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Arteriovenous malformations (AVMs) are abnormal high flow shunts between arteries and veins with major negative impact on the cardiovascular system. Inherited loss-of-function (LOF) mutations in endoglin, encoding an endothelial cell (EC) expressed co-receptor for BMP9/10, causes the disease HHT1/Osler-Weber-Rendu, characterized by bleeding and AVMs. Here we observe increased activity of the downstream signalling complex mTORC1 within the retinal vasculature of HHT mouse models. To investigate its importance in AVM biology, concerning subvascular action, cell specificity, signalling strength and kinetics we combine timed genetic and antibody-based models of HHT with genetic mTORC1 inhibition or activation through EC specific deletion of Rptor or Tsc1. Results demonstrate that EC mTORC1 activation is secondary to endoglin LOF and mainly a consequence of systemic effects following AVM. While genetic EC inhibition of mTORC1 only showed tendencies towards reduced AVM severity, EC overactivation counterintuitively reduced it, implying that mTORC1 must be within a certain range to facilitate AVM. Complete inhibition of mTORC1 signalling by rapamycin provided the strongest therapeutic effect, pointing to potential involvement of RAPTOR-independent pathways or AVM-promoting effects of non-ECs in this pathology., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Clinical manifestations of hereditary hemorrhagic telangiectasia (HHT) include vascular malformations of the skin, nasal mucosa, gastrointestinal tract, lungs, liver and central nervous system. These malformations range from punctate telangiectasias to larger arteriovenous malformations within visceral organs and the central nervous system. Vascular malformations increase risk for acute and chronic bleeding, anemia, as well secondary complications related to arterial-venous shunting. Diagnosis can be made with the Curaçao criteria, which includes the presence of epistaxis, telangiectasias, arteriovenous malformations, and first-degree family member with HHT. Nearly all patients with HHT will have a pathogenic variant in the ENG or ACVRL1 genes, while a smaller number will have a variant in SMAD4 or no clear genetic etiology. While there is no cure for HHT, medical management of vascular complications may include oral tranexamic acid and IV bevacizumab. Endovascular and surgical treatments are clinically indicated when the benefits outweigh the risks of the interventions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Purpose of Review: Hereditary hemorrhagic telangiectasia (HHT) diagnostic and management approach for pediatrics underwent significant advances over the last couple of years., Recent Findings: In 2020, new guidelines for HHT were published that included a pediatric section thus attracting special focus into the childhood presentation., Summary: Curacao criteria are specific, but not sensitive enough in children. Genetic testing is encouraged for all family members even if asymptomatic. Standardized scoring for epistaxis is strongly encouraged, as it allows monitoring and can stratify therapeutic approaches. Early screening for pulmonary and brain visceral arteriovenous malformations (AVMs) in pediatric patients with confirmed genetic alterations of HHT should be instituted. Graded trans-esophageal echocardiogram with agitated saline contrast can be used as screening method for pulmonary AVMs. As pulmonary AVMs can develop throughout lifetime, guidelines recommend repeated screening even in asymptomatic patients at least every 5 years. Signs of stroke in childhood are more subtle than in adults. Cerebral imaging in early childhood can identify brain AVMs that may benefit from early intervention. Embolization of high-risk pulmonary and cerebral AVMs should be performed at specialized centers even at pediatric age. One or two classic HHT telangiectasia can be considered diagnostic in children. Antibiotic prophylaxis with dental procedures continues to be recommended., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Hereditary Hemorrhagic Telangiectasia (HHT) is an autosomal vascular dysplasia characterized by the presence of mucocutaneous telangiectasia and arteriovenous malformations in solid organs. The Curaçao criteria and/or detection of ALK1, ENG, and SMAD4 gene mutations are used for diagnosis. Juvenile Polyposis Syndrome (JPS) is diagnosed according to the number and localization of juvenile polyps, and family history of JPS. Both entities have a low prevalence. Mutation of SMAD4 leads to a combined syndrome of these two conditions called HHT-JPS Overlap Syndrome. We aim to describe the clinical characteristics associated with this condition focusing on long term follow up and review of the literature. A cross-sectional descriptive study of HHT-JPS cases from an HHT Institutional Registry was designed. Patients were eligible for this case series if they fulfilled both HHT and JPS diagnostic criteria and/or mutation on SMAD4. A comprehensive review was conducted on the clinical phenotype associated with HHT and its gastrointestinal involvement. Fourteen patients from eleven families in 788 previously HHT-diagnosed patients met the inclusion criteria. The ages ranged between 25 and 70 years old and 12 were females. In addition to the typical signs/symptoms of HHT, two distinct phenotypes were observed. Nine patients predominantly exhibited initially upper, while five showed predominantly initially lower gastrointestinal involvement. Numerous musculoskeletal and cardiovascular anomalies were also identified. The observed phenotypic diversity, particularly in gastrointestinal involvement, underscores the need for tailored clinical approaches. Comprehensive assessments identified associated musculoskeletal and cardiovascular anomalies, emphasizing the systemic nature of HHT-JPS., Competing Interests: Declarations Competing interests The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Increased endothelial cell proliferation is a hallmark of arteriovenous malformations (AVMs) in hereditary hemorrhagic telangiectasia (HHT). Here, we report a cyclin-dependent kinase 6 (CDK6)-driven mechanism of cell cycle deregulation involved in endothelial cell proliferation and HHT pathology. Specifically, endothelial cells from the livers of HHT mice bypassed the G1/S checkpoint and progressed through the cell cycle at an accelerated pace. Phosphorylated retinoblastoma (pRB1)-a marker of G1/S transition through the restriction point-accumulated in endothelial cells from retinal AVMs of HHT mice and endothelial cells from skin telangiectasia samples from HHT patients. Mechanistically, inhibition of activin receptor-like kinase 1 signaling increased key restriction point mediators, and treatment with the CDK4/6 inhibitors palbociclib or ribociclib blocked increases in pRB1 and retinal AVMs in HHT mice. Palbociclib also improved vascular pathology in the brain and liver, and slowed cell cycle progression in endothelial cells and endothelial cell proliferation. Endothelial cell-specific deletion of CDK6 was sufficient to protect HHT mice from AVM pathology. Thus, clinically approved CDK4/6 inhibitors might have the potential to be repurposed for HHT., Competing Interests: Competing interests The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Hereditary hemorrhagic telangiectasia (HHT) is an inherited disorder of vascular malformations characterized by mucocutaneous telangiectases and arteriovenous malformations (AVMs) in internal organs. HHT is caused by inheritance of a loss of function mutation in one of three genes. Although individuals with HHT are haploinsufficient for one of these genes throughout their entire body, rather than exhibiting a systemic vascular phenotype, vascular malformations occur as focal lesions in discrete anatomic locations. The inconsistency between genotype and phenotype has provoked debate over whether haploinsufficiency or a different mechanism gives rise to the vascular malformations. We previously showed that HHT-associated skin telangiectases develop by a two-hit mutation mechanism in an HHT gene. However, somatic mutations were identified in only half of the telangiectases, raising the question whether a second-hit somatic mutation is a necessary (required) event in HHT pathogenesis. Here, we show that another mechanism for the second hit is loss of heterozygosity across the chromosome bearing the germline mutation. Secondly, we investigate the two-hit mutation mechanism for internal organ AVMs, the source of much of the morbidity of HHT. Here, we identified somatic molecular genetic events in eight liver telangiectases, including point mutations and a loss of heterozygosity event. We also identified somatic mutations in one pulmonary AVM and two brain AVMs, confirming that mucocutaneous and internal organ vascular malformations undergo the same molecular mechanisms. Together, these data argue that bi-allelic loss of function in an HHT gene is a required event in the pathogenesis of HHT-associated vascular malformations., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024. Published by Elsevier Inc.)

