A disease locus for hereditary haemorrhagic telangiectasia maps to chromosome 9q33-34

Gastrointestinal angiodysplasia in a patient with type 2 von Willebrand's disease and analysis of exon 28 of the von Willebrand factor gene

Although the association between gastrointestinal angiodysplasia and von Willebrand's disease has been suggested, molecular mechanisms involved in the formation of angiodysplasia in patients with von Willebrand's disease remained undetermined. We examined exon 28 of the von Willebrand factor gene in a patient with both von Willebrand's disease and recurrent bleeding from angiodysplasia in the duodenum as well as his father's, and found a point mutation, C 3916-->T (amino acid substitution; Arg 543-->Trp), in the A1 domain of the von Willebrand factor gene. This mutation was identical with a previously reported mutation in a patient with von Willebrand's disease complicated with gastrointestinal angiodysplasia.

Umbilical vein and placental vessels from newborns with hereditary haemorrhagic telangiectasia type 1 genotype are normal despite reduced expression of endoglin

Hereditary haemorrhagic telangiectasia, HHT, is an autosomal dominant disorder that affects approximately 1 in 8000 people. HHT1 is associated with mutations in the ENG (Endoglin) gene and with haploinsufficiency. The disorder is characterized by focally dilated vessels, which can lead to arteriovenous malformations and serious complications even in young children. In the current study, umbilical cord and placenta samples from newborns with ENG mutations were analyzed to estimate the level of corresponding protein and look for potential vascular dysplasia. We confirmed, using metabolic labelling and flow cytometry, that endoglin levels were significantly reduced to median values of 47 per cent (range 32-56 per cent) and 58 per cent (46-90 per cent), respectively, in human umbilical vein endothelial cells derived from newborns with ENG mutations (HHT1 group; n=18) relative to samples from newborns shown not to have the familial mutation (non-HHT group). We also quantified the relative expression of endoglin by estimating the endoglin/PECAM-1 staining ratio in tissue sections. We observed significantly lower values in the HHT1 group, compared to the non-HHT group for the umbilical vein (n=9; median 0.6 vs 0.9; ranges 0.2-1.0 and 0.5-1.5) and for placental stem villus vessels (n=9 and 10; median 0.42 vs 0.93; ranges 0.24-0.58 and 0.56-1.18). No differences in the estimated umbilical vein cross-sectional area and in the proportion of vessels present in placental villi were observed in sections from the HHT1 group relative to the non-HHT group. Thus, blood vessels from HHT1 individuals are maintained intact in the umbilical vein and placenta during pregnancy and delivery, despite a significant reduction in endoglin expression.

The rare phakomatoses

This article outlines the clinical, central nervous system, and neuropathologic features,pathogenesis, genetics, molecular biology, and neuroimaging characteristics of the rare vascular phakomatoses, melanophakomatoses, and organoid phakomatoses.

Familial trigeminal neuralgia: case reports and review of the literature

The paroxysmal facial pain of trigeminal neuralgia is usually idiopathic, but familial cases have been described. We describe a family with apparent autosomal dominant transmission of trigeminal neuralgia. Our cases and a review of the literature suggest that the etiology of trigeminal neuralgia may be vascular compression of the fifth cranial nerve. Autosomal dominant vascular and epileptic disorders are reviewed, and possible relationships to familial trigeminal neuralgia are considered.

Management of patients with brain arteriovenous malformations

Arteriovenous malformations (AVMs) of the brain, which are probably genetically determined, are errors in the development of the vasculature that, together with the effects of blood flow, may lead to a focal arteriovenous shunt. Clinically, the adult patient may present with acute or chronic neurological symptoms-fixed or unstable-such as deficits, seizures or headache. Sometimes the lesion is an incidental finding. In about half of the patients, the revealing event is an intracranial haemorrhage. The prevalence of AVM in the western world is probably <0.01% and the detection rate is about one per 100,000 person-years. Most AVMs are revealed in patients 20-40 years of age. Therefore, the risk of developing neurological symptoms from an AVM, usually because of haemorrhage, increases with patient age. In the young adult population, AVMs are significant risk factors for hemorrhagic stroke. This risk increases with AVM volume and is higher in centrally located AVMs. Almost all patients with AVM are subjected to treatment, either by surgery, radiosurgery or embolisation, with the functional aim of reducing the risk of haemorrhage or to alleviate neurological symptoms with an acceptable treatment risk. Few neurocentres have physicians highly skilled in all treatment modalities. Therefore, the prescribed treatment may not be defined from an objective assessment of what is optimal for each individual patient, but rather from local expertise. In this context, more and better data about the natural history and the outcome of different treatments, as well as predictive models, would be valuable to help to optimise the management. Management strategies obviously differ according to local preferences, but results presented in the literature suggest the following strategy: (I) cortically located AVMs with a nidus volume <10 ml could be operated, with or without presurgical embolisation, unless there is a single feeder that can easily be catheterised and embolised for obliteration or other obvious target for embolisation, such as pseudoaneurysms or large fistulae; (II) centrally located AVMs with a nidus volume <10 ml should be treated by radiosurgery, unless suitable for embolisation as indicated above; (III) patients harbouring AVMs with a nidus volume >10 ml could benefit from targeted partial embolisation followed by radiosurgery or surgery, depending on the angioarchitecture; and (IV) AVMs >20 ml nidus volume usually have a high treatment risk with any treatment modality and are not obvious targets for treatment at all.

