Loss-of-Function Mutations in ELMO2 Cause Intraosseous Vascular Malformation by Impeding RAC1 Signaling

Genetic mutations and phenotype characteristics in peripheral vascular malformations: A systematic review

Vascular malformations (VMs) are clinically diverse with regard to the vessel type, anatomical location, tissue involvement and size. Consequently, symptoms and disease impact differ significantly. Diverse causative mutations in more and more genes are discovered and play a major role in the development of VMs. However, the relationship between the underlying causative mutations and the highly variable phenotype of VMs is not yet fully understood. In this systematic review, we aimed to provide an overview of known causative mutations in genes in VMs and discuss associations between the causative mutations and clinical phenotypes. PubMed and EMBASE libraries were systematically searched on November 9th, 2022 for randomized controlled trials and observational studies reporting causative mutations in at least five patients with peripheral venous, lymphatic, arteriovenous and combined malformations. Study quality was assessed with the Newcastle-Ottawa Scale. Data were extracted on patient and VM characteristics, molecular sequencing method and results of molecular analysis. In total, 5667 articles were found of which 69 studies were included, reporting molecular analysis in a total of 4261 patients and 1686 (40%) patients with peripheral VMs a causative mutation was detected. In conclusion, this systematic review provides a comprehensive overview of causative germline and somatic mutations in various genes and associated phenotypes in peripheral VMs. With these findings, we attempt to better understand how the underlying causative mutations in various genes contribute to the highly variable clinical characteristics of VMs. Our study shows that some causative mutations lead to a uniform phenotype, while other causal variants lead to more varying phenotypes. By contrast, distinct causative mutations may lead to similar phenotypes and result in almost indistinguishable VMs. VMs are currently classified based on clinical and histopathology features, however, the findings of this systematic review suggest a larger role for genotype in current diagnostics and classification.

ELMO2 biallelic pathogenic variants in a patient with gingival hypertrophy and cherubism phenotype: Case report and molecular review

Ramon syndrome (OMIM #266270) was first described in a patient with cherubism, gingival fibromatosis, epilepsy, intellectual disability, hypertrichosis, and stunted growth. In 2018, Mehawej et al. described a patient with Ramon syndrome in whom a homozygous variant in ELMO2 was identified, suggesting that this gene may be the causative for this syndrome. ELMO2 biallelic pathogenic variants were also described in patients with a primary intraosseous vascular malformation (PIVM; OMIM #606893). These patients presented gingival bleeding and cherubism phenotype. Herein, a patient with gingival hypertrophy, neurodevelopmental delay, and cherubism phenotype with a novel homozygous predicted loss-of-function (LOF) variant in the ELMO2 gene and family recurrence was reported. A surgical approach to treat gingival bleeding and mandible vascular malformation was also described. Furthermore, this study includes a comprehensive literature review of molecular data regarding the ELMO2 gene. All the variants, except one described in the ELMO2, were predicted as LOF, including our patient's variant. There is an overlapping between PIVM, also caused by LOF biallelic variants in the ELMO2 gene, and Ramon syndrome, which can suggest that they are not different entities. However, due to a limited number of cases described with molecular evaluation, it is hard to establish a genotype-phenotype correlation. Our study supports that LOF pathogenic biallelic variants in the ELMO2 gene cause a phenotype that has cherubism and gingival hypertrophy as main characteristics.

DOCK3-Associated Neurodevelopmental Disorder-Clinical Features and Molecular Basis

The protein product of DOCK3 is highly expressed in neurons and has a role in cell adhesion and neuronal outgrowth through its interaction with the actin cytoskeleton and key cell signaling molecules. The DOCK3 protein is essential for normal cell growth and migration. Biallelic variants in DOCK3 associated with complete or partial loss of function of the gene were recently reported in six patients with intellectual disability and muscle hypotonia. Only one of the reported patients had congenital malformations outside of the CNS. Further studies are necessary to better determine the prevalence of DOCK3-associated neurodevelopmental disorders and the frequency of non-CNS clinical manifestations in these patients. Since deficiency of the DOCK3 protein product is now an established pathway of this neurodevelopmental condition, supplementing the deficient gene product using a gene therapy approach may be an efficient treatment strategy.