Germline SMAD4 pathogenic variants (PVs) cause juvenile polyposis syndrome (JPS), which is known for an increased risk of gastrointestinal juvenile polyps and gastrointestinal cancer. Many patients with SMAD4 PV also show signs of hereditary hemorrhagic telangiectasia (HHT) and some patients have aneurysms and dissections of the thoracic aorta. Here we describe two patients with a germline SMAD4 PV and a remarkable clinical presentation including multiple medium-sized arterial aneurysms. More data are needed to confirm whether the more extensive vascular phenotype and the other described features in our patients are indeed part of a broader JPS spectrum., (© 2024 The Authors. American Journal of Medical Genetics Part A published by Wiley Periodicals LLC.)

Introduction: Hereditary Hemorrhagic Telangiectasia (HHT) is charactered by telangiectasia and arteriovenous malformations (AVMs). Recurrent visceral and mucocutaneous bleeding is frequently reported among HHT patients, while data on the prevalence of thrombosis remains limited. This study aims to describe the clinical manifestations and molecular biological characteristics of HHT patients., Methods: We conducted a retrospective study at Ruijin Hospital, affiliated with Shanghai Jiao Tong University School of Medicine. A total of 24 HHT patients, observed between January 2019 and December 2023, were included. We recorded the biological, clinical, and therapeutic events, with particular attention to bleeding and thrombotic events. Gene mutation analysis and blood constituent measurements were performed., Results: The prevalence of bleeding among all HHT patients was 100 %, while thrombotic events were noted in 41.70 % of cases. Hepatic arteriovenous malformations (HAVMs) were identified in six patients, pulmonary arteriovenous malformations (PAVMs) in five patients, and cerebral arteriovenous malformations (CAVMs) in one patient. For patients with thrombosis, the discontinuation rates were 23.08 % for antiplatelet therapy and 33.33 % for anticoagulant therapy due to the increased risk of bleeding. Genetic mutations related to HHT were present in 16 patients, with ACVRL1 (activin A receptor-like type 1) mutations being the most frequent at 41.67 %, followed by ENG (endoglin) mutations at 20.83 %, and GDF2 (growth differentiation factor 2) mutations at 4.17 %. The incidence of PAVMs was 75.00 % in HHT1 patients with ENG mutations and 20 % in HHT2 patients with ACVRL1 mutations, while HAVMs occurred in 0 % and 40.00 % of these groups, respectively. Patients were divided into non-AVMs and AVMs groups. Compared to normal controls, von Willebrand factor (vWF) activity was significantly increased in all HHT patients (149.10 % vs. 90.65 %, P < 0.001). In the non-AVMs group, the median level of stromal cell-derived factor-1 (SDF-1) was significantly elevated (124.31 pg/mL vs. 2413.57 pg/mL, P < 0.05), while vWF antigen levels were markedly higher in the AVMs group (165.30 % vs. 130.60 %, P = 0.021). Further grouping of HHT patients based on bleeding and thrombosis phenotypes revealed that those with thrombosis had significantly higher median percentages of schistocytes (3.50 % vs. 0 %, P = 0.002), ferritin concentrations (318.50 μg/L vs. 115.50 μg/L, P = 0.001), and lactate dehydrogenase (LDH) levels (437 U/L vs. 105 U/L, P < 0.001). There were no significant differences in the activity of vWF, protein C (PC), protein S (PS), and factor VIII (FVIII) between the two groups., Conclusion: This study highlighted the complex relationship between arteriovenous malformations and genetic mutations in HHT patients. A comprehensive assessment of bleeding and thrombosis risks should be conducted for each HHT patient, additionally, further clinical studies are needed to explore the risk factors for thrombosis and anticoagulant-related bleeding in HHT., Competing Interests: Declaration of competing interest The authors state that there are no conflicts of interest to disclose. We would like to thank all of the patients who participated in this study and the physicians who offer help in diagnosis and management. This study was supported by Shanghai Natural Science Foundation Project (22ZR1439500) to Yeling Lu., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Hereditary haemorrhagic telangiectasia is a genetic condition of abnormal blood vessel formation resulting from an imbalance of pro- and anti-angiogenic products of the transforming growth factor β/bone morphogenetic protein signalling pathway which contributes to vascular remodelling and maintenance. Hepatic vascular malformations are common although less frequently symptomatic, but may result in high-output cardiac failure, portal hypertension and biliary ischaemia. Whilst the understanding of the genetic and cell signalling pathways that are the hallmark of hereditary haemorrhagic telangiectasia have been clarified, there remain challenges in therapy for these patients. Only patients with symptomatic hepatic vascular malformations require treatment, with most (63%) responding to first-line medical therapy. For non-responders, bevacizumab is effective in reducing cardiac output in those with heart failure secondary to hepatic vascular malformations as well as other manifestations of the disease. Although liver transplantation is the only curative option, optimal timing is critical. Novel anti-angiogenetic drugs and those that target aberrant cell signalling pathway are being explored., (© 2024 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Objective: To explore the genetic basis and pathogenesis for a child with type I Hereditary hemorrhagic telangiectasia (HHTⅠ) and Splenic sinus shore cell hemangioma (LCA)., Methods: A child with HHT complicated with LCA diagnosed at the First Affiliated Hospital of Dali University in April 2022 was selected as the study subject. Clinical data of the child and her relatives were collected, and pathogenic variants were screened by whole exome sequencing. Candidate variant was verified by Sanger sequencing and bioinformatic analysis., Results: The patient, a 16-year-old female, had recurrent epitaxis since childhood, which sometimes necessitated hemostasis treatment. She also had splenectomy due to splenic rupture and was diagnosed with LCA. Her father and grandmother also had a history of recurrent epitaxis. Her father had deceased due to cerebral vascular rupture. The child was found to harbor a c.360+1G>A variant in the ENG gene. The same variant was not found in her asymptomatic mother and brother., Conclusion: The c.360+1G>A variant of the ENG gene probably underlay the pathogenesis in this child.

