Heritable Thoracic Aortic Disease

“Understanding heritable thoracic aortic disease for better and personalized patient management”

MISSION

The mission of our group is to improve the diagnosis, risk stratification, and treatment of patients with heritable thoracic aortic disease (HTAD), a condition with potentially lethal complications. In our group, we approach this issue from different angles, integrating patient data and clinical studies with experiments in animal models, including both mice and zebrafish. We aim to achieve a more reliable identification of causative genetic variants and a better understanding of genetic modifiers of disease. We also perform fundamental research to study mechanisms of disease and find new therapeutic targets. Our goal is to translate fundamental and clinical research findings to enable a more precise clinical management of HTAD. The insights gained through our research efforts could function as a blueprint for future studies of other heritable (cardiovascular) diseases.

DISEASES

Heritable Thoracic Aortic Disorders (HTAD), with a focus on Marfan syndrome (MFS)

MFS-related cardiomyopathy and arrhythmia

TOOLS

Clinical and genetic studies

Zebrafish models

Mouse models

CONTACT

E-MAIL

htad.cmgg@uzgent.be

All publications

Click the link below for an updated list containing all publications of the research group. A number of key papers are highlighted below on this page.

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Arrhythmia and impaired myocardial function in heritable thoracic aortic disease : an international retrospective cohort study

Background: Heritable thoracic aortic diseases (HTAD), typically entailing aortic complications, can be caused by pathogenic variants or likely pathogenic variants (PV/LPVs) in several genes, including fibrillin1 (FBN1), Actin Alpha2 (ACTA2) and genes encoding components of the transforming growth factor (TGF)-beta signaling pathway. In addition to aortic complications, non-aortic cardiac disease such as impaired myocardial function and/or arrhythmia have been increasingly reported, mainly in Marfan syndrome with underlying FBN1 PV/LPVs and are acknowledged as additional causes of morbidity and mortality. The prevalence of these manifestations in the various HTAD entities is largely unknown. Methods: This international multicentre retrospective study collected data on patients with HTAD presenting non-aortic cardiac disease. A total of 9 centers from 7 different countries participated. Patients 12 years or older carrying a PV/LPV in one of the following genes: FBN1, TGFBR1, TGFBR2, TGFB2, TGFB3, SMAD3 and ACTA2 were screened. Non-aortic cardiac disease included impaired myocardial function and/or arrhythmia. Impaired myocardial function was defined as (a)symptomatic reduced ejection fraction (EF<50%). Arrhythmias included atrial fibrillation (AF), atrial flutter (AFL), ventricular tachycardia (VT), ventricular fibrillation (VF) and (aborted) sudden cardiac death (presumed arrhythmogenic) (SCD). Results: Medical records of 3219 patients with HTAD were screened (2761, 385 and 73 carrying a PV/LPV in FBN1, in a TGF-beta signaling gene and in ACTA2 respectively). Non-aortic cardiac disease was reported 142 times in 101 patients (3.1%) (age 37 [range 12-77] years, 39% female): 88 patients carrying an FBN1 PV/LPV and 13 carrying a PV/LPV in one of the TGF-beta signaling genes. Neither impaired myocardial function nor arrhythmia was reported in screened patients carrying a PV/LPV in ACTA2. Among the 142 reported non-aortic cardiac diseases, 68 (48%) were impaired myocardial function, 47 (33%) were AF/AFL and 27 (19%) were VT/VF/SCD. Among the patients with non-aortic cardiac disease, prior cardiac surgery was noted in 80% and severe valvular disease (valvular surgery or severe valvular regurgitation) in 58%, while 18% of the patients developed non-aortic cardiac disease in the absence of any of the latter. Conclusions: In patients with HTAD, arrhythmia and impaired myocardial function was reported in patients with PV/LPVs in FBN1 and in the TGF-beta signaling genes and not in patients harboring PV/LPVs in ACTA2. Though infrequent, non-aortic cardiac disease should be acknowledged as potentially severe, also occurring in young patients with no underlying significant valvular or aortic disease.

