ALK1 Research Articles

Age-Dependent Lethality in Novel Transgenic Mouse Models of Central Nervous System Arteriovenous Malformations

The lack of an appropriate animal model has been a limitation in studying hemorrhage from arteriovenous malformations (AVMs) in the central nervous system. Novel mouse central nervous system AVM models were generated by conditionally deleting the activin receptor-like kinase (Alk1; Acvrl1) gene with the SM22-Cre transgene. All mice developed AVMs in their brain and/or spinal cord, and >80% of them showed a paralysis or lethality phenotype due to internal hemorrhages during the first 10 to 15 weeks of life. The mice that survived this early lethal period, however, showed significantly reduced lethality rates even though they carried multiple AVMs. The age-dependent change in hemorrhage rates allowed us to identify molecular factors uniquely upregulated in the rupture-prone AVM lesions. Upregulation of angiopoietin 2 and a few inflammatory genes were identified in the hemorrhage-prone lesions, which may be comparable with human pathology. These models will be an exceptional tool to study pathophysiology of AVM hemorrhage.

Hemodynamic and clinical onset in patients with hereditary pulmonary arterial hypertension and BMPR2 mutations

BackgroundMutations in the bone morphogenetic protein receptor 2 (BMPR2) gene can lead to idiopathic pulmonary arterial hypertension (IPAH). This study prospectively screened for BMPR2 mutations in a large cohort of PAH-patients and compared clinical features between BMPR2 mutation carriers and non-carriers.MethodsPatients have been assessed by right heart catheterization and genetic testing. In all patients a detailed family history and pedigree analysis have been obtained. We compared age at diagnosis and hemodynamic parameters between carriers and non-carriers of BMPR2 mutations. In non-carriers with familial aggregation of PAH further genes/gene regions as the BMPR2 promoter region, the ACVRL1, Endoglin, and SMAD8 genes have been analysed.ResultsOf the 231 index patients 22 revealed a confirmed familial aggregation of the disease (HPAH), 209 patients had sporadic IPAH. In 49 patients (86.3% of patients with familial aggregation and 14.3% of sporadic IPAH) mutations of the BMPR2 gene have been identified. Twelve BMPR2 mutations and 3 unclassified sequence variants have not yet been described before. Mutation carriers were significantly younger at diagnosis than non-carriers (38.53 ± 12.38 vs. 45.78 ± 11.32 years, p < 0.001) and had a more severe hemodynamic compromise. No gene defects have been detected in 3 patients with HPAH.ConclusionThis study identified in a large prospectively assessed cohort of PAH- patients new BMPR2 mutations, which have not been described before and confirmed previous findings that mutation carriers are younger at diagnosis with a more severe hemodynamic compromise. Thus, screening for BMPR2 mutations may be clinically useful.

Angiogenesis regulation by TGFβ signalling: clues from an inherited vascular disease

Studies of rare genetic diseases frequently reveal genes that are fundamental to life, and the familial vascular disorder HHT (hereditary haemorrhagic telangiectasia) is no exception. The majority of HHT patients are heterozygous for mutations in either the ENG (endoglin) or the ACVRL1 (activin receptor-like kinase 1) gene. Both genes are essential for angiogenesis during development and mice that are homozygous for mutations in Eng or Acvrl1 die in mid-gestation from vascular defects. Recent development of conditional mouse models in which the Eng or Acvrl1 gene can be depleted in later life have confirmed the importance of both genes in angiogenesis and in the maintenance of a normal vasculature. Endoglin protein is a co-receptor and ACVRL1 is a signalling receptor, both of which are expressed primarily in endothelial cells to regulate TGFβ (transforming growth factor β) signalling in the cardiovasculature. The role of ACVRL1 and endoglin in TGFβ signalling during angiogenesis is now becoming clearer as interactions between these receptors and additional ligands of the TGFβ superfamily, as well as synergistic relationships with other signalling pathways, are being uncovered. The present review aims to place these recent findings into the context of a better understanding of HHT and to summarize recent evidence that confirms the importance of endoglin and ACVRL1 in maintaining normal cardiovascular health.

Endoplasmic reticulum quality control is involved in the mechanism of endoglin-mediated hereditary haemorrhagic telangiectasia.