Comparative Morphological, Metabolic and Transcriptome Analyses in elmo1−/−, elmo2−/−, and elmo3−/− Zebrafish Mutants Identified a Functional Non-Redundancy of the Elmo Proteins

The ELMO protein family consists of the homologues ELMO1, ELMO2 and ELMO3. Several studies have shown that the individual ELMO proteins are involved in a variety of cellular and developmental processes. However, it has poorly been understood whether the Elmo proteins show similar functions and act redundantly. To address this question, elmo1−/−, elmo2−/− and elmo3−/− zebrafish were generated and a comprehensive comparison of the phenotypic changes in organ morphology, transcriptome and metabolome was performed in these mutants. The results showed decreased fasting and increased postprandial blood glucose levels in adult elmo1−/−, as well as a decreased vascular formation in the adult retina in elmo1−/−, but an increased vascular formation in the adult elmo3−/− retina. The phenotypical comparison provided few similarities, as increased Bowman space areas in adult elmo1−/− and elmo2−/− kidneys, an increased hyaloid vessel diameter in elmo1−/− and elmo3−/− and a transcriptional downregulation of the vascular development in elmo1−/−, elmo2−/−, and elmo3−/− zebrafish larvae. Besides this, elmo1−/−, elmo2−/−, and elmo3−/− zebrafish exhibited several distinct changes in the vascular and glomerular structure and in the metabolome and the transcriptome. Especially, elmo3−/− zebrafish showed extensive differences in the larval transcriptome and an impaired survivability. Together, the data demonstrated that the three zebrafish Elmo proteins regulate not only similar but also divergent biological processes and mechanisms and show a low functional redundancy.

Pathophysiological Mechanisms in Neurodevelopmental Disorders Caused by Rac GTPases Dysregulation: What's behind Neuro-RACopathies

Rho family guanosine triphosphatases (GTPases) regulate cellular signaling and cytoskeletal dynamics, playing a pivotal role in cell adhesion, migration, and cell cycle progression. The Rac subfamily of Rho GTPases consists of three highly homologous proteins, Rac 1-3. The proper function of Rac1 and Rac3, and their correct interaction with guanine nucleotide-exchange factors (GEFs) and GTPase-activating proteins (GAPs) are crucial for neural development. Pathogenic variants affecting these delicate biological processes are implicated in different medical conditions in humans, primarily neurodevelopmental disorders (NDDs). In addition to a direct deleterious effect produced by genetic variants in the RAC genes, a dysregulated GTPase activity resulting from an abnormal function of GEFs and GAPs has been involved in the pathogenesis of distinctive emerging conditions. In this study, we reviewed the current pertinent literature on Rac-related disorders with a primary neurological involvement, providing an overview of the current knowledge on the pathophysiological mechanisms involved in the neuro-RACopathies.

Venous Malformations in Childhood: Clinical, Histopathological and Genetics Update

Our knowledge in vascular anomalies has grown tremendously in the past decade with the identification of key molecular pathways and genetic mutations that drive the development of vascular tumors and vascular malformations. This has led us to better understand the pathogenesis of vascular lesions, refine their diagnosis and update their classification while also exploring the opportunity for a targeted molecular treatment. This paper aims to provide an overview of venous malformations (VM) in childhood. Specific entities include common VMs, cutaneo-mucosal VM, blue rubber bleb nevus syndrome or Bean syndrome, glomuvenous malformation, cerebral cavernous malformation, familial intraosseous vascular malformation and verrucous venous malformation. The clinicopathological features and the molecular basis of each entity are reviewed.