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An overview of investigational and experimental drug treatment strategies for Marfan syndrome

Marfan syndrome (MFS) is a heritable connective tissue disorder caused by pathogenic variants in the gene coding for the extracellular matrix protein fibrillin-1. While the disease affects multiple organ systems, the most life-threatening manifestations are aortic aneurysms leading to dissection and rupture. Other cardiovascular complications, including mitral valve prolapse, primary cardiomyopathy, and arrhythmia, also occur more frequently in patients with MFS. The standard medical care relies on cardiovascular imaging at regular intervals, along with pharmacological treatment with β-adrenergic receptor blockers aimed at reducing the aortic growth rate. When aortic dilatation reaches a threshold associated with increased risk of dissection, prophylactic surgical aortic replacement is performed. Although current clinical management has significantly improved the life expectancy of patients with MFS, no cure is available and fatal complications still occur, underscoring the need for new treatment options. In recent years, preclinical studies have identified a number of potentially promising therapeutic targets. Nevertheless, the translation of these results into clinical practice has remained challenging. In this review, we present an overview of the currently available knowledge regarding the underlying pathophysiological processes associated with MFS cardiovascular pathology. We then summarize the treatment options that have been developed based on this knowledge and are currently in different stages of preclinical or clinical development, provide a critical review of the limitations of current studies and highlight potential opportunities for future research.

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Association of mitral annular disjunction with cardiovascular outcomes among patients with Marfan syndrome

IMPORTANCE Mitral annular disjunction (MAD) has received particular interest in patients with mitral valve prolapse, ventricular tachycardia, and sudden cardiac death. The clinical significance of MAD for patients with Marfan syndrome (MFS) remains largely unexplored. OBJECTIVE To define the prevalence of MAD and examine its association with cardiovascular outcomes and arrhythmia among patients with MFS. DESIGN, SETTING, AND PARTICIPANTS This retrospective, single-center cohort study included 142 patients with a diagnosis of MFS based on the revised Ghent criteria and a confirmed (likely) pathogenic variant in the FBN1 gene who underwent regular follow-up between January 1, 2004, and December 31, 2019. MAIN OUTCOMES AND MEASURES The presence of MAD was assessed by echocardiography, and the extent of MAD was categorized in tertiles. Patients also underwent resting electrocardiography and 24-hour Holter monitoring. Outcomes included aortic events (aortic dissection or prophylactic aortic surgery), arrhythmic events (defined as sustained ventricular tachycardia or sudden cardiac death), and mitral valve surgery. RESULTS A total of 142 patients ( 72 female patients [51%]; median age at first examination, 25 years [range, 2-64 years]) were evaluated. Forty-eight patients (34%) had MAD. Patients with MAD had larger aortic root z scores than patients without MAD (4.1 [interquartile range, 2.8-5.7] vs 3.0 [interquartile range, 1.8-4.0]; P<.001) and more often had mitral valve prolapse (34 of 48 [71%] vs 14 of 94 [15%]; P<.001), ventricular ectopy (14 of 33 [42%] vs 15 of 70 [21%]; P=.03), and nonsustained ventricular tachycardia (13 of 33 [39%] vs 12 of 70 [17%]; P=.01). During follow-up, aortic events occurred at similar rates among patients with vs without MAD (15 of 43 [35%] vs 21 of 84 [25%]; P=.24), but patients in the upper MAD tertile (>10 mm) showed a higher occurrence of aortic events compared with patients with MAD of 10 mm or smaller (9 of 15 [60%] vs 6 of 28 [21%]; P=.01). Patients with arrhythmic events (n = 5) and patients requiring mitral valve surgery (n = 7) were observed exclusively in the group displaying MAD. CONCLUSIONS AND RELEVANCE This study suggests that MAD among patients with MFS is associated with the occurrence of arrhythmic events, a higher need for mitral valve intervention, and, among patients with extensive MAD, more aortic events. Cardiac imaging for patients with MFS should consider the assessment of MAD as a potential marker for adverse outcomes.

