Reduced penetrance and variable expressivity of familial thoracic aortic aneurysms/dissections

Genetic variants in childhood-onset dilatation of thoracic aorta in a consanguineous population

INTRODUCTION

Childhood-onset thoracic aortic dilatation (TAD) is a heterogenous group of genetic conditions the inheritance of which is largely dominant. To our knowledge, the influence of consanguinity on childhood-onset TAD has not been addressed systematically. We aim to study a cohort of children with TAD in our highly consanguineous population.

METHODS

Children with TAD were consecutively recruited. Based on the likelihood of a founder mutation, genetic test was categorized to either targeted gene testing or multi-gene sequencing, followed by genetic screening of first-degree relatives. Clinical data and outcome were reviewed.

RESULTS

Thirty-three children, from 20 families, had childhood-onset TAD. Genetic test was positive in 20 children, from 13 families, providing a yield of 65 % (13/20). The median age of onset of TAD was 4.5 years. Eight variants were detected in 4 genes (FBN1, EFEMP2, ACTA2, KANSL1) with a homozygous EFEMP2 variant found in 6 families (46.2 %). Surgical intervention was required in 14 (70 %) cases (13 with EFEMP2, 1 with FBN1 variants) at a median age of 3.5 years. All patients are alive (ages range:3-31 years).

CONCLUSIONS

Our work illustrates the impact of consanguinity on the genetics of childhood-onset TAD elucidating severe presentation of recessively inherited form. Our data underscores the importance of genetic screening and early recognition of TAD to achieve excellent outcome.

A De Novo Missense MYLK Variant Leading to Nonsyndromic Thoracic Aortic Aneurysm and Dissection Identified by Segregation Analysis

Nonsyndromic hereditary thoracic aortic aneurysm and dissection (TAAD) is an autosomal dominant disease; however, it is frequently difficult to identify the causative genes. We report in this study a 33-year-old Japanese male with TAAD (Stanford type A) that is complicated with severe aortic regurgitation. There was no family history of aortic diseases in the patient nor any specific clinical features suggestive of connective tissue diseases, such as Marfan syndrome. Genetic testing identified candidate causative variants in two different genes: MYLK (c.4819G > A, p.[Gly1607Ser]) and FBN1 (c.365G > A, p.[Arg122His]). Familial cosegregation analysis revealed that the novel de novo MYLK variant was present only in the proband, and the FBN1 variant was also found in his nonaffected mother, and thus the MYLK variant was classified as likely pathogenic. MYLK is a causative gene for nonsyndromic TAAD that requires careful management; however, the number of reports is limited. Accumulating data on the pathogenicity of rare variants by performing a comprehensive pedigree analysis would help establish better treatment strategies for life-threatening hereditary TAAD cases.

2022 ACC/AHA guideline for the diagnosis and management of aortic disease: A report of the American Heart Association/American College of Cardiology Joint Committee on Clinical Practice Guidelines

AIM

The "2022 ACC/AHA Guideline for the Diagnosis and Management of Aortic Disease" provides recommendations to guide clinicians in the diagnosis, genetic evaluation and family screening, medical therapy, endovascular and surgical treatment, and long-term surveillance of patients with aortic disease across its multiple clinical presentation subsets (ie, asymptomatic, stable symptomatic, and acute aortic syndromes).

METHODS

A comprehensive literature search was conducted from January 2021 to April 2021, encompassing studies, reviews, and other evidence conducted on human subjects that were published in English from PubMed, EMBASE, the Cochrane Library, CINHL Complete, and other selected databases relevant to this guideline. Additional relevant studies, published through June 2022 during the guideline writing process, were also considered by the writing committee, where appropriate.

STRUCTURE

Recommendations from previously published AHA/ACC guidelines on thoracic aortic disease, peripheral artery disease, and bicuspid aortic valve disease have been updated with new evidence to guide clinicians. In addition, new recommendations addressing comprehensive care for patients with aortic disease have been developed. There is added emphasis on the role of shared decision making, especially in the management of patients with aortic disease both before and during pregnancy. The is also an increased emphasis on the importance of institutional interventional volume and multidisciplinary aortic team expertise in the care of patients with aortic disease.

Genetically Triggered Thoracic Aortic Disease: Who Should be Tested?

Up to 25% of patients with thoracic aortic disease have an underlying Mendelian pathogenic variant. This is a heterogeneous group of disorders known as heritable thoracic aortic diseases (HTAD). Diagnosing associated pathogenic gene variants and syndromes is critical, as the underlying genetics have an implication in medical management, surveillance, thresholds for surgical intervention, surgical risk, pregnancy risk, and risk of inheritance by the offspring. Recently released 2022 American College of Cardiology/American Heart Association guidelines for the diagnosis and management of aortic diseases provide specific recommendations to identify patients at risk for heritable conditions and who should undergo genetic testing.

2022 ACC/AHA Guideline for the Diagnosis and Management of Aortic Disease: A Report of the American Heart Association/American College of Cardiology Joint Committee on Clinical Practice Guidelines

AIM

The "2022 ACC/AHA Guideline for the Diagnosis and Management of Aortic Disease" provides recommendations to guide clinicians in the diagnosis, genetic evaluation and family screening, medical therapy, endovascular and surgical treatment, and long-term surveillance of patients with aortic disease across its multiple clinical presentation subsets (ie, asymptomatic, stable symptomatic, and acute aortic syndromes).

METHODS

A comprehensive literature search was conducted from January 2021 to April 2021, encompassing studies, reviews, and other evidence conducted on human subjects that were published in English from PubMed, EMBASE, the Cochrane Library, CINHL Complete, and other selected databases relevant to this guideline. Additional relevant studies, published through June 2022 during the guideline writing process, were also considered by the writing committee, where appropriate. Structure: Recommendations from previously published AHA/ACC guidelines on thoracic aortic disease, peripheral artery disease, and bicuspid aortic valve disease have been updated with new evidence to guide clinicians. In addition, new recommendations addressing comprehensive care for patients with aortic disease have been developed. There is added emphasis on the role of shared decision making, especially in the management of patients with aortic disease both before and during pregnancy. The is also an increased emphasis on the importance of institutional interventional volume and multidisciplinary aortic team expertise in the care of patients with aortic disease.

