Aneurysms-Osteoarthritis Syndrome. SMAD3 Gene Mutations

163 Pages·2016·12.671 MB·English

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

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
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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
xi
Preface
In Aneurysms-Osteoarthritis Syndrome: SMAD3 Gene Mutations, we seek to
provide the reader with a practical approach to the clinical management of pa-
tients 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, cardio-
thoracic 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 encoun-
tered. We outline how to diagnose them and how to treat and manage your AOS
patients in daily clinical practice. We describe genotype and phenotype correla-
tions 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 subchap-
ters 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 acknowl-
edge the great help provided by the editorial staff at Elsevier Publishing.
D. van der Linde
B.L. Loeys
J.W. Roos-Hesselink
xiii
Chapter 1
Genetics of Aneurysms-
Osteoarthritis Syndrome
I.M.B.H. van de Laar, MD, PhD, B.L. Loeys, MD, PhD
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 se-
quenced 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].
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 muta-
tions: 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
Aneurysms-Osteoarthritis Syndrome. http://dx.doi.org/10.1016/B978-0-12-802708-0.00001-6
Copyright © 2017 Elsevier Inc. All rights reserved. 1
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FIGURE 1.1 SMAD3 mutations in eight families with Aneurysms-Osteoarthritis syndrome (AOS). (A) Schematic representation of the ro
SMAD3 gene. Boxes represent exons 1–9 with the untranslated regions (UTRs). The three main functional domains—MH1, MH2, and the linker m
e
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.)
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FIGURE 1.1 (Continued) r |
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FIGURE 1.1 (Continued)
Genetics of Aneurysms-Osteoarthritis Syndrome Chapter | 1 5
cohort. This rate is comparable with the 2% frequency of mutations in the cohort
of nonsyndromic familial thoracic aortic aneurysm and dissection patients report-
ed 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 iden-
tified. 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 path-
way that is crucial for TGF-β signal transmission. We investigated the effect of
SMAD3 mutations on the aortic wall via the histology and immunohistochem-
istry 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).
We also studied the expression of several members of the TGF-β pathway,
including total SMAD3 (nonphosphorylated and phosphorylated forms), phos-
phorylated 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 in-
creased (rather than decreased) TGF-β signaling, as was observed by the in-
creased 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).
CTGF immunolabeling showed a markedly increased cytoplasmatic ex-
pression in the medial vascular smooth muscle cells (VSMCs) of the cases
(Fig. 1.3). This upregulation of both the upstream ligands and the down-
stream 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 syn-
drome, 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.
6 Aneurysms-Osteoarthritis Syndrome
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 dis-
plays abnormal architecture of the aortic media and a dissection tear in the case. A Verhoeff-van Gie-
son 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.)
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 essen-
tial in cartilage maintenance. Later studies have also revealed a vascular pheno-
type in SMAD3 knock-out mice that is characterized by progressive age-induced
aortic root, ascending aorta dilation, aneurysm rupture, and aortic dissection [9].