Exome Sequencing Identifies Candidate Genetic Modifiers of Syndromic and Familial Thoracic Aortic Aneurysm Severity

Short-Term Disruption of TGFβ Signaling in Adult Mice Renders the Aorta Vulnerable to Hypertension-Induced Dissection

Hypertension and transient increases in blood pressure from extreme exertion are risk factors for aortic dissection in patients with age-related vascular degeneration or inherited connective tissue disorders. Yet, the common experimental model of angiotensin II-induced aortopathy in mice appears independent of high blood pressure as lesions do not occur in response to an alternative vasoconstrictor, norepinephrine, and are not prevented by co-treatment with a vasodilator, hydralazine. We investigated vasoconstrictor administration to adult mice 1 week after disruption of TGFβ signaling in smooth muscle cells. Norepinephrine increased blood pressure and induced aortic dissection by 7 days and even within 30 minutes that was rescued by hydralazine; results were similar with angiotensin II. Changes in regulatory contractile molecule expression were not of pathological significance. Rather, reduced synthesis of extracellular matrix yielded a vulnerable aortic phenotype by decreasing medial collagen, most dynamically type XVIII, and impairing cell-matrix adhesion. We conclude that transient and sustained increases in blood pressure cause dissection in aortas rendered vulnerable by inhibition of TGFβ-driven extracellular matrix production by smooth muscle cells. A corollary is that medial fibrosis, a frequent feature of medial degeneration, may afford some protection against aortic dissection.

Genetic profile in patients with complicated acute aortic syndrome: the GEN-AOR study

INTRODUCTION AND OBJECTIVES

Genetic testing is becoming increasingly important for diagnosis and personalized treatments in aortopathies. Here, we aimed to genetically diagnose a group of acute aortic syndrome (AAS) patients consecutively admitted to an intensive care unit and to explore the clinical usefulness of AAS-associated variants during treatment decision-making and family traceability.

METHODS

We applied targeted next-generation sequencing, covering 42 aortic diseases genes in AAS patients with no signs consistent with syndromic conditions. Detected variants were segregated by Sanger sequencing in available family members. Demographic features, risk factors and clinical symptoms were statistically analyzed by Fisher or Fisher-Freeman-Halton Exact tests, to assess their relationship with genetic results.

RESULTS

Analysis of next-generation sequencing data in 73 AAS patients led to the detection of 34 heterozygous candidate variants in 14 different genes in 32 patients. Family screening was performed in 31 relatives belonging to 9 families. We found 13 relatives harboring the family variant, of which 10 showed a genotype compatible with the occurrence of AAS. Statistical tests revealed that the factors associated with a positive genetic diagnosis were the absence of hypertension, lower age, family history of AAS and absence of pain.

CONCLUSIONS

Our findings broaden the spectrum of the genetic background for AAS. In addition, both index patients and studied relatives benefited from the results obtained, establishing the most appropriate level of surveillance for each group. Finally, this strategy could be reinforced by the use of stastistically significant clinical features as a predictive tool for the hereditary character of AAS.

CLINICALTRIALS

gov (Identifier: NCT04751058).

Thoracic Aortic Aneurysm and Dissection: Review and Recommendations for Evaluation

ABSTRACT

Aortic dissection and rupture (collectively termed "sudden aortic death") are commonly encountered by forensic pathologists, with an estimated incidence at autopsy between 0.6% and 7.7%. Despite this, there is no standard of practice for the evaluation of sudden aortic death at autopsy.Recent studies have shown 20% of patients with thoracic aortic aneurysm or dissection (TAAD) have an identifiable genetic syndrome, and 19% will have an affected first-degree relative. The past 2 decades have seen identification of new culprit genes and syndromes, which can have subtle or nonexistent external phenotypes. A high index of suspicion is warranted to identify possible hereditary TAAD (H-TAAD), allowing family members to obtain screening to avoid catastrophic vascular events. Forensic pathologists need broad knowledge of the spectrum of H-TAAD and awareness of the relative significance of hypertension, pregnancy, substance use, and microscopic changes of aortic architecture.This article reviews the common subtypes of H-TAAD, including Marfan syndrome, vascular Ehlers-Danlos, Loeys-Dietz, and familial thoracic aortic aneurysm and dissection. Recommendations for the evaluation of sudden aortic death at autopsy are presented, including (1) performance of a complete autopsy, (2) documentation of aortic circumference and valve morphology, (3) notifying family of the need for screening, and (4) preservation of a sample for potential genetic testing.