Endoglin gene mutations and polymorphisms in Italian patients with hereditary haemorrhagic telangiectasia

Autosomal-dominant hereditary haemorrhagic telangiectasia (HHT) is a genetically heterogeneous disease caused by mutations in at least two different loci. We screened for mutations in four Italian families where segregation studies showed clear evidence of linkage to the endoglin (ENG) locus. In addition, one sporadic case and three patients with pulmonary arteriovenous malformations, belonging to small nuclear families unsuitable for linkage analysis, were included in the screening. The proband from each family was investigated using single-strand conformation polymorphism and heteroduplex analysis; potential variants were sequenced. Four novel and one previously reported mutation were detected, as well as three new polymorphisms. The novel mutations included deletions in exon 1 (patient 581/02), exon 5 (patient 780/01) and exon 7 (patient 700/01), and a C-->T229 substitution in exon 3 (patient 462/02). When analysing patient 700/01 and his affected daughter, we encountered a mutant ENG allele with two mutations--a deletion in exon 7 and a substitution in exon 12--which converts isoleucine 575 into threonine, in a non-conserved region. Both mutations were absent in the two healthy sons of the patient, while the polymorphic variant in exon 12 was present in his healthy father. These results and haplotype-segregation studies suggest that a de novo deletion had occurred in the gamete of paternal origin. For the first time the parental germline in which a de novo HHT mutation occurred has been identified.

Vascular malformations: localized defects in vascular morphogenesis

Vascular anomalies are localized defects of the vasculature, and usually affect a limited number of vessels in a restricted area of the body. They are subdivided into vascular malformations and vascular tumours. Most are sporadic, but Mendelian inheritance is observed in some families. By genetic analysis, several causative genes have been identified during the last 10 years. This has shed light into the pathophysiological pathways involved. Interestingly, in most cases, the primary defect seems to affect the characteristics of endothelial cells. Only mutations in the glomulin gene, responsible for hereditary glomuvenous malformations, are thought to directly affect vascular smooth-muscle cells.

Liver disease in hereditary hemorrhagic telangiectasia

Hereditary hemorrhagic telangiectasia (HHT), also known as Osler-Weber-Rendu disease, is an hereditary disorder that results in fibrovascular dysplasia with the development of telangiectasias and arteriovenous malformations. It predominantly involves the skin, mucous membranes, viscera, lungs, and brain. Hereditary hemorrhagic telangiectasia shows great genetic heterogeneity, and its phenotypes have been classified based on the recently identified mutated genes: endoglin (HHT-1) and activin-like kinase receptor-1 (HHT-2). Other families with phenotypic HHT do not bear these mutations; therefore, other genes are probably involved as well. Liver involvement is reported in up to 30% of persons affected by HHT. Large arteriovenous malformations in the liver can lead to significant complications, including high-output congestive heart failure, portal hypertension, hepatic encephalopathy, biliary ischemia, and liver failure. Embolization of large arteriovenous malformations in the liver remains controversial; however, liver transplantation can successfully eradicate these complications.

Hereditary haemorrhagic telangiectasia (Osler-Weber-Rendu syndrome): otorhinolaryngological manifestations

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant disorder affecting blood vessels of the skin, mucous membrane and viscera. The otorhinolaryngologist is the commonest clinician involved in management as epistaxis occurs in 93% of the patients. As marked advances have recently been made regarding the pathogenesis and management of the condition, the otorhinolaryngological perspective is reviewed.

Cerebrovascular manifestations in 321 cases of hereditary hemorrhagic telangiectasia

BACKGROUND AND PURPOSE

Patients with hereditary hemorrhagic telangiectasia (HHT) are at risk for developing cerebral vascular malformations and pulmonary arteriovenous fistulae. We assessed the risk of neurological dysfunction from these malformations and fistulae.

METHODS

Three hundred twenty-one consecutive patients with HHT seen at a single institution over a 20-year period were studied. Any evidence of prior neurological symptoms or presence of an intracranial vascular malformation was recorded. All cases of possible cerebral arteriovenous malformation were confirmed by conventional arteriography.

RESULTS

Twelve patients (3.7%) had a history of cerebral vascular malformations. Ten patients had arteriovenous malformations, 1 had a dural arteriovenous fistula, and 1 had a cavernous malformation. Seven patients (2.1%) presented with intracranial hemorrhage, 2 presented with seizures alone, and 3 were discovered incidentally. The average age at the time of symptomatic intracranial hemorrhage was 25.4 years. All patients with a history of intracranial hemorrhage were classified as Rankin grade I or II at a mean follow-up interval of 6.0 years. A history of cerebral infarction or transient ischemic attack was found in 29.6% of patients with HHT and a pulmonary arteriovenous fistula.

