Aneurysms-Osteoarthritis Syndrome: SMAD3 Gene Mutations

By Denise van der Linde, Jolien Roos-Hesselink and Bart L. Loeys

Aneurysms-Osteoarthritis Syndrome: SMAD3 Gene Mutations is a first-of-its-kind compilation of the genetic discovery, research, and care associated with AOS. With the field of genetically triggered aortopathies growing, this important reference will compile the newest discoveries in this field, allowing cardiologists, cardio-thoracic surgeons, clinical geneticists, vascular surgeons, orthopedic surgeons, and researchers to gain the knowledge they need without having to gather the data from various sources.

Coverage includes genotype and phenotype correlations, the functional role of SMAD3, and insights into the role of TGFbeta signaling in aortic disease. The book will increase knowledge about AOS, providing awareness and better patient care for this aggressive disease.

• Covers Aneurysms-Osteoarthritis Syndrome, from genetic discovery to patient care
• Contains clinical management guidance on optimal cardiovascular treatments and surgery
• Explains the autosomal dominant syndromes caused by mutations in the SMAD3 gene
• Identifies the key features of this syndrome, including arterial aneurysms and tortuosity, early onset arthritis, and mild craniofacial features

• Language: English
• Publisher: Elsevier Science
• Release date: Oct 3, 2016
• ISBN: 9780128027110

Denise van der Linde

Dr. Van Der Linde is an experienced researcher with in the field of congenital hearts defect and genetic aortic disease in adults. She has published over 20 articles in international journals and published her work in several international conferences around the world. During her PhD she was involved in the first description of (cardio)vascular consequences of the new Aneurysms-Osteoarthritis Syndrome. After her PhD, she did a post doc research period about genetic aortic disease in Sydney, Australia. She is currently back in Rotterdam, The Netherlands, working as a cardiologist in training.

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Aneurysms-Osteoarthritis Syndrome

SMAD3 Gene Mutations

Denise van der Linde, MD, MSc, PhD

Department of Cardiology, Erasmus University Medical Center Rotterdam, The Netherlands

Bart L. Loeys, MD, PhD

Center of Medical Genetics, Antwerp University Hospital Antwerp, Belgium; and the Department of Human Genetics Radboud University Medical Center Nijmegen, The Netherlands

Jolien W. Roos-Hesselink, MD, PhD

Department of Cardiology, Erasmus University Medical Center Rotterdam, The Netherlands