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant genetic condition affecting the vascular system and is characterised by epistaxis, arteriovenous malformations and mucocutaneous and gastrointestinal telangiectases. This disorder affects approximately 1 in 8,000 people worldwide. Significant morbidity is associated with this condition in affected individuals, and anaemia can be a consequence of repeated haemorrhages from telangiectasia in the gut and nose. In the majority of the cases reported, the condition is caused by mutations in either ACVRL1 or endoglin genes, which encode components of the TGF-beta signalling pathway. Numerous missense mutations in endoglin have been reported as causative defects for HHT but the exact underlying cellular mechanisms caused by these mutations have not been fully established despite data supporting a role for the endoplasmic reticulum (ER) quality control machinery. For this reason, we examined the subcellular trafficking of twenty-five endoglin disease-causing missense mutations. The mutant proteins were expressed in HeLa and HEK293 cell lines, and their subcellular localizations were established by confocal fluorescence microscopy alongside the analysis of their N-glycosylation profiles. ER quality control was found to be responsible in eight (L32R, V49F, C53R, V125D, A160D, P165L, I271N and A308D) out of eleven mutants located on the orphan extracellular domain in addition to two (C363Y and C382W) out of thirteen mutants in the Zona Pellucida (ZP) domain. In addition, a single intracellular domain missense mutant was examined and found to traffic predominantly to the plasma membrane. These findings support the notion of the involvement of the ER's quality control in the mechanism of a significant number, but not all, missense endoglin mutants found in HHT type 1 patients. Other mechanisms including loss of interactions with signalling partners as well as adverse effects on functional residues are likely to be the cause of the mutant proteins' loss of function.

Mosaic ACVRL1 and ENG mutations in hereditary haemorrhagic telangiectasia patients

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant disorder caused by mutations in the ACVRL1, ENG, and SMAD4 genes. HHT is commonly characterised by small arteriovenous malformations (AVMs) known as...

Hepatic Arteriovenous Malformations from Hereditary Hemorrhagic Telangiectasia Presenting as High-Output Cardiac Failure with Biliary Necrosis

Purpose: Case: A 47-year-old man presented with worsening dyspnea on exertion, unremitting epigastric pain, jaundice, and fevers. He denied any epistaxis, hemoptysis, gingival or gastrointestinal bleeding. Exam showed icteric sclerae, a loud systolic ejection murmur over the apex, a loud bruit over a tender epigastrium, and hepatosplenomegaly. Initial labs showed total bilirubin 3.7 mg/dL, AST 43 U/L, ALT 55 U/L, alkaline phosphatase 579 U/L, and INR 1.1. Blood cultures grew Streptococcus anginosus. Abdominal CT showed diffuse angiomatous tissue, early opacification of all hepatic veins, and biliary necrosis in segment 7. Aortogram showed hugely dilated celiac, replaced left and common hepatic arteries. Cardiac output was 18.2 L/min. Patient was positive for ACVRL1 gene mutation. Endoscopies and additional imaging did not show any other telangiectasias. Despite 4 weeks of IV antibiotics, patient had recurrent fevers, worsening pain, and increasing jaundice. Repeat labs now showed total bilirubin 21, AST 129, ALT 104, ALKP 738, and blood cultures again grew Streptococcus anginosus. Repeat abdominal CT showed progressive biliary necrosis now affecting segments 2-4. Urgent liver transplantation was successfully performed, with resolution of patient's heart failure symptoms and abdominal pain. Discussion: Hereditary hemorrhagic telangiectasia, or Osler-Weber-Rendu syndrome, with hepatic involvement is rare. Diffuse hepatic arteriovenous shunting can result in high-output heart failure, as well as progressive biliary ischemia with necrosis and sepsis. Epigastric pain can occur due to enteric arterial “steal” syndrome. Urgent liver transplantation is indicated and therapeutic for cardiac failure and biliary sepsis.Figure: [758] Aortogram with hugely dilated celiac and replaced hepatic arteries.Figure: [758] Abdominal CT with diffuse angiomatous tissue, early hepatic vein opacifcation, and biliary necrosis.