2022 ACC/AHA Guideline for the Diagnosis and Management of Aortic Disease: A Report of the American Heart Association/American College of Cardiology Joint Committee on Clinical Practice Guidelines

AIM

The "2022 ACC/AHA Guideline for the Diagnosis and Management of Aortic Disease" provides recommendations to guide clinicians in the diagnosis, genetic evaluation and family screening, medical therapy, endovascular and surgical treatment, and long-term surveillance of patients with aortic disease across its multiple clinical presentation subsets (ie, asymptomatic, stable symptomatic, and acute aortic syndromes).

METHODS

A comprehensive literature search was conducted from January 2021 to April 2021, encompassing studies, reviews, and other evidence conducted on human subjects that were published in English from PubMed, EMBASE, the Cochrane Library, CINHL Complete, and other selected databases relevant to this guideline. Additional relevant studies, published through June 2022 during the guideline writing process, were also considered by the writing committee, where appropriate.

STRUCTURE

Recommendations from previously published AHA/ACC guidelines on thoracic aortic disease, peripheral artery disease, and bicuspid aortic valve disease have been updated with new evidence to guide clinicians. In addition, new recommendations addressing comprehensive care for patients with aortic disease have been developed. There is added emphasis on the role of shared decision making, especially in the management of patients with aortic disease both before and during pregnancy. The is also an increased emphasis on the importance of institutional interventional volume and multidisciplinary aortic team expertise in the care of patients with aortic disease.

Genetic screening in heritable thoracic aortic disease—rationale, potentials and pitfalls

Thoracic aortic aneurysms are silent yet deadly clinical entities which may elude detection until an acutely life-threatening aortic dissection or rupture occurs. Approximately 20% of patients with thoracic aortic aneurysms or dissection have a positive family history, indicating a strong genetic component to the aetiology. Genetic screening in such hereditary thoracic aortic disease (HTAD) may thus be beneficial in detecting causative genetic mutations in affected patients, identifying asymptomatic family members who may be at risk, and in guiding the optimal timing of preventative surgery in those with confirmed genetic aortopathy. Genetic screening can facilitate personalised aortic care tailored to an individual's specific genetic abnormality, with the aim of mitigating the significant morbidity burden and premature mortality associated with HTAD. This review examines the rationale for genetic screening in HTAD, its potential applications, current limitations and potential future directions.

Genetically engineered animal models for Marfan syndrome: challenges associated with the generation of pig models for diseases caused by haploinsufficiency

Recent developments in reproductive biology have enabled the generation of genetically engineered pigs as models for inherited human diseases. Although a variety of such models for monogenic diseases are currently available, reproduction of human diseases caused by haploinsufficiency remains a major challenge. The present study compares the phenotypes of mouse and pig models of Marfan syndrome (MFS), with a special focus on the expressivity and penetrance of associated symptoms. Furthermore, investigation of the gene regulation mechanisms associated with haploinsufficiency will be of immense utility in developing faithful MFS pig models.

Connective Tissue Disorders and Cardiovascular Complications: The Indomitable Role of Transforming Growth Factor-β Signaling

Marfan Syndrome (MFS) and Loeys-Dietz Syndrome (LDS) represent heritable connective tissue disorders that segregate with a similar pattern of cardiovascular defects (thoracic aortic aneurysm, mitral valve prolapse/regurgitation, and aortic dilatation with regurgitation). This pattern of cardiovascular defects appears to be expressed along a spectrum of severity in many heritable connective tissue disorders and raises suspicion of a relationship between the normal development of connective tissues and the cardiovascular system. With overwhelming evidence of the involvement of aberrant Transforming Growth Factor-beta (TGF-β) signaling in MFS and LDS, this signaling pathway may represent the common link in the relationship between connective tissue disorders and their associated cardiovascular complications. To further explore this hypothetical link, this chapter will review the TGF-β signaling pathway, the heritable connective tissue syndromes related to aberrant TGF-β signaling, and will discuss the pathogenic contribution of TGF-β to these syndromes with a primary focus on the cardiovascular system.

Update on the genetic risk for thoracic aortic aneurysms and acute aortic dissections: implications for clinical care

Genetic variation plays a significant role in predisposing individuals to thoracic aortic aneurysms and dissections. Advances in genomic research have led to the discovery of 11 genes validated to cause heritable thoracic aortic disease (HTAD). Identifying the pathogenic variants responsible for aortic disease in affected patients confers substantial clinical utility by establishing a definitive diagnosis to inform tailored treatment and management, and enables identification of at-risk relatives to prevent downstream morbidity and mortality. The availability and access to clinical genetic testing has improved dramatically such that genetic testing is considered an integral part of the clinical evaluation for patients with thoracic aortic disease. This review provides an update on our current understanding of the genetic basis of thoracic aortic disease, practical recommendations for genetic testing, and clinical implications.

Epidemiology of thoracoabdominal aortic aneurysms

Thoracoabdominal aortic aneurysms, although rare, continue to be associated with high morbidity and mortality in the modern era of vascular surgery, and knowledge of this disease is essential for those in clinical practice. Given the clinically silent nature of the disease, it is difficult to determine disease incidence, with most epidemiologic recommendations not made based on evidence regarding those diagnosed with the disease, but extrapolated from data on surgical outcomes. It appears that although men are more likely to develop thoracoabdominal aortic aneurysms, the distribution is not as skewed as in abdominal aortic aneurysms. Current evidence suggests that Black and Hispanic patients continue to have disproportionately poor disease outcomes, mostly attributed to later presentation and undergoing interventions at lower-volume centers. Although select patients meet criteria for disease screening based on personal or family history of aneurysmal disease, general population screening has not been recommended by any professional organization to date. Vascular surgeons need to continue to be at the forefront of thoracoabdominal aortic aneurysm management, especially as care becomes centered around comprehensive "aortic care centers" and as more endovascular therapies become available.

