A Case of Trisomy 13 Mosaicism Presenting with a Severe Aortic Root Dilatation and Marfanoid Habitus due to an Unpredictable Cytogenetic Mechanism.

In this report, we present a new case of mosaic trisomy 13 with prolonged survival, firstly detected by array-CGH analysis which was carried out because of moderate intellectual disability with postaxial hexadactyly, dermatologic features, ventricular septal defect, bicuspid aortic valve, and aortic dystrophy in a 19-year-old male patient. In a subset of 15% of the cells, the patient carried a derivative chromosome 10 generated by a nonreciprocal (10;13) translocation inherited from his healthy mother who carried the translocation in a balanced and homogeneous state. FISH analyses showed interstitial telomeric sequences at the breakpoints. To our knowledge, this is the second report of a patient with trisomy 13 mosaicism displaying a severe aortic root dilatation. We also discuss the mechanisms which could explain the mosaic state, the most likely one being related to the instability of the interstitial telomere.

Fibrillins.

Fibrillins are one of the major components of supramolecular fibrous structures in the extracellular matrix of elastic and nonelastic tissues, termed microfibrils. Microfibrils provide tensile strength in nonelastic tissues and scaffolds for the assembly of tropoelastin in elastic tissues, and act a regulator of growth factor bioavailability and activity in connective tissues. Mutations in fibrillins lead to a variety of connective tissue disorders including Marfan syndrome, stiff skin syndrome, dominant Weill-Marchesani syndrome, and others. Therefore, fibrillins are frequently studied to understand the pathophysiology of these diseases and to identify effective treatment strategies. Extraction of endogenous microfibrils from cells and tissues can aid in obtaining structural insights of microfibrils. Recombinant production of fibrillins is an important tool which can be utilized to study the properties of normal fibrillins and the consequences of disease causing mutations. Other means of studying the role of fibrillins in the context of various physiological settings is by knocking down the mRNA expression and analyzing its downstream consequences. It is also important to study the interactome of fibrillins by protein-protein interactions, which can be derailed in pathological situations. Interacting proteins can affect the assembly of fibrillins in cells and tissues or can affect the levels of growth factors in the matrix. This chapter describes important techniques in the field that facilitate answering relevant questions of fibrillin biology and pathophysiology.

The TGF-ß Signalling Network in Muscle Development, Adaptation and Disease.

Skeletal muscle possesses remarkable ability to change its size and force-producing capacity in response to physiological stimuli. Impairment of the cellular processes that govern these attributes also affects muscle mass and function in pathological conditions. Myostatin, a member of the TGF-ß family, has been identified as a key regulator of muscle development, and adaptation in adulthood. In muscle, myostatin binds to its type I (ALK4/5) and type II (ActRIIA/B) receptors to initiate Smad2/3 signalling and the regulation of target genes that co-ordinate the balance between protein synthesis and degradation. Interestingly, evidence is emerging that other TGF-ß proteins act in concert with myostatin to regulate the growth and remodelling of skeletal muscle. Consequently, dysregulation of TGF-ß proteins and their associated signalling components is increasingly being implicated in muscle wasting associated with chronic illness, ageing, and inactivity. The growing understanding of TGF-ß biology in muscle, and its potential to advance the development of therapeutics for muscle-related conditions is reviewed here.

The Expanding Clinical Spectrum of Extracardiovascular and Cardiovascular Manifestations of Heritable Thoracic Aortic Aneurysm and Dissection.

More than 30 heritable conditions are associated with thoracic aortic aneurysm and dissection (TAAD). Heritable syndromic conditions, such as Marfan syndrome, Loeys-Dietz syndrome, and vascular Ehlers-Danlos syndrome, have somewhat overlapping systemic features, but careful clinical assessment usually enables a diagnosis that can be validated with genetic testing. Nonsyndromic FTAAD can also occur and in 20%-25% of these probands mutations exist in genes that encode elements of the extracellular matrix, signalling pathways (especially involving transforming growth factor-ß), and vascular smooth muscle cytoskeletal and contractile processes. Affected individuals with either a syndromic presentation or isolated TAAD can have mutations in the same gene. In this review we focus on the genes currently known to have causal mutations for syndromic and isolated FTAAD and outline the range of associated extracardiovascular and cardiovascular manifestations with each.

[Clinical and Genetic Characteristics of Russian Marfan Patients].

