Identification and validation of a novel pathogenic variant in GDF2 (BMP9) responsible for hereditary hemorrhagic telangiectasia and pulmonary arteriovenous malformations

Cracking the code of the cardiovascular enigma: hPSC-derived endothelial cells unveil the secrets of endothelial dysfunction

Endothelial dysfunction is a central contributor to the development of most cardiovascular diseases and is characterised by the reduced synthesis or bioavailability of the vasodilator nitric oxide together with other abnormalities such as inflammation, senescence, and oxidative stress. The use of patient-specific and genome-edited human pluripotent stem cell-derived endothelial cells (hPSC-ECs) has shed novel insights into the role of endothelial dysfunction in cardiovascular diseases with strong genetic components such as genetic cardiomyopathies and pulmonary arterial hypertension. However, their utility in studying complex multifactorial diseases such as atherosclerosis, metabolic syndrome and heart failure poses notable challenges. In this review, we provide an overview of the different methods used to generate and characterise hPSC-ECs before comprehensively assessing their effectiveness in cardiovascular disease modelling and high-throughput drug screening. Furthermore, we explore current obstacles that will need to be overcome to unleash the full potential of hPSC-ECs in facilitating patient-specific precision medicine. Addressing these challenges holds great promise in advancing our understanding of intricate cardiovascular diseases and in tailoring personalised therapeutic strategies.

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

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

Hereditary hemorrhagic telangiectasia: from signaling insights to therapeutic advances

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.

Medical Management and Therapeutic Updates on Vascular Anomalies of the Head and Neck: Part 2

Discovery of inherited and somatic genetic mutations, along with advancements in clinical and scientific research, has improved understanding of vascular anomalies and changed the treatment paradigm. With aim of minimizing need for invasive procedures and improving disease outcomes, molecularly targeted medications and anti-angiogenesis agents have become important as both adjuncts to surgery, and increasingly, as the primary treatment of vascular anomalies. This article highlights the commonly used and emerging therapeutic medications for non-malignant vascular tumors and vascular malformations in addition to medical management of associated hematologic abnormalities.

Pathogenic Variant Frequencies in Hereditary Haemorrhagic Telangiectasia Support Clinical Evidence of Protection from Myocardial Infarction

Hereditary haemorrhagic telangiectasia (HHT) is a vascular dysplasia inherited as an autosomal dominant trait, due to a single heterozygous loss-of-function variant, usually in ACVRL1 (encoding activin receptor-like kinase 1 [ALK1]), ENG (encoding endoglin [CD105]), or SMAD4. In a consecutive single-centre series of 37 positive clinical genetic tests performed in 2021-2023, a skewed distribution pattern was noted, with 30 of 32 variants reported only once, but ACVRL1 c.1231C>T (p.Arg411Trp) identified as the disease-causal gene in five different HHT families. In the same centre's non-overlapping 1992-2020 series where 110/134 (82.1%) HHT-causal variants were reported only once, ACVRL1 c.1231C>T (p.Arg411Trp) was identified in nine further families. In a 14-country, four-continent HHT Mutation Database where 181/250 (72.4%) HHT-causal variants were reported only once, ACVRL1 c.1231C>T (p.Arg411Trp) was reported by 12 different laboratories, the adjacent ACVRL1 c.1232G>A (p.Arg411Gln) by 14, and ACVRL1 c.1120C>T (p.Arg374Trp) by 18. Unlike the majority of HHT-causal ACVRL1 variants, these encode ALK1 protein that reaches the endothelial cell surface but fails to signal. Six variants of this type were present in the three series and were reported 6.8-25.5 (mean 8.9) times more frequently than the other ACVRL1 missense variants (all p-values < 0.0039). Noting lower rates of myocardial infarction reported in HHT, we explore potential mechanisms, including a selective paradigm relevant to ALK1's role in the initiating event of atherosclerosis, where a plausible dominant negative effect of these specific variants can be proposed. In conclusion, there is an ~9-fold excess of kinase-inactive, cell surface-expressed ACVRL1/ALK1 pathogenic missense variants in HHT. The findings support further examination of differential clinical and cellular phenotypes by HHT causal gene molecular subtypes.