Experimental study on bone formation with a novel borosilicate glass combined with platelet-rich plasma

Objective To evaluate the osteogenesis of a novel borosilicate glass materials combined with platelet-rich plasma in repairing segmental bone defects. Methods 36 New Zealand white rabbits which bilateral radius were resected into l.5cm bone defect, were divided into 4 groups averagely depending on implanted materials: group A (one side: D-Alk- 1B, another side: D-Alk- 1B +PRP), group B (one side:D-Alk- 1B +PRP, another side: β-TCP); group C (one side: β-TCP, another side: experimental bone defect),and group D(one side:D-Alk-1 B,another side :experimental bone defect). The specimens were examined after 4, 8,12 weeks; the osteogenesis was evaluated through gross observation, X-ray radiograph,histological examination,scanning electron microscope and Micro-CT. Results There were similar results about gross observation,X-ray radiograph ,histological examination. After 4, 8, 12 weeks ,D-Alk-1B materials, β-TCP and D-Alk-1 B + PRP group had better osteogenesis ability than the experimental control group (P ＜0.05); D-Alk-lB + PRP had the best performance, better than D-Alk-1B and β-TCP (P＜0.05); D-Alk-1B were similar to β-TCP (P＞0.05). D-Alk-1 B materials degradated faster than β-TCP materials, and the porous structure of the materials disappeared after degradation. D-Alk-1B materials intergrated with host's bone was better than β-TCP materials. Conclusion D-Alk-1B material have good biological activity, histocompatibility and biodegradation and simiar presence of bone formation compared withβ-TCP in the aspect of repairing the segmental bone defect, the combination of PRP and D-Alk-1 B strengthened osteogenesis in vivo. Key words: Borates; Biocompatiable materials; Platelet-rich plasma; Osteogenesis

Abcès cérébelleux révélant une malformation artérioveineuse pulmonaire isolée en dehors de la maladie de Rendu-Osler

Brain abscesses occur in 5 to 13 % of patients with pulmonary arteriovenous malformation (PAVM), more often present in Rendu-Osler-Weber disease or hereditary hemorrhagic telangiectasia (HHT). A 51-year-old man with a history of transient Parinaud syndrome at 37 years complained of headache for 2 months before acute onset of a left cerebellar syndrome without fever. CT-scan and MRI of the head revealed a heterogeneous left cerebellar lesion. A brain abscess was drained and all signs resolved. CT-scan of the chest revealed a left lingual PAVM; occlusion was incomplete after coil embolization. He had no feature of HHT and no mutation in ENG and ACVRL1 genes. A second embolization was performed 5 months later, but the malformation was not occluded at 6 months. We report the seventh case of PAVM complicated by a cerebellar abscess. The right to left shunt in PAVM results in hypoxemia, secondary polycythemia and paradoxical embolization of infective organisms bypassing the pulmonary filter. Combining different MRI techniques (in particular diffusion and proton MR spectroscopy) provides invaluable data for the diagnosis of brain abscess. Careful search for PAVM must be undertaken, particularly in adults with cryptogenic abscess, to avoid further abscess formation or stroke.

Clinical Outcomes of Pulmonary Arterial Hypertension in Patients Carrying an ACVRL1 (ALK1) Mutation

Activin A receptor type II-like kinase-1 (ACVRL1, also known as ALK1) mutation is a cause of hereditary hemorrhagic telangiectasia (HHT) and/or heritable pulmonary arterial hypertension (PAH). To describe the characteristics of patients with PAH carrying an ACVRL1 mutation. We reviewed clinical, functional, and hemodynamic characteristics of 32 patients with PAH carrying an ACVRL1 mutation, corresponding to 9 patients from the French PAH Network and 23 from literature analysis. These cases were compared with 370 patients from the French PAH Network (93 with a bone morphogenetic protein receptor type 2 [BMPR2] mutation and 277 considered as idiopathic cases without identified mutation). Distribution of mutations in the ACVRL1 gene in patients with PAH was compared with the HHT Mutation Database. At diagnosis, ACVRL1 mutation carriers were significantly younger (21.8 +/- 16.7 yr) than BMPR2 mutation carriers and noncarriers (35.7 +/- 14.9 and 47.6 +/- 16.3 yr, respectively; P < 0.0001). In seven of the nine patients from the French PAH Network, PAH diagnosis preceded manifestations of HHT. ACVRL1 mutation carriers had better hemodynamic status at diagnosis, but none responded to acute vasodilator challenge and they had shorter survival when compared with other patients with PAH despite similar use of specific therapies. ACVRL1 mutations in exon 10 were more frequently observed in patients with PAH, as compared with what was observed in the HHT Mutation Database (33.3 vs. 5%; P < 0.0001). ACVRL1 mutation carriers were characterized by a younger age at PAH diagnosis. Despite less severe initial hemodynamics and similar management, these patients had worse prognosis compared with other patients with PAH, suggesting more rapid disease progression.