The results of direct DNA diagnostics in nine patients with Marfan syndrome, aged from two to 52 years old, and four unhealthy relatives with the same disease from two unrelated families have been presented for the first time in Russia. Eight mutations in the gene FBN1 were revealed. One patient demonstrated a substitution with unknown clinical importance, which was previously described in the SN P database as rsl 12287730 with a frequency of incidence of 0.1%. Out of the eight mutations, two (25%) were previously described, and the other six mutations (75%) were revealed for the first time. These mutations revealed by us were of the following types: three mutations (37.5%) produced a shift in the open reading frame (two deletions and one insertion), three mutations (12.5%) involved a splicing site, and one (12.5%) nonsense mutation was also noted. Our data contradict previous reports that claimed that the majority of mutations in the FBN1 gene represented missense mutations. Such inconsistency could result from a small size of the examined sample or from substitutions that produced alteration in the splicing site (as we have demonstrated here). The distribution of the revealed mutations was uniform along the whole gene. The results of the conducted comparative analysis of genetic and phenotypic indices was in complete agreement with previously reported results. The developed direct method of DNA diagnostics was fully informative, as we managed in all nine examined patients to confirm their clinical diagnosis using a molecular and genetic approach.

Molecular pathogenesis of Marfan syndrome.

Marfan syndrome (MFS) is a genetic disorder that affects multiple organs. Mortality imposed by aortic aneurysm and dissections represent the most serious clinical manifestation of MFS. Progressive pathological aortic root enlargement as the result of degeneration of microfibril architecture and consequential loss of extracellular matrix integrity due to fibrillin-1 (FBN1) mutations are commonly diagnosed clinical manifestations of MFS. However, overlapping clinical manifestations with other aneurysmal disorders present a significant challenge in early and accurate diagnosis of MFS. While FBN1 mutations, abnormal transforming growth factor-ß signaling and dysregulated matrix metalloproteinases have been implicated in MFS, clinically accepted risk-stratifying biomarkers have yet to be reliably identified. In this review, we summarize current consensus and recent insights in the understanding of MFS pathogenesis. Finally, we introduce the application of induced pluripotent stem cells (iPSCs) as cellular models for MFS and its potential as a novel platform into providing better appreciation of mechanisms underlying MFS diverse manifestations in the cardiovascular system.

High prevalence of obstructive sleep apnea in Marfan's syndrome.

OBJECTIVE: To review the current evidence about the prevalence of obstructive sleep apnea in patients with Marfan's syndrome, and discuss some proposed potential mechanisms for this relationship. DATA SOURCES: The data in this review were mainly from Medline and PubMed articles published in English from 1990 to 2013. The search term was "Marfan's syndrome and sleep apnea". STUDY SELECTION: Clinical evidence about the epidemiology of obstructive sleep apnea in patients with Marfan's syndrome; the mechanism that causes obstructive sleep apnea; interventional therapy for patients with Marfan's syndrome, and coexisting obstructive sleep apnea. RESULTS: A high prevalence of obstructive sleep apnea exists in patients with Marfan's syndrome. The potential reasons are craniofacial abnormalities and lax upper airway muscles, which lead to high nasal airway resistance and upper airway collapse. Obstructive sleep apnea mechanically deteriorates aortic dilatation and accelerates progression of aortic aneurysms. The condition is reversible and rapid maxillary expansion and adequate continuous positive airway pressure therapy are possible effective therapies to delay the expansion of aortic diameter in patients with Marfan's syndrome. CONCLUSIONS: Obstructive sleep apnea is strongly associated with Marfan's syndrome. Craniofacial abnormalities and lax upper airway are the main mechanisms. Untreated obstructive sleep apnea accelerates progression of aortic dissection and rupture. Effective therapies for obstructive sleep apnea could postpone the aortic dilatation in patients with Marfan's syndrome.

A Pkd1-Fbn1 genetic interaction implicates TGF-ß signaling in the pathogenesis of vascular complications in autosomal dominant polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) is a common cause of renal failure that is due to mutations in two genes, PKD1 and PKD2. Vascular complications, including aneurysms, are a well recognized feature of ADPKD, and a subgroup of families exhibits traits reminiscent of Marfan syndrome (MFS). MFS is caused by mutations in fibrillin-1 (FBN1), which encodes an extracellular matrix protein with homology to latent TGF-ß binding proteins. It was recently demonstrated that fibrillin-1 deficiency is associated with upregulation of TGF-ß signaling. We investigated the overlap between ADPKD and MFS by breeding mice with targeted mutations in Pkd1 and Fbn1. Double heterozygotes displayed an exacerbation of the typical Fbn1 heterozygous aortic phenotype. We show that the basis of this genetic interaction results from further upregulation of TGF-ß signaling caused by Pkd1 haploinsufficiency. In addition, we demonstrate that loss of PKD1 alone is sufficient to induce a heightened responsiveness to TGF-ß. Our data link the interaction of two important diseases to a fundamental signaling pathway.