CONCLUSIONS

The risk of intracranial hemorrhage is low among people with HHT. Furthermore, a majority of these patients have a good functional outcome after hemorrhage. The data do not suggest a compelling indication for routine screening of patients with HHT for asymptomatic cerebral vascular malformations. By comparison, pulmonary arteriovenous fistulae are a much more frequent cause of neurological symptoms in this population.

Hereditary haemorrhagic telangiectasia simulating biliary tree obstruction secondary to malignant porta hepatis lymphadenopathy

Hereditary telangiectasis is an uncommon condition and is thus not usually considered in the differential diagnosis of porta hepatis lymphadenopathy causing biliary tree obstruction. The present case illustrates a patient in whom tortuous vessels in the porta hepatis simulated masses on delayed contrast-enhanced CT with subsequent referral for biopsy.

A hereditary haemorrhagic telangiectasia family with pulmonary involvement is unlinked to the known HHT genes, endoglin and ALK-1

BACKGROUND

Pulmonary arteriovenous malformations (PAVMs) occur in over 25% of patients with the autosomal dominant disorder hereditary haemorrhagic telangiectasia (HHT). Mutations in two genes, endoglin and ALK-1, are known to cause HHT. Each encodes a protein expressed on vascular endothelial cells and involved in signalling by members of the transforming growth factor (TGF)-beta superfamily. To date, PAVMs have not been detected in ALK-1 families. There is evidence from a single HHT family without pulmonary involvement that a third HHT gene may exist. To establish the existence of a further HHT gene responsible for PAVMs, linkage analyses were performed on an expanded PAVM-HHT family in which HHT did not result from endoglin mutations.

METHODS

Family members were assessed clinically to assign HHT disease status and were screened for PAVMs. DNA was extracted from blood obtained from 20 individuals of known disease status. Short tandem repeat polymorphic markers spanning the intervals containing the endoglin and ALK-1 genes were amplified by the polymerase chain reaction using (33)P-labelled oligonucleotide primers, separated by denaturing polyacrylamide gel electrophoresis (PAGE), and the resultant autoradiographs were examined for allele sizes. Linkage analyses were performed using MLINK and GENEHUNTER.

RESULTS

Twelve members spanning four generations were affected with HHT. Two had proven PAVMs, one with a classical appearance, the other exhibiting microscopic PAVMs exacerbated by pregnancy. Two point lod and multipoint lod scores significantly excluded linkage to endoglin and ALK-1 in this pedigree.

CONCLUSIONS

This study confirms the existence of a third HHT locus that accounts for disease in some HHT patients with pulmonary involvement.

Mutation and expression analysis of the endoglin gene in hereditary hemorrhagic telangiectasia reveals null alleles

Hereditary Hemorrhagic Telangiectasia (HHT) is an autosomal dominant disorder characterized by multisystemic vascular dysplasia and recurrent hemorrhage from the sites of vascular lesions. Two genes have been identified for HHT. Endoglin, a TGF-beta binding protein which maps to chromosome 9q3, is the gene for HHT1. The type and location of most of the previously described mutations in the endoglin (ENG) gene suggested a dominant-negative model of receptor-complex dysfunction for the molecular basis of this disorder. In this article we describe 11 novel ENG mutations in HHT kindreds, which include missense and splice-site mutations. Two identical missense mutations in unrelated families disrupt the start codon of the gene. In addition, some frameshift and nonsense mutations lead to very low or undetectable levels of transcript from the mutant allele. These combined data suggest that the nature of most ENG mutations is to create a null (nonfunctional) allele, and that there is no requirement for the synthesis of a truncated endoglin protein in the pathogenesis of HHT.

Embolotherapy in the bronchial and pulmonary circulations

This two-part article first discusses the role of bronchial artery transcatheter embolotherapy in the management of patients with hemoptysis. Following this discussion, the authors review pulmonary arteriovenous malformations, their embolization, follow-up protocols, and outcome criteria as currently practiced at the authors' Vascular Malformation Center.

Endoglin expression is reduced in normal vessels but still detectable in arteriovenous malformations of patients with hereditary hemorrhagic telangiectasia type 1

Endoglin is predominantly expressed on endothelium and is mutated in hereditary hemorrhagic telangiectasia (HHT) type 1 (HHT1). We report the analysis of endoglin in tissues of a newborn (family 2), who died of a cerebral arteriovenous malformation (CAVM), and in a lung specimen surgically resected from a 78-year-old patient (family 5), with a pulmonary AVM (PAVM). The clinically affected father of the newborn revealed a novel mutation that was absent in his parents and was identified as a duplication of exons 3 to 8, by quantitative multiplex polymerase chain reaction. The corresponding mutant protein (116-kd monomer) and the missense mutant protein (80-kd monomer) present in family 5 were detected only as transient intracellular species and were unreactive by Western blot analysis and immunostaining. Normal endoglin (90-kd monomer) was reduced by 50% on peripheral blood-activated monocytes of the HHT1 patients. When analyzed by immunostaining and densitometry, presumed normal blood vessels of the newborn lung and brain and vessels adjacent to the adult PAVM showed a 50% reduction in the endoglin/PECAM-1 ratio. A similar ratio was observed in the CAVM and PAVM, suggesting that all blood vessels of HHT1 patients express reduced endoglin in situ and that AVMs are not attributed to a focal loss of endoglin.