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Marfan syndrome

Marfan syndrome (MFS) is an autosomal dominant, age-related but highly penetrant condition with substantial intrafamilial and interfamilial variability. MFS is caused by pathogenetic variants in FBN1, which encodes fibrillin-1, a major structural component of the extracellular matrix that provides support to connective tissues, particularly in arteries, the pericondrium and structures in the eye. Up to 25% of individuals with MFS have de novo variants. The most prominent manifestations of MFS are asymptomatic aortic root aneurysms, aortic dissections, dislocation of the ocular lens (ectopia lentis) and skeletal abnormalities that are characterized by overgrowth of the long bones. MFS is diagnosed based on the Ghent II nosology; genetic testing confirming the presence of a FBN1 pathogenetic variant is not always required for diagnosis but can help distinguish MFS from other heritable thoracic aortic disease syndromes that can present with skeletal features similar to those in MFS. Untreated aortic root aneurysms can progress to life-threatening acute aortic dissections. Management of MFS requires medical therapy to slow the rate of growth of aneurysms and decrease the risk of dissection. Routine surveillance with imaging techniques such as transthoracic echocardiography, CT or MRI is necessary to monitor aneurysm growth and determine when to perform prophylactic repair surgery to prevent an acute aortic dissection. Marfan syndrome (MFS) is a genetic disorder affecting the connective tissue, caused by mutations in FBN1 (which encodes fibrillin-1, a structural component of the extracellular matrix); individuals with MFS usually present with cardiovascular (aortic aneurysms and dissections), skeletal and ocular manifestations.

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Spontaneous right ventricular pseudoaneurysms and increased arrhythmogenicity in a mouse model of Marfan syndrome

Patients with Marfan syndrome (MFS), a connective tissue disorder caused by pathogenic variants in the gene encoding the extracellular matrix protein fibrillin-1, have an increased prevalence of primary cardiomyopathy, arrhythmias, and sudden cardiac death. We have performed an in-depth in vivo and ex vivo study of the cardiac phenotype of Fbn1mgR/mgR mice, an established mouse model of MFS with a severely reduced expression of fibrillin-1. Using ultrasound measurements, we confirmed the presence of aortic dilatation and observed cardiac diastolic dysfunction in male Fbn1mgR/mgR mice. Upon post-mortem examination, we discovered that the mutant mice consistently presented myocardial lesions at the level of the right ventricular free wall, which we characterized as spontaneous pseudoaneurysms. Histological investigation demonstrated a decrease in myocardial compaction in the MFS mouse model. Furthermore, continuous 24 h electrocardiographic analysis showed a decreased heart rate variability and an increased prevalence of extrasystolic arrhythmic events in Fbn1mgR/mgR mice compared to wild-type littermates. Taken together, in this paper we document a previously unreported cardiac phenotype in the Fbn1mgR/mgR MFS mouse model and provide a detailed characterization of the cardiac dysfunction and rhythm disorders which are caused by fibrillin-1 deficiency. These findings highlight the wide spectrum of cardiac manifestations of MFS, which might have implications for patient care.

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Myocardial disease and ventricular arrhythmia in Marfan syndrome : a prospective study

Background Aortic root dilatation and-dissection and mitral valve prolapse are established cardiovascular manifestations in Marfan syndrome (MFS). Heart failure and arrhythmic sudden cardiac death have emerged as additional causes of morbidity and mortality. Methods To characterize myocardial dysfunction and arrhythmia in MFS we conducted a prospective longitudinal case-control study including 86 patients with MFS (55.8% women, mean age 36.3 yr-range 13-70 yr-) and 40 age-and sex-matched healthy controls. Cardiac ultrasound, resting and ambulatory ECG (AECG) and NT-proBNP measurements were performed in all subjects at baseline. Additionally, patients with MFS underwent 2 extra evaluations during 30 +/- 7 months follow-up. To study primary versus secondary myocardial involvement, patients with MFS were divided in 2 groups: without previous surgery and normal/mild valvular function (MFS-1; N = 55) and with previous surgery or valvular dysfunction (MFS-2; N = 31). Results Compared to controls, patients in MFS-1 showed mild myocardial disease reflected in a larger left ventricular end-diastolic diameter (LVEDD), lower TAPSE and higher amount of (supra) ventricular extrasystoles [(S)VES]. Patients in MFS-2 were more severely affected. Seven patients (five in MFS-2) presented decreased LV ejection fraction. Twenty patients (twelve in MFS-2) had non-sustained ventricular tachycardia (NSVT) in at least one AECG. Larger LVEDD and higher amount of VES were independently associated with NSVT. Conclusion Our study shows mild but significant myocardial involvement in patients with MFS. Patients with previous surgery or valvular dysfunction are more severely affected. Evaluation of myocardial function with echocardiography and AECG should be considered in all patients with MFS, especially in those with valvular disease and a history of cardiac surgery.