Thoracic aortic aneurysm gene dictionary

Thoracic aortic aneurysm is typically clinically silent, with a natural history of progressive enlargement until a potentially lethal complication such as rupture or dissection occurs. Underlying genetic predisposition strongly influences the risk of thoracic aortic aneurysm and dissection. Familial cases are more virulent, have a higher rate of aneurysm growth, and occur earlier in life. To date, over 30 genes have been associated with syndromic and non-syndromic thoracic aortic aneurysm and dissection. The causative genes and their specific variants help to predict the disease phenotype, including age at presentation, risk of dissection at small aortic sizes, and risk of other cardiovascular and systemic manifestations. This genetic "dictionary" is already a clinical reality, allowing us to personalize care based on specific causative mutations for a substantial proportion of these patients. Widespread genetic sequencing of thoracic aortic aneurysm and dissection patients has been and continues to be crucial to the rapid expansion of this dictionary and ultimately, the delivery of truly personalized care to every patient.

A Postpartum Type A Dissection

A 28-year-old woman with familial thoracic aortic aneurysm and dissection syndrome and a mildly dilated aorta presented 3 days postpartum with a type A aortic dissection. This case illustrates the unpredictability of this disease and the challenges with risk stratification of women with underlying aortopathy contemplating pregnancy. (Level of Difficulty: Intermediate.)

Genetics of Thoracic and Abdominal Aortic Diseases

Dissections or ruptures of aortic aneurysms remain a leading cause of death in the developed world, with the majority of deaths being preventable if individuals at risk are identified and properly managed. Genetic variants predispose individuals to these aortic diseases. In the case of thoracic aortic aneurysm and dissections (thoracic aortic disease), genetic data can be used to identify some at-risk individuals and dictate management of the associated vascular disease. For abdominal aortic aneurysms, genetic associations have been identified, which provide insight on the molecular pathogenesis but cannot be used clinically yet to identify individuals at risk for abdominal aortic aneurysms. This compendium will discuss our current understanding of the genetic basis of thoracic aortic disease and abdominal aortic aneurysm disease. Although both diseases share several pathogenic similarities, including proteolytic elastic tissue degeneration and smooth muscle dysfunction, they also have several distinct differences, including population prevalence and modes of inheritance.

The genetics and biomechanics of thoracic aortic diseases

Thoracic aortic aneurysms and aortic dissections (TAAD) are highly fatal emergencies within cardiothoracic surgery. With increasing age, thoracic aneurysms become more prevalent and pose an even greater threat when they develop into aortic dissections. Both diseases are multifactorial and are influenced by a multitude of physiological and biomechanical processes. Structural stability of aorta can be disrupted by genes, such as those for extracellular matrix and contractile protein, as well as telomere dysfunction, which leads to senescence of smooth muscle and endothelial cells. Biomechanical changes such as increased luminal pressure imposed by hypertension are also very prevalent and lead to structural instability. Furthermore, ageing is associated with a pro-inflammatory state that exacerbates degeneration of vessel wall, facilitating the development of both aortic aneurysms and aortic dissection. This literature review provides an overview of the aetiology and pathophysiology of both thoracic aneurysms and aortic dissections. With an improved understanding, new therapeutic targets may eventually be identified to facilitate treatment and prevention of these diseases.

Systematic Review of Studies That Have Evaluated Screening Tests in Relatives of Patients Affected by Nonsyndromic Thoracic Aortic Disease

Background Nonsyndromic thoracic aortic diseases ( NS - TADs ) are often silent entities until they present as life-threatening emergencies. Despite familial inheritance being common, screening is not the current standard of care in NS - TAD s. We sought to determine the incidence of aortic diseases, the predictive accuracy of available screening tests, and the effectiveness of screening programs in relatives of patients affected by NS - TADs . Methods and Results A systematic literature search on PubMed/ MEDLINE , Embase, and the Cochrane Library was conducted from inception to the end of December 2017. The search was supplemented with the Online Mendelian Inheritance in Man database. A total of 53 studies were included, and a total of 2696 NS - TAD relatives were screened. Screening was genetic in 49% of studies, followed by imaging techniques in 11% and a combination of the 2 in 40%. Newly affected individuals were identified in 33%, 24%, and 15% of first-, second-, and third-degree relatives, respectively. Familial NS - TAD s were primarily attributed to single-gene mutations, expressed in an autosomal dominant pattern with incomplete penetrance. Specific gene mutations were observed in 25% of the screened families. Disease subtype and genetic mutations stratified patients with respect to age of presentation, aneurysmal location, and aortic diameter before dissection. Relatives of patients with sporadic NS - TAD s were also found to be affected. No studies evaluated the predictive accuracy of imaging or genetic screening tests, or the clinical or cost-effectiveness of an NS - TAD screening program. Conclusions First- and second-degree relatives of patients affected by both familial and sporadic NS - TAD s may benefit from personalized screening programs.

Preconception Counseling for Patients With Thoracic Aortic Aneurysms

PURPOSE OF THE REVIEW

Acute aortic dissection is a potentially catastrophic cardiovascular emergency that is associated with a high mortality rate. Pregnancy, with its attendant hormonal and physiological changes, increases the risk of dissection in women with known thoracic aortic aneurysms. In this review, we highlight the importance of preconception counseling to help women with known thoracic aortic aneurysms better understand their risk of dissection and the heritable nature of thoracic aortic disease and its associated syndromes.

RECENT FINDINGS

The risk of aortic dissection during pregnancy differs according to the underlying etiology of thoracic aortic aneurysm and the degree of aortic dilatation at baseline. Guideline-specific management of women with thoracic aortic aneurysms in pregnancy reduces their risk of dissection. Management of pregnant women with thoracic aortic aneurysms requires an intensive multidisciplinary approach to maximize the chances of a successful outcome for both the mother and fetus. Preconception counseling provides an opportunity to optimize patients medically and to consider potential prophylactic aortic repair prior to pregnancy.

Human aortic aneurysm genomic dictionary: is it possible?