Table of Contents

Cover

Title page

Copyright

List of Contributors

Preface

Chapter 1: Genetics of Aneurysms-Osteoarthritis Syndrome

Abstract

1. Genetics

2. Pathophysiology

3. The TGF-β pathway: the canonical signaling

4. The role of the TGF-β pathway in aneurysm formation

Chapter 2: Cardiovascular Phenotype of Aneurysms-Osteoarthritis Syndrome

Abstract

1. Introduction

2. Aortic aneurysms

3. Arterial aneurysms throughout the body

4. Arterial tortuosity

5. Dissections and cardiovascular mortality

6. Congenital heart defects

7. Mitral valve anomalies and atrial fibrillation

8. Left ventricular function and hypertrophy

9. NT-proBNP as a biomarker

10. Arterial stiffness

11. Pregnancy

12. Conclusions

Chapter 3: Systemic Features of Aneurysms-Osteoarthritis Syndrome

Abstract

1. Joint anomalies

2. Skeletal anomalies

3. Craniofacial abnormalities

4. Neurological features

5. Immunological features

6. Additional features

7. Classification of Aneurysms-Osteoarthritis syndrome

Chapter 4: Differential Diagnosis in Heritable Thoracic Aortic Diseases

Abstract

1. Introduction

Chapter 4a: Marfan Syndrome

Abstract

1. Definitions and diagnosis

2. Clinical genetic aspects of Marfan syndrome

3. Clinical manifestations

4. Etiology and pathophysiology

5. Management and treatment of Marfan syndrome

6. Pregnancy with Marfan syndrome

Chapter 4b: Loeys-Dietz Syndrome

Abstract

1. Initial description

2. Clinical features

3. Diagnostic criteria

4. Expanding genetic basis

5. Pathophysiology

Chapter 4c: Ehlers-Danlos Syndrome

Abstract

1. Introduction

2. Clinical presentation

3. Subtypes of Ehlers-Danlos syndrome

Chapter 4d: Bicuspid Aortic Valve

Abstract

1. Introduction

2. Definition

3. Embryology of the aortic valve and proximal aorta

4. Genes involved in the malformation of the conotruncus

5. The relationship between aortic dilatation and bicuspid aortic valve

6. Clinical presentation of patients with a bicuspid aortic valve

7. Evaluation of patients with bicuspid aortic valve

8. Treatment

Chapter 4e: Turner Syndrome

Abstract

1. Introduction

2. Genetics

3. Cardiovascular disease

Chapter 5: Cardiovascular Imaging in Aneurysm-Osteoarthritis Syndrome

Abstract

1. Aortic anatomy

2. Imaging techniques

3. Imaging of aortic aneurysms

4. Imaging of small and medium-size vessels

5. Imaging of aortic dissections

6. Imaging after aortic surgery

Chapter 6: Treatment Options

Abstract

1. Introduction

Chapter 6a: Optimal Cardiovascular Medical Treatment

Abstract

1. Beta-blockers: standard of care?

2. From symptomatic to causal treatment

3. Angiotensin receptor blockers: an alternative treatment strategy?

4. Future treatment options

Chapter 6b: Cardiothoracic Surgical Experience

Abstract

1. Introduction

2. Indications for elective aortic root surgery

3. Surgical technique for valve-sparing aortic root replacement

4. Elective valve-sparing aortic root replacement experience

5. Recommendations for elective aortic root surgery

6. Conclusions

Chapter 6c: Vascular Interventions and Surgical Experience

Abstract

1. Introduction

2. Involvement of the visceral and iliac arteries in Aneurysms-Osteoarthritis syndrome

3. Visceral and iliac artery aneurysm growth

4. Open vascular interventions

5. Endovascular interventions

6. Recommendations for open and endovascular interventions

7. Conclusions

Chapter 6d: Orthopedic Evaluation and Treatment Options

Abstract

1. Introduction

2. Etiology and pathogenesis

3. Musculoskeletal evaluation and phenotypic presentation

4. Osteoarthritis

5. Osteochondritis dissecans

6. Spinal disorders

7. Conclusions

Chapter 6e: Genetic Counseling

Abstract

1. Introduction

2. Counseling procedure

3. Genetic testing in minors

4. Reproductive options

Chapter 6f: Approach to Clinical Management

Abstract

1. Introduction

2. Initial screening

3. Monitoring and referral

4. Children

5. Psychosocial adjustment

6. A multidisciplinary team approach

7. Conclusions

Index

Copyright

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List of Contributors

J.A. Bekkers MD, PhD,     Erasmus University Medical Center, Rotterdam, The Netherlands

P.K. Bos MD, PhD,     Erasmus University Medical Centre, Rotterdam, The Netherlands

R.G. Chelu MD,     Erasmus University Medical Centre, Rotterdam, The Netherlands

J. de Backer MD, PhD,     University Hospital Ghent, Ghent, Belgium

A.L. Duijnhouwer MD,     Radboud University Medical Centre, Nijmegen, The Netherlands

B.L. Loeys MD, PhD

Antwerp University Hospital/University of Antwerp, Antwerp, Belgium

Radboud University Medical Centre, Nijmegen, The Netherlands

K. Nieman MD, PhD,     Erasmus University Medical Centre, Rotterdam, The Netherlands

J.W. Roos-Hesselink MD, PhD,     Erasmus University Medical Centre, Rotterdam, The Netherlands

J. Timmermans MD,     Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands

I.M.B.H. van de Laar MD, PhD,     Erasmus University Medical Centre, Rotterdam, The Netherlands

A.E. van den Bosch MD, PhD,     Erasmus University Medical Centre, Rotterdam, The Netherlands

A.T. van den Hoven BSc,     Erasmus University Medical Centre, Rotterdam, The Netherlands

D. van der Linde MD, MSc, PhD,     Erasmus University Medical Centre, Rotterdam, The Netherlands

H.J.M. Verhagen MD, PhD,     Erasmus University Medical Center, Rotterdam, The Netherlands