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Genetic testing for aortopathies : primer for the nongeneticist

Purpose of review Although the majority of thoracic aortic aneurysms and dissections (TAD) in the overall population are mainly related to arterial hypertension and atherosclerosis, Heritable Thoracic Aortic Disease (HTAD) are increasingly recognized, especially in younger individuals. As fatal events in the setting of HTAD are preventable with timely detection and appropriate management, this review aims to provide an overview of the genetic basis of HTAD and practical recommendations for genetic evaluation in this setting. Recent findings Thanks in part to a number of important efforts to set up (inter)national networks and consortia for collecting clinical and genetic data from patients with these rare disorders, significant progress has been made in understanding the natural evolution of these disorders. These insights are now starting to enable the development of recommendations for the management of these patients. In addition, pathogenic variants in a number of new genes have been identified in HTAD patients. On the basis of more extensive genetic screening in cohorts of patients with TAD, it is becoming clear that there is no strict boundary between syndromal and nonsyndromal HTAD entities. It is, therefore, important to at least consider genetic evaluation, not only for patients presenting with syndromic forms but also for more isolated TAD. Finally, there are indications that we will -- up to a certain point -- soon be able to draw up a more precise policy for individual patients, based on the underlying genetic defects Genetic evaluation in (young) patients with both syndromic and nonsyndromic forms of HTAD should be considered and is helpful for the development of more precise medicine.

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Sleep apnea and the impact on cardiovascular risk in patients with Marfan syndrome

Background: Marfan syndrome (MFS) is an inherited connective tissue disorder characterized by ectopia lentis, aortic root dilation and dissection and specific skeletal features. Obstructive sleep apnea (OSA) in MFS has been described earlier but the prevalence and its relation with the cardiovascular risk is still controversial. This study aimed to further investigate these aspects. Methods: In this prospective longitudinal study, we performed an attended polysomnography in 40 MFS patients (60% women, 37 +/- 12.8 years) and evaluated several cardiovascular parameters through echocardiography, resting electrocardiogram, 24 hr-Holter monitoring and serum NT-ProBNP measurements. Results: We found that OSA was present in 42.5% of the patients and that higher body mass index was the most important factor associated with the presence of OSA. We observed that overweight was present in 27.5% of the patients in the whole cohort and in 55.6% if >40 years. Furthermore, when evaluating the impact of OSA on the cardiovascular system, we observed that patients with OSA tended to have higher systolic blood pressure, larger distal aortic diameters and a higher prevalence of ventricular arrhythmia. These differences were, however, not significant after adjusting for confounders. Conclusions: Our study shows a high prevalence of OSA and a high prevalence of overweight in MFS patients. We found some trends between OSA and cardiovascular features but we could not establish a solid association. Our study, however might be underpowered, and a multicenter collaborative study could be very useful to answer some important open questions.

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Clinical validity of genes for heritable thoracic aortic aneurysm and dissection

BACKGROUND: Thoracic aortic aneurysms progressively enlarge and predispose to acute aortic dissections. Up to 25% of individuals with thoracic aortic disease harbor an underlying Mendelian pathogenic variant. An evidence-based strategy for selection of genes to test in hereditary thoracic aortic aneurysm and dissection (HTAAD) helps inform family screening and intervention to prevent life-threatening thoracic aortic events. OBJECTIVES: The purpose of this study was to accurately identify genes that predispose to HTAAD using the Clinical Genome Resource (ClinGen) framework. METHODS: We applied the semiquantitative ClinGen framework to assess presumed gene-disease relationships between 53 candidate genes and HTAAD. Genes were classified as causative for HTAAD if they were associated with isolated thoracic aortic disease and were clinically actionable, triggering routine aortic surveillance, intervention, and family cascade screening. All gene-disease assertions were evaluated by a pre-defined curator-expert pair and subsequently discussed with an expert panel. RESULTS: Genes were classified based on the strength of association with HTAAD into 5 categories: definitive (n = 9), strong (n = 2), moderate (n = 4), limited (n = 15), and no reported evidence (n = 23). They were further categorized by severity of associated aortic disease and risk of progression. Eleven genes in the definitive and strong groups were designated as "HTAAD genes" (category A). Eight genes were classified as unlikely to be progressive (category B) and 4 as low risk (category C). The remaining genes were recent genes with an uncertain classification or genes with no evidence of association with HTAAD. CONCLUSIONS: The ClinGen framework is useful to semiquantitatively assess the strength of gene-disease relationships for HTAAD. Gene categories resulting from the curation may inform clinical laboratories in the development, interpretation, and subsequent clinical implications of genetic testing for patients with aortic disease.