Estrogen therapy for hereditary haemorrhagic telangiectasia (HHT): Effects of raloxifene, on Endoglin and ALK1 expression in endothelial cells

Hereditary haemorrhagic telangiectasia (HHT), or Rendu-Osler-Weber syndrome, is an autosomal dominant vascular disease. The clinical manifestations are epistaxis, mucocutaneous and gastrointestinal telangiectases, and arteriovenous malformations. There are two predominant types of HHT caused by mutations in Endoglin (ENG) and activin receptor-like kinase 1 (ALK1) (ACVRL1) genes, HHT1 and HHT2, respectively. No cure for HHT has been found and there is a current need to find new effective drug treatments for the disease. Some patients show severe epistaxis which interferes with their quality of life. We report preliminary results obtained with Raloxifene to treat epistaxis in postmenopausal HHT women diagnosed with osteoporosis. We tried to unravel the molecular mechanisms involved in the therapeutic effects of raloxifene. ENG and ACVRL1 genes code for proteins involved in the transforming growth factor beta pathway and it is widely accepted that haploinsufficiency is the origin for the pathogenicity of HHT. Therefore, identification of drugs able to increase the expression of those genes is essential to propose new therapies for HHT. In vitro results show that raloxifene increases the protein and mRNA expression of ENG and ALK1 in cultured endothelial cells. Raloxifene also stimulates the promoter activity of these genes, suggesting a transcriptional regulation of ENG and ALK1. Furthermore, Raloxifene improved endothelial cell functions like tubulogenesis and migration in agreement with the reported functional roles of Endoglin and ALK1. Our pilot study provides a further hint that oral administration of raloxifene may be beneficial for epistaxis treatment in HHT menopausal women. The molecular mechanisms of raloxifene involve counteracting the haploinsufficiency of ENG and ALK1.

Multiple Sequence Variants in Hereditary Hemorrhagic Telangiectasia Cases: Illustration of Complexity in Molecular Diagnostic Interpretation

Hereditary hemorrhagic telangiectasia is an autosomal dominant disease caused by mutations in the ACVRL1 and ENG genes characterized by arterio-venous malformations and telangiectases. Over 700 mutations have been described in these two genes, and missense mutations are common. We describe 10 cases in which more than one potentially pathogenic mutation was identified. We report that 8 novel missense mutations, as well as previously reported pathogenic missense mutations, were seen in combination with a second mutation, which raises questions with regards to their respective pathogenicity. Our data and discussion indicate the challenges of classifying missense mutations as pathogenic or benign and the value of co-segregation studies, as well as suggest that there may be hereditary hemorrhagic telangiectasia gene mutations that have only mild phenotypic effects. We present evidence to suggest that four missense mutations (ENG p.G331S, ENG p.L8P, ENG p.P452L and ACVRL1 p.C344R) are pathogenic, two novel mutations (ACVRL1 p.A311T and ENG p.S576G) are neutral, and two previously reported disease-causing mutations are benign or have suspected benign variants (ACVRL1 p.A482V and ENG p.V504M). We conclude that for the purpose of establishing a causative hereditary hemorrhagic telangiectasia mutation in a family proband, all exons and intron/exon borders of both genes should be sequenced and deletion/duplication analysis should be performed unless a mutation that is well-proven to be pathogenic is identified.

Near-fatal haemorrhage from pulmonary arteriovenous malformation in HHT with increased cardiac output