The Genetics and Typical Traits of Thoracic Aortic Aneurysm and Dissection

Genetic predisposition and risk factors such as hypertension and smoking can instigate the development of thoracic aortic aneurysm (TAA), which can lead to highly lethal aortic wall dissection and/or rupture. Monogenic defects in multiple genes involved in the elastin-contractile unit and the TGFβ signaling pathway have been associated with TAA in recent years, along with several genetic modifiers and risk-conferring polymorphisms. Advances in omics technology have also provided significant insights into the processes behind aortic wall degeneration: inflammation, epigenetics, vascular smooth muscle phenotype change and depletion, reactive oxygen species generation, mitochondrial dysfunction, and angiotensin signaling dysregulation. These recent advances and findings might pave the way for a therapy that is capable of stopping and perhaps even reversing aneurysm progression.

Tracking an Elusive Killer: State of the Art of Molecular-Genetic Knowledge and Laboratory Role in Diagnosis and Risk Stratification of Thoracic Aortic Aneurysm and Dissection

The main challenge in diagnosing and managing thoracic aortic aneurysm and dissection (TAA/D) is represented by the early detection of a disease that is both deadly and “elusive”, as it generally grows asymptomatically prior to rupture, leading to death in the majority of cases. Gender differences exist in aortic dissection in terms of incidence and treatment options. Efforts have been made to identify biomarkers that may help in early diagnosis and in detecting those patients at a higher risk of developing life-threatening complications. As soon as the hereditability of the TAA/D was demonstrated, several genetic factors were found to be associated with both the syndromic and non-syndromic forms of the disease, and they currently play a role in patient diagnosis/prognosis and management-guidance purposes. Likewise, circulating biomarker could represent a valuable resource in assisting the diagnosis, and several studies have attempted to identify specific molecules that may help with risk stratification outside the emergency department. Even if promising, those data lack specificity/sensitivity, and, in most cases, they need more testing before entering the “clinical arena”. This review summarizes the state of the art of the laboratory in TAA/D diagnostics, with particular reference to the current and future role of molecular-genetic testing.

Identification of a common polymorphism in COQ8B acting as a modifier of thoracic aortic aneurysm severity

Thoracic aortic aneurysm (TAA) predisposes to sudden, life-threatening aortic dissection. The factors that regulate interindividual variability in TAA severity are not well understood. Identifying a molecular basis for this variability has the potential to improve clinical risk stratification and advance mechanistic insight. We previously identified COQ8B, a gene important for biosynthesis of coenzyme Q, as a candidate genetic modifier of TAA severity. Here, we investigated the physiological role of COQ8B in human aortic smooth muscle cells (SMCs) and further tested its genetic association with TAA severity. We find COQ8B protein localizes to mitochondria in SMCs, and loss of mitochondrial COQ8B leads to increased oxidative stress, decreased mitochondrial respiration, and altered expression of SMC contractile genes. Oxidative stress and mitochondrial cristae defects were prevalent in the medial layer of human proximal aortic tissues in individuals with TAA, and COQ8B expression was decreased in TAA SMCs compared with controls. A common single nucleotide polymorphism (SNP) rs3865452 in COQ8B (c.521A>G [p.His174Arg]) was associated with decreased rate of aortic root dilation in young individuals with TAA. In addition, the SNP was less frequent in a second cohort of early-onset thoracic aortic dissection (TAD) cases compared with controls. COQ8B protein levels in aortic SMCs were increased in TAA individuals homozygous for rs3865452 compared with those homozygous for the reference allele. Thus, COQ8B is important for aortic SMC metabolism, which is dysregulated in TAA, and rs3865452 may decrease TAA severity by increasing the COQ8B level. Genotyping rs3865452 may be useful for clinical risk stratification and tailored aortopathy management.

