<em>SMAD4</em> mutations found in unselected HHT patients

C Gallione

J Richards

T Letteboer

D Rushlow

J van Amstel+3 authors

C J Gallione, T P Leedom, D A Marchuk, Duke University Medical Center, Durham, NC, USA

J A Richards, A Ganguly, Genetic Diagnostic Laboratory, University of Pennsylvania School of Medicine, Philadelphia, PA, USA

T G W Letteboer, J K Ploos van Amstel, DBG‐Department of Medical Genetics, University Medical Center, Utrecht, the Netherlands

D Rushlow, N L Prigoda, HHT Solutions, Toronto Western Hospital, Toronto, Canada

A Castells, Gastroenterology Department, Hospital Clínic, IDIBAPS, University of Barcelona, Barcelona, Spain

C J J Westermann, St. Antonius Hospital, Nieuwegein, the Netherlands

R E Pyeritz, Departments of Medicine & Genetics, Institute for Translational Medicine and Therapeutics, University of Pennsylvania School of Medicine, Philadelphia, PA, USA

Correspondence to: Dr D A Marchuk
Department of Molecular Genetics and Microbiology, Box 3175, Duke University Medical Center, Durham, NC 27710; march004@mc.duke.edu

C J Gallione, T P Leedom, D A Marchuk, Duke University Medical Center, Durham, NC, USAJ A Richards, A Ganguly, Genetic Diagnostic Laboratory, University of Pennsylvania School of Medicine, Philadelphia, PA, USAT G W Letteboer, J K Ploos van Amstel, DBG‐Department of Medical Genetics, University Medical Center, Utrecht, the NetherlandsD Rushlow, N L Prigoda, HHT Solutions, Toronto Western Hospital, Toronto, CanadaA Castells, Gastroenterology Department, Hospital Clínic, IDIBAPS, University of Barcelona, Barcelona, SpainC J J Westermann, St. Antonius Hospital, Nieuwegein, the NetherlandsR E Pyeritz, Departments of Medicine & Genetics, Institute for Translational Medicine and Therapeutics, University of Pennsylvania School of Medicine, Philadelphia, PA, USACorrespondence to: Dr D A Marchuk
Department of Molecular Genetics and Microbiology, Box 3175, Duke University Medical Center, Durham, NC 27710; march004@mc.duke.edu

Received 2006 Feb 6; Revised 2006 Mar 28; Accepted 2006 Mar 30.

Abstract

Background

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant disease exhibiting multifocal vascular telangiectases and arteriovenous malformations. The majority of cases are caused by mutations in either the endoglin (ENG) or activin receptor‐like kinase 1 (ALK1, ACVRL1) genes; both members of the transforming growth factor (TGF)‐β pathway. Mutations in SMAD4, another TGF‐β pathway member, are seen in patients with the combined syndrome of juvenile polyposis (JP) and HHT (JP‐HHT).

Methods

We sought to determine if HHT patients without any apparent history of JP, who were undergoing routine diagnostic testing, would have mutations in SMAD4. We tested 30 unrelated HHT patients, all of whom had been referred for DNA based testing for HHT and were found to be negative for mutations in ENG and ALK1.

Results

Three of these people harboured mutations in SMAD4, a rate of 10% (3/30). The SMAD4 mutations were similar to those found in other patients with the JP‐HHT syndrome.

Conclusions

The identification of SMAD4 mutations in HHT patients without prior diagnosis of JP has significant and immediate clinical implications, as these people are likely to be at risk of having JP‐HHT with the associated increased risk of gastrointestinal cancer. We propose that routine DNA based testing for HHT should include SMAD4 for samples in which mutations in neither ENG nor ALK1 are identified. HHT patients with SMAD4 mutations should be screened for colonic and gastric polyps associated with JP.