To the Editor: We read with interest the report by Montani et al. [1] of fatal rupture of pulmonary arteriovenous malformation (AVM) in a patient with hereditary haemorrhagic telangiectasis (HHT) and severe pulmonary arterial hypertension (PAH) confirmed by right heart catheterisation. The authors hypothesised that bleeding from pulmonary AVM may have been facilitated by increased mean pulmonary artery pressure ( P pa). Here, we report a patient with near-fatal haemorrhage from pulmonary AVM, probably facilitated by increased cardiac output, but without severe PAH. A 35-yr-old female nonsmoker, with a history of obesity and fenfluramide use 10 yrs previously for 2 months, was admitted for exertional dyspnoea during pregnancy. Arterial blood gases showed arterial oxygen tension ( P a,O2) of 8.2 kPa, and arterial carbon dioxide tension of 3.5 kPa, with markedly increased alveolar–arterial oxygen tension difference on 100% oxygen (74 kPa, normally <18.6 kPa). Chest radiograph revealed numerous pulmonary AVMs. Transthoracic contrast echocardiography showed estimated systolic P pa of 47 mmHg with moderate dilatation of the right heart cavities, and extracardiac right-to-left shunting. She had recurrent epistaxis since childhood, numerous characteristic telangiectasiae, and possible familial HHT in her paternal grandmother. HHT was diagnosed according to the Curacao criteria [2]. One deletion was found in exon 9 of the ENG gene, and analysis of the ACVRL1 gene was normal. Long-term oxygen therapy was initiated. Emergency caesarean delivery was performed at 25 weeks of gestation because of …

Detection of a significant association between mutations in the ACVRL1 gene and hepatic involvement in German patients with hereditary haemorrhagic telangiectasia

Hereditary haemorrhagic telangiectasia (HHT) is a heterogeneous multisystemic dysplasia of the vascular tissue. This autosomal dominant inherited disorder shows a wide variation in its phenotypic expression. Between 8 and 78% of the HHT patients show arteriovenous malformations of the liver. The molecular basis for hepatic manifestation is still unknown. Two genes are known to play a major role in the development of HHT: activin A receptor type II-like 1 gene (ACVRL1) and ENG. Previously, we and others showed that hepatic involvement is associated with mutations in the ACVRL1 gene, but rarely caused by ENG mutations. Here, we report about the sequencing analysis of a new cohort of 18 adult HHT patients. In these patients, we identified eight novel (four in ACVRL1 and four in ENG) and eight already known mutations. Statistical analysis of our entire data revealed significant differences in the distribution of ACVRL1 and ENG mutations among HHT patients with and without liver involvement (p = 0.0016). The positive predictive value for type 2 HHT (ACVRL1 positive) patients to develop liver disease until the age of 52 years is 68.4%. We conclude that molecular genetic testing of HHT patients is important for prognosis with respect to liver disease.

Evaluation of previously nonscreened hereditary hemorrhagic telangiectasia patients shows frequent liver involvement and early cardiac consequences

Hereditary hemorrhagic telangiectasia (HHT) is a genetic disease characterized by cutaneous, mucosal, and sometimes visceral arteriovenous malformations. Severe hepatic manifestations have been characterized in a subgroup of patients, but few data are available in previously nonscreened patients. We prospectively evaluated liver involvement and its cardiac consequences in such patients. Between 2000 and 2005, we prospectively evaluated the clinical, biological, and hepatic Doppler sonography (DS) characteristics of 102 consecutive HHT patients (mean age, 52.5 years; range, 19-88; 80.4%) with an identified genetic mutation. Patients were segregated into three different severity groups according to DS values. Factors predictive of an abnormal DS, according to predetermined criteria, and of a high cardiac index were identified by logistic and linear regression analysis, respectively. Abnormal liver biology and clinical signs of hepatic involvement were present in 35.3% and 27.5% of cases, respectively. Abnormal DS (defined as at least enlargement of the main hepatic artery) was observed in 56 (54.9%) cases, and direct or indirect signs of significant fistulas were present in 26 (25.5%) cases. Abnormal liver biology and a mutation involving the ACVRL1 gene were predictive of hepatic ultrasound (US) abnormalities. The diameter of the main hepatic artery and the presence of focal nodular hyperplasia (FNH) were predictive of a higher cardiac index. This large prospective series of previously nonscreened HHT patients identified a subgroup at risk of liver involvement (patients with abnormal liver biology and ACVRL1 mutations) and a subgroup with a higher cardiac index: future studies will show whether such patients would benefit from systematic DS screening and long-term cardiac surveillance.