Thoracic aortic aneurysm (TAA), a typically silent but frequently lethal disease, is strongly influenced by underlying genetics. Approximately 30 genes have been associated with syndromic and non-syndromic familial thoracic aortic aneurysm and dissection (TAAD) to date. An estimated 30% of patients with non-syndromic familial TAAD, which is typically inherited in an autosomal dominant manner, have a mutation in one of these genes. The underlying genetic mutation helps predict patients' clinical presentation, risk of aortic dissection at small aortic sizes (< 5.0 cm), and risk of other cardiovascular disease. As a result, a TAAD genomic dictionary based on these genes is necessary to provide optimal patient care, but is not on its own sufficient as this disease is typically inherited with reduced penetrance and has widely variable expressivity. Next-generation sequencing has been and will continue to be critical for identifying novel genes and variants associated with TAAD as well as genotype-phenotype correlations that will allow for management to be targeted to not only the underlying gene harboring the pathogenic variant but also the specific mutation identified. The aortic dictionary, to which a clinician can turn to obtain information on clinical consequences of a specific genetic variants, is not only possible, but has been substantially written already. As additional entries to the dictionary are made, truly personalized, genetically based, aneurysm care can be delivered.

Whole exome sequencing identifies FBN1 mutations in two patients with early‑onset type B aortic dissection

The etiology of thoracic aortic aneurysm and dissection (TAAD) is complex and heterogeneous. Emerging evidence has demonstrated that genetic causes may be a consideration in early‑onset TAAD. Owing to overlapping clinical phenotypes and the genetic heterogeneity of TAAD, it is challenging for clinicians to make a molecular diagnosis of TAAD, particularly in those who present with non‑specific syndromic features. In order to identify the causative mutation in two young patients with acute type B aortic dissection without syndromic features, whole exome sequencing (WES) was performed in the present study. A missense mutation (c.G6953A:p.C2318Y) and a nonsense mutation (c.C4786T:p.R1596X) were identified in the fibrillin 1 gene in patients T287 and T267, respectively. The present study emphasized the necessity of genetic testing for young patients with type B aortic dissection. WES is a timely, robust and inexpensive technique for molecular diagnosis, particularly for TAAD caused by numerous genes. Genetic diagnosis of Marfan syndrome could aid in periodic surveillance, prophylactic surgical measures, and genetic counseling.

Open Versus Endovascular or Hybrid Thoracic Aortic Aneurysm Repair

Thoracic aortic aneurysms are associated with significant morbidity and mortality. There are multiple underlying etiologies, including genetic abnormalities, that have important implications in their natural history. The variable histologic, anatomic, and clinical presentations necessitate careful consideration of available treatment options. Surgical repair of these aneurysms has been the mainstay of treatment; however, these approaches can carry a relatively high risk of morbidity and mortality. Endovascular approaches have now become first-line therapy for descending thoracic aneurysms, and with advancements in graft technology, endovascular approaches are being increasingly employed for hybrid repairs of the aortic arch and even the ascending aorta. However, to date, clinical outcomes from randomized trials and long-term follow-up are limited. As technology continues to advance, there is the potential for further integration of surgical and endovascular treatments so that patients have the best opportunity for a favorable outcome.

Genes Associated with Thoracic Aortic Aneurysm and Dissection: An Update and Clinical Implications

Thoracic aortic aneurysm (TAA) is a lethal disease, with a natural history of enlarging progressively until dissection or rupture occurs. Since the discovery almost 20 years ago that ascending TAAs are highly familial, our understanding of the genetics of thoracic aortic aneurysm and dissection (TAAD) has increased exponentially. At least 29 genes have been shown to be associated with the development of TAAD, the majority of which encode proteins involved in the extracellular matrix, smooth muscle cell contraction or metabolism, or the transforming growth factor-β signaling pathway. Almost one-quarter of TAAD patients have a mutation in one of these genes. In this review, we provide a summary of TAAD-associated genes, associated clinical features of the vasculature, and implications for surgical treatment of TAAD. With the widespread use of next-generation sequencing and development of novel functional assays, the future of the genetics of TAAD is bright, as both novel TAAD genes and variants within the genes will continue to be identified.

Therapeutics Targeting Drivers of Thoracic Aortic Aneurysms and Acute Aortic Dissections: Insights from Predisposing Genes and Mouse Models

Thoracic aortic diseases, including aneurysms and dissections of the thoracic aorta, are a major cause of morbidity and mortality. Risk factors for thoracic aortic disease include increased hemodynamic forces on the ascending aorta, typically due to poorly controlled hypertension, and heritable genetic variants. The altered genes predisposing to thoracic aortic disease either disrupt smooth muscle cell (SMC) contraction or adherence to an impaired extracellular matrix, or decrease canonical transforming growth factor beta (TGF-β) signaling. Paradoxically, TGF-β hyperactivity has been postulated to be the primary driver for the disease. More recently, it has been proposed that the response of aortic SMCs to the hemodynamic load on a structurally defective aorta is the primary driver of thoracic aortic disease, and that TGF-β overactivity in diseased aortas is a secondary, unproductive response to restore tissue function. The engineering of mouse models of inherited aortopathies has identified potential therapeutic agents to prevent thoracic aortic disease.

Identification of a missense mutation of COL3A1 in a Chinese family with atypical Ehlers-Danlos syndrome using targeted next-generation sequencing

Aortopathy represents an important cause of mortality in industrialized countries, with a number of genes identified as predispose factors. It can be difficult to identify the genetic lesions underlying this disorder, particularly when the phenotype is atypical. The present study performed targeted next-generation sequencing of 428 genes associated with cardiovascular diseases in a family with aortopathy, the proband of which presented with abdominal aortic aneurysm rupture only, with tissue fragility noted in surgery. After targeted capture, sequencing and bioinformatics analysis, a missense mutation, p.A1259T, was identified in the collagen type III α1 (COL3A1) gene and co-segregated with the disease in the family. Crystal structure modeling revealed abnormal hydrogen bonds generated by the mutation, which likely affected the spatial structure of the procollagen C-propeptide. Mutations in the procollagen C-propeptide are rare and genotype-phenotype correlation may explain the atypical manifestations of affected individuals. The results of the present study suggested that targeted gene capture combined with next-generation sequencing can serve as a useful technique in the genetic diagnosis of aortopathy, particularly in the content of an atypical phenotype.