A Novel Human Biospecimen Repository for Clinical and Molecular Investigation of Thoracic Aortopathy

Thoracic aortic aneurysm (TAA) is a heritable aortopathy with significant morbidity and mortality, affecting children and adults. Genetic causes, pathobiological mechanisms, and prognostic markers are incompletely understood. In 2015, the Collaborative Human Aortopathy Repository (CHAR) was created to address these fundamental gaps. Patients with thoracic aortopathy, associated genetic diagnoses, or aortic valve disease are eligible for prospective enrollment. Family members and controls are also enrolled. Detailed clinical and family data are collected, and blood and aortic tissue biospecimens are processed for broad usage. A total of 1047 participants were enrolled. The mean age in 834 affected participants was 47 ± 22 (range <1 to 88) years and 580 were male (70%). A total of 156 (19%) were under the age of 21 years. Connective tissue diagnoses such as Marfan syndrome were present in 123 (15%). Unaffected participants included relatives (N = 176) and healthy aorta tissue controls (N = 37). Aortic or aortic valve biospecimens were acquired from over 290 and 110 participants, respectively. RNA and protein were extracted from cultured aortic smooth muscle cells (SMCs) for 90 participants. Over 1000 aliquots of aortic SMCs were cryopreserved. The CHAR’s breadth, robust biospecimen processing, and phenotyping create a unique, multipronged resource to accelerate our understanding of human aortopathy.

Characterization of the Rate of Aortic Dilation in Young Patients with Thoracic Aortic Aneurysm

Longitudinal changes in aortic diameters of young patients with thoracic aortic aneurysm (TAA) have not been completely described, particularly over long periods of follow-up. This retrospective study sought to characterize the rates of proximal aortic dilation in young patients, identify risk factors for TAA progression, and evaluate the predictive utility of early echocardiographic follow-up. Inclusion criteria were: (1) TAA or TAA-predisposing genetic diagnosis, (2) age < 25 years at first echocardiogram, and (3) minimum of 5 years of echocardiographic follow-up. Proximal aortic diameters were measured by echocardiography and Z-scores calculated to index for body surface area. TAA severity was classified as no TAA (Z-score < 2), mild (Z-score 2 to 4), or at least moderate (Z-score > 4). Among 141 included patients, mean age at first echocardiogram was 7.3 ± 3.5 years. Mean follow-up duration was 9.8 ± 3.5 years. Fifty five patients had a genetic syndrome, and 38 of the non-syndromic patients had bicuspid aortic valve (BAV). The rate of aortic dilation was significantly higher at the ascending aorta than other aortic segments. BAV and age > 10 years at first echocardiogram were associated with increased rate of ascending aorta dilation. At the ascending aorta, over 25% of patients had categorical increase in TAA severity between first and last echocardiograms, and such patients demonstrated higher rate of dilation within their first 2 years of follow-up. These longitudinal findings highlight progressive ascending aorta dilation in young patients, which may worsen around adolescence. This may help determine timing of follow-up and target ages for clinical trials.

A Novel Recurrent COL5A1 Genetic Variant Is Associated With a Dysplasia-Associated Arterial Disease Exhibiting Dissections and Fibromuscular Dysplasia

OBJECTIVE

While rare variants in the COL5A1 gene have been associated with classical Ehlers-Danlos syndrome and rarely with arterial dissections, recurrent variants in COL5A1 underlying a systemic arteriopathy have not been described. Monogenic forms of multifocal fibromuscular dysplasia (mFMD) have not been previously defined. Approach and Results: We studied 4 independent probands with the COL5A1 pathogenic variant c.1540G>A, p.(Gly514Ser) who presented with arterial aneurysms, dissections, tortuosity, and mFMD affecting multiple arteries. Arterial medial fibroplasia and smooth muscle cell disorganization were confirmed histologically. The COL5A1 c.1540G>A variant is predicted to be pathogenic in silico and absent in gnomAD. The c.1540G>A variant is on a shared 160.1 kb haplotype with 0.4% frequency in Europeans. Furthermore, exome sequencing data from a cohort of 264 individuals with mFMD were examined for COL5A1 variants. In this mFMD cohort, COL5A1 c.1540G>A and 6 additional relatively rare COL5A1 variants predicted to be deleterious in silico were identified and were associated with arterial dissections (P=0.005).