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A heart for fibrillin : spatial arrangement in adult wild-type murine myocardial tissue

Fibrillins are major constituents of microfibrils, which are essential components of the extracellular matrix of connective tissues where they contribute to the tissue homeostasis. Although it is known that microfibrils are abundantly expressed in the left ventricle of the heart, limited data are available about the presence of microfibrils in the other parts of the myocardial tissue and whether there are age or sex-related differences in the spatial arrangement of the microfibrils. This basic knowledge is essential to better understand the impact of fibrillin-1 pathogenic variants on the myocardial tissue as seen in Marfan related cardiomyopathy. We performed histological analyses on wild-type male and female murine myocardial tissue collected at different time-points (1, 3 and 6 months). Fibrillin-1 and -2 immunofluorescence stainings were performed on cross-sections at the level of the apex, the mid-ventricles and the atria. In addition, other myocardial matrix components such as collagen and elastin were also investigated. Fibrillin-1 presented as long fibres in the apex, mid-ventricles and atria. The spatial arrangement differed between the investigated regions, but not between age groups or sexes. Collagen had a similar broad spatial arrangement to that of fibrillin-1, whereas elastic fibres were primarily present in the atria and the vessels. In contrast to fibrillin-1, limited amounts of fibrillin-2 were observed. Fibrillin-rich fibres contribute to the architecture of the myocardial tissue in a region-dependent manner in wild-type murine hearts. This knowledge is helpful for future experimental set-ups of studies evaluating the impact of fibrillin-1 pathogenic variants on the myocardial tissue.

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Sex, pregnancy and aortic disease in Marfan syndrome

Background : Sex-related differences as well as the adverse effect of pregnancy on aortic disease outcome are well-established phenomena in humans with Marfan syndrome (MFS). The underlying mechanisms of these observations are largely unknown. Objectives : In an initial (pilot) step we aimed to confirm the differences between male and female MFS patients as well as between females with and without previous pregnancy. We then sought to evaluate whether these findings are recapitulated in a pre-clinical model and performed in-depth cardiovascular phenotyping of mutant male and both nulliparous and multiparous female Marfan mice. The effect of 17 beta-estradiol on fibrillin-1 protein synthesis was compared in vitro using human aortic smooth muscle cells and fibroblasts. Results : Our small retrospective study of aortic dimensions in a cohort of 10 men and 20 women with MFS (10 pregnant and 10 non-pregnant) confirmed that aortic root growth was significantly increased in the pregnant group compared to the non-pregnant group (0.64mm/year vs. 0.12mm/year, p = 0.018). Male MFS patients had significantly larger aortic root diameters compared to the non-pregnant and pregnant females at baseline and follow-up (p = 0.002 and p = 0.007, respectively), but no significant increase in aortic root growth was observed compared to the females after follow-up (p = 0.559 and p = 0.352). In the GT-8/+ MFS mouse model, multiparous female Marfan mice showed increased aortic diameters when compared to nulliparous females. Aortic dilatation in multiparous females was comparable to Marfan male mice. Moreover, increased aortic diameters were associated with more severe fragmentation of the elastic lamellae. In addition, 17 beta-estradiol was found to promote fibrillin-1 production by human aortic smooth muscle cells. Conclusions : Pregnancy-related changes influence aortic disease severity in otherwise protected female MFS mice and patients. There may be a role for estrogen in the female sex protective effect.

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Tailoring the American College of Medical Genetics and Genomics and the Association for Molecular Pathology guidelines for the interpretation of sequenced variants in the FBN1 gene for Marfan syndrome : proposal for a disease- and gene-specific guideline