The DOCK protein family in vascular development and disease

The vascular network is established and maintained through the processes of vasculogenesis and angiogenesis, which are tightly regulated during embryonic and postnatal life. The formation of a functional vasculature requires critical cellular mechanisms, such as cell migration, proliferation and adhesion, which are dependent on the activity of small Rho GTPases, controlled in part by the dedicator of cytokinesis (DOCK) protein family. Whilst the majority of DOCK proteins are associated with neuronal development, a growing body of evidence has indicated that members of the DOCK family may have key functions in the control of vasculogenic and angiogenic processes. This is supported by the involvement of several angiogenic signalling pathways, including chemokine receptor type 4 (CXCR4), vascular endothelial growth factor (VEGF) and phosphatidylinositol 3-kinase (PI3K), in the regulation of specific DOCK proteins. This review summarises recent progress in understanding the respective roles of DOCK family proteins during vascular development. We focus on existing in vivo and in vitro models and known human disease phenotypes and highlight potential mechanisms of DOCK protein dysfunction in the pathogenesis of vascular disease.

Mutations in MC4R facilitate the angiogenic activity in patients with orbital venous malformation

IMPACT STATEMENT

The detailed molecular mechanism of orbital venous malformation (OVM) is still not clear. Using whole exome sequencing, 4 types of melanocortin 4 receptor (MC4R) mutation were detected in 7 of 27 patients with OVM, and all types of MC4R mutations resulted in the upregulation of MC4R expression. In vitro study indicated that MC4R has impacts on the proliferation, cell cycle, migration, and tube formation of the endothelial cells. Moreover, MC4R mutations altered the downstream signaling, including cAMP concentration and the expression levels of several PI3K/AKT/mTOR downstream genes, including p21, cyclin B1, ITGA10, and ITGA11. MC4R mutations may lead to the pathogenesis of OVM through modulating the downstream signaling to alter the angiogenic activity of endothelial cells.

A Primer on a Comprehensive Genetic Approach to Vascular Anomalies

The field of vascular anomalies has grown tremendously in the last few decades with the identification of key molecular pathways and genetic mutations that drive the formation and progression of vascular anomalies. Understanding these pathways is critical for the classification of vascular anomalies, patient care, and development of novel therapeutics. The goal of this review is to provide a basic understanding of the classification of vascular anomalies and knowledge of their underlying molecular pathways. Here we provide an organizational framework for phenotype/genotype correlation and subsequent development of a diagnostic and treatment roadmap. With the increasing importance of genetics in the diagnosis and treatment of vascular anomalies, we highlight the importance of clinical geneticists as part of a comprehensive multidisciplinary vascular anomalies team.

Genetics of vascular malformation and therapeutic implications

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

A Low-Cost Time-Correlated Single Photon Counting Portable DNA Analyzer

Photon-counting analysis of nucleic acids plays a key role in many diagnostics applications for its accurate and non-invasive nature. However, conventional photon-counting instrumentations are bulky and expensive due to the use of conventional optics and a lack of optimization of electronics. In this paper, we present a portable, low-cost time-correlated single photon-counting (TCSPC) analysis system for DNA detection. Both optical and electronic subsystems are carefully designed to provide effective emission filtering and size reduction, delivering good DNA detection and fluorescence lifetime extraction performance. DNA detection has been verified by fluorescence lifetime measurements of a V-carbazole conjugated fluorophore lifetime bioassay. The time-to-digital module of the proposed TCSPC system achieves a full width at half maximum (FWHM) timing resolution from 121 to 145 ps and a differential non-linearity (DNL) between −8.5% and +9.7% of the least significant bit (LSB) within the 500 ns full-scale range (FSR). With a detection limit of 6.25 nM and a dynamic range of 6.8 ns, the proposed TCSPC system demonstrates the enabling technology for rapid, point-of-care DNA diagnostics.