Interpreting and Integrating Clinical and Anatomic Pathology Results

The continuing education course on integrating clinical and anatomical pathology data was designed to communicate the importance of using a weight of evidence approach to interpret safety findings in toxicology studies. This approach is necessary, as neither clinical nor anatomic pathology data can be relied upon in isolation to fully understand the relationship between study findings and the test article. Basic principles for correlating anatomic pathology and clinical pathology findings and for integrating these with other study end points were reviewed. To highlight these relationships, a series of case examples, presented jointly by a clinical pathologist and an anatomic pathologist, were used to illustrate the collaborative effort required between clinical and anatomical pathologists. In addition, the diagnostic utility of traditional liver biomarkers was discussed using results from a meta-analysis of rat hepatobiliary marker and histopathology data. This discussion also included examples of traditional and novel liver and renal biomarker data implementation in nonclinical toxicology studies to illustrate the relationship between discrete changes in biochemistry and tissue morphology.

WES/WGS Reporting of Mutations from Cardiovascular "Actionable" Genes in Clinical Practice: A Key Role for UMD Knowledgebases in the Era of Big Databases

High-throughput next-generation sequencing such as whole-exome and whole-genome sequencing are being rapidly integrated into clinical practice. The use of these techniques leads to the identification of secondary variants for which decisions about the reporting or not to the patient need to be made. The American College of Medical Genetics and Genomics recently published recommendations for the reporting of these variants in clinical practice for 56 "actionable" genes. Among these, seven are involved in Marfan Syndrome And Related Disorders (MSARD) resulting from mutations of the FBN1, TGFBR1 and 2, ACTA2, SMAD3, MYH11 and MYLK genes. Here, we show that mutations collected in UMD databases for MSARD genes (UMD-MSARD) are rarely reported, including the most frequent ones, in global scale initiatives for variant annotation such as the NHLBI GO Exome Sequencing Project (ESP), the Exome Aggregation Consortium (ExAC), and ClinVar. The predicted pathogenic mutations reported in global scale initiatives but absent in locus-specific databases (LSDBs) mainly correspond to rare events. UMD-MSARD databases are therefore the only resources providing access to the full spectrum of known pathogenic mutations. They are the most comprehensive resources for clinicians and geneticists to interpret MSARD-related variations not only primary variants but also secondary variants.

PRKG1 and genetic diagnosis of early-onset thoracic aortic disease

BACKGROUND

The 20% of thoracic aortic aneurysms and dissections independent from the main connective tissue syndromes and expected to be familial has gained importance over the past years. The more frequent pattern of inheritance of these nonsyndromic cases is autosomal dominant with incomplete penetrance and variable expression. Although many candidate genes exist, unresolved familial cases suggest still unravelled genetic variation. The main purpose of this study was to establish the genetic diagnosis of one of those.

MATERIALS AND METHODS

To begin with, we applied a candidate gene approach based on both traditional and a customized massive parallel sequencing panel, followed by Illumina HiSeq 2000 whole exome sequencing of four family members affected by early-onset thoracic aortic disease and two unaffected relatives. We prioritized whole exome sequencing results based on variant location, type and frequency in general population databases and performed segregation analysis in 14 family members using traditional sequencing.

RESULTS

After the negative results we obtained with candidate gene approaches, the analysis and prioritization of whole exome sequencing results brought out the heterozygote c.530G>A:p.Arg177Gln PRKG1 variant (NM_001098512), located in one of the aortic smooth muscle cell contractile apparatus genes. This candidate variant segregated with thoracic aortic disease, as it was present in seven affected and absent in five unaffected family members, further supporting its causality.

CONCLUSIONS

This was the second time PRKG1 was associated with thoracic aortic disease, highlighting and reaffirming it as a strong candidate for gene-based diagnosis of nonsyndromic early-onset cases.

Do Familial Aortic Dissections Tend to Occur at the Same Age?

BACKGROUND

Prediction of the age at aortic dissection for family members of aortic dissection patients would enhance early detection and clinical management. We sought to determine whether these dissections tend to cluster by age in family members of the dissection patients.

METHODS

Ages at dissection were examined, including 51 sporadic dissectors (one dissection in family) and 39 familial dissectors (two or more dissections in family) from 16 families. Differences between sporadic and familial dissectors and relationships between ages at dissection in family members were analyzed by linear regression and clustering analysis.

RESULTS

Age at dissection was significantly younger in familial versus sporadic dissectors (54.1 ± 15.2 years versus 63.1±12.4 years, p = 0.002). Regression analysis of pairs of family member ages at dissection found a moderately close linear fit (R² = 0.35). Cluster analysis indicated that age at onset of family dissectors increases as age of proband dissector increases. More than 50% of familial dissections occurred within 10 years of the median onset age for any given age decade. For familial dissectors with onset age of 30 to 49 years, 71% of other family member dissections also occurred at age 30 to 49 years, and no dissections occurred above the age of 63 years. For familial dissectors with onset age of 60 to 79 years, 80% of other family member dissections occurred beyond the age of 50 years.

CONCLUSIONS

Familial dissections occur earlier than sporadic dissections. Dissections cluster by age in families, and age at onset can predict the age of other dissectors. This finding argues for consideration of prophylactic resection of an aneurysm in family members approaching the age at onset of prior thoracic aortic dissection.

Familial non-syndromal thoracic aortic aneurysms and dissections - Incidence and family screening outcomes

BACKGROUND

Non-syndromal thoracic aortic aneurysm and dissection (ns-TAAD) is a genetic aortopathy, with uncertain incidence. This study documented the incidence of ns-TAAD and outcomes of family screening over 15years.

METHODS

Consecutive series of 2385 patients with aortic disease in prospective registry (2000 to 2014), including 675 undergoing surgery. Diagnosis of ns-TAAD included family history, aortic imaging, tissue pathology and mutation testing. Screening was offered to relatives of ns-TAAD probands, with follow-up for affected individuals.

RESULTS

There were 270 ns-TAAD probands (74% males), including 116 (43%) presenting with aortic dissection. Among surgical cases, a diagnosis of ns-TAAD was established for 116 (17%). Age of probands was 50.4±14.1years, with aortic diameter of 51±12mm. Screening of 581 at-risk relatives identified 216 new ns-TAAD cases (detection rate=37%). Among 71 probands with known family history, screening identified 130 new affected relatives and among 53 probands with no family history, screening identified 86 new affected relatives. Mean age of new affected relatives at diagnosis was 44±18years, with aortic diameter of 42±7mm, including 42 with diameter>50mm. Ten-year mortality was similar for probands without dissection (7.7±3.1%) and new affected relatives (11.4±4.0%) but greater for probands surviving initial dissection (27.6±7.8%, p=0.003).