J.M.A. Verhagen MD,     Erasmus University Medical Centre, Rotterdam, The Netherlands

M.W. Wessels MD, PhD,     Erasmus University Medical Centre, Rotterdam, The Netherlands

Preface

In Aneurysms-Osteoarthritis Syndrome: SMAD3 Gene Mutations, we seek to provide the reader with a practical approach to the clinical management of patients with Aneurysms-Osteoarthritis syndrome (AOS) and related disorders. With the rapid pace of developments in the field of heritable thoracic aortic diseases, simply keeping up-to-date with the latest research and putting this information in a practical context is a challenging task. With a dedicated team of editors and contributors, Aneurysms-Osteoarthritis Syndrome: SMAD3 Gene Mutations is an essential guide for cardiologists, (clinical) geneticists, cardiothoracic and vascular surgeons, orthopedic surgeons, radiologists, neurologists, fellows, and researchers who seek a contemporary update and overview of the entire spectrum of aortic aneurysm syndromes.

Starting from the genetic etiology of this disease, we take you on a journey through the numerous cardiovascular and systemic features that can be encountered. We outline how to diagnose them and how to treat and manage your AOS patients in daily clinical practice. We describe genotype and phenotype correlations and provide insights into the role of TGF-beta signaling in aortic disease. A practical algorithm summarizing screening and follow-up guidelines for the multidisciplinary clinical care for AOS patients is also included.

In the evolving field of heritable thoracic aortic diseases, the heterogeneous genetic causes of syndromes are currently being unraveled. Many overlapping clinical features make it increasingly difficult to label patients with a specific disease or syndrome. Therefore, an important part of this textbook is dedicated to the differential diagnosis of heritable thoracic aortic diseases, with subchapters focused on Marfan, Loeys-Dietz, Ehlers-Danlos, bicuspid aortic valve, and Turner syndromes.

Only key references are included so that readability is not inhibited by overly dense text. This textbook is made visually appealing by the use of color images, informative tables, and algorithm flow charts.

We give special thanks to our contributors for their devoted efforts, without which this text would not have been possible. Furthermore, we wish to acknowledge the great help provided by the editorial staff at Elsevier Publishing.

D. van der Linde

B.L. Loeys

J.W. Roos-Hesselink

Chapter 1

Genetics of Aneurysms-Osteoarthritis Syndrome

I.M.B.H. van de Laar MD, PhD

B.L. Loeys MD, PhD

Abstract

In 2011, classical genome-wide linkage studies and positional cloning successfully identified a new gene involved in both syndromic and nonsyndromic forms of aortic aneurysms—namely, the SMAD3 gene. The SMAD3 gene plays a role in signal transmission in the transforming growth factor-beta (TGF-β) pathway. Heterozygous loss-of-function mutations in the SMAD3 gene lead to a paradoxical enhancement of aortic wall TGF-β signaling. The TGF-β signaling pathway and its implication in the pathogenesis of aortic aneurysms are examined in detail in this chapter.

Keywords

SMAD3

aortic aneurysm

osteoarthritis

genome-wide linkage analysis

pathophysiology

TGF-β pathway

1. Genetics

In 2011, we investigated four generations of a family of Dutch origin, with 22 individuals presenting arterial aneurysms and dissections and/or skeletal or cutaneous abnormalities. The segregation reflected autosomal dominant inheritance and variable expression (Fig. 1.1; family 1). Aiming to map the disease gene, we performed a genome-wide linkage analysis using 250k SNP arrays and obtained a significant multipoint LOD [logarithms (base 10) of odds] score of 3.6 on chromosome 15q22.33. The 12.8-Mb candidate region that was identified by fine-mapping contained an interesting candidate gene involved in the transforming growth factor-beta (TGF-β) signaling pathway—namely, the SMAD3 gene. In family 1, a heterozygous SMAD3 mutation—c.859C > T (p.Arg287ArgTrp)—was found to segregate with the phenotype. To evaluate the frequency of SMAD3 mutations among individuals with aneurysms, we sequenced all SMAD3 exons in 99 individuals with thoracic aortic aneurysms and dissections and features similar to those in patients with Marfan syndrome (MFS) but without FBN1, TGFBR1, and TGFBR2 mutations. We found heterozygous SMAD3 mutations in 2 out of 99 cases—c.741–742delAT (p.Thr247ProfsX61) and c.782C > T (p.Thr261Ile) (Fig. 1.1; families 2 and 3) [1].