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disease characterized by the development of arteriovenous malformations (AVMs) that can result in significant morbidity and mortality. HHT is caused primarily by mutations in bone morphogenetic protein receptors ACVRL1/ALK1, a signaling receptor, or endoglin (ENG), an accessory receptor. Because overexpression of Acvrl1 prevents AVM development in both Acvrl1 and Eng null mice, enhancing ACVRL1 expression may be a promising approach to development of targeted therapies for HHT. Therefore, we sought to understand the molecular mechanism of ACVRL1 regulation. We previously demonstrated in zebrafish embryos that acvrl1 is predominantly expressed in arterial endothelial cells and that expression requires blood flow. Here, we document that flow dependence exhibits regional heterogeneity and that acvrl1 expression is rapidly restored after reinitiation of flow. Furthermore, we find that acvrl1 expression is significantly decreased in mutants that lack the circulating Alk1 ligand, Bmp10, and that, in the absence of flow, intravascular injection of BMP10 or the related ligand, BMP9, restores acvrl1 expression in an Alk1-dependent manner. Using a transgenic acvrl1:egfp reporter line, we find that flow and Bmp10 regulate acvrl1 at the level of transcription. Finally, we observe similar ALK1 ligand-dependent increases in ACVRL1 in human endothelial cells subjected to shear stress. These data suggest that ligand-dependent Alk1 activity acts downstream of blood flow to maintain or enhance acvrl1 expression via a positive feedback mechanism, and that ALK1 activating therapeutics may have dual functionality by increasing both ALK1 signaling flux and ACVRL1 expression., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Background: Both hereditary haemorrhagic telangiectasia (HHT) and juvenile polyposis syndrome (JPS) are known to be caused by SMAD4 pathogenic variants, with overlapping symptoms for both disorders in some patients. Additional connective tissue disorders have also been reported. Here, we describe carriers of SMAD4 variants followed in an HHT reference centre to further delineate the phenotype., Methods: Observational study based on data collected from the Clinical Investigation for the Rendu-Osler Cohort database., Results: Thirty-three participants from 15 families, out of 1114 patients with HHT, had an SMAD4 variant (3%).Regarding HHT, 26 out of 33 participants (88%) had a definite clinical diagnosis based on Curaçao criteria. Complication frequencies were as follows: epistaxis (n=27/33, 82%), cutaneous telangiectases (n=19/33, 58%), pulmonary arteriovenous malformations (n=17/32, 53%), hepatic arteriovenous malformations (AVMs) (n=7/18, 39%), digestive angiodysplasia (n=13/22, 59%). No cerebral AVMs were diagnosed.Regarding juvenile polyposis, 25 out of 31 participants (81%) met the criteria defined by Jass et al for juvenile polyposis syndrome. Seven patients (21%) had a prophylactic gastrectomy due to an extensive gastric polyposis incompatible with endoscopic follow-up, and four patients (13%) developed a digestive cancer.Regarding connective tissue disorders, 20 (61%) had at least one symptom, and 4 (15%) participants who underwent echocardiography had an aortic dilation., Conclusion: We describe a large cohort of SMAD4 variant carriers in the context of HHT. Digestive complications are frequent, early and diffuse, justifying endoscopy every 2 years. The HHT phenotype, associating pulmonary and hepatic AVMs, warrants systematic screening. Connective tissue disorders broaden the phenotype associated with SMAD4 gene variants and justify systematic cardiac ultrasound and skeletal complications screening., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Telangiectases and arteriovenous malformations (AVMs) are the characteristic lesions of Hereditary Hemorrhagic Telangiectasia (HHT). Somatic second-hit loss-of-function variations in the HHT causative genes, ENG and ACVRL1 , have been described in dermal telangiectasias. It is unclear if somatic second-hit mutations also cause the formation of AVMs and nasal telangiectasias in HHT. To investigate the genetic mechanism of AVM formation in HHT, we evaluated multiple affected tissues from fourteen individuals. DNA was extracted from fresh/frozen tissue of 15 nasal telangiectasia, 4 dermal telangiectasia, and 9 normal control tissue biopsies, from nine unrelated individuals with HHT. DNA from six formalin-fixed paraffin-embedded (FFPE) AVM tissues (brain, lung, liver, and gallbladder) from five individuals was evaluated. A 736 vascular malformation and cancer gene next-generation sequencing (NGS) panel was used to evaluate these tissues down to 1% somatic mosaicism. Somatic second-hit mutations were identified in three in four AVM biopsies (75%) or half of the FFPE (50%) samples, including the loss of heterozygosity in ENG in one brain AVM sample, in which the germline mutation occurred in a different allele than a nearby somatic mutation (both are loss-of-function mutations). Eight of nine (88.9%) patients in whom telangiectasia tissues were evaluated had a somatic mutation ranging from 0.68 to 1.96% in the same gene with the germline mutation. Six of fifteen (40%) nasal and two of four (50%) dermal telangiectasia had a detectable somatic second hit. Additional low-level somatic mutations in other genes were identified in several telangiectasias. This is the first report that nasal telangiectasias and solid organ AVMs in HHT are caused by very-low-level somatic biallelic second-hit mutations.