CONCLUSIONS

Up to 1 in 6 patients undergoing aortic surgery have features of ns-TAAD, frequently presenting as aortic dissection but at later age than other genetic aortopathies. Family screening identifies affected relatives in up to half of ns-TAAD probands, many of whom already have significant aortic dilatation.

Recurrent Rare Genomic Copy Number Variants and Bicuspid Aortic Valve Are Enriched in Early Onset Thoracic Aortic Aneurysms and Dissections

Thoracic Aortic Aneurysms and Dissections (TAAD) are a major cause of death in the United States. The spectrum of TAAD ranges from genetic disorders, such as Marfan syndrome, to sporadic isolated disease of unknown cause. We hypothesized that genomic copy number variants (CNVs) contribute causally to early onset TAAD (ETAAD). We conducted a genome-wide SNP array analysis of ETAAD patients of European descent who were enrolled in the National Registry of Genetically Triggered Thoracic Aortic Aneurysms and Cardiovascular Conditions (GenTAC). Genotyping was performed on the Illumina Omni-Express platform, using PennCNV, Nexus and CNVPartition for CNV detection. ETAAD patients (n = 108, 100% European American, 28% female, average age 20 years, 55% with bicuspid aortic valves) were compared to 7013 dbGAP controls without a history of vascular disease using downsampled Omni 2.5 data. For comparison, 805 sporadic TAAD patients with late onset aortic disease (STAAD cohort) and 192 affected probands from families with at least two affected relatives (FTAAD cohort) from our institution were screened for additional CNVs at these loci with SNP arrays. We identified 47 recurrent CNV regions in the ETAAD, FTAAD and STAAD groups that were absent or extremely rare in controls. Nine rare CNVs that were either very large (>1 Mb) or shared by ETAAD and STAAD or FTAAD patients were also identified. Four rare CNVs involved genes that cause arterial aneurysms when mutated. The largest and most prevalent of the recurrent CNVs were at Xq28 (two duplications and two deletions) and 17q25.1 (three duplications). The percentage of individuals harboring rare CNVs was significantly greater in the ETAAD cohort (32%) than in the FTAAD (23%) or STAAD (17%) cohorts. We identified multiple loci affected by rare CNVs in one-third of ETAAD patients, confirming the genetic heterogeneity of TAAD. Alterations of candidate genes at these loci may contribute to the pathogenesis of TAAD.

Structure of the Elastin-Contractile Units in the Thoracic Aorta and How Genes That Cause Thoracic Aortic Aneurysms and Dissections Disrupt This Structure

The medial layer of the aorta confers elasticity and strength to the aortic wall and is composed of alternating layers of smooth muscle cells (SMCs) and elastic fibres. The SMC elastin-contractile unit is a structural unit that links the elastin fibres to the SMCs and is characterized by the following: (1) layers of elastin fibres that are surrounded by microfibrils; (2) microfibrils that bind to the integrin receptors in focal adhesions on the cell surface of the SMCs; and (3) SMC contractile filaments that are linked to the focal adhesions on the inner side of the membrane. The genes that are altered to cause thoracic aortic aneurysms and aortic dissections encode proteins involved in the structure or function of the SMC elastin-contractile unit. Included in this gene list are the genes encoding protein that are structural components of elastin fibres and microfibrils, FBN1, MFAP5, ELN, and FBLN4. Also included are genes that encode structural proteins in the SMC contractile unit, including ACTA2, which encodes SMC-specific α-actin and MYH11, which encodes SMC-specific myosin heavy chain, along with MYLK and PRKG1, which encode kinases that control SMC contraction. Finally, mutations in the gene encoding the protein linking integrin receptors to the contractile filaments, FLNA, also predispose to thoracic aortic disease. Thus, these data suggest that functional SMC elastin-contractile units are important for maintaining the structural integrity of the aorta.

Molecular mechanisms of inherited thoracic aortic disease - from gene variant to surgical aneurysm

Aortic dissection is a catastrophic event that has a high mortality rate. Thoracic aortic aneurysms are the clinically silent precursor that confers an increased risk of acute aortic dissection. There are several gene mutations that have been identified in key structural and regulatory proteins within the aortic wall that predispose to thoracic aneurysm formation. The most common and well characterised of these is the FBN1 gene mutation that is known to cause Marfan syndrome. Others less well-known mutations include TGF-β1 and TGF-β2 receptor mutations that cause Loeys-Dietz syndrome, Col3A1 mutations causing Ehlers-Danlos Type 4 syndrome and Smad3 and-4, ACTA2 and MYHII mutations that cause familial thoracic aortic aneurysm and dissection. Despite the variation in the proteins affected by these genetic mutations, there is a unifying pathological end point of medial degeneration within the wall of the aorta characterised by vascular smooth muscle cell loss, fragmentation and loss of elastic fibers, and accumulation of proteoglycans and glycosaminoglycans within vascular smooth muscle cell-depleted areas of the aortic media. Our understanding of these mutations and their post-translational effects has led to a greater understanding of the pathophysiology that underlies thoracic aortic aneurysm formation. Despite this, there are still many unanswered questions regarding the molecular mechanisms. Further elucidation of the signalling pathways will help us identify targets that may be suitable modifiers to enhance treatment of this often fatal condition.

Identification and surgical repair of familial thoracic aortic aneurysm and dissection caused by TGFBR1 mutation

BACKGROUND

This study aimed at exploring the causative gene and summarizing the clinical characteristics in a Chinese thoracic aortic aneurysm and dissection (TAAD) family.

METHODS

Family members were examined for features of syndromic genetic diseases by clinician and geneticist. Genomic DNA was extracted from 2 distantly related members with definite TAAD for exome sequencing.

RESULTS

A pathogenic mutation (rs111426349, c.1459C >T) of transforming growth factor β receptor 1 (TGFBR1) was confirmed, which result in the amino acid substitution p.R487W. Fourteen TGFBR1 mutation carriers were detected among 39 tested members in this family. The average age at diagnosis of aortic root dilatation or aneurysm was 23.2 ± 12.6 years (range 3-37 years). Early onset of aortic root dilatation was significant in this family without reported phenotypes. The David procedure was performed prophylactically in 3 carriers of this family.