Expression analysis of four endoglin missense mutations suggests that haploinsufficiency is the predominant mechanism for hereditary hemorrhagic telangiectasia type 1

ENDOGLIN codes for a homodimeric membrane glycoprotein that interacts with receptors for members of the TGF-beta superfamily and is the gene mutated in the autosomal dominant vascular disorder hereditary hemorrhagic telangiectasia type 1 (HHT1). We recently demonstrated that functional endoglin was expressed at half levels on human umbilical vein endothelial cells (HUVECs) and peripheral blood activated monocytes from HHT1 patients. Two types of mutant protein were previously analyzed, the product of an exon 3 skip which was expressed as a transient intracellular species and prematurely truncated proteins that were undetectable in patient samples. Here we report the analysis of four proteins resulting from point mutations, with missense codons G52V and C53R in exon 2, W149C in exon 4 and L221P in exon 5. Metabolic labeling of activated monocytes from confirmed, clinically affected patients revealed reduced expression of fully processed normal endoglin in all cases. Pulse-chase analysis with HUVECs from a newborn with the C53R substitution indicated that mutant endoglin remained intracellular as a precursor form and did not impair processing of the normal protein. Biotinylation of cell surface proteins, metabolic labeling and pulse-chase analysis revealed that none of the engineered missense mutants was significantly expressed at the surface of COS-1 transfectants. Thus, these four HHT1 missense mutations lead to transient intracellular species which cannot interfere with normal endoglin function. These data suggest that haploinsufficiency, leading to reduced levels of one of the major surface glyco-proteins of vascular endothelium, is the predominant mechanism underlying the HHT1 phenotype.

Four tumor suppressor loci on chromosome 9q in bladder cancer: evidence for two novel candidate regions at 9q22.3 and 9q31

The most common genetic alteration identified in transitional cell carcinoma (TCC) of the bladder is loss of heterozygosity (LOH) on chromosome 9. However, localization of tumor suppressor genes on 9q has been hampered by the low frequency of subchromosomal deletions. We have analysed 139 primary, initial low stage TCC of the bladder using a panel of 28 microsatellite markers spanning chromosome 9 at an average distance of 5 Mb, following a primer-extension preamplification (PEP) technique. Sixty-seven (48%) tumors showed LOH at one or more loci and partial deletions were detected in 62 (45%) tumors; apparent monosomy 9 was detected in only five (4%) tumors. Deletions were more frequent on 9q (44%) than on 9p (23%), the latter being mostly associated with 9q deletion, suggesting that alteration of genes on 9q may be an early event associated with superficial papillary tumors. Combined data from the cases with partial 9q deletions displayed four candidate regions for tumor suppressor loci, based on the frequency of deletion observed and tumors with unique deletions at these sites. In two tumors, the unique partial deletion comprised D9S12 at 9q22.3, a region encompassing loci for the Gorlin syndrome and multiple self-healing squamous epithelioma gene. In two other tumors, the single LOH was identified at the D9S172 locus at 9q31-32 where the dysautonia and Fukuyama-type congenital muscular dystrophy genes have been located. One tumor showed unique LOH at the GSN locus at 9q33, a region frequently deleted in other sporadic tumors while the fourth region of deletion was observed at 9q34 between ASS and ABL-1, in two tumors. This region is frequently deleted in tumors and encompasses the locus for the hereditary hemorrhagic telangiectasia gene. These findings suggest four target regions on 9q within which suppressor genes for TCC may reside.

Genetic mapping of a novel familial form of infantile hemangioma

Infantile hemangiomas are the most common tumor of infancy, occurring with an incidence of up to 10% of all births. They are benign but highly proliferative lesions involving aberrant localized growth of capillary endothelium. Although most hemangiomas occur sporadically and as single lesions, or in conjunction with pleiotropic genetic syndromes, we have previously identified six kindreds where hemangiomas appear to segregate as an autosomal dominant trait with high penetrance. Four such families contain affected individuals in three or more generations. In the current study, blood samples from five of these families were collected and used in a whole genome linkage search at 10-cM resolution. We established evidence for linkage to 5q in three families, and evidence for locus heterogeneity. The three 5q-linked families were further genotyped to generate haplotype information and narrow the candidate interval. Based on recombination breakpoint analysis, the interval exists between markers D5S2490 and D5S408, spanning 55 cM, and corresponding to 5q31-33. Using information from affected and unaffected individuals, the interval spans 38 cM between markers D5S1469 and D5S211. Three candidate genes involved with blood vessel growth map to this region: fibroblast growth factor receptor-4 (FGFR4), platelet-derived growth factor receptor-beta (PDG-FRB), and fms-related tyrosine kinase-4 (FLT4). The genes and gene products associated with familial hemangiomas may be involved somatically in the more common sporadic cases.