Analysis of ENG and ACVRL1 genes in 137 HHT Italian families identifies 76 different mutations (24 novel). Comparison with other European studies

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disorder causing vascular dysplasias. About 70-80% of HHT patients carries mutations in ENG or ACVRL1 genes, which code for a TGFbeta receptor type III and I respectively. Molecular data on a large cohort of Italian HHT patients are presented, discussing the significance of missense and splice site mutations. Mutation analysis in ENG and ACVRL1 genes was performed using single strand conformation polymorphisms (SSCP), denaturing high performance liquid chromatography (DHPLC) and subsequent direct sequencing. Overall, 101 mutations were found, with ACVRL1 involved in 71% of cases. The highest number of mutations (28/101 subjects, 14/76 different mutations referring to both genes) was in ACVRL1, exon 3. Mutation analysis was then extended to a total of 356 family members, and 162 proven to carry the mutation. New polymorphisms were identified in both genes, and evidence that ENG P131L change is not a disease-causing mutation was also provided. An in silico analysis was performed in order to characterize splice-site mutations. These results were compared to other European national studies and data from Italy, France and Spain were consistent for an higher incidence of ACVRL1 mutations.

Identifying Common Genetic Variants by High-Resolution Melting

Heteroduplex scanning techniques usually detect all heterozygotes, including common variants not of clinical interest. We conducted high-resolution melting analysis on the 24 exons of the ACVRL1 and ENG genes implicated in hereditary hemorrhagic telangiectasia (HHT). DNA in samples from 13 controls and 19 patients was PCR amplified in the presence of LCGreen I, and all 768 exons melted in an HR-1 instrument. We used 10 wild-type controls to identify common variants, and the remaining samples were blinded, amplified, and analyzed by melting curve normalization and overlay. Unlabeled probes characterized the sequence of common variants. Eleven common variants were associated with 8 of the 24 HHT exons, and 96% of normal samples contained at least 1 variant. As a result, the positive predictive value (PPV) of a heterozygous exon was low (31%), even in a population of predominantly HHT patients. However, all common variants produced unique amplicon melting curves that, when considered and eliminated, resulted in a PPV of 100%. In our blinded study, 3 of 19 heterozygous disease-causing variants were missed; however, 2 were clerical errors, and the remaining false negative would have been identified by difference analysis. High-resolution melting analysis is a highly accurate heteroduplex scanning technique. With many exons, however, use of single-sample instruments may lead to clerical errors, and routine use of difference analysis is recommended. Common variants can be identified by their melting curve profiles and genotyped with unlabeled probes, greatly reducing the false-positive results common with scanning techniques.

Arteriovenous Malformation

Object. Important central nervous system (CNS) manifestations in patients with hereditary hemorrhagic telangiectasia (HHT) include arteriovenous malformations (AVMs) and dural arteriovenous fistulas (DAVFs). Hereditary hemorrhagic telangiectasia is caused by germline mutations of two genes: ENG (HHT Type 1) and ACVRL1 (HHT Type 2). The ENG gene variations have been associated with the formation of intracranial aneurysms. The authors studied whether sequence variations in ACVRL1 or ENG are associated with the development of clinically sporadic arteriovenous dysplasias and aneurysms of the CNS. Methods. The coding sequence (in 44 patients with AVMs and 27 with aneurysms) and the 5′ end and the polyA site (in 53 patients with AVMs) of the ACVRL1 gene were analyzed for sequence variations using direct sequencing and single-strand conformational polymorphism analysis. One ENG and three ACVRL1 gene polymorphisms were genotyped using restriction enzyme–based analysis in 101 patients with sporadic AVMs and DAVFs of the CNS, 79 patients treated for intracranial aneurysms, and 202 control volunteers. The authors identified a statistically significant association between the IVS3 −35A/T polymorphism in intron 3 of the ACVRL1 gene and the development of AVMs and DAVFs (p = 0.004; odds ratio [OR] 1.73; 95% confidence interval [CI] 1.19–2.51; after adjustments for age and sex), but not aneurysms (crude OR 0.82; 95% CI 0.55–1.18). Conclusions. The results of this study link ACVRL1 (HHT Type 2 gene) to the formation of the clinically sporadic variants of vascular malformations of the CNS most commonly seen in patients with HHT, that is, AVMs and DAVFs.