Background: The introduction of next-generation sequencing techniques has substantially increased the identification of new genetic variants and hence the necessity of accurate variant interpretation. In 2015, the American College of Medical Genetics and Genomics and the Association for Molecular Pathology proposed new variant interpretation guidelines. Gene-specific characteristics were, however, not considered, sometimes leading to inconsistent variant interpretation. Methods: To allow a more uniform interpretation of variants in the FBN1 (fibrillin-1) gene, causing Marfan syndrome, we tailored these guidelines to this gene and disease. We adapted 15 of the 28 general criteria and classified 713 FBN1 variants previously identified in our laboratory as causal mutation or variant of uncertain significance according to these adapted guidelines. We then compared the agreement between previous methods and the adapted American College of Medical Genetics and Genomics and the Association for Molecular Pathology criteria. Results: Agreement between the methods was 86.4% (K-alpha, 0.6). Application of the tailored guidelines resulted in an increased number of variants of uncertain significance (14.5% to 24.2%). Of the 85 variants that were downscaled to likely benign or variant of uncertain significance, 59.7% were missense variants outside a well-established functional site. Available clinical- or segregation data, necessary to further classify these types of variants, were in many cases insufficient to aid the classification. Conclusions: Our study shows that classification of variants remains challenging and may change over time. Currently, a higher level of evidence is necessary to classify a variant as pathogenic. Gene-specific guidelines may be useful to allow a more precise and uniform interpretation of the variants to accurately support clinical decision-making.

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Intrinsic cardiomyopathy in Marfan syndrome: results from in- and ex-vivo studies of the Fbn1C1039G/+ model and longitudinal findings in humans

BACKGROUND: Mild intrinsic cardiomyopathy in patients with Marfan syndrome (MFS) has consistently been evidenced by independent research groups. So far, little is known about the long-term evolution and pathophysiology of this finding. METHODS:To gain more insights into the pathophysiology of MFS-related cardiomyopathy, we performed in-vivo and ex-vivo studies of 11 Fbn1(C1039G/+) mice and 9 wild-type (WT) littermates. Serial ultrasound findings obtained in mice were correlated to the human phenotype. We therefore reassessed left ventricular (LV) function parameters over a 6-y follow-up period in 19 previously reported MFS patients, in whom we documented mild LV dysfunction. RESULTS: Fbn1(C1039G/+) mice demonstrated LV contractile dys-function. Subsequent ex-vivo studies of the myocardium of adult mutant mice revealed upregulation of TGF beta-related pathways and consistent abnormalities of the microfibrillar network, implicating a role for microfibrils in the mechanical properties of the myocardium. Echocardiographic parameters did not indicate clinical significant deterioration of LV function during follow-up in our patient cohort. CONCLUSION: In analogy with what is observed in the majority of MFS patients, the Fbn1(C1039G/+) mouse model demonstrates mild intrinsic LV dysfunction. Both extracellular matrix and molecular alterations are implicated in MFS-related cardiomyopathy. This model may now enable us to study therapeutic interventions on the myocardium in MFS.

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Gene panel sequencing in heritable thoracic aortic disorders and related entities: results of comprehensive testing in a cohort of 264 patients

Background: Heritable Thoracic Aortic Disorders (H-TAD) may present clinically as part of a syndromic entity or as an isolated (nonsyndromic) manifestation. About one dozen genes are now available for clinical molecular testing. Targeted single gene testing is hampered by significant clinical overlap between syndromic H-TAD entities and the absence of discriminating features in isolated cases. Therefore panel testing of multiple genes has now emerged as the preferred approach. So far, no data on mutation detection rate with this technique have been reported. Methods: We performed Next Generation Sequencing (NGS) based screening of the seven currently most prevalent H-TAD-associated genes (FBN1, TGFBR1/2, TGFB2, SMAD3, ACTA2 and COL3A1) on 264 samples from unrelated probands referred for H-TAD and related entities. Patients fulfilling the criteria for Marfan syndrome (MFS) were only included if targeted FBN1 sequencing and MLPA analysis were negative. Results: A mutation was identified in 34 patients (13%): 12 FBN1, one TGFBR1, two TGFBR2, three TGFB2, nine SMAD3, four ACTA2 and three COL3A1 mutations. We found mutations in FBN1 (N = 3), TGFBR2 (N = 1) and COL3A1 (N = 2) in patients without characteristic clinical features of syndromal H-TAD. Six TAD patients harboring a mutation in SMAD3 and one TAD patient with a TGFB2 mutation fulfilled the diagnostic criteria for MFS. Conclusion: NGS based H-TAD panel testing efficiently reveals a mutation in 13% of patients. Our observations emphasize the clinical overlap between patients harboring mutations in syndromic and nonsyndromic H-TAD related genes as well as within syndromic H-TAD entities, justifying a widespread application of this technique.

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