Figure 1.1   SMAD3 mutations in eight families with Aneurysms-Osteoarthritis syndrome (AOS).

(A) Schematic representation of the SMAD3 gene. Boxes represent exons 1–9 with the untranslated regions (UTRs). The three main functional domains—MH1, MH2, and the linker region—are indicated. Mutations previously identified in the AOS are depicted in black font, and mutations identified in this study are depicted in blue. (B) Simplified family trees of eight unrelated families with AOS. Squares indicate males, and circles represent females. A horizontal line above the symbol indicates medical examination by one of us. Owing to the lack of space, generation III from family 1 is split into two levels. An arrow points to the index patient. The upper-right blue square indicates the presence of osteoarthritis, the lower-right red square the presence of a thoracic aortic aneurysm, the lower-left green square the presence of an aneurysm in any other artery, and the upper-left yellow square the presence of arterial tortuosity. Open symbols are individuals with a normal or unknown phenotype. Four individuals with open symbols (family 1, patient II-10, V-5, V-12; and family 3, patient III-2) had other signs of AOS not indicated in the legend. A question mark (?) indicates sudden cardiovascular death, possibly from an arterial rupture or dissection without autopsy. Age of death is displayed below the symbol. The presence (+/−) or absence (−/−) of a SMAD3 mutation is indicated underneath. (Reprinted with permission from the article by Van de Laar et al., Phenotypic spectrum of the SMAD3-related aneurysms-osteoarthritis syndrome. J Med Genet 2012;49(1):47–57.)

Later, our SMAD3 sequence analysis of 393 patients with thoracic aortic aneurysms and dissections (without mutations in the FBN1, TGFBR1, and TGFBR2 genes) revealed five additional novel heterozygous SMAD3 mutations: c.313delG (p.Ala105ProfsX11), c.539_540insC (p.Pro180ThrfxX7), c.788C > T (p.Pro263Leu), c.1045G > C (p.Ala349Pro), and c.1080dupT (p.Glu361X) (Fig. 1.1; families 4–8) [2]. All missense mutations segregated with the phenotype, affected by highly conserved amino acids, were predicted to be pathogenic by four computerized algorithms and absent from controls. Other pathogenic mutations introduced a frameshift or stop codon.

The incidence of SMAD3 mutations in the thoracic aortic aneurysms and dissections cohort seems rather rare, because it was found in only 1–2% of our cohort. This rate is comparable with the 2% frequency of mutations in the cohort of nonsyndromic familial thoracic aortic aneurysm and dissection patients reported by Ellen S. Regalado et al. [3]. However, recent studies have revealed a slightly higher incidence (3–4%) of SMAD3 mutations in a large cohort of both syndromic and nonsyndromic thoracic aortic aneurysm and dissection patients [4].

As of now, 36 different SMAD3 gene mutations have been published in the literature, but many more unpublished SMAD3 mutations have been identified. Yvonne Hilhorst-Hofstee et al. reported a small interstitial deletion of chromosome 15, leading to disruption of the SMAD3 gene [5]. The SMAD3 gene contains three main functional domains—namely, the MH1 and the MH2 domains and the linker region, with mutations occurring throughout the entire 9 exon-containing gene. The most likely effect of these mutations is a loss of function, with TGF-β signals not being propagated via SMAD3. Until now, no clear genotype–phenotype correlation has been established.

2. Pathophysiology

The SMAD3 gene encodes the SMAD3 protein, a member of the TGF-β pathway that is crucial for TGF-β signal transmission. We investigated the effect of SMAD3 mutations on the aortic wall via the histology and immunohistochemistry of aorta fragments obtained during surgery or autopsy. Disorganization of the tunica media with fragmentation and loss of elastic fibers, mucoid medial degeneration, and accumulation of collagen in the media were observed with varying degrees of severity (Fig. 1.2).

Figure 1.2   Histology of aortic media in Aneurysms-Osteoarthritis syndrome.

