therapies targeted to specific mutations, with obvious parallels to cancer treatment now allow the pediatric hematologist-oncologist to assume a more prominent role in clinical care and research for patients with these diagnoses. We summarize genes and genetic loci that have been associated with vascular anomalies and offer guidelines for patient evaluations.

Blood vascular abnormalities in Rasa1(R780Q) knockin mice: implications for the pathogenesis of capillary malformation-arteriovenous malformation

Capillary malformation-arteriovenous malformation (CM-AVM) is an autosomal dominant blood vascular (BV) disorder characterized by CM and fast flow BV lesions. Inactivating mutations of the RASA1 gene are the cause of CM-AVM in most cases. RASA1 is a GTPase-activating protein that acts as a negative regulator of the Ras small GTP-binding protein. In addition, RASA1 performs Ras-independent functions in intracellular signal transduction. Whether CM-AVM results from loss of an ability of RASA1 to regulate Ras or loss of a Ras-independent function of RASA1 is unknown. To address this, we generated Rasa1 knockin mice with an R780Q point mutation that abrogates RASA1 catalytic activity specifically. Homozygous Rasa1(R780Q/R780Q) mice showed the same severe BV abnormalities as Rasa1-null mice and died midgestation. This finding indicates that BV abnormalities in CM-AVM develop as a result of loss of an ability of RASA1 to control Ras activation and not loss of a Ras-independent function of this molecule. More important, findings indicate that inhibition of Ras signaling is likely to represent an effective means of therapy for this disease.

Arteriovenous malformations

Arteriovenous malformations (AVMs) are fast-flow vascular malformations composed of a complex vessel network directly connecting feeding arteries to draining veins. The intervening normal capillary network is absent. Proper diagnosis and treatment of AVMs is challenging and in need of an interdisciplinary team of experienced physicians. Careful analysis of the clinical features and evaluation of therapeutic options represent the basis for successful management of AVMs. This article will focus on the clinical and radiological findings and in particular on interdisciplinary management strategies of AVMs including minimally invasive endovascular and surgical treatment.

Genetics of vascular malformations

Vascular anomalies are developmental defects of the vasculature and encompass a variety of disorders. The majority of these occur sporadically, yet a few are reported to be familial. The identification of genes mutated in the different malformations provides insight into their etiopathogenic mechanisms and the specific roles the associated proteins play in vascular development and maintenance. It is becoming evident that somatic mosaicism plays a major role in the formation of vascular lesions. The importance of utilizing Next-Generating Sequencing (NGS) for high-throughput and "deep" screening of both blood and lesional DNA and RNA is thus emphasized, as the somatic changes are present in low quantities. There are several examples where NGS has already accomplished discovering these changes. The identification of all the causative genes and unraveling of a holistic overview of the pathogenic mechanisms should enable generation of in vitro and in vivo models and lead to development of more effective treatments, not only targeted on symptoms.

A review of vascular anomalies: genetics and common syndromes

Vascular tumors and malformations are unique in that affected cells exhibit disrupted angiogenesis. The current treatment options often yield suboptimal results. New insight into the genetics and molecular basis of vascular anomalies may pave the way for potential development of targeted therapy. The authors review the genetic and molecular basis of vascular anomalies and common associated syndromes.

Pelvic vascular malformations

Vascular malformations (VMs) comprise a wide spectrum of lesions that are classified by content and flow characteristics. These lesions, occurring in both focal and diffuse forms, can involve any organ and tissue plane and can cause significant morbidity in both children and adults. Since treatment strategy depends on the type of malformation, correct diagnosis and classification of a vascular lesion are crucial. Slow-flow VMs (venous and lymphatic malformations) are often treated by sclerotherapy, whereas fast-flow lesions (arteriovenous malformations) are generally managed with embolization. In addition, some cases of VMs are best treated surgically. This review will present an overview of VMs in the female pelvis as well as a discussion of endovascular therapeutic techniques.