Pulmonary arteriovenous malformations (PAVMs) are vascular anomalies resulting in abnormal connections between pulmonary arteries and veins. In 80% of cases, PAVMs are present from birth, but clinical manifestations are rarely seen in childhood. These congenital malformations are typically associated with Hereditary Hemorrhagic Telangiectasia (HHT), a rare disease that affects 1 in 5000/8000 individuals. HHT disease is frequently caused by mutations in genes involved in the TGF-β pathway. However, approximately 15% of patients do not have a genetic diagnosis and, among the genetically diagnosed, more than 33% do not meet the Curaçao criteria. This makes clinical diagnosis even more challenging in the pediatric age group. Here, we introduce an 8-year-old patient bearing a severe phenotype of multiple diffuse PAVMs caused by an unknown mutation which ended in lung transplantation. Phenotypically, the case under study follows a molecular pattern which is HHT-like. Therefore, molecular- biological and cellular-functional analyses have been performed in primary endothelial cells (ECs) isolated from the explanted lung. The findings revealed a loss of functionality in lung endothelial tissue and a stimulation of endothelial-to-mesenchymal transition. Understanding the molecular basis of this transition could potentially offer new therapeutic strategies to delay lung transplantation in severe cases.

Constitutional loss of SMAD4 function results in Juvenile Polyposis-Hereditary Haemorrhagic Telangiectasia Overlap Syndrome (JP-HHT). A retrospective multi-centre case-note review identified 28 patients with a pathogenic SMAD4 variant from 13 families across all Scottish Clinical Genetics Centres. This provided a complete clinical picture of the Scottish JP-HHT cohort. Colonic polyps were identified in 87% (23/28) and gastric polyps in 67% (12/18) of screened patients. Complication rates were high: 43% (10/23) of patients with polyps required a colectomy and 42% (5/12) required a gastrectomy. Colorectal cancer occurred in 25% (7/28) of patients, at a median age of 33 years. Pulmonary arteriovenous malformations were identified in 42% (8/19) of screened patients. 88% (23/26) and 81% (17/21) of patients exhibited JP and HHT features respectively, with 70% (14/20) demonstrating features of both conditions. We have shown that individuals with a pathogenic SMAD4 variant are all at high risk of both gastrointestinal neoplasia and HHT-related vascular complications, requiring a comprehensive screening programme., (© 2024. The Author(s).)