Functional filter for whole-genome sequencing data identifies HHT and stress-associated non-coding SMAD4 polyadenylation site variants >5 kb from coding DNA

Despite whole-genome sequencing (WGS), many cases of single-gene disorders remain unsolved, impeding diagnosis and preventative care for people whose disease-causing variants escape detection. Since early WGS data analytic steps prioritize protein-coding sequences, to simultaneously prioritize variants in non-coding regions rich in transcribed and critical regulatory sequences, we developed GROFFFY, an analytic tool that integrates coordinates for regions with experimental evidence of functionality. Applied to WGS data from solved and unsolved hereditary hemorrhagic telangiectasia (HHT) recruits to the 100,000 Genomes Project, GROFFFY-based filtration reduced the mean number of variants/DNA from 4,867,167 to 21,486, without deleting disease-causal variants. In three unsolved cases (two related), GROFFFY identified ultra-rare deletions within the 3' untranslated region (UTR) of the tumor suppressor SMAD4, where germline loss-of-function alleles cause combined HHT and colonic polyposis (MIM: 175050). Sited >5.4 kb distal to coding DNA, the deletions did not modify or generate microRNA binding sites, but instead disrupted the sequence context of the final cleavage and polyadenylation site necessary for protein production: By iFoldRNA, an AAUAAA-adjacent 16-nucleotide deletion brought the cleavage site into inaccessible neighboring secondary structures, while a 4-nucleotide deletion unfolded the downstream RNA polymerase II roadblock. SMAD4 RNA expression differed to control-derived RNA from resting and cycloheximide-stressed peripheral blood mononuclear cells. Patterns predicted the mutational site for an unrelated HHT/polyposis-affected individual, where a complex insertion was subsequently identified. In conclusion, we describe a functional rare variant type that impacts regulatory systems based on RNA polyadenylation. Extension of coding sequence-focused gene panels is required to capture these variants.

Defining the clinical validity of genes reported to cause pulmonary arterial hypertension

PURPOSE

Pulmonary arterial hypertension (PAH) is a rare, progressive vasculopathy with significant cardiopulmonary morbidity and mortality. Genetic testing is currently recommended for adults diagnosed with heritable, idiopathic, anorexigen-, hereditary hemorrhagic telangiectasia-, and congenital heart disease-associated PAH, PAH with overt features of venous/capillary involvement, and all children diagnosed with PAH. Variants in at least 27 genes have putative evidence for PAH causality. Rigorous assessment of the evidence is needed to inform genetic testing.

METHODS

An international panel of experts in PAH applied a semi-quantitative scoring system developed by the NIH Clinical Genome Resource to classify the relative strength of evidence supporting PAH gene-disease relationships based on genetic and experimental evidence.

RESULTS

Twelve genes (BMPR2, ACVRL1, ATP13A3, CAV1, EIF2AK4, ENG, GDF2, KCNK3, KDR, SMAD9, SOX17, and TBX4) were classified as having definitive evidence and 3 genes (ABCC8, GGCX, and TET2) with moderate evidence. Six genes (AQP1, BMP10, FBLN2, KLF2, KLK1, and PDGFD) were classified as having limited evidence for causal effects of variants. TOPBP1 was classified as having no known PAH relationship. Five genes (BMPR1A, BMPR1B, NOTCH3, SMAD1, and SMAD4) were disputed because of a paucity of genetic evidence over time.

CONCLUSION

We recommend that genetic testing includes all genes with definitive evidence and that caution be taken in the interpretation of variants identified in genes with moderate or limited evidence. Genes with no known evidence for PAH or disputed genes should not be included in genetic testing.