RASA1 functions in EPHB4 signaling pathway to suppress endothelial mTORC1 activity

Vascular malformations are linked to mutations in RAS p21 protein activator 1 (RASA1, also known as p120RasGAP); however, due to the global expression of this gene, it is unclear how these mutations specifically affect the vasculature. Here, we tested the hypothesis that RASA1 performs a critical effector function downstream of the endothelial receptor EPHB4. In zebrafish models, we found that either RASA1 or EPHB4 deficiency induced strikingly similar abnormalities in blood vessel formation and function. Expression of WT EPHB4 receptor or engineered receptors with altered RASA1 binding revealed that the ability of EPHB4 to recruit RASA1 is required to restore blood flow in EPHB4-deficient animals. Analysis of EPHB4-deficient zebrafish tissue lysates revealed that mTORC1 is robustly overactivated, and pharmacological inhibition of mTORC1 in these animals rescued both vessel structure and function. Furthermore, overexpression of mTORC1 in endothelial cells exacerbated vascular phenotypes in animals with reduced EPHB4 or RASA1, suggesting a functional EPHB4/RASA1/mTORC1 signaling axis in endothelial cells. Tissue samples from patients with arteriovenous malformations displayed strong endothelial phospho-S6 staining, indicating increased mTORC1 activity. These results indicate that deregulation of EPHB4/RASA1/mTORC1 signaling in endothelial cells promotes vascular malformation and suggest that mTORC1 inhibitors, many of which are approved for the treatment of certain cancers, should be further explored as a potential strategy to treat patients with vascular malformations.

Sturge-Weber syndrome: from the past to the present

Sturge-Weber syndrome is a rare sporadic neurocutaneous syndrome the hallmark of which is a facial port-wine stain involving the first division of the trigeminal nerve, ipsilateral leptomeningeal angiomata and angioma involving the ipsilateral eye. Our understanding of the disease process has vastly improved since it was first described in 1879, with recent identification of an activating somatic mutation in the GNAQ gene found in association with both Sturge-Weber syndrome and non-syndromic facial port-wine stain. Sturge-Weber syndrome is marked by a variable but usually progressive course in early childhood characterised by seizures, stroke-like episodes, headaches, neurological and cognitive deterioration, hemiparesis, glaucoma and visual field defects. More recently, the increased prevalance of otolaryngological, endocrine and emotional-behavioural issues have been established. Neurophysiology and neuroimaging studies provide information regarding the evolution of changes in Sturge-Weber syndrome over time. Early recognition and aggressive management of symptoms remains cornerstone in the management of this syndrome. An international collaborative effort is needed to maximise our understanding of the natural history and response to interventions in Sturge-Weber Syndrome.

An expanding role for RAS GTPase activating proteins (RAS GAPs) in cancer

The RAS pathway is one of the most commonly deregulated pathways in human cancer. Mutations in RAS genes occur in nearly 30% of all human tumors. However in some tumor types RAS mutations are conspicuously absent or rare, despite the fact that RAS and downstream effector pathways are hyperactivated. Recently, RAS GTPase Activating Proteins (RAS GAPs) have emerged as an expanding class of tumor suppressors that, when inactivated, provide an alternative mechanism of activating RAS. RAS GAPs normally turn off RAS by catalyzing the hydrolysis of RAS-GTP. As such, the loss of a RAS GAP would be expected to promote excessive RAS activation. Indeed, this is the case for the NF1 gene, which plays an established role in a familial tumor predisposition syndrome and a variety of sporadic cancers. However, there are 13 additional RAS GAP family members in the human genome. We are only now beginning to understand why there are so many RAS GAPs, how they differentially function, and what their potential role(s) in human cancer are. This review will focus on our current understanding of RAS GAPs in human disease and will highlight important outstanding questions.