A fourth locus for hereditary hemorrhagic telangiectasia maps to chromosome 7

Hereditary hemorrhagic telangiectasia (HHT) is a genetically and clinically heterogeneous multisystem vascular dysplasia. Mutations of the endoglin and ACVRL1 genes are known to cause HHT. However, existence of HHT families in which linkage to these genes has been excluded has suggested that other gene(s) can cause HHT in some families. Recently, a family was reported to be linked to chromosome 5q, the HHT3 locus. Here we report on linkage results on a family with classic features of HHT, albeit a less severe phenotype with regards to epistaxis and telangiectases, in which linkage to HHT1, HHT2, and HHT3 is ruled out. Whole genome linkage analysis and fine mapping results suggested a 7 Mb region on the short arm of chromosome 7 (7p14) between STR markers D7S2252 and D7S510. We obtained a maximum two point LOD score of 3.60 with the STR marker D7S817. This region was further confirmed by haplotype analysis. These findings suggest the presence of another gene causing HHT (HHT4). The features in this family that strongly suggest the presence of a hereditary, multisystem vascular dysplasia would be easily missed during the typical evaluation and management of a patient with an AVM. This family helps emphasize the need to obtain a very detailed, targeted medical and family history for even mild, infrequent but recurring nosebleed, subtle telangiectases. Further studies of the candidate region and the identification of the gene responsible for the vascular anomalies in this family will add to our understanding of vascular morphogenesis and related disorders.

Novel mutations inENGandACVRL1identified in a series of 200 individuals undergoing clinical genetic testing for hereditary hemorrhagic telangiectasia (HHT): correlation of genotype with phenotype

Hereditary hemorrhagic telangiectasia (HHT; Osler-Weber-Rendu disease) is an autosomal dominant disease characterized by arteriovenous malformations ranging from cutaneous and mucous membrane telangiectasias to more severe pulmonary, gastrointestinal, and cerebral arteriovenous malformations (AVMs). Acute complications from bleeding or pulmonary shunting may be catastrophic. However, when diagnosed early, the complications can usually be prevented. Mutations in two genes, Endoglin (ENG) and activin receptor-like kinase 1 (ACVRL1 or ALK1) have been associated with HHT. We describe the results of mutation analysis on a consecutive series of 200 individuals undergoing clinical genetic testing for HHT. The observed sensitivity of mutation detection was similar to that in other series with strict ascertainment criteria. A total of 127 probands were found, with sequence changes consisting of 103 unique alterations, 68 of which were novel. In addition, eight intragenic rearrangements in the ENG gene and two in the ACVRL1 gene were identified in a subset of coding sequence mutation-negative individuals. Most individuals tested could be categorized by the number of HHT diagnostic criteria present. Surprisingly, almost 50% of the cases with a single symptom were found to have a significant sequence alteration; three of these reported only nosebleeds. Genetic testing can confirm the clinical diagnosis in individuals and identify presymptomatic mutation carriers. As many of the complications of HHT disease can be prevented, a confirmed molecular diagnosis provides an opportunity for early detection of AVMs and management of the disease.

Association of a polymorphism of the ACVRL1 gene with sporadic arteriovenous malformations of the central nervous system

Important central nervous system (CNS) manifestations in patients with hereditary hemorrhagic telangiectasia (HHT) include arteriovenous malformations (AVMs) and dural arteriovenous fistulas (DAVFs). Hereditary hemorrhagic telangiectasia is caused by germline mutations of two genes: ENG (HHT Type 1) and ACVRL1 (HHT Type 2). The ENG gene variations have been associated with the formation of intracranial aneurysms. The authors studied whether sequence variations in ACVRL1 or ENG are associated with the development of clinically sporadic arteriovenous dysplasias and aneurysms of the CNS. The coding sequence (in 44 patients with AVMs and 27 with aneurysms) and the 5' end and the polyA site (in 53 patients with AVMs) of the ACVRL1 gene were analyzed for sequence variations using direct sequencing and single-strand conformational polymorphism analysis. One ENG and three ACVRL1 gene polymorphisms were genotyped using restriction enzyme-based analysis in 101 patients with sporadic AVMs and DAVFs of the CNS, 79 patients treated for intracranial aneurysms, and 202 control volunteers. The authors identified a statistically significant association between the IVS3 -35A/T polymorphism in intron 3 of the ACVRL1 gene and the development of AVMs and DAVFs (p = 0.004; odds ratio [OR] 1.73; 95% confidence interval [CI] 1.19-2.51; after adjustments for age and sex), but not aneurysms (crude OR 0.82; 95% CI 0.55-1.18). The results of this study link ACVRL1 (HHT Type 2 gene) to the formation of the clinically sporadic variants of vascular malformations of the CNS most commonly seen in patients with HHT, that is, AVMs and DAVFs.