Detection of 15 novel mutations in 52 children from 40 families with the Marfan or Loeys-Dietz syndrome and phenotype-genotype correlations.

We report about 52 pediatric patients of 40 different families with confirmed Marfan syndrome (MFS) in 49 patients and Loeys-Dietz syndrome (LDS) in 3 patients. We found 39 different mutations, 15 of them being novel. Phenotype-genotype correlation in the 49 MFS patients showed that the majority of patients carrying mutations in exons 1-21 had ectopic lens (80%). Patients having mutations in exons 23-32 had a higher probability of aortic root dilation, in 50% even above a z score of 3. We found three children with neonatal MFS form, two of them with novel mutations. Of the three LDS patients, only one presented with the typical phenotype of LDS type 1.

Bone lessons from Marfan syndrome and related disorders: fibrillin, TGF-B and BMP at the balance of too long and too short.

The extracellular matrix (ECM) is a complex entity with structural proteins (such as fibrillins, collagen, elastin), ground substance (proteoglycans), modifying enzymes (ADAMTS, PLOD, lysyloxidases (LOX)) and cytokines that regulate morphogenesis, growth, homeostasis and repair (transforming growth factor-beta [TGF-beta], bone morphogenic protein [BMP]). Over the last decade, the intimate relationship between structural proteins and these growth factors has emerged. The study of the extracellular matrix in human conditions and relevant mouse models is gradually unmasking the key role of these structural molecules in the regulation of the bio-availability of these growth factors. Major progress has been made in the study of the cardiovascular system (1) and the first clues in the skeletal system have emerged. (2) In this review, we will discuss the clinical, molecular, and pathogenic aspects of Marfan syndrome, Loeys-Dietz syndrome and related disorders with emphasis on the role of fibrillins and TGF-beta.

Are we ignoring the dilated thoracic aorta?

The pathophysiology of thoracic aortic aneurysm (TAA) formation involves a complex interplay of genetic predisposition, cardiovascular risk factors, and hemodynamic forces. The medical community has resorted to the use of pharmacologic agents based on weak data transplanted from either abdominal aortic aneurysms (AAAs) or Marfan syndrome. However, aneurysms differ significantly based on their anatomic location and etiology. Epidemiologic and experimental data demonstrate that different genetic and nongenetic risk factors as well as diverse physiologic processes are responsible for the development and progression of sporadic TAA, familial TAA, and AAA. Therefore, these disease processes need to be considered as distinct entities and not hastily grouped together. The extrapolation of data from one aneurysmal disease process to another is still ill-founded and potentially harmful. Clinical trials in TAA are required before medical therapies, such as ß-blockers, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, statins, or macrolide antibiotics, can be recommended.

The translational science of Marfan syndrome.

Marfan syndrome has changed over the last few years: new diagnostic criteria have been proposed, new clinical entities recognised and life expectancy increased. The role of fibrillin 1, which was initially thought to be mainly structural, has been shown to also be functional. The altered transforming growth factor ß pathway is better understood, the importance of epigenetic factors has been demonstrated and recent data suggest that many of the observations made in Marfan syndrome can actually be made in thoracic aortic aneurysm from diverse aetiologies. Besides transforming growth factor ß, the role of metalloproteinase, the fibrinolytic/coagulation system, is being suggested in the progression of the disease. A relationship between the type of fibrillin 1 (FBN1) gene mutation and the mechanism for the disease (haplo-insufficiency vs negative dominance), as well as some genotype/phenotype correlations, has been observed, although the main challenge of recognising gene modifiers has yet to explain tremendous variability despite similar mutation. This progress has led to new hopes for tomorrow's therapies, some of which are being tested in clinics, whereas others are still in the field of animal models. Here we review some of the new data obtained in the understanding of the pathophysiology and genetics of this disease.

[Molecular biological aspects of Marfan syndromes]. / Molekylærbiologiske aspekter af Marfansyndromer.