Zebrafish models of cerebrovascular disease

Perturbations in cerebral blood flow and abnormalities in blood vessel structure are the hallmarks of cerebrovascular disease. While there are many genetic and environmental factors that affect these entities through a heterogeneous group of disease processes, the ultimate final pathologic insult in humans is defined as a stroke, or damage to brain parenchyma. In the case of ischemic stroke, blood fails to reach its target destination whereas in hemorrhagic stroke, extravasation of blood occurs outside of the blood vessel lumen, resulting in direct damage to brain parenchyma. As these acute events can be neurologically devastating, if not fatal, development of novel therapeutics are urgently needed. The zebrafish (Danio rerio) is an attractive model for the study of cerebrovascular disease because of its morphological and physiological similarity to human cerebral vasculature, its ability to be genetically manipulated, and its fecundity allowing for large-scale, phenotype-based screens.

Long non-coding RNA expression profiles in hereditary haemorrhagic telangiectasia

Hereditary Haemorrhagic Telangiectasia (HHT) is an autosomal dominantly inherited vascular disease characterized by the presence of mucocutaneous telangiectasia and arteriovenous malformations in visceral organs. HHT is predominantly caused by mutations in ENG and ACVRL1, which both belong to the TGF-β signalling pathway. The exact mechanism of how haploinsufficiency of ENG and ACVRL1 leads to HHT manifestations remains to be identified. As long non-coding RNAs (lncRNAs) are increasingly recognized as key regulators of gene expression and constitute a sizable fraction of the human transcriptome, we wanted to assess whether lncRNAs play a role in the molecular pathogenesis of HHT manifestations. By microarray technology, we profiled lncRNA transcripts from HHT nasal telangiectasial and non-telangiectasial tissue using a paired design. The microarray probes were annotated using the GENCODE v.16 dataset, identifying 4,810 probes mapping to 2,811 lncRNAs. Comparing HHT telangiectasial tissue with HHT non-telangiectasial tissue, we identified 42 lncRNAs that are differentially expressed (q<0.001). Using GREAT, a tool that assumes cis-regulation, we showed that differently expressed lncRNAs are enriched for genomic loci involved in key pathways concerning HHT. Our study identified lncRNAs that are aberrantly expressed in HHT telangiectasia and indicates that lncRNAs may contribute to regulate protein-coding loci in HHT. These results suggest that the lncRNA component of the transcriptome deserves more attention in HHT. A deeper understanding of lncRNAs and their role in telangiectasia formation possesses potential for discovering therapeutic targets in HHT.

Ras pathway inhibition prevents neovascularization by repressing endothelial cell sprouting

Vascular networks develop from a growing vascular front that responds to VEGF and other guidance cues. Angiogenesis is required for normal tissue function, but, under conditions of stress, inappropriate vascularization can lead to disease. Therefore, inhibition of angiogenic sprouting may prevent neovascularization in patients with blinding neovascular eye diseases, including macular degeneration. VEGF antagonists have therapeutic benefits but also can elicit off-target effects. Here, we found that the Ras pathway, which functions downstream of a wide range of cytokines including VEGF, is active in the growing vascular front of developing and pathological vascular networks. The endogenous Ras inhibitor p120RasGAP was expressed predominately in quiescent VEGF-insensitive endothelial cells and was ectopically downregulated in multiple neovascular models. MicroRNA-132 negatively regulated p120RasGAP expression. Experimental delivery of α-miR-132 to developing mouse eyes disrupted tip cell Ras activity and prevented angiogenic sprouting. This strategy prevented ocular neovascularization in multiple rodent models even more potently than the VEGF antagonist, VEGF-trap. Targeting microRNA-132 as a therapeutic strategy may prove useful for treating multiple neovascular diseases of the eye and for preventing vision loss regardless of the neovascular stimulus.

p120RasGAP is a mediator of rho pathway activation and tumorigenicity in the DLD1 colorectal cancer cell line

KRAS is mutated in ∼40% of colorectal cancer (CRC), and there are limited effective treatments for advanced KRAS mutant CRC. Therefore, it is crucial that downstream mediators of oncogenic KRAS continue to be studied. We identified p190RhoGAP as being phosphorylated in the DLD1 CRC cell line, which expresses a heterozygous KRAS G13D allele, and not in DKO4 in which the mutant allele has been deleted by somatic recombination. We found that a ubiquitous binding partner of p190RhoGAP, p120RasGAP (RasGAP), is expressed in much lower levels in DKO4 cells compared to DLD1, and this expression is regulated by KRAS. Rescue of RasGAP expression in DKO4 rescued Rho pathway activation and partially rescued tumorigenicity in DKO4 cells, indicating that the combination of mutant KRAS and RasGAP expression is crucial to these phenotypes. We conclude that RasGAP is an important effector of mutant KRAS in CRC.