Hereditary hemorrhagic telangiectasia involving portal venous system: A case report and review of the literature

BACKGROUND

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant genetic disorder with an incidence of approximately 1 in 5000 in the general population. It is characterized by vasodilation, which affects specific organs, such as the skin, mucous membranes, brain, lungs, gastrointestinal tract, liver, and others. However, HHT rarely involves the portal venous system to cause serious clinical complications.

CASE SUMMARY

A 68-year-old woman was admitted to the emergency department due to four consecutive days of abdominal pain and bloody stool and was subsequently diagnosed with HHT. Computed tomography angiography confirmed the presence of an arteriovenous fistula (AVFs). Considering this specific manifestation, whole exome sequencing was performed. After a comprehensive evaluation, a selective superior mesenteric artery embolization was prioritized to avoid intestinal ischemia. The postoperative symptoms of the patient were quickly relieved. Unfortunately, two months post-procedure the patient died from intestinal necrosis and abdominal infection related to remaining AVFs.

CONCLUSION

For patients with diffuse superior mesenteric AVFs, selective mesenteric arterial embolization may lead to positive short-term outcomes.

The Role and Therapeutic Implications of Inflammation in the Pathogenesis of Brain Arteriovenous Malformations

Brain arteriovenous malformations (bAVMs) are focal vascular lesions composed of abnormal vascular channels without an intervening capillary network. As a result, high-pressure arterial blood shunts directly into the venous outflow system. These high-flow, low-resistance shunts are composed of dilated, tortuous, and fragile vessels, which are prone to rupture. BAVMs are a leading cause of hemorrhagic stroke in children and young adults. Current treatments for bAVMs are limited to surgery, embolization, and radiosurgery, although even these options are not viable for ~20% of AVM patients due to excessive risk. Critically, inflammation has been suggested to contribute to lesion progression. Here we summarize the current literature discussing the role of the immune system in bAVM pathogenesis and lesion progression, as well as the potential for targeting inflammation to prevent bAVM rupture and intracranial hemorrhage. We conclude by proposing that a dysfunctional endothelium, which harbors the somatic mutations that have been shown to give rise to sporadic bAVMs, may drive disease development and progression by altering the immune status of the brain.

uAUG creating variants in the 5'UTR of ENG causing Hereditary Hemorrhagic Telangiectasia

Hereditary Hemorrhagic Telangiectasia (HHT) is a rare, autosomal dominant, vascular disorder. About 80% of cases are caused by pathogenic variants in ACVRL1 (also known as ALK1) and ENG, with the remaining cases being unexplained. We identified two variants, c.-79C>T and c.-68G>A, in the 5'UTR of ENG in two unrelated patients. They create upstream AUGs at the origin of upstream overlapping open reading frames (uoORFs) ending at the same stop codon. To assess the pathogenicity of these variants, we performed functional assays based on the expression of wild-type and mutant constructs in human cells and evaluated their effect on ALK1 activity in a BMP-response element assay. This assay is mandatory for molecular diagnosis and has been so far only applied to coding ENG variants. These variants were associated with a decrease of protein levels in HeLa and HUVEC cells and a decreased ability to activate ALK1. We applied the same experiments on three additional uoORF-creating variants (c.-142A>T, c.-127C>T and c.-10C>T) located in the 5'UTR of ENG and previously reported in HHT patients. We found that all the analyzed variants alter protein levels and function. Additional experiments relying on an artificial deletion in our mutated constructs show that identified uAUGs could initiate the translation indicating that the associated effect is translation-dependent. Overall, we have identified two 5'UTR ENG variations in HHT patients and shed new light on the role of upstream ORFs on ENG regulation. Our findings contribute to the amelioration of molecular diagnosis in HHT.