CONCLUSIONS

Familial TAAD caused by TGFBR1 mutation (c.1459C >T) was confirmed in a large Chinese Han ethnic family using exome sequencing. Aggressively prophylactic David procedure may be not necessary at a smaller aortic size in familial TAAD patients with TGFBR1 mutation and further observation is warranted.

Use of genetics for personalized management of heritable thoracic aortic disease: how do we get there?

The major diseases affecting the thoracic aorta are aortic aneurysms and acute aortic dissections. Medical treatments can slow the enlargement of aneurysms, but the mainstay of treatment to prevent premature death resulting from dissection is surgical repair of the thoracic aortic aneurysm, which is typically recommended when the aortic diameter reaches 5.0 to 5.5 cm. Studies of patients with acute aortic dissections, however, indicate that as many as 60% of dissections occur at aortic diameters smaller than 5.5 cm. Clinical predictors are therefore needed to distinguish those at risk for dissection at an aortic diameter smaller than 5.0 cm and to determine the aortic diameter that justifies the risk of surgical repair to prevent an acute aortic dissection. Data from genetic studies during the past decade have established that mutations in specific genes can distinguish patients at risk for the disease and predict the risk of early dissection at diameters smaller than 5.0 cm. This information has the potential to optimize the timing of aortic surgery to prevent acute dissections.

Network-based analysis of genotype-phenotype correlations between different inheritance modes

MOTIVATION

Recent studies on human disease have revealed that aberrant interaction between proteins probably underlies a substantial number of human genetic diseases. This suggests a need to investigate disease inheritance mode using interaction, and based on which to refresh our conceptual understanding of a series of properties regarding inheritance mode of human disease.

RESULTS

We observed a strong correlation between the number of protein interactions and the likelihood of a gene causing any dominant diseases or multiple dominant diseases, whereas no correlation was observed between protein interaction and the likelihood of a gene causing recessive diseases. We found that dominant diseases are more likely to be associated with disruption of important interactions. These suggest inheritance mode should be understood using protein interaction. We therefore reviewed the previous studies and refined an interaction model of inheritance mode, and then confirmed that this model is largely reasonable using new evidences. With these findings, we found that the inheritance mode of human genetic diseases can be predicted using protein interaction. By integrating the systems biology perspectives with the classical disease genetics paradigm, our study provides some new insights into genotype-phenotype correlations.

CONTACT

haodapeng@ems.hrbmu.edu.cn or biofomeng@hotmail.com

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Familial thoracic aortic aneurysm with dissection presenting as flash pulmonary edema in a 26-year-old man

We are reporting a case of familial thoracic aortic aneurysm and dissection in a 26-year-old man with no significant past medical history and a family history of dissecting aortic aneurysm in his mother at the age of 40. The patient presented with cough, shortness of breath, and chest pain. Chest X-ray showed bilateral pulmonary infiltrates. CT scan of the chest showed a dissection of the ascending aorta. The patient underwent aortic dissection repair and three months later he returned to our hospital with new complaints of back pain. CT angiography showed a new aortic dissection extending from the left carotid artery through the bifurcation and into the iliac arteries. The patient underwent replacement of the aortic root, ascending aorta, total aortic arch, and aortic valve. The patient recovered well postoperatively. Genetic studies of the patient and his children revealed no mutations in ACTA2, TGFBR1, TGFBR2, TGFB2, MYH11, MYLK, SMAD3, or FBN1. This case report focuses on a patient with familial TAAD and discusses the associated genetic loci and available screening methods. It is important to recognize potential cases of familial TAAD and understand the available screening methods since early diagnosis allows appropriate management of risk factors and treatment when necessary.

The spectrum of FBN1, TGFβR1, TGFβR2 and ACTA2 variants in 594 individuals with suspected Marfan Syndrome, Loeys-Dietz Syndrome or Thoracic Aortic Aneurysms and Dissections (TAAD)

INTRODUCTION

In this study, patients suspected of having a clinical diagnosis of Marfan Syndrome (MFS), Loeys-Dietz Syndrome (LDS) and Thoracic Aortic Aneurysms and Dissections (TAAD) were referred for genetic testing and examined for mutations in the FBN1, TGFβR1, TGFβR2 and ACTA2 genes.

METHODS

We examined 594 samples from unrelated individuals and different combinations of genes were sequenced, including one or more of the following: FBN1, TGFβR1, TGFβR2, ACTA2, and, in some cases, FBN1 was analyzed by MLPA to detect large deletions.

RESULTS

A total of 112 patients had a positive result. Of those, 61 had a clinical diagnosis of MFS, eight had LDS, three had TAAD and 40 patients had clinical features with no specific diagnosis provided. A total of 44 patients had an inconclusive result; of these, 12 patients were referred with a clinical diagnosis of MFS, 4 with LDS and 9 with TAAD and 19 had no clinical diagnosis. A total of 89 mutations were novel.

CONCLUSION

This study reveals the rate of detection of variants in several genes associated with MFS, LDS and TAAD. The evaluation of patients by individuals with expertise in the field may decrease the likelihood of ordering unnecessary molecular testing. Nevertheless, genetic testing supports the diagnosis of MFS, LDS and TAAD.

Novel SMAD3 Mutation in a Patient with Hypoplastic Left Heart Syndrome with Significant Aortic Aneurysm

Aneurysms-osteoarthritis syndrome (AOS) caused by haploinsufficiency of SMAD3 is a recently described cause of syndromic familial thoracic aortic aneurysm and dissection (TAAD). We identified a novel SMAD3 mutation in a patient with hypoplastic left heart syndrome (HLHS) who developed progressive aortic aneurysm requiring surgical replacement of the neoaortic root, ascending aorta, and proximal aortic arch. Family screening for the mutation revealed that his father, who has vascular and skeletal features of AOS, and his brother, who is asymptomatic, also have the pathogenic mutation. This is the first case report of a SMAD3 mutation in a patient with hypoplastic left heart syndrome. This case highlights the importance of genetic testing for known causes of aneurysm in patients with congenital heart disease who develop aneurysmal disease as it may significantly impact the management of those patients and their family members.