Successful treatment of a congenital extra-truncal vascular malformation by orally administered propranolol

Abstract The β-blocker propranolol has become a valuable and effective drug for the treatment of infantile hemangiomas. Its therapeutic action probably results from vasoconstriction, blocking of angiogenesis through effects on vascular endothelial growth factor and induction of apoptosis. It is reasonable to suggest that propranolol can also be used effectively in the treatment of other vascular abnormalities. This case report describes propranolol treatment of vascular malformations such as Klippel-Trénaunay syndrome or Parkes-Weber syndrome in adults.

Lymphatic vessel abnormalities arising from disorders of Ras signal transduction

A number of genetic diseases in man have been described in which abnormalities in the development and function of the lymphatic vascular (LV) system are prominent features. The genes that are mutated in these diseases are varied and include genes that encode lymphatic endothelial cell (LEC) growth factor receptors and their ligands and transcription factors that control LEC fate and function. In addition, an increasing number of genes have been identified that encode components of the Ras signal transduction pathway that conveys signals from cell surface receptors to regulate cell growth, proliferation, and differentiation. Gene targeting studies performed in mice have confirmed that the LV system is particularly susceptible to perturbations in the Ras pathway.

Nocturnal headaches and pulsatile cranial mass: the tip of an iceberg

BACKGROUND

Capillary malformation-arteriovenous malformation (CM-AVM) disorder is a newly defined hereditary disorder of the vasculature with typical defining features that include cutaneous capillary malformations associated with high-flow lesions in various other organ systems. Mutations on the RASA1 gene are reported to be associated with a variety of vascular malformations and present with a widely varying phenotype.

PATIENT

A healthy 3 year old presented with acute onset of severe nocturnal headaches, nausea, and vomiting associated with a 2-cm pulsatile mass and prominent superficial veins on her forehead. Neuroimaging demonstrated a complex vascular malformation with multiple arteriovenous fistulae and cavernous angiomas present in multiple locations in the brain, but not in any other organ system.

RESULTS

The patient was found to have a mutation of the RASA1 gene, which has not been previously described in the literature.

CONCLUSIONS

This case describes a new RASA1 mutation with a phenotype that has not been previously described with a combination of pial fistulae and intracranial AV fistula in the absence of arteriovenous malformations.

RASA1 mutations and associated phenotypes in 68 families with capillary malformation-arteriovenous malformation

Capillary malformation-arteriovenous malformation (CM-AVM) is an autosomal-dominant disorder, caused by heterozygous RASA1 mutations, and manifesting multifocal CMs and high risk for fast-flow lesions. A limited number of patients have been reported, raising the question of the phenotypic borders. We identified new patients with a clinical diagnosis of CM-AVM, and patients with overlapping phenotypes. RASA1 was screened in 261 index patients with: CM-AVM (n = 100), common CM(s) (port-wine stain; n = 100), Sturge-Weber syndrome (n = 37), or isolated AVM(s) (n = 24). Fifty-eight distinct RASA1 mutations (43 novel) were identified in 68 index patients with CM-AVM and none in patients with other phenotypes. A novel clinical feature was identified: cutaneous zones of numerous small white pale halos with a central red spot. An additional question addressed in this study was the "second-hit" hypothesis as a pathophysiological mechanism for CM-AVM. One tissue from a patient with a germline RASA1 mutation was available. The analysis of the tissue showed loss of the wild-type RASA1 allele. In conclusion, mutations in RASA1 underscore the specific CM-AVM phenotype and the clinical diagnosis is based on identifying the characteristic CMs. The high incidence of fast-flow lesions warrants careful clinical and radiologic examination, and regular follow-up.