Argon plasma coagulation for the treatment of hereditary hemorrhagic telangiectasia

OBJECTIVES

Patients with (HHT) often suffer from recurrent epistaxis, which poses considerable therapeutic problems. Theoretical considerations render argon plasma coagulation (APC) a promising new therapeutic approach.

STUDY DESIGN

In a prospective study 12 patients (aged 8-68 y) who presented with a long history of treatment for epistaxis were treated with telangiectasia in the nasal mucosa. After 2 weeks and again after 4 months the treatment results were evaluated by questionnaire.

METHODS

APC is based on high-frequency electric energy transmitted through ionized argon gas to the tissue in a noncontact mode. Coagulation and desiccation of tissue are limited to 1 to 2 mm of penetration and therefore risk of tissue damage is low. Coagulative effects are best in tissue with high electrical conductivity, especially blood vessels.

RESULTS

All patients were satisfied with the postoperative results. Frequency and intensity of bleeding were significantly reduced. All patients reported better postoperative results than with any other treatment they had received previously.

CONCLUSION

First clinical experience shows that APC is a useful alternative for the treatment of telangiectasia in the nasal mucosa and should be a therapeutic option for this disease.

Mutant endoglin in hereditary hemorrhagic telangiectasia type 1 is transiently expressed intracellularly and is not a dominant negative

Endoglin (CD105), a component of the TGF-beta 1 receptor complex, is the target gene for the dominantly inherited vascular disorder hereditary hemorrhagic telangiectasia type 1 (HHT1). We have identified a novel endoglin splice site mutation, leading to an in-frame deletion of exon 3, in a new-born from a family with HHT. Expression of normal and mutant endoglin proteins was analyzed in umbilical vein endothelial cells from this baby and in activated monocytes from the affected father. In both samples, only normal dimeric endoglin (160 kD) was observed at the cell surface, at 50% of control levels. Despite an intact transmembrane region, mutant protein was only detectable by metabolic labeling, as an intracellular homodimer of 130 kD. In monocytes from three clinically affected HHT1 patients, with known mutations creating premature stop codons in exons 8 and 10, surface endoglin was also reduced by half and no mutant was detected. Overexpression into COS-1 cells of endoglin cDNA truncated in exons 7 and 11, revealed their intracellular expression, inability to be secreted and to form heterodimers at the cell surface. These results indicate that mutated forms of endoglin are transiently expressed intracellularly and not likely to act as dominant negative proteins, as proposed previously. A reduction in the level of functional endoglin is thus involved in the generation of HHT1, and associated arteriovenous malformations.

The activin receptor-like kinase 1 gene: genomic structure and mutations in hereditary hemorrhagic telangiectasia type 2

The activin receptor-like kinase 1 gene (ALK-1) is the second locus for the autosomal dominant vascular disease hereditary hemorrhagic telangiectasia (HHT). In this paper we present the genomic structure of the ALK-1 gene, a type I serine-threonine kinase receptor expressed predominantly in endothelial cells. The coding region is contained within nine exons, spanning < 15 kb of genomic DNA. All introns follow the GT-AG rule, except for intron 6, which has a TAG/gcaag 5' splice junction. The positions of introns in the intracellular domain are almost identical to those of the mouse serine-threonine kinase receptor TSK-7L. By sequencing ALK-1 from genomic DNA, mutations were found in six of six families with HHT either shown to link to chromosome 12q13 or in which linkage of HHT to chromosome 9q33 had been excluded. Mutations were also found in three of six patients from families in which available linkage data were insufficient to allow certainty with regard to the locus involved. The high rate of detection of mutations by genomic sequencing of ALK-1 suggests that this will be a useful diagnostic test for HHT2, particularly where preliminary linkage to chromosome 12q13 can be established. In two cases in which premature termination codons were found in genomic DNA, the mutant mRNA was either not present or present at barely detectable levels. These data suggest that mutations in ALK-1 are functionally null alleles.

Hepatic vascular malformations in hereditary hemorrhagic telangiectasia: Doppler sonographic screening in a large family

BACKGROUND/AIMS

The prevalence of hepatic vascular malformations in hereditary hemorrhagic telangiectasia has been estimated in the literature on clinical criteria, thus giving unreliable data. In our study the presence of hepatic vascular malformations in hereditary hemorrhagic telangiectasia was evaluated in a large Italian family by using Doppler sonography findings were compared to computed tomography and angiography results. Clinical features were related to the severity of hepatic vascular malformations.

METHODS

Seventy-three relatives were checked for the presence of signs of hereditary hemorrhagic telangiectasia. Abdominal Doppler ultrasonography was performed in all of them. Every subject with a positive Doppler ultrasonography for hepatic vascular malformations underwent abdominal computed tomography and celiac angiography.