CONCLUSIONS

COL5A1 c.1540G>A is the first recurring variant recognized to be associated with arterial dissections and mFMD. This variant presents with a phenotype reminiscent of vascular Ehlers-Danlos syndrome. A shared haplotype among probands supports the existence of a common founder. Relatively rare COL5A1 genetic variants predicted to be deleterious by in silico analysis were identified in ≈2.7% of mFMD cases, and as they were enriched in patients with arterial dissections, may act as disease modifiers. Molecular testing for COL5A1 should be considered in patients with a phenotype overlapping with vascular Ehlers-Danlos syndrome and mFMD.

Aortic "Disease-in-a-Dish": Mechanistic Insights and Drug Development Using iPSC-Based Disease Modeling

Thoracic aortic diseases, whether sporadic or due to a genetic disorder such as Marfan syndrome, lack effective medical therapies, with limited translation of treatments that are highly successful in mouse models into the clinic. Patient-derived induced pluripotent stem cells (iPSCs) offer the opportunity to establish new human models of aortic diseases. Here we review the power and potential of these systems to identify cellular and molecular mechanisms underlying disease and discuss recent advances, such as gene editing, and smooth muscle cell embryonic lineage. In particular, we discuss the practical aspects of vascular smooth muscle cell derivation and characterization, and provide our personal insights into the challenges and limitations of this approach. Future applications, such as genotype-phenotype association, drug screening, and precision medicine are discussed. We propose that iPSC-derived aortic disease models could guide future clinical trials via “clinical-trials-in-a-dish”, thus paving the way for new and improved therapies for patients.

Reactive Oxygen Species and Oxidative Stress in the Pathogenesis and Progression of Genetic Diseases of the Connective Tissue

Connective tissue is known to provide structural and functional “glue” properties to other tissues. It contains cellular and molecular components that are arranged in several dynamic organizations. Connective tissue is the focus of numerous genetic and nongenetic diseases. Genetic diseases of the connective tissue are minority or rare, but no less important than the nongenetic diseases. Here we review the impact of reactive oxygen species (ROS) and oxidative stress on the onset and/or progression of diseases that directly affect connective tissue and have a genetic origin. It is important to consider that ROS and oxidative stress are not synonymous, although they are often closely linked. In a normal range, ROS have a relevant physiological role, whose levels result from a fine balance between ROS producers and ROS scavenge enzymatic systems. However, pathology arises or worsens when such balance is lost, like when ROS production is abnormally and constantly high and/or when ROS scavenge (enzymatic) systems are impaired. These concepts apply to numerous diseases, and connective tissue is no exception. We have organized this review around the two basic structural molecular components of connective tissue: The ground substance and fibers (collagen and elastic fibers).

The Role of Genetics in Risk Stratification of Thoracic Aortic Aneurysm Dissection

Thoracic aortic aneurysms are prevalent in the Western population and are often caused by genetic defects. If undetected, aneurysms can dissect or rupture, which are events associated with a high mortality rate. Hitherto no cure exists other than elective surgery if aneurysm dimensions reach a certain threshold. In the past decades, genotype-phenotype associations have emerged that enable clinicians to start stratifying patients according to risk for dissection. Nonetheless, risk assessment is—to this day—confounded by the lack of full comprehension of underlying genetics and modifying genetic risk factors that complicate the yet established genotype-phenotype correlations. Further research that focuses on identifying these additional risk markers is crucial.

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.

Exome sequencing of extreme phenotypes in bronchopulmonary dysplasia

Bronchopulmonary dysplasia is the most common chronic respiratory disease in premature infants with growing evidence that genetic factors contribute largely to moderate and severe cases. We assessed by exome sequencing if rare genetic variants could account for extremely severe phenotypes. We selected 6 infants born very preterm with severe bronchopulmonary dysplasia and 8 very preterm born controls for exome sequencing. We filtered whole exome sequencing results to include only rare variants and selected variants and/or genes with variants that were present in at least 2 cases and absent in controls. We selected variants, all heterozygous, in 9 candidate genes, 7 with a putative role in lung development and 2 that displayed 3 variations in 3 different cases, independently of their potential role in lung development. Sequencing of 5 other severe cases for these variants did not replicate our results.Conclusion: In selected preterm born infants with severe bronchopulmonary dysplasia and controls, we failed to find any rare variant shared by several infants with an extremely severe phenotype. Our results are not consistent with the role of rare causative variants in bronchopulmonary dysplasia's development and argue for the highly polygenic nature of susceptibility of this disorder.What is Known:• Bronchopulmonary dysplasia is a multifactorial disease resulting from complex environmental and genetic interactions occurring in an immature lung.• It is not known whether rare genetic variants in coding regions could account for extreme phenotypes of the disease.What is New:• In a group of infants with an extreme phenotype of bronchopulmonary dysplasia and in comparison to controls, no common genetic variants were found, nor did variants that were select in other exome studies in this setting.• These results argue for the highly polygenic nature of susceptibility of bronchopulmonary dysplasia.