An institutional series and literature review of pial arteriovenous fistulas in the pediatric population: clinical article

OBJECT

Pial arteriovenous fistulas (PAVFs) are a rare form of cerebrovascular disease that tend to be overrepresented in the pediatric population. There have been limited studies of the clinical features and outcomes in this group of patients. Here, the authors attempt to better delineate this clinical entity with institutional cases and a review of the literature.

METHODS

A retrospective review of cases at our institution was performed to identify all pediatric patients treated for a PAVF between 2000 and 2012.

RESULTS

Five patients treated for a PAVF were identified. Patients had a mean age of 1.9 years at diagnosis, and the most common presenting symptoms were seizure and macrocephaly. Patients were treated primarily with embolization, and 3 patients required both N-butyl cyanoacrylate (NBCA) glue and coiling. Four of the patients had complete obliteration of the PAVF and had a pediatric overall performance category score of either 1 (n = 3) or 2 (n = 1) at follow-up. There was 1 death due to heart failure. Analysis of the literature review suggested that a younger age or presence of intracerebral hemorrhage (ICH) or congestive heart failure (CHF) at presentation likely predicts a worse prognosis. Older patients presented more often with ICH, whereas younger patients presented significantly more often in CHF. The majority of pediatric patients reported on in the literature were treated with endovascular embolization, most commonly with NBCA glue alone. Most patients (65.4%) in the literature had an excellent outcome without neurological deficit.

CONCLUSIONS

Pial AVFs represent a serious yet rare form of cerebrovascular disease. Pediatric patients with ICH or CHF at presentation or those who are very young are likely to have a worse prognosis. Endovascular management of these patients has greatly changed the natural history of this disease, but the complication and mortality rates suggest the need for continued insights and advances in treatment.

Small G Proteins in the Cardiovascular System: Physiological and Pathological Aspects

Small G proteins exist in eukaryotes from yeast to human and constitute the Ras superfamily comprising more than 100 members. This superfamily is structurally classified into five families: the Ras, Rho, Rab, Arf, and Ran families that control a wide variety of cell and biological functions through highly coordinated regulation processes. Increasing evidence has accumulated to identify small G proteins and their regulators as key players of the cardiovascular physiology that control a large panel of cardiac (heart rhythm, contraction, hypertrophy) and vascular functions (angiogenesis, vascular permeability, vasoconstriction). Indeed, basal Ras protein activity is required for homeostatic functions in physiological conditions, but sustained overactivation of Ras proteins or spatiotemporal dysregulation of Ras signaling pathways has pathological consequences in the cardiovascular system. The primary object of this review is to provide a comprehensive overview of the current progress in our understanding of the role of small G proteins and their regulators in cardiovascular physiology and pathologies.

VarRanker: rapid prioritization of sequence variations associated with human disease

BACKGROUND

Identification of the genetic alterations responsible for human disease is a central challenge facing medical genetics. While many algorithms have been developed to predict the degree of damage caused by a given sequence alteration, few tools are able to incorporate information about a given phenotype of interest.

METHODS

Here, we describe an algorithm and web-based application which take into account both the probability that a variant damages the function of a gene as well as the relevance of the gene to a given phenotype. Phenotypes are described by a list of scored terms supplied by the user. These terms are then used to search a variety of public databases including NCBI gene summaries, PubMed abstracts, and Gene Ontology terms, and protein-protein interactions in String-DB to determine a relevance score. The overall ranking is determined by the product of the functional damage score and the relevance score, such that highly ranked variants are likely to be damaging and in genes of interest.

RESULTS

We demonstrate the method on several test cases including samples with Hereditary Hemorrhagic Telangiectasia (HHT) and Diamond-Blackfan Anemia (DBA). We have also implemented a web-based application which allows public access to the VarRanker algorithm.

CONCLUSIONS

Automated searching of public literature and online databases may substantially decrease the amount of time required to identify the mutations underlying human disease. However, several ad-hoc and subjective decisions must be made, and the results of such analyses are likely to depend on the researcher and the state of the literature and databases involved.