Aortic media from a control (donor, left column) and case (right column) with a SMAD3 mutation resulting in p.Thr247fsX61 (III-2, family 2). Scale bars correspond to 100 μm. Hematoxylin–eosin staining displays abnormal architecture of the aortic media and a dissection tear in the case. A Verhoeff-van Gieson staining for elastin (dark purple fibers); note the disarray, fragmentation, and loss of elastic fibers in case versus control. A dissection tear is shown. A Masson’s trichrome staining for collagen (green) shows intense collagen staining and disruption of the medial architecture in the case. (Reprinted with permission from the article by Van de Laar et al., Mutations in SMAD3 cause a syndromic form of aortic aneurysms and dissections with early-onset osteoarthritis. Nat Genet 2011;43(2):121–126.)

We also studied the expression of several members of the TGF-β pathway, including total SMAD3 (nonphosphorylated and phosphorylated forms), phosphorylated SMAD2 (pSMAD2), TGF-β1 and connective tissue growth factor (CTGF), by immunohistochemistry. Despite the loss-of-function nature of the SMAD3 mutations, the patient-derived aortic tissues showed evidence of increased (rather than decreased) TGF-β signaling, as was observed by the increased labeling intensity of all the studied markers. TGF-β1 expression was present throughout the aneurismal aortic media, whereas the controls only showed substantial expression in the media adjacent to the adventitia layer, which normally shows the highest level of activity (Fig. 1.3).

Figure 1.3   Immunohistochemistry in Aneurysms-Osteoarthritis syndrome.

Aortic wall (from top to bottom, adventitia, media and intima layers) from a control (donor) and a case with a SMAD3 mutation resulting in p.Arg287Trp (IV-3, family 1). TGF-β1 immunostaining; note the increased TGF-β1 expression through the aortic media, whereas the control only shows marked expression in the outer media adjacent to the adventitia. Connective tissue growth factor (CTGF) immunolabeling is shown. CTGF is a TGF-β-responsive product that normally induces collagen synthesis. Note the increased labeling in the cytoplasm of media cells from the case compared to the donor. Scale bars, 200 μm; inset scale bars, 50 μm. Photomicrographs from the middle section of the aortic media show phosphorylated SMAD2 (pSMAD2) immunolabeling with marked nuclear staining in the case. Total SMAD3 (phosphorylated and nonphosphorylated SMAD3) immunostaining shows increased nuclear and cytoplasmatic labeling in the case as compared to the donor. Scale bars, 100 μm; inset scale bars, 50 μm. (Reprinted with permission from the article by Van de Laar et al., Mutations in SMAD3 cause a syndromic form of aortic aneurysms and dissections with early-onset osteoarthritis. Nat Genet 2011;43(2):121–126.)

CTGF immunolabeling showed a markedly increased cytoplasmatic expression in the medial vascular smooth muscle cells (VSMCs) of the cases (Fig. 1.3). This upregulation of both the upstream ligands and the downstream targets of the TGF-β pathway in the thoracic aortic wall of the AOS cases was similar to that of patients with other syndromic and nonsyndromic aneurysms, including MFS, Loeys-Dietz syndrome, arterial tortuosity syndrome, aneurysms associated with the bicuspid aortic valve, and degenerative aneurismal aortic disease [6–8]. This similarity clearly indicates the existence of common (TGF-β-related) pathogenic mechanisms leading to arterial wall disease.

Studies in SMAD3 knock-out mice have revealed a phenotype resembling human osteoarthritis, including the abnormal calcification of the synovial joints with osteophytes (knee, vertebral bones, sternum), loss of articular cartilage, intervertebral disc degeneration, and hypertrophic differentiation of articular chondrocytes. These studies confirmed that SMAD3-mediated signals are essential in cartilage maintenance. Later studies have also revealed a vascular phenotype in SMAD3 knock-out mice that is characterized by progressive age-induced aortic root, ascending aorta dilation, aneurysm rupture, and aortic dissection [9].

3. The TGF-β pathway: the canonical signaling

The disruption of TGF-β signaling has been implicated in the pathogenesis of many diseases, including aortic aneurysms. This complex pathway has been studied extensively in the past in the context of these diseases, particularly because of its utility as a therapeutic target. TGF-β induces canonical (SMAD-dependent) and noncanonical pathways.

Canonical TGF-β signaling