Abstract: For monogenic diseases caused by pathogenic loss-of-function DNA variants, attention focuses on dysregulated gene-specific pathways, usually considering molecular subtypes together within causal genes. To better understand phenotypic variability in hereditary hemorrhagic telangiectasia (HHT), we subcategorized pathogenic DNA variants in ENG/endoglin, ACVRL1/ALK1, and SMAD4 if they generated premature termination codons (PTCs) subject to nonsense-mediated decay. In 3 patient cohorts, a PTC-based classification system explained some previously puzzling hemorrhage variability. In blood outgrowth endothelial cells (BOECs) derived from patients with ACVRL1+/PTC, ENG+/PTC, and SMAD4+/PTC genotypes, PTC-containing RNA transcripts persisted at low levels (8%-23% expected, varying between replicate cultures); genes differentially expressed to Bonferroni P < .05 in HHT+/PTC BOECs clustered significantly only to generic protein terms (isopeptide-bond/ubiquitin-like conjugation) and pulse-chase experiments detected subtle protein maturation differences but no evidence for PTC-truncated protein. BOECs displaying highest PTC persistence were discriminated in unsupervised hierarchical clustering of near-invariant housekeeper genes, with patterns compatible with higher cellular stress in BOECs with >11% PTC persistence. To test directionality, we used a HeLa reporter system to detect induction of activating transcription factor 4 (ATF4), which controls expression of stress-adaptive genes, and showed that ENG Q436X but not ENG R93X directly induced ATF4. AlphaFold accurately modeled relevant ENG domains, with AlphaMissense suggesting that readthrough substitutions would be benign for ENG R93X and other less rare ENG nonsense variants but more damaging for Q436X. We conclude that PTCs should be distinguished from other loss-of-function variants, PTC transcript levels increase in stressed cells, and readthrough proteins and mechanisms provide promising research avenues., (© 2024 American Society of Hematology. Published by Elsevier Inc. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant form of vascular dysplasia. Genetic diagnosis is made by identifying loss-of-function variants in genes, such as ENG and ACVRL1. However, the causal mechanisms of various variants of unknown significance remains unclear. In this study, we analyzed 12 Japanese patients from 11 families who were clinically diagnosed with HHT. Sequencing analysis identified 11 distinct variants in ACVRL1 and ENG. Three of the 11 were truncating variants, leading to a definitive diagnosis, whereas the remaining eight were splice-site and missense variants that required functional analyses. In silico splicing analyses demonstrated that three variants, c.526-3C > G and c.598C > G in ACVRL1, and c.690-1G > A in ENG, caused aberrant splicing, as confirmed by a minigene assay. The five remaining missense variants were p.Arg67Gln, p.Ile256Asn, p.Leu285Pro, and p.Pro424Leu in ACVRL and p.Pro165His in ENG. Nanoluciferase-based bioluminescence analyses demonstrated that these ACVRL1 variants impaired cell membrane trafficking, resulting in the loss of bone morphogenetic protein 9 (BMP9) signal transduction. In contrast, the ENG mutation impaired BMP9 signaling despite normal cell membrane expression. The updated functional analysis methods performed in this study will facilitate effective genetic testing and appropriate medical care for patients with HHT., (© 2024 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Heterozygous activin receptor-like kinase 1 (ALK1) mutations are associated with two vascular diseases: hereditary hemorrhagic telangiectasia (HHT) and more rarely pulmonary arterial hypertension (PAH). Here, we aimed to understand the impact of ALK1 mutations on BMP9 and BMP10 transcriptomic responses in endothelial cells. Endothelial colony-forming cells (ECFCs) and microvascular endothelial cells (HMVECs) carrying loss of function ALK1 mutations were isolated from newborn HHT and adult PAH donors, respectively. RNA-sequencing was performed on each type of cells compared to controls following an 18 h stimulation with BMP9 or BMP10. In control ECFCs, BMP9 and BMP10 stimulations induced similar transcriptomic responses with around 800 differentially expressed genes (DEGs). ALK1-mutated ECFCs unexpectedly revealed highly similar transcriptomic profiles to controls, both at the baseline and upon stimulation, and normal activation of Smad1/5 that could not be explained by a compensation in cell-surface ALK1 level. Conversely, PAH HMVECs revealed strong transcriptional dysregulations compared to controls with > 1200 DEGs at the baseline. Consequently, because our study involved two variables, ALK1 genotype and BMP stimulation, we performed two-factor differential expression analysis and identified 44 BMP9-dysregulated genes in mutated HMVECs, but none in ECFCs. Yet, the impaired regulation of at least one hit, namely lunatic fringe (LFNG), was validated by RT-qPCR in three different ALK1-mutated endothelial models. In conclusion, ALK1 heterozygosity only modified the BMP9/BMP10 regulation of few genes, including LFNG involved in NOTCH signaling. Future studies will uncover whether dysregulations in such hits are enough to promote HHT/PAH pathogenesis, making them potential therapeutic targets, or if second hits are necessary., (© 2024. The Author(s).)