Clinical and Molecular Study of ELMO-2-Related Massive Intraosseous Vascular Malformations: Lessons Learned From 25 Years of Follow-up

Massive intraosseous vascular malformations, a relatively rare entity in the vascular malformation spectrum, deserves attention as involving the membranous bones of the craniofacial skeleton and may lead to severe life-threatening hemorrhages and even death. The main aim of this study was to summarize the 25 years of clinical experience with these vascular malformation osseous patients, focus on the molecular and genetic aspect of the clinical entity, and to emphasize the certain challenging conditions in the treatment of these patients. All the patients appeared to be unaffected at birth, whereas initial symptoms occasionally began with painless swelling in the mandible in early childhood. The disease was progressive in behavior especially in the pubertal ages and was specifically involving the maxilla and mandible of the craniofacial skeleton in all the patients. Calvarium and cranial base were the second most common involved regions among these patients (62.5%). Clavicular (50%), costal (25%), and vertebral (25%) involvements were also a significant manifestation of the disease. Tissue samples obtained from the affected individuals and the blood samples from their families were matched, revealing a loss of function mutation in the ELMO-2 gene of chromosome 20 leading to developmental abnormality of the vascular structures via RAC1 signaling and leading to abnormally enlarged vessels in the intraosseus portion of the membranous bone. Immunohistochemical staining revealed positive CD31 and smooth muscle actin staining but negative proliferation and maturity markers such as Ki-67, desmin, h-caldesmon, and myofibroblast-like desmin. The follow-up of 3 of 5 patients ended up with mortality (60%). vascular malformation osseous is intraosseous vascular malformation with aggressive biological behavior associated with ELMO-2 gene mutation. Further studies for obtaining prenatal diagnosis and achievement of gene therapy should take place. As the disease rapidly progresses as the affected individual grows, surgical interventions should be taken into consideration before the initiation of complications.

Structure of BAI1/ELMO2 complex reveals an action mechanism of adhesion GPCRs via ELMO family scaffolds

The brain-specific angiogenesis inhibitor (BAI) subfamily of adhesion G protein-coupled receptors (aGPCRs) plays crucial roles in diverse cellular processes including phagocytosis, myoblast fusion, and synaptic development through the ELMO/DOCK/Rac signaling pathway, although the underlying molecular mechanism is not well understood. Here, we demonstrate that an evolutionarily conserved fragment located in the C-terminal cytoplasmic tail of BAI-aGPCRs is specifically recognized by the RBD-ARR-ELMO (RAE) supramodule of the ELMO family scaffolds. The crystal structures of ELMO2-RAE and its complex with BAI1 uncover the molecular basis of BAI/ELMO interactions. Based on the complex structure we identify aGPCR-GPR128 as another upstream receptor for the ELMO family scaffolds, most likely with a recognition mode similar to that of BAI/ELMO interactions. Finally, we map disease-causing mutations of BAI and ELMO and analyze their effects on complex formation.

Genetic testing for vascular anomalies

Vascular anomalies (VAs) have phenotypic variability within the same entity, overlapping clinical features between different conditions, allelic and locus heterogeneity and the same disorder can be inherited in different ways. Most VAs are sporadic (paradominant inheritance or de novo somatic or germline mutations), but hereditary forms (autosomal dominant or recessive) have been described. This Utility Gene Test was developed on the basis of an analysis of the literature and existing diagnostic protocols. The genetic test is useful for confirming diagnosis, as well as for differential diagnosis, couple risk assessment and access to clinical trials.

Homozygous mutation in ELMO2 may cause Ramon syndrome

We report on a girl, born to first cousin Lebanese parents, with intellectual disability, seizures, repeated gingivorrhagia, enlarged lower and upper jaws, overgrowth of the gums, high arched and narrow palate, crowded teeth, hirsutism of the back, large abdomen and a small umbilical hernia. Cysts of the mandible, fibrous dysplasia of bones, and enlarged adenoids causing around 60% narrowing of the nasopharyngeal airways were noted at radiographic examination. Her brother presented with the same features in addition to a short stature, an ostium secundum, and more pronounced intellectual disability. He died at the age of 8 years from a severe pulmonary infection and repeated bleeding episodes. A clinical diagnosis of Ramon syndrome was made. Whole exome sequencing studies performed on the family revealed the presence of a novel homozygous missense mutation in ELMO2 gene, p.I606S in the affected individuals. Loss of function mutations in ELMO2 have been recently described in another clinically distinct condition: primary intraosseous vascular malformation or intraosseous hemangioma, called VMOS. Review of the literature and differential diagnoses are discussed.