Keywords: hereditary haemorrhagic telangiectasia (HHT), juvenile polyposis (JP), endoglin (ENG), activin receptor‐like kinase 1 (ALK1, ACVRL1), SMAD4

Abstract

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant disease of vascular dysplasia. The symptoms of HHT include epistaxis, telangiectases, and arteriovenous malformations (AVMs), which are most often found in the lungs, brain, liver, and gastrointestinal tract. There is wide variation in penetrance and severity of these symptoms in patients even within the same family,¹ suggesting that environmental or other genetic factors influence the phenotype. Mutations in either one of two genes cause HHT. Mutations in the endoglin (ENG) gene are responsible for HHT1² and mutations in the activin receptor‐like kinase 1 (ALK1) gene for HHT2.³ Both of these genes encode TGF‐β binding proteins and play important roles in regulating endothelial cell growth.⁴⁵

Screening for mutations in either ENG or ALK1 in HHT patient cohorts yields mutation detection rates of between 62% and 93%.⁶⁷⁸⁹¹⁰¹¹¹²¹³¹⁴ The failure to achieve a 100% detection rate is not unique to HHT. This range of mutation detection rates is similar to that found for many other mendelian disorders,¹⁵ implying that most, if not all, mutation scans share common detection limitations. In the case of HHT, people may have large deletions or insertions, deep intronic mutations affecting splicing, or regulatory mutations in either ENG or ALK1. A subset of the mutation negative samples may instead have a mutation in the as yet undiscovered HHT3 gene recently linked to chromosome 5.¹⁶ Because the majority of HHT patients have been found to have mutations in ENG or ALK1, it is probable that only a small fraction of the remaining cases will be caused by mutations in other genes.

SMAD4 is a key downstream effector of transforming growth factor (TGF)‐β signalling. Mutations in SMAD4 and BMPR1A are known to be causative for juvenile polyposis (JP).¹⁷¹⁸ JP is characterised by the presence of five or more hamartomatous gastrointestinal polyps, or any number of polyps in addition to a family history of polyposis.¹⁹ There is an increased risk of gastrointestinal cancers associated with these polyps. Recently, SMAD4 was identified as mutated in a subset of HHT patients with JP, a condition termed JP‐HHT syndrome,²⁰ in which juvenile polyps and anaemia are the predominant clinical features. HHT symptoms vary among patients, but all meet the Curaçao criteria for being either definitely or possibly affected.²¹ There is a high penetrance of AVMs in this JP‐HHT cohort, particularly in young patients. Importantly, each of these patients has symptoms of both JP and HHT.

Both JP and HHT are diseases known to have a range of clinical presentations and to be variably penetrant.¹²² One feature common to both disorders is gastrointestinal (GI) bleeding, potentially confounding the correct diagnosis. Because of this potential for uncertainty in diagnoses, we questioned whether, among a cohort of ENG and ALK1 mutation negative HHT cases, there were occult cases of JP‐HHT, diagnosed as only having the HHT component of the combined phenotype. Using sequence analysis for SMAD4 mutations, we screened 30 people from an unselected group of HHT patients, who had been referred for DNA based testing for HHT and found to be negative for mutations in either ENG or ALK1.

ACKNOWLEDGEMENTS

We would first like to thank the patients for their participation in this study. We also thank K Vandezande at HHT Solutions for helpful discussions. A Castells has received funding from the Ministerio de Educación y Ciencia (SAF 04‐07190) and from the Instituto de Salud Carlos III (RC03/02 and RC03/10). D A Marchuk has received funding from the National Institutes of Health (R01 HL49171).

Note added in proof: Further examination of patient records revealed that patient 5068 has colon polyps. This individual also has a liver AVM, migrolines and clubbing of the figures.

ACKNOWLEDGEMENTS

Abbreviations

ALK1 - activin receptor‐like kinase 1

AVM - arteriovenous malformation

ENG - endoglin

GI - gastrointestinal

JP - juvenile polyposis

TGF - transforming growth factor

Abbreviations

Footnotes

Competing interests: there are no competing interests

Footnotes

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