Background: Bone morphogenetic proteins 9 and 10 (BMP9 and BMP10), encoded by GDF2 and BMP10 , respectively, play a pivotal role in pulmonary vascular regulation. GDF2 variants have been reported in pulmonary arterial hypertension (PAH) and hereditary haemorrhagic telangiectasia (HHT). However, the phenotype of GDF2 and BMP10 carriers remains largely unexplored., Methods: We report the characteristics and outcomes of PAH patients in GDF2 and BMP10 carriers from the French and Dutch pulmonary hypertension registries. A literature review explored the phenotypic spectrum of these patients., Results: 26 PAH patients were identified: 20 harbouring heterozygous GDF2 variants, one homozygous GDF2 variant, four heterozygous BMP10 variants, and one with both GDF2 and BMP10 variants. The prevalence of GDF2 and BMP10 variants was 1.3% and 0.4%, respectively. Median age at PAH diagnosis was 30 years, with a female/male ratio of 1.9. Congenital heart disease (CHD) was present in 15.4% of the patients. At diagnosis, most of the patients (61.5%) were in New York Heart Association Functional Class III or IV with severe haemodynamic compromise (median (range) pulmonary vascular resistance 9.0 (3.3-40.6) WU). Haemoptysis was reported in four patients; none met the HHT criteria. Two patients carrying BMP10 variants underwent lung transplantation, revealing typical PAH histopathology. The literature analysis showed that 7.6% of GDF2 carriers developed isolated HHT, and identified cardiomyopathy and developmental disorders in BMP10 carriers., Conclusions: GDF2 and BMP10 pathogenic variants are rare among PAH patients, and occasionally associated with CHD. HHT cases among GDF2 carriers are limited according to the literature. BMP10 full phenotypic ramifications warrant further investigation., Competing Interests: Conflict of interest: H.J. Bogaard reports grants from Ferrer, MSD, Novartis, Dutch Cardiovascular Alliance and Janssen, and lecture honoraria from Janssen, outside the submitted work. L. Savale reports grants from Acceleron, AOP Orphan, Janssen, Merck and ShouTi, consulting fees from Acceleron, Bayer, Janssen and Merck, and lecture honoraria from Janssen and Merck, outside the submitted work. X. Jaïs reports grants from Acceleron, Janssen, MSD and Bayer Healthcare, lecture honoraria from Janssen and MSD, and travel support from MSD, outside the submitted work. L. Meijboom reports participation on an advisory board for Janssen, outside the submitted work. A. Chaouat reports consulting fees from Gossamer, lecture honoraria from Chiesi, travel support from AstraZeneca, MSD and J&J, outside the submitted work. V. Cottin reports consulting fees and lecture honoraria from Ferrer/United Therapeutics, outside the submitted work. C. Guignabert reports grants from Acceleron Pharma, MSD, Corterial pharmaceuticals, Structure Therapeutics (ex-ShouTi) and Janssen, and lecture honoraria from MSD, outside the submitted work. O. Sitbon reports grants from Acceleron (now MSD), AOP Orphan, Janssen (formerly Actelion) and MSD, consulting fees from Acceleron (now MSD), Altavant (now Enzyvant), AOP Orphan, Ferrer, Gossamer Bio, Janssen (formerly Actelion) and MSD, lecture honoraria from AOP Orphan, Janssen (formerly Actelion), Ferrer and MSD, and advisory board participation with Altavant (now Enzyvant), Gossamer Bio, Janssen (formerly Actelion) and MSD, outside the submitted work. D. Bonnet reports consulting fees from Janssen and Merck, and advisory board participation with Lupin, outside the submitted work. M. Humbert reports grants from Acceleron, AOP Orphan, Janssen, Merck and ShouTi, consulting fees from Acceleron, Aerovate, Altavant, AOP Orphan, Bayer, Chiesi, Ferrer, Janssen, Merck, MorphogenIX, ShouTi and United Therapeutics, lecture honoraria from Janssen and Merck, and advisory board participation with Acceleron, Altavant, Janssen, Merck and United Therapeutics, outside the submitted work. D. Montani reports grants from Acceleron, Janssen and Merck MSD, consulting fees from Acceleron, Janssen, Merck MSD and Ferrer, and lecture honoraria from Bayer, Janssen, Boehringer, Chiesi, GSK, Ferrer and Merck MSD, outside the submitted work. The remaining authors have no potential conflicts of interest to disclose., (Copyright ©The authors 2024. For reproduction rights and permissions contact permissions@ersnet.org.)

Osler-Weber-Rendu syndrome or Hereditary Haemorrhagic Telangiectasia (HHT) is a rare condition, with very few reported cases, especially in Pakistan. As healthcare workers, we encounter multiple cases of recurrent epistaxis in the emergency as well as outpatient departments. However, patients are usually treated symptomatically without a thorough workup. HHT should be considered among the differentials for recurrent epistaxis, as a clinical diagnosis can be made with detailed family history and physical examination. Here is the case of a 58-year-old male who presented to the Gastroenterology OPD, Combined Military Hospital, Lahore, in November 2021, with complaints of generalised weakness and blood in stools. He had a history of recurrent epistaxis and telangiectasias, and further inquiry revealed a strong family history of similar symptoms. He was diagnosed as a case of Osler-Weber- Rendu Syndrome. Informed consent was taken from the patient prior to the writing of the manuscript.

Hereditary hemorrhagic telangiectasia (HHT), also known as Rendu-Osler-Weber disease, is a dominant inherited vascular disorder. The clinical diagnosis is based on the Curaçao criteria and pathogenic variants in the ENG and ACVRL1 genes are responsible for most cases of HHT. Four families with a negative targeted gene panel and selected by a multidisciplinary team were selected and whole-genome sequencing was performed according to the recommendations of the French National Plan for Genomic Medicine. Structural variations were confirmed by standard molecular cytogenetic analysis (FISH). In two families with a definite diagnosis of HHT, we identified two different paracentric inversions of chromosome 9, both disrupting the ENG gene. These inversions are considered as pathogenic and causative for the HHT phenotype of the patients. This is the first time structural variations are reported to cause HHT. As such balanced events are often missed by exon-based sequencing (panel, exome), structural variations may be an under-recognized cause of HHT. Genome sequencing for the detection of these events could be suggested for patients with a definite diagnosis of HHT and in whom no causative pathogenic variant was identified., (Copyright © 2024 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Hereditary hemorrhagic telangiectasia (HHT), also known as Osler-Rendu-Weber syndrome, is a rare autosomal dominant disorder characterized by vascular malformations. This comprehensive review aimed to provide an overview and summarize various aspects of HHT, including the genetic abnormalities, complications associated with visceral arteriovenous malformations (AVMs), prognosis of HHT, quality of life (QOL), and treatment of epistaxis. In addition, this review highlights the challenges in diagnosing HHT and emphasizes the critical role of otolaryngologists in the early detection of HHT. Otolaryngologists can refer patients with refractory epistaxis for AVM screening to expedite intervention. Mutation of the genes involved in the transforming growth factor-β signaling pathway leads to the incidence of HHT, resulting in the formation of abnormal blood vessel formation. These vascular malformations commonly manifest as telangiectasia on the skin and mucous membranes; however, epistaxis remains the hallmark symptom of HHT. The impact of HHT goes beyond the visible symptoms and often includes the formation of life-threatening visceral AVMs in the lungs, liver, and brain. The prognosis of patients with HHT is closely related to the development of these complications, necessitating timely diagnosis and intervention. Refractory epistaxis diminishes the QOL of patients with HHT. The management of epistaxis ranges from conservative measures to advanced interventions such as prevention, conservative treatments, ablation, surgical procedures, and the administration of anti-angiogenic agents. However, effective management requires a multidisciplinary approach. The diagnosis of HHT remains challenging due to its variable presentation and lack of awareness among physicians. This review highlights the importance of reducing the duration between symptom onset and diagnosis. Otolaryngologists who are experienced in the management of refractory epistaxis can aid in identifying potential cases of HHT. They can facilitate the initiation of screening for visceral AVMs via prompt recognition of the signs and symptoms of HHT, contributing to improved patient outcomes. Early detection and intervention through screening can extend the life expectancy of patients with HHT to levels comparable with that of the general population. In conclusion, this review provides insight into various aspects of HHT and emphasizes the importance of timely diagnosis and intervention in the mitigation of the potentially life-threatening complications associated with this disorder. Otolaryngologists play a critical role in this process, serving as gatekeepers to the identification of cases of HHT and implementation of appropriate screening and management pathways, thereby improving the life expectancy and QOL of patients., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflict of interest., (Copyright © 2023. Published by Elsevier B.V.)