RESULTS

Forty family members proved to be affected by hereditary hemorrhagic telangiectasia. Of these, hepatic vascular malformations were evidenced by Doppler ultrasonography in 13 females. Doppler ultrasongraphy demonstrated minimal hepatic vascular abnormalities in three subjects, moderate in three, and severe in seven. Doppler study was diagnostic for arteriovenous shunt with hepatic veins in seven cases and with portal vein in two. Computed tomography failed to demonstrate hepatic vascular malformations in two cases, while angiography confirmed the Doppler sonographic findings in all cases. Cholestasis was present in subjects with moderate and severe hepatic vascular malformations.

CONCLUSIONS

Doppler sonography is the ideal imaging technique to screen hereditary hemorrhagic telangiectasia affected families for hepatic vascular malformations. These malformations do not appear to be age-dependent, but sex-dependent. Cholestasis is the main clinical sign, and it seems to correlate with the severity of hepatic vascular derangement.

Pulmonary arteriovenous malformations: diagnosis and transcatheter embolotherapy

The recent long-term studies from England, France, and the Netherlands, as well as our own, indicate that transcatheter embolotherapy is definitive treatment for PAVM. More recently, Puskas et al have questioned transcatheter embolotherapy as a primary treatment for patients with PAVM (4,56). Their opinion was based on two recurrences among five patients treated with transcatheter embolotherapy. It is not clear why one of the late recurrences in the series by Puskas et al happened, and the other recurrence could have been dut to early deflation of the balloon. Nevertheless, we believe that the collective experience in the larger series reporting on transcatheter embolotherapy of PAVM supports the use of embolotherapy as a primary modality of treatment. Because many patients have bilateral pulmonary malformations and many pulmonary malformations will grow with time, repeated surgical intervention is not ideal therapy. The recurrence rate of 8% reported by Remy et al using coils, and 2% reported by Pollak et al using balloons and coils supports our contention that transcatheter embolotherapy is durable and should be the initial treatment. Also, recurrences are easily retreated by transcatheter embolotherapy with durable results (54). We favor detachable balloons over coils for occluding PAVMs because immediate cross-sectional occlusion of the segmental artery is obtained in a position that preserves the most normal branches. The necessity for repeated introduction of coils, when using the coil method, contributes to longer procedure times with an increased risk of air introduction and, in our experience, a greater risk of postprocedure pleurisy. At the same time, we appreciate that approximately 70% of PAVMs can be occluded equally well with balloons or coils. We also believe that coils have unique advantages over balloons in specific anatomic situations including oversized arteries (where coils are the only option) and for occlusion of the aneurysm of a PAVM. As with all forms of embolotherapy, the interventionalist is best served by having more than one option of treatment, which for PAVM includes both balloons and coils. In summary, PAVMs are effectively managed by means of transcatheter embolotherapy. This therapy has been demonstrated to be safe and durable. Careful technique with modifications depending on the angioarchitecture of the PAVM is required. Patients with PAVMs require follow-up at 1 month and 1 year. While observations documenting serial growth of small PAVMs are somewhat limited, there is published evidence to support their growth with time (35,36). Because of these reports and our unpublished observations, we believe that patients with treated PAVM need long-term follow-up every 5 years to detect growth of small PAVMs that will ultimately reach a size where they may cause paradoxical embolization and stroke (1).

Mutations in the activin receptor-like kinase 1 gene in hereditary haemorrhagic telangiectasia type 2

Hereditary haemorrhagic telangiectasia, or Osler-Rendu-Weber (ORW) syndrome, is an autosomal dominant vascular dysplasia. So far, two loci have been demonstrated for ORW. Linkage studies established an ORW locus at chromosome 9q3; endoglin was subsequently identified as the ORW1 gene. A second locus, designated ORW2, was mapped to chromosome 12. Here we report a new 4 cM interval for ORW2 that does not overlap with any previously defined. A 1.38-Mb YAC contig spans the entire interval. It includes the activin receptor like kinase 1 gene (ACVRLK1 or ALK1), a member of the serine-threonine kinase receptor family expressed in endothelium. We report three mutations in the coding sequence of the ALK1 gene in those families which show linkage of the ORW phenotype to chromosome 12. Our data suggest a critical role for ALK1 in the control of blood vessel development or repair.

Hereditary haemorrhagic telangiectasia with extensive liver involvement is not caused by either HHT1 or HHT2

Hereditary haemorrhagic telangiectasia (HHT) is a genetically heterogeneous dominant disorder. Two disease loci have been mapped to chromosomes 9q3 and 12q. In a large pedigree, with an unusually high number of patients with liver vascular malformations, both previously mapped loci have been excluded. The loci for two other inherited vascular malformation diseases, cerebral cavernous malformations and multiple cutaneous and mucosal venous malformations, have also been excluded. Thus we conclude that at least a third, as yet unmapped, HHT locus does exist, possibly associated with high frequency of liver involvement.

[A patient with Rendu-Osler-Weber disease and pulmonary arteriovenous malformations treated satisfactorily by embolization]

A 41-years-old woman with multiple arteriovenous lung malformations in a context of Rendu-Osler-Weber disease is described. The patient had a history of cutaneous and mucosal telangiectasia, frequent epistaxis and one episode of central artery embolism in the right retina. Malformations in the vascular territories of both lungs (right lower lobe and lingula) were detected by X-rays and magnetic resonance. Progressive dyspnea along with serious antecedents indicated that aggressive treatment was required. The malformations were embolized in the vascular radiology treatment center.