TGF-β signaling in health and disease

The TGF-β regulatory system plays crucial roles in the preservation of organismal integrity. TGF-β signaling controls metazoan embryo development, tissue homeostasis, and injury repair through coordinated effects on cell proliferation, phenotypic plasticity, migration, metabolic adaptation, and immune surveillance of multiple cell types in shared ecosystems. Defects of TGF-β signaling, particularly in epithelial cells, tissue fibroblasts, and immune cells, disrupt immune tolerance, promote inflammation, underlie the pathogenesis of fibrosis and cancer, and contribute to the resistance of these diseases to treatment. Here, we review how TGF-β coordinates multicellular response programs in health and disease and how this knowledge can be leveraged to develop treatments for diseases of the TGF-β system.

Novel vascular roles of human endoglin in pathophysiology

Endoglin, alias CD105, is a human membrane glycoprotein highly expressed in vascular endothelial cells. It is involved in angiogenesis and angiogenesis-related diseases, including the rare vascular pathology known as hereditary hemorrhagic telangiectasia type 1. Although endoglin acts as an accessory receptor for members of the transforming growth factor-β family, in recent years, emerging evidence has shown a novel functional role for this protein beyond the transforming growth factor-β system. In fact, endoglin has been found to be an integrin counterreceptor involved in endothelial cell adhesion processes during pathological inflammatory conditions and primary hemostasis. Furthermore, a circulating form of endoglin, also named as soluble endoglin, whose levels are abnormally increased in different pathological conditions, such as preeclampsia, seems to act as an antagonist of membrane-bound endoglin and as a competitor of the fibrinogen-integrin interaction in platelet-dependent thrombus formation. These studies suggest that membrane-bound endoglin and circulating endoglin are important components involved in vascular homeostasis and hemostasis.

[Hereditary hemorrhagic telangiectasia]

Hereditary hemorrhagic telangiectasia, also known as Rendu-Osler - Weber disease, is a rare, autosomal dominant vascular disease, with prevalence of 1/5,000. The condition is characterized by muco-cutaneous telangiectasias, which are responsible for a hemorrhagic syndrome of variable severity, as well as arteriovenous malformations (AVMs) appearing in the lungs, the liver, and the nervous system. They can be the source of shunts, which may be associated with high morbidity (neurological ischemic stroke, brain abscess, high-output heart failure, biliary ischemia…). It is therefore crucial to establish a clinical diagnosis using the Curaçao criteria or molecular diagnosis based on genetic analysis of the ENG, ACVRL1, SMAD4 and GDF2 genes. In most cases, multidisciplinary management allows patients to have normal life expectancy. Advances in interventional radiology and better understanding of the pathophysiology of angiogenesis have resulted in improved therapeutic management. Anti-angiogenic treatments, such as bevacizumab (BVZ, an anti-VEGF antibody), have proven to be effective in cases involving bleeding complications and severe liver damage with cardiac repercussions. Other anti-angiogenic agents are currently being investigated, including tyrosine kinase inhibitors.

Genetics of brain arteriovenous malformations and cerebral cavernous malformations

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

[Dysfunction of endothelial BMP-9 signaling in pulmonary vascular disease]

The signaling pathway of the bone morphogenetic protein (BMP)-9 binding to the endothelial receptor BMP receptor type II (BMPR-II), activin receptor-like kinase-1 (ALK1) and the coreceptor endoglin is essential to maintain the pulmonary vascular integrity. Dysregulation of this pathway is implicated in numerous vascular diseases, such as pulmonary arterial hypertension (PAH), hereditary hemorrhagic telangiectasia (HHT) and hepatopulmonary syndrome (HPS). This article aims to provide a comprehensive review of the implication of the BMP-9/BMPR-II/ALK1/endoglin pathway in the pathophysiology of these diseases.