Background: Distinct endothelial cell cycle states (early G1 versus late G1) provide different "windows of opportunity" to enable the differential expression of genes that regulate venous versus arterial specification, respectively. Endothelial cell cycle control and arteriovenous identities are disrupted in vascular malformations including arteriovenous shunts, the hallmark of hereditary hemorrhagic telangiectasia (HHT). To date, the mechanistic link between endothelial cell cycle regulation and the development of arteriovenous malformations (AVMs) in HHT is not known., Methods: We used BMP (bone morphogenetic protein) 9/10 blocking antibodies and endothelial-specific deletion of activin A receptor like type 1 ( Alk1 ) to induce HHT in Fucci (fluorescent ubiquitination-based cell cycle indicator) 2 mice to assess endothelial cell cycle states in AVMs. We also assessed the therapeutic potential of inducing endothelial cell cycle G1 state in HHT to prevent AVMs by repurposing the Food and Drug Administration-approved CDK (cyclin-dependent kinase) 4/6 inhibitor (CDK4/6i) palbociclib., Results: We found that endothelial cell cycle state and associated gene expressions are dysregulated during the pathogenesis of vascular malformations in HHT. We also showed that palbociclib treatment prevented AVM development induced by BMP9/10 inhibition and Alk1 genetic deletion. Mechanistically, endothelial cell late G1 state induced by palbociclib modulates the expression of genes regulating arteriovenous identity, endothelial cell migration, metabolism, and VEGF-A (vascular endothelial growth factor A) and BMP9 signaling that collectively contribute to the prevention of vascular malformations., Conclusions: This study provides new insights into molecular mechanisms leading to HHT by defining how endothelial cell cycle is dysregulated in AVMs because of BMP9/10 and Alk1 signaling deficiencies, and how restoration of endothelial cell cycle control may be used to treat AVMs in patients with HHT., Competing Interests: None.

Hereditary hemorrhagic telangiectasia (HHT), also called Rendu-Osler syndrome, is a group of rare genetic diseases characterized by autosomal dominance, multisystemic vascular dysplasia, and age-related penetrance. This includes arteriovenous malformations (AVMs) in the skin, brain, lung, liver, and mucous membranes. The correlations between the phenotype and genotype for HHT are not clear. An HHT Chinese pedigree was recruited. Whole exome sequencing (WES) analysis, Sanger verification, and co-segregation were conducted. Western blotting was performed for monitoring ENG/VEGFα signaling. As a result, a nonsense, heterozygous variant for ENG/CD105: c.G1169A:p. Trp390Ter of the proband with hereditary hemorrhagic telangiectasia type 1 (HHT1) was identified, which co-segregated with the disease in the M666 pedigree. Western blotting found that, compared with the normal levels associated with non-carrier family members, the ENG protein levels in the proband showed approximately a one-half decrease (47.4% decrease), while levels of the VEGFα protein, in the proband, showed approximately a one-quarter decrease (25.6% decrease), implying that ENG haploinsufficiency, displayed in the carrier of this variant, may affect VEGFα expression downregulation. Pearson and Spearman correlation analyses further supported TGFβ/ENG/VEGFα signaling, implying ENG regulation in the blood vessels. Thus, next-generation sequencing including WES should provide an accurate strategy for gene diagnosis, therapy, genetic counseling, and clinical management for rare genetic diseases including that in HHT1 patients.

Hereditary hemorrhagic telangiectsia (HHT) is an inherited vascular disorder with highly variable expressivity, affecting up to 1 in 5,000 individuals. This disease is characterized by small arteriovenous malformations (AVMs) in mucocutaneous areas (telangiectases) and larger visceral AVMs in the lungs, liver, and brain. HHT is caused by loss-of-function mutations in the BMP9-10/ENG/ALK1/SMAD4 signaling pathway. This Review presents up-to-date insights on this mutated signaling pathway and its crosstalk with proangiogenic pathways, in particular the VEGF pathway, that has allowed the repurposing of new drugs for HHT treatment. However, despite the substantial benefits of these new treatments in terms of alleviating symptom severity, this not-so-uncommon bleeding disorder still currently lacks any FDA- or European Medicines Agency-approved (EMA-approved) therapies.