Molecular mechanisms of thoracic aortic dissection

Thoracic aortic dissection (TAD) is a highly lethal vascular disease. In many patients with TAD, the aorta progressively dilates and ultimately ruptures. Dissection formation, progression, and rupture cannot be reliably prevented pharmacologically because the molecular mechanisms of aortic wall degeneration are poorly understood. The key histopathologic feature of TAD is medial degeneration, a process characterized by smooth muscle cell depletion and extracellular matrix degradation. These structural changes have a profound impact on the functional properties of the aortic wall and can result from excessive protease-mediated destruction of the extracellular matrix, altered signaling pathways, and altered gene expression. Review of the literature reveals differences in the processes that lead to ascending versus descending and sporadic versus hereditary TAD. These differences add to the complexity of this disease. Although tremendous progress has been made in diagnosing and treating TAD, a better understanding of the molecular, cellular, and genetic mechanisms that cause this disease is necessary to developing more effective preventative and therapeutic treatment strategies.

Genetics of thoracic aortic aneurysm: at the crossroad of transforming growth factor-β signaling and vascular smooth muscle cell contractility

Aortic aneurysm, including both abdominal aortic aneurysm and thoracic aortic aneurysm, is the cause of death of 1% to 2% of the Western population. This review focuses only on thoracic aortic aneurysms and dissections. During the past decade, the genetic contribution to the pathogenesis of thoracic aortic aneurysms and dissections has revealed perturbed extracellular matrix signaling cascade interactions and deficient intracellular components of the smooth muscle contractile apparatus as the key mechanisms. Based on the study of different Marfan mouse models and the discovery of several novel thoracic aortic aneurysm genes, the involvement of the transforming growth factor-β signaling pathway has opened unexpected new avenues. Overall, these discoveries have 3 important consequences. First, the pathogenesis of thoracic aortic aneurysms and dissections is better understood, although some controversy still exists. Second, the management strategies for the medical and surgical treatment of thoracic aortic aneurysms and dissections are becoming increasingly gene-tailored. Third, the pathogenetic insights have delivered new treatment options that are currently being investigated in large clinical trials.

Successes and challenges of using whole exome sequencing to identify novel genes underlying an inherited predisposition for thoracic aortic aneurysms and acute aortic dissections

Thoracic aortic aneurysms involving the aortic root and/or ascending aorta can lead to acute aortic dissections. Approximately 20% of patients with thoracic aortic aneurysms and dissections (TAAD) have a family history of the disease, referred to as familial TAAD (FTAAD) that can be inherited in an autosomal dominant manner with variable expression with respect to disease presentation, age of onset and associated features. Whole exome sequencing (WES) has been used to identify causative mutations in novel genes for TAAD. The strategy used to reduce the large number of rare variants identified using WES is to sequence distant relatives with TAAD and filter for heterozygous rare variants that are shared between the relatives, predicted to disrupt protein function and segregate with the TAAD phenotype in other family members. Putative genes are validated by identifying additional families with a causative mutation in the genes. This approach has successfully identified novel genes for FTAAD.

A balanced translocation truncates Neurotrimin in a family with intracranial and thoracic aortic aneurysm

BACKGROUND

Balanced chromosomal rearrangements occasionally have strong phenotypic effects, which may be useful in understanding pathobiology. However, conventional strategies for characterising breakpoints are laborious and inaccurate. We present here a proband with a thoracic aortic aneurysm (TAA) and a balanced translocation t(10;11) (q23.2;q24.2). Our purpose was to sequence the chromosomal breaks in this family to reveal a novel candidate gene for aneurysm.

METHODS AND RESULTS

Intracranial aneurysm (IA) and TAAs appear to run in the family in an autosomal dominant manner: After exploring the family history, we observed that the proband's two siblings both died from cerebral haemorrhage, and the proband's parent and parent's sibling died from aortic rupture. After application of a genome-wide paired-end DNA sequencing method for breakpoint mapping, we demonstrate that this translocation breaks intron 1 of a splicing isoform of Neurotrimin at 11q25 in a previously implicated candidate region for IAs and AAs (OMIM 612161).

CONCLUSIONS

Our results demonstrate the feasibility of genome-wide paired-end sequencing for the characterisation of balanced rearrangements and identification of candidate genes in patients with potentially disease-associated chromosome rearrangements. The family samples were gathered as a part of our recently launched National Registry of Reciprocal Balanced Translocations and Inversions in Finland (n=2575), and we believe that such a registry will be a powerful resource for the localisation of chromosomal aberrations, which can bring insight into the aetiology of related phenotypes.

High-density oligonucleotide-based resequencing assay for mutations causing syndromic and non-syndromic forms of thoracic aortic aneurysms and dissections

Thoracic aortic aneurysm and dissection is associated with increasing mortality rate that may occur as part of a syndrome or as an isolated familial condition. Several genes have been implicated in causing TAAD, though an appropriate genetic test for their parallel testing is not yet available. Herein, we describe the novel 117-kb "MFSTAAD chip" that may help to understand the genetic basis of TAAD. A custom duplicate resequencing assay was developed to cover eight genes previously described in TAAD; FBN1, TGFBR1&2, COL3A1, MYH11, ACTA2, SLC2A10 and NOTCH1. GSEQ and SeqC software were used for data analysis. The analytical sensitivity of the assay was validated by the recognition of 182 known mutations (153 point mutations, 21 deletions, 7 insertions and 1 duplication) and a cohort of 28 patients were selected to determine the mutation yield, whereby 18 of them were previously negative for mutations in the genes FBN1 and TGFBR2. The assay had significantly higher sensitivity for point mutations (100%) and the largest deletion of 16 bp was detectable through a decline in the hybridization strength. The overall analytical sensitivity was 85%. Mutation testing of 28 unrelated TAAD patients revealed 4 known and 6 possibly pathogenic mutations with a mutation yield of 32%. The MFSTAAD chip is an alternative tool to next-generation sequencing that allows parallel analysis of several genes on a single platform. Refinements in the probe design and data analysis software will increase the analytical sensitivity of insertions and deletions making this assay even more applicable for clinical testing.