A GDF2 missense mutation potentially involved in the pathogenesis of hereditary hemorrhagic telangiectasia: a case report

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant vascular disease. ENG and ACVRL1 gene variants account for up to 96% of all cases, while the remaining cases are caused by SMAD4 or GDF2 variants, or by currently undiscovered mutations in coding or non-coding regions. Here, we report a 47-year-old man who presented with duodenal bulb bleeding and chronic anemia. Physical examination also revealed bleeding from the skin and gingiva. His parents were cousins and one brother and one sister died in infancy from anemia and bleeding. Head computed tomography angiography (CTA) revealed a complete fetal posterior cerebral artery located in the left side, and pulmonary CTA showed pulmonary arterial hypertension. The patient was diagnosed with HHT. Peripheral blood was collected for whole-exome sequencing. Sequencing revealed a mutation in the GDF2 gene, which encodes bone morphogenetic protein-9 (BMP-9). The detected variant, c.352A > T(p.Ile118Phe), was predicted to be a neutral polymorphism; however, the patient's plasma BMP-9 levels were greatly reduced; we predicted that this might be caused by the GDF2 variant and might be involved in the HHT pathogenesis. Further research in cell lines and animal models is needed to verify the correlation between this GDF2 variant and the pathogenesis of HHT.

BMP10 functions independently from BMP9 for the development of a proper arteriovenous network

Hereditary hemorrhagic telangiectasia (HHT) is a genetic vascular disorder characterized by the presence of arteriovenous malformation (AVM) in multiple organs. HHT is caused by mutations in genes encoding major constituents for transforming growth factor-β (TGF-β) family signaling: endoglin (ENG), activin receptor-like kinase 1 (ALK1), and SMAD4. The identity of physiological ligands for this ENG-ALK1 signaling pertinent to AVM formation has yet to be clearly determined. To investigate whether bone morphogenetic protein 9 (BMP9), BMP10, or both are physiological ligands of ENG-ALK1 signaling involved in arteriovenous network formation, we generated a novel Bmp10 conditional knockout mouse strain. We examined whether global Bmp10-inducible knockout (iKO) mice develop AVMs at neonatal and adult stages in comparison with control, Bmp9-KO, and Bmp9/10-double KO (dKO) mice. Bmp10-iKO and Bmp9/10-dKO mice showed AVMs in developing retina, postnatal brain, and adult wounded skin, while Bmp9-KO did not display any noticeable vascular defects. Bmp10 deficiency resulted in increased proliferation and size of endothelial cells in AVM vessels. The impaired neurovascular integrity in the brain and retina of Bmp10-iKO and Bmp9/10-dKO mice was detected. Bmp9/10-dKO mice exhibited the lethality and vascular malformation similar to Bmp10-iKO mice, but their phenotypes were more pronounced. Administration of BMP10 protein, but not BMP9 protein, prevented retinal AVM in Bmp9/10-dKO and endothelial-specific Eng-iKO mice. These data indicate that BMP10 is indispensable for the development of a proper arteriovenous network, whereas BMP9 has limited compensatory functions for the loss of BMP10. We suggest that BMP10 is the most relevant physiological ligand of the ENG-ALK1 signaling pathway pertinent to HHT pathogenesis.

Insights into bone morphogenetic proteins in cardiovascular diseases

Bone morphogenetic proteins (BMPs) are secretory proteins belonging to the transforming growth factor-β (TGF-β) superfamily. These proteins play important roles in embryogenesis, bone morphogenesis, blood vessel remodeling and the development of various organs. In recent years, as research has progressed, BMPs have been found to be closely related to cardiovascular diseases, especially atherosclerosis, vascular calcification, cardiac remodeling, pulmonary arterial hypertension (PAH) and hereditary hemorrhagic telangiectasia (HHT). In this review, we summarized the potential roles and related mechanisms of the BMP family in the cardiovascular system and focused on atherosclerosis and PAH.

A rare homozygous missense GDF2 (BMP9) mutation causing PAH in siblings: Does BMP10 status contribute?