Clinical heterogeneity in hereditary haemorrhagic telangiectasia: are pulmonary arteriovenous malformations more common in families linked to endoglin?

Pulmonary arteriovenous malformations (PAVMs) occur in up to 27% of patients with hereditary haemorrhagic telangiectasia (HHT) and are associated with a rate of paradoxical cerebral embolism at presentation of up to 36%. At least two different loci have been shown for HHT. Mutations in endoglin have been found in some families and the locus designated ORW1. In other families this locus has been excluded. In this paper we confirm that in families linked to ORW1 there is a prevalence of PAVMs among affected members of 29.2%, compared to a prevalence of 2.9% in families in which this locus has been excluded (chi 2 = 19.2, p < 0.001). This information can be used to decide how to screen HHT patients for PAVMs.

A second locus for hereditary hemorrhagic telangiectasia maps to chromosome 12

Hereditary hemorrhagic telangiectasia (HHT) or Osler-Rendu-Weber (ORW) disease is an autosomal dominant vascular dysplasia. Initial linkage studies identified an ORW gene localized to 9q33-q34 but with some families clearly excluding this region. A probable correlation in clinical phenotype between the 9q3-linked families and unlinked families was described with a significantly lower incidence of pulmonary arteriovenous malformations observed in the unlinked families. In this study we examined four unrelated ORW families for which linkage to chromosome 9q33-q34 has been previously excluded. Linkage was established for all four families to markers on chromosome 12, with a combined maximum lod score of 10.77 (theta = 0.04) with D12S339. Mapping of crossovers using haplotype analysis indicated that the candidate region lies in an 11-CM interval between D12S345 and D12S339, in the pericentromeric region of chromosome 12. A map location for a second ORW locus is thus established that exhibits a significantly reduced incidence of pulmonary involvement.

A gene for familial venous malformations maps to chromosome 9p in a second large kindred

Venous malformations are a common form of vascular anomaly that cause pain and disfigurement and can be life threatening if they involve critical organs. They occur sporadically or in a familial form, where multiple lesions are usually present. We have identified a large kindred showing autosomal dominant inheritance of venous malformations. Using this family we confirm linkage of a familial form of venous malformations to chromosome 9p. We suggest that blue rubber bleb naevus syndrome can be considered a particular manifestation of this form of familial venous malformations. The candidate region for this gene encompasses the interferon gene cluster and the MTS1 (p16) tumour suppressor gene.

COL5A1: fine genetic mapping and exclusion as candidate gene in families with nail-patella syndrome, tuberous sclerosis 1, hereditary hemorrhagic telangiectasia, and Ehlers-Danlos Syndrome type II

COL5A1, the gene for the alpha 1 chain of type V collagen, has been considered a candidate gene for certain diseases based on chromosomal location and/or disease phenotype. We have employed 3'-untranslated region RFLPs to exclude COL5A1 as a candidate gene in families with tuberous sclerosis 1, Ehlers-Danlos syndrome type II, and nail-patella syndrome. In addition, we describe a polymorphic simple sequence repeat (SSR) within a COL5A1 intron. This SSR is used to exclude COL5A1 as a candidate gene in hereditary hemorrhagic telangiectasia (Osler-Rendu-Weber disease) and to add COL5A1 to the existing map of "index" markers of chromosome 9 by evaluation of the COL5A1 locus on the CEPH 40-family reference pedigree set. This genetic mapping places COL5A1 between markers D9S66 and D9S67.

Toward a molecular understanding of congenital heart disease

BACKGROUND

This review discusses the incidence and importance of congenital heart disease (CHD), the reasons that investigation of causative mechanisms for human CHD has been slow, and the limitations of the multifactorial theory for the etiology of CHD.

METHODS AND RESULTS

The molecular defects underlying three vasculopathies--Marfan's syndrome (fibrillin), supravalvar aortic stenosis, and Williams' syndrome (elastin)--and hereditary telangiectasia are presented to emphasize the role of microfibrils and extracellular matrix in the pathophysiology of these vascular defects. Animal models of CHD, including situs inversus, canine conotruncal malformations, and chick neural crest ablation, are examined to emphasize how such studies relate to human CHD, especially by pointing to single-gene defects for conotruncal malformations, candidate loci for situs inversus, and phenotypic variability caused by neural crest lesions. The crucial role of cardiac transcription factors in heart morphogenesis is emphasized by review of gene knockout studies of these factors, which cause fetal death secondary to heart maldevelopment. Several lines of evidence demonstrating genetic etiologies of human CHD are also presented, including the mapping of familial atrial septal defects, to prove that one anatomic type of CHD may be due to single-gene defects at different loci. Review of atrioventricular canal, both secondary to trisomy 21 and as an autosomal-dominant familial defect, reiterates this conclusion. The evidence that monosomy on chromosome 22 causes multiple types of CHD, including aortic arch and conotruncal defects as part of the CATCH-22 syndrome, is presented, with results supporting the idea that deletions at this site alone may cause 5% of surgically treated CHD.