Marfan syndrome (MFS) is a hereditary connective tissue disorder. Studies of MFS have established the critical contribution of fibrillin-1 deficiency to disease progression through altered cell-matrix interactions and dysregulated TGF-ß signalling. It is now known that the disease is caused by altered regulation of TGF-ß. As a result, the definition of MFS- and MFS-related diseases as the prototypical structural disorder of the connective tissue has changed to that of a developmental abnormality with broad and complex effects on the morphogenesis and tissue remodelling.

Identification of a novel lethal fibrillin-1 gene mutation in a Chinese Marfan family and correlation of 3' fibrillin-1 gene mutations with phenotype.

BACKGROUND: Mutations in the fibrillin-1 gene have been identified in patients with Marfan syndrome (MFS). This study aimed to identify the molecular defects in the fibrillin-1 gene in a Chinese family with Marfan syndrome, accompanied by aortic aneurysms/dissection. METHODS: Two patients and one non-carrier in the family underwent complete physical, ophthalmic, and cardiovascular examinations. Genomic DNA was extracted from leukocytes of venous blood of these individuals in the family as well as 50 healthy normal controls. Polymerase chain reaction amplification and direct sequencing of all 65 coding exons of fibrillin-1 gene were analyzed. RESULTS: We found a novel mutation (c.8547T > G, p.Tyr2849X) in exon 65 of fibrillin-1 gene in a Chinese proband with Marfan syndrome, accompanied by aortic aneurysms/dissection. Sudden death at a young age of affected members was seen due to aortic aneurysms/dissection. By evaluating genotype-phenotype correlations of patients with mutations in the 3' end of fibrillin-1 gene (exons 64 and 65), we also found that the presence of nonsense mutations occurring in exons 64 and 65 appeared to be an indicator of early-onset aortic risk and sudden death. CONCLUSIONS: These results expand the mutation spectrum of fibrillin-1 gene and help in the study of the molecular pathogenesis of Marfan syndrome, indicating that mutations occurring in the 3' end of fibrillin-1 gene may play an independent functional role in the pathogenesis of Marfan syndrome.

Discrete contributions of elastic fiber components to arterial development and mechanical compliance.

OBJECTIVE: Even though elastin and fibrillin-1 are the major structural components of elastic fibers, mutations in elastin and fibrillin-1 lead to narrowing of large arteries in supravalvular aortic stenosis and dilation of the ascending aorta in Marfan syndrome, respectively. A genetic approach was therefore used here to distinguish the differential contributions of elastin and fibrillin-1 to arterial development and compliance. METHODS AND RESULTS: Key parameters of cardiovascular function were compared among adult mice haploinsufficient for elastin (Eln(+/-)), fibrillin-1 (Fbn1(+/-)), or both proteins (dHet). Physiological and morphological comparisons correlate elastin haploinsufficiency with increased blood pressure and vessel length and tortuosity in dHet mice, and fibrillin-1 haploinsufficiency with increased aortic diameter in the same mutant animals. Mechanical tests confirm that elastin and fibrillin-1 impart elastic recoil and tensile strength to the aortic wall, respectively. Additional ex vivo analyses demonstrate additive and overlapping contributions of elastin and fibrillin-1 to the material properties of vascular tissues. Lastly, light and electron microscopy evidence implicates fibrillin-1 in the hypertension-promoted remodeling of the elastin-deficient aorta. CONCLUSIONS: These results demonstrate that elastin and fibrillin-1 have both differential and complementary roles in arterial wall formation and function, and advance our knowledge of the structural determinants of vascular physiology and disease.

Therapy of Marfan syndrome.

Marfan syndrome is a common inherited disorder of connective tissue caused by deficiency of the matrix protein fibrillin-1. Effective surgical therapy for the most life-threatening manifestation, aortic root aneurysm, has led to a nearly normal lifespan for affected individuals who are appropriately recognized and treated. Traditional medical therapies, such as beta-adrenergic receptor blockade, are used to slow pathologic aortic growth and decrease the risk of aortic dissection by decreasing hemodynamic stress. New insights regarding the pathogenesis of Marfan syndrome have developed from investigation of murine models of this disorder. Fibrillin-1 deficiency is associated with excess signaling by transforming growth factor beta (TGFbeta). TGFbeta antagonists have shown great success in improving or preventing several manifestations of Marfan syndrome in these mice, including aortic aneurysm. These results highlight the potential for development of targeted therapies based on discovery of disease genes and interrogation of pathogenesis in murine models.