Pulmonary arterial hypertension (PAH) is a disease characterized by pathological remodeling of the pulmonary vasculature causing elevated pulmonary artery pressures and ultimately, right ventricular failure from chronic pressure overload. Heterozygous pathogenic GDF2 (encoding bone morphogenetic protein 9 (BMP9)) variants account for some (>1%) adult PAH cases. Only three pediatric PAH cases, harboring homozygous or compound heterozygous variants, are reported to date. Ultra-rare pathogenic GDF2 variants are reported in hereditary hemorrhagic telangiectasia and overlapping disorders characterized by telangiectasias and arteriovenous malformations (AVMs). Here, we present two siblings with PAH homozygous for a GDF2 mutation that impairs BMP9 proprotein processing and reduces growth factor domain availability. We confirm an absence of measurable plasma BMP9 whereas BMP10 levels are detectable and serum-dependent endothelial BMP activity is evident. This contrasts with the absence of activity which we reported in two children with homozygous pathogenic GDF2 nonsense variants, one with PAH and one with pulmonary AVMs, both with telangiectasias, suggesting loss of BMP10 and endothelial BMP activity in the latter may precipitate telangiectasia development. An absence of phenotype in related heterozygous GDF2 variant carriers suggests incomplete penetrance in PAH and AVM-related diseases, indicating that additional somatic and/or genetic modifiers may be necessary for disease precipitation.

Computational analysis of prodomain cysteines in human TGF-β proteins reveals frequent loss of disulfide-dependent regulation in tumors

The functionally diverse members of the human Transforming Growth Factor-β (TGF-β) family are tightly regulated. TGF-β regulation includes 2 disulfide-dependent mechanisms-dimerization and partner protein binding. The specific cysteines participating in these regulatory mechanisms are known in just 3 of the 33 human TGF-β proteins. Human prodomain alignments revealed that 24 TGF-β prodomains contain conserved cysteines in 2 highly exposed locations. There are 3 in the region of the β8 helix that mediates dimerization near the prodomain carboxy terminus. There are 2 in the Association region that mediates partner protein binding near the prodomain amino terminus. The alignments predict the specific cysteines contributing to disulfide-dependent regulation of 72% of human TGF-β proteins. Database mining then identified 9 conserved prodomain cysteine mutations and their disease phenotypes in 7 TGF-β proteins. Three common adenoma phenotypes for prodomain cysteine mutations suggested 7 new regulatory heterodimer pairs. Two common adenoma phenotypes for prodomain and binding partner cysteine mutations revealed 17 new regulatory interactions. Overall, the analysis of human TGF-β prodomains suggests a significantly expanded scope of disulfide-dependent regulation by heterodimerization and partner protein binding; regulation that is often lost in tumors.

Endothelial cilia dysfunction in pathogenesis of hereditary hemorrhagic telangiectasia

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

Case report: Conquer a complex variant: Coronary-pulmonary artery fistulas, atrial septal defect and bicuspid pulmonary valve, under beating heart surgery

Coronary artery to pulmonary artery fistula (CPAF) is a congenital or acquired abnormal channel between arteries, with a left-to-right cardiac shunting, which may lead to myocardial ischemia, arrhythmia, thrombotic complications, and heart failure. CPAF is usually detected by coronary angiography but few reports have used beating-heart surgery as a detection method. The patient in this case report is a 39-year-old male diagnosed with atrial septal defect (ASD), bicuspid pulmonary valve, and moderate tricuspid regurgitation (TR). He is asymptomatic. In preoperative evaluation, significant CPAF was suspected using echocardiography. The patient refused coronary angiography due to allergic history. Therefore, the cardiac team designed and performed on-pump beating-heart surgery (OPBHS) to detect and repair these disorders, and suggested OPBHS as a myocardial protection strategy for the patient at low surgical risk. A rare and complex cardiovascular case with CPAFs from two branches of the left anterior descending coronary (LAD) artery to the main pulmonary artery (MPA) with ASD, bicuspid pulmonary valve, and moderate TR has not yet been reported in the literature, and its embryological hypothesis has been further analyzed in this report.