CONCLUSIONS

We conclude that (1) human CHD is frequently due to single-gene defects and that even sporadic defects may arise from a single-gene abnormality; (2) a common genetic defect may cause several apparently different forms of CHD; (3) elucidation of the genetic basis of CHD provides clues to normal cardiovascular developmental biology; (4) the same cardiac malformation can be caused by mutant genes at different loci; and (5) interactions of clinical investigators (cardiologists and cardiothoracic surgeons) with basic scientists should allow more rapid progress in defining the genetic basis of CHD.

Comparative mapping of 50 human chromosome 9 loci in the laboratory mouse

We have set out to produce a comprehensive comparative map between human chromosome 9 (HSA9) and the laboratory mouse. The mouse homologues of 50 loci that were known to map to HSA9 were mapped by interspecific backcross linkage analysis. Ten loci from the short arm of HSA9 were mapped, and 40 from HSA9q, with 24 markers coming from the HSA9q33-q34 region--a part of the chromosome known to be very gene rich. Fifteen new assignments have been made--Ak3, Ctsl, Cntfr, C8g, D2H9S46E, Eng, Gcnt1, Irebp, Pappa, Ptgds, Snf212, Tal2, Tmod, Vav2, and Vldlr, the human homologues of which all map to HSA9. In addition, the assignment of Snf212 and Vldlr to MMU19 has defined a new region of synteny between the proximal portion of the short arm of HSA9 and the mouse.

Genetic heterogeneity in hereditary haemorrhagic telangiectasia

A locus causing hereditary haemorrhagic telangiectasia (HHT) has recently been mapped to 9q34 in four families and designated HHT1. In this paper, the results of a linkage study showing genetic heterogeneity in four families in whom HHT is segregating are reported. All the previously reported 9q34 linked families contain at least one affected member with a symptomatic pulmonary arteriovenous malformation. We postulate that clinical heterogeneity may also be a feature of HHT with a significantly higher predisposition to symptomatic PAVMs associated with the HHT1 linked families.

Linkage of hereditary haemorrhagic telangiectasia to chromosome 9q34 and evidence for locus heterogeneity

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant disorder with unknown pathophysiology that is characterised by arteriovenous lesions and recurrent haemorrhage in virtually every organ. Linkage of HHT to markers on chromosome 9q has recently been reported. In this study we report confirmation of this localisation in three unrelated families of Dutch origin. A fourth unrelated HHT family, in which considerably fewer pulmonary arteriovenous malformations (PAVM) were present, yielded evidence for non-linkage to this region. We conclude that HHT is a genetically heterogeneous disorder and our results indicate that the presence of PAVM may be more common in patients with a chromosome 9 linked form of HHT than in patients with the non-linked form.

Genetic heterogeneity in hereditary haemorrhagic telangiectasia: possible correlation with clinical phenotype

Hereditary haemorrhagic telangiectasia (HHT) or Osler-Weber-Rendu syndrome is an autosomal dominant vascular dysplasia characterised by recurrent haemorrhage. Our initial linkage studies found an HHT gene to be localised to 9q3 in two large kindreds. In the present study, we examine an additional five unrelated HHT families. Linkage analysis in this region resulted in a peak multipoint location score of 13.03, 10 cM proximal of D9S60. We found significant evidence for heterogeneity of HHT. Multipoint analysis supports the family specific two point studies with odds of 3,000,000:1 showing linkage and heterogeneity over linkage and homogeneity. Four of the seven families give a posterior probability of > 99% of being of the linked type, and three families appear unlinked to this region of 9q, and by multipoint analysis completely exclude the candidate region for HHT. Two new crossovers in affected persons in one of the linked families further define the proximal border of the candidate region on 9q3. A possible correlation in clinical phenotype between the 9q3 linked families and unlinked families is described. Although six of the seven families clearly meet the clinical criteria for HHT diagnosis, a significant absence of pulmonary arteriovenous malformations is seen in all three 9q3 unlinked families. Genetic heterogeneity of HHT and its potential correlation with a clinical phenotype may have a significant impact on the clinical management and treatment of HHT patients.

Endoglin, a TGF-beta binding protein of endothelial cells, is the gene for hereditary haemorrhagic telangiectasia type 1

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant disorder characterized by multisystemic vascular dysplasia and recurrent haemorrhage. Linkage for some families has been established to chromosome 9q33-q34. In the present study, endoglin, a transforming growth factor beta (TGF-beta) binding protein, was analysed as a candidate gene for the disorder based on chromosomal location, expression pattern and function. We have identified mutations in three affected individuals: a C to G substitution converting a tyrosine to a termination codon, a 39 base pair deletion and a 2 basepair deletion which creates a premature termination codon. We have identified endoglin as the HHT gene mapping to 9q3 and have established HHT as the first human disease defined by a mutation in a member of the TGF-beta receptor complex.