Endothelial cells (ECs) respond to concurrent stimulation by biochemical factors and wall shear stress (SS) exerted by blood flow. Disruptions in flow-induced responses can result in remodeling issues and cardiovascular diseases, but the detailed mechanisms linking flow-mechanical cues and biochemical signaling remain unclear. Activin receptor-like kinase 1 (ALK1) integrates SS and ALK1-ligand cues in ECs; ALK1 mutations cause hereditary hemorrhagic telangiectasia (HHT), marked by arteriovenous malformation (AVM) development. However, the mechanistic underpinnings of ALK1 signaling modulation by fluid flow and the link to AVMs remain uncertain. We recorded EC responses under varying SS magnitudes and ALK1 ligand concentrations by assaying pSMAD1/5/9 nuclear localization using a custom multi-SS microfluidic device and a custom image analysis pipeline. We extended the previously reported synergy between SS and BMP9 to include BMP10 and BMP9/10. Moreover, we demonstrated that this synergy is effective even at extremely low SS magnitudes (0.4 dyn/cm 2 ) and ALK1 ligand range (femtogram/mL). The synergistic response to ALK1 ligands and SS requires the kinase activity of ALK1. Moreover, ALK1's basal activity and response to minimal ligand levels depend on endocytosis, distinct from cell-cell junctions, cytoskeleton-mediated mechanosensing, or cholesterol-enriched microdomains. However, an in-depth analysis of ALK1 receptor trafficking's molecular mechanisms requires further investigation.

Competing Interests: Competing interests: None declared.

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disorder affecting 1 in 5000-8000 individuals. Hereditary hemorrhagic telangiectasia type 1 (HHT1) is the most common HHT and manifests as diverse vascular malformations ranging from mild symptoms such as epistaxis and mucosal and cutaneous telangiectases to severe arteriovenous malformations (AVMs) in the lungs, brain or liver. HHT1 is caused by heterozygous mutations in the ENG gene, which encodes endoglin, the TGFβ homodimeric co-receptor. It was previously shown that some endoglin HHT1-causing variants failed to traffic to the plasma membrane due to their retention in the endoplasmic reticulum (ER) and consequent degradation by ER-associated degradation (ERAD). Endoglin is a homodimer formed in the ER, and we therefore hypothesized that mixed heterodimers might form between ER-retained variants and WT protein, thus hampering its maturation and trafficking to the plasma membrane causing dominant negative effects. Indeed, HA-tagged ER-retained mutants formed heterodimers with Myc-tagged WT endoglin. Moreover, variants L32R, V105D, P165L, I271N and C363Y adversely affected the trafficking of WT endoglin by reducing its maturation and plasma membrane localization. These results strongly suggest dominant negative effects exerted by these ER-retained variants aggravating endoglin loss of function in patients expressing them in the heterozygous state with the WT allele. Moreover, this study may help explain some of the variability observed among HHT1 patients due to the additional loss of function exerted by the dominant negative effects in addition to that due to haploinsufficiency. These findings might also have implications for some of the many conditions impacted by ERAD., (© 2024 The Authors. Traffic published by John Wiley & Sons Ltd.)

Purpose: Hereditary hemorrhagic telangiectasia (HHT) is a dominantly inherited disorder that involves epistaxis, mucocutaneous telangiectases, and visceral arteriovenous malformations (AVMs). This study aims to investigate the genetic causes in a Chinese family with HHT., Methods: HHT was confirmed according to Curaçao's diagnostic criteria. Three patients diagnosed with HHT and healthy members were recruited. Whole-exome sequencing (WES) and sanger sequencing were performed to define the patient's genetically pathogenic factor., Results: The proband presented with recurrent epistaxis, hepatopulmonary arteriovenous malformation, and adenocarcinoma. A novel frameshift mutation (c.1376&#95;1377delAC, p.H459Lfs*41) of the ENG gene was revealed in affected individuals by WES. There was no report of this variant and predicted to be highly damaging by causing truncation of the ENG protein., Conclusion: We report a novel variant in the ENG gene in Chinese that extends the mutational and phenotypic spectra of the ENG gene, and also demonstrates the feasibility of WES in the application of genetic diagnosis of HHT., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Background: Hereditary hemorrhagic telangiectasia (HHT) is a rare vascular disease inherited in an autosomal dominant manner. Disease-causing variants in endoglin (ENG) and activin A receptor type II-like 1 (ACVRL1) genes are detected in around 90% of the patients; also 2% of patients harbor pathogenic variants at SMAD4 and GDF2. Importantly, the genetic cause of 8% of patients with clinical HHT remains unknown. Here, we present new putative genetic drivers of HHT., Methods: To identify new HHT genetic drivers, we performed exome sequencing of 19 HHT patients and relatives with unknown HHT genetic etiology. We applied a multistep filtration strategy to catalog deleterious variants and prioritize gene candidates based on their known relevance in endothelial cell biology. Additionally, we performed in vitro validation of one of the identified variants., Results: We identified variants in the INHA, HIF1A, JAK2, DNM2, POSTN, ANGPTL4, FOXO1 and SMAD6 genes as putative drivers in HHT. We have identified the SMAD6 p.(Glu407Lys) variant in one of the families; this is a loss-of-function variant leading to the activation of the BMP/TGFβ signaling in endothelial cells., Conclusions: Variants in these genes should be considered for genetic testing in patients with HHT phenotype and negative for ACVRL1/ENG mutations., Competing Interests: Declaration of Competing Interest Authors declare that they have no conflict of interest., (Copyright © 2023. Published by Elsevier B.V.)