An update on preclinical models of hereditary haemorrhagic telangiectasia: Insights into disease mechanisms

Endoglin (ENG) is expressed on the surface of endothelial cells (ECs) where it efficiently binds circulating BMP9 and BMP10 ligands to initiate activin A receptor like type 1 (ALK1) protein signalling to protect the vascular architecture. Patients heterozygous for ENG or ALK1 mutations develop the vascular disorder known as hereditary haemorrhagic telangiectasia (HHT). Many patients with this disorder suffer from anaemia, and are also at increased risk of stroke and high output heart failure. Recent work using animal models of HHT has revealed new insights into cellular and molecular mechanisms causing this disease. Loss of the ENG (HHT1) or ALK1 (HHT2) gene in ECs leads to aberrant arteriovenous connections or malformations (AVMs) in developing blood vessels. Similar phenotypes develop following combined EC specific loss of SMAD1 and 5, or EC loss of SMAD4. Taken together these data point to the essential role of the BMP9/10-ENG-ALK1-SMAD1/5-SMAD4 pathway in protecting the vasculature from AVMs. Altered directional migration of ECs in response to shear stress and increased EC proliferation are now recognised as critical factors driving AVM formation. Disruption of the ENG/ALK1 signalling pathway also affects EC responses to vascular endothelial growth factor (VEGF) and crosstalk between ECs and vascular smooth muscle cells. It is striking that the vascular lesions in HHT are both localised and tissue specific. Increasing evidence points to the importance of a second genetic hit to generate biallelic mutations, and the sporadic nature of such somatic mutations would explain the localised formation of vascular lesions. In addition, different pro-angiogenic drivers of AVM formation are likely to be at play during the patient’s life course. For example, inflammation is a key driver of vessel remodelling in postnatal life, and may turn out to be an important driver of HHT disease. The current wealth of preclinical models of HHT has led to increased understanding of AVM development and revealed new therapeutic approaches to treat AVMs, and form the topic of this review.

Hereditary haemorrhagic telangiectasia in Danish patients with pathogenic variants in SMAD4: a nationwide study

BACKGROUND AND AIMS

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant condition characterised by recurrent epistaxis, telangiectatic lesions in the skin and mucosal membranes, and arteriovenous malformations (AVMs) in various organs. In 3%-5% of patients, HHT is caused by pathogenic germline variants (PVs) in SMAD4, and these patients often have additional symptoms of juvenile polyposis syndrome and thoracic aneurysms. The phenotypic spectrum of SMAD4-associated HHT is less known, including the penetrance and severity of HHT. We aimed to investigate the phenotypic spectrum of HHT manifestations in Danish patients with PVs in SMAD4 and compare the findings with current literature.

METHODS

The study is a retrospective nationwide study with all known Danish patients with PVs in SMAD4. In total, 35 patients were included. The patients were identified by collecting data from genetic laboratories, various databases and clinical genetic departments across the country. Clinical information was mainly collected from the Danish HHT-Centre at Odense University Hospital.

RESULTS

Twenty-nine patients with PVs in SMAD4 (83%) were seen at the HHT-Centre. Seventy-six per cent of these fulfilled the Curaçao criteria, 86% experienced recurrent epistaxis and 83% presented with telangiectatic lesions at different anatomical localisations. Almost 60% had AVMs, mainly pulmonary and hepatic, while none was found to have cerebral AVMs. Fifteen per cent had thoracic aortic abnormalities.

CONCLUSION

We present a nationwide study of one of the largest populations of patients with PVs in SMAD4 that has systematically been examined for HHT manifestations. The patients presented the full spectrum of HHT-related manifestations and the majority fulfilled the Curaçao criteria.

Whole genome sequences discriminate hereditary hemorrhagic telangiectasia phenotypes by non-HHT deleterious DNA variation

The abnormal vascular structures of hereditary hemorrhagic telangiectasia (HHT) often cause severe anemia due to recurrent hemorrhage, but HHT causal genes do not predict the severity of hematological complications. We tested for chance inheritance and clinical associations of rare deleterious variants in which loss-of-function causes bleeding or hemolytic disorders in the general population. In double-blinded analyses, all 104 patients with HHT from a single reference center recruited to the 100 000 Genomes Project were categorized on new MALO (more/as-expected/less/opposite) sub-phenotype severity scales, and whole genome sequencing data were tested for high impact variants in 75 HHT-independent genes encoding coagulation factors, or platelet, hemoglobin, erythrocyte enzyme, and erythrocyte membrane constituents. Rare variants (all gnomAD allele frequencies <0.003) were identified in 56 (75%) of these 75 HHT-unrelated genes. Deleteriousness assignments by Combined Annotation Dependent Depletion (CADD) scores >15 were supported by gene-level mutation significance cutoff scores. CADD >15 variants were identified in 38/104 (36.5%) patients with HHT, found for 1 in 10 patients within platelet genes; 1 in 8 within coagulation genes; and 1 in 4 within erythrocyte hemolytic genes. In blinded analyses, patients with greater hemorrhagic severity that had been attributed solely to HHT vessels had more CADD-deleterious variants in platelet (Spearman ρ = 0.25; P = .008) and coagulation (Spearman ρ = 0.21; P = .024) genes. However, the HHT cohort had 60% fewer deleterious variants in platelet and coagulation genes than expected (Mann-Whitney test P = .021). In conclusion, patients with HHT commonly have rare variants in genes of relevance to their phenotype, offering new therapeutic targets and opportunities for informed, personalized medicine strategies.

A Formative Study of the Implementation of Whole Genome Sequencing in Northern Ireland

Background: The UK 100,000 Genomes Project was a transformational research project which facilitated whole genome sequencing (WGS) diagnostics for rare diseases. We evaluated experiences of introducing WGS in Northern Ireland, providing recommendations for future projects. Methods: This formative evaluation included (1) an appraisal of the logistics of implementing and delivering WGS, (2) a survey of participant self-reported views and experiences, (3) semi-structured interviews with healthcare staff as key informants who were involved in the delivery of WGS and (4) a workshop discussion about interprofessional collaboration with respect to molecular diagnostics. Results: We engaged with >400 participants, with detailed reflections obtained from 74 participants including patients, caregivers, key National Health Service (NHS) informants, and researchers (patient survey n = 42; semi-structured interviews n = 19; attendees of the discussion workshop n = 13). Overarching themes included the need to improve rare disease awareness, education, and support services, as well as interprofessional collaboration being central to an effective, mainstreamed molecular diagnostic service. Conclusions: Recommendations for streamlining precision medicine for patients with rare diseases include administrative improvements (e.g., streamlining of the consent process), educational improvements (e.g., rare disease training provided from undergraduate to postgraduate education alongside genomics training for non-genetic specialists) and analytical improvements (e.g., multidisciplinary collaboration and improved computational infrastructure).

New Mutations and Pathogenesis of Pulmonary Hypertension: Progress and Puzzles in Disease Pathogenesis

Pulmonary arterial hypertension (PAH) is a complex multifactorial disease with poor prognosis characterized by functional and structural alterations of the pulmonary circulation causing marked increase in pulmonary vascular resistance, ultimately leading to right heart failure and death. Mutations in the gene encoding BMPRII-a receptor for the TGF-β (transforming growth factor-beta) superfamily-account for over 70% of families with PAH and ≈20% of sporadic cases. In recent years, however, less common or rare mutations in other genes have been identified. This review will consider how these newly discovered PAH genes could help to provide a better understanding of the molecular and cellular bases of the maintenance of the pulmonary vascular integrity, as well as their role in the PAH pathogenesis underlying occlusion of arterioles in the lung. We will also discuss how insights into the genetic contributions of these new PAH-related genes may open up new therapeutic targets for this, currently incurable, cardiopulmonary disorder.