The Genetics of Thoracic Aortic Aneurysms and Dissection: A Clinical Perspective

Thoracic aortic aneurysm and dissection (TAAD) affects many patients globally and has high mortality rates if undetected. Once thought to be solely a degenerative disease that afflicted the aorta due to high pressure and biomechanical stress, extensive investigation of the heritability and natural history of TAAD has shown a clear genetic basis for the disease. Here, we review both the cellular mechanisms and clinical manifestations of syndromic and non-syndromic TAAD. We particularly focus on genes that have been linked to dissection at diameters <5.0 cm, the current lower bound for surgical intervention. Genetic screening tests to identify patients with TAAD associated mutations that place them at high risk for dissection are also discussed.

Collagen XV, a multifaceted multiplexin present across tissues and species

Type XV collagen is a non-fibrillar collagen that is associated with basement membranes and belongs to the multiplexin subset of the collagen superfamily. Collagen XV was initially studied because of its sequence homology with collagen XVIII/endostatin whose anti-angiogenic and anti-tumorigenic properties were subjects of wide interest in the past years. But during the last fifteen years, collagen XV has gained growing attention with increasing number of studies that have attributed new functions to this widely distributed collagen/proteoglycan hybrid molecule. Despite the cumulative evidence of its functional pleiotropy and its evolutionary conserved function, no review compiling the current state of the art about collagen XV is currently available. Here, we thus provide the first comprehensive view of the knowledge gathered so far on the molecular structure, tissue distribution and functions of collagen XV in development, tissue homeostasis and disease with an evolutionary perspective. We hope that our review will open new roads for promising research on collagen XV in the coming years.

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Type XV collagen belongs to the multiplexin subset of the collagen superfamily.

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It is evolutionarily conserved collagen and associated with basement membranes.

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This collagen/proteoglycan hybrid molecule contains an anti-angiogenic restin domain.

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It has important functions in the cardiovascular and the neuromuscular systems.

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Its expression is dysregulated in various diseases including cancers.

Comparisons of dual isogenic human iPSC pairs identify functional alterations directly caused by an epilepsy associated SCN1A mutation

Over 1250 mutations in SCN1A, the Nav1.1 voltage-gated sodium channel gene, are associated with seizure disorders including GEFS+. To evaluate how a specific mutation, independent of genetic background, causes seizure activity we generated two pairs of isogenic human iPSC lines by CRISPR/Cas9 gene editing. One pair is a control line from an unaffected sibling, and the mutated control carrying the GEFS+ K1270T SCN1A mutation. The second pair is a GEFS+ patient line with the K1270T mutation, and the corrected patient line. By comparing the electrophysiological properties in inhibitory and excitatory iPSC-derived neurons from these pairs, we found the K1270T mutation causes cell type-specific alterations in sodium current density and evoked firing, resulting in hyperactive neural networks. We also identified differences associated with genetic background and interaction between the mutation and genetic background. Comparisons within and between dual pairs of isogenic iPSC-derived neuronal cultures provide a novel platform for evaluating cellular mechanisms underlying a disease phenotype and for developing patient-specific anti-seizure therapies.

Basement membrane collagens and disease mechanisms

Basement membranes (BMs) are specialised extracellular matrix (ECM) structures and collagens are a key component required for BM function. While collagen IV is the major BM collagen, collagens VI, VII, XV, XVII and XVIII are also present. Mutations in these collagens cause rare multi-systemic diseases but these collagens have also been associated with major common diseases including stroke. Developing treatments for these conditions will require a collective effort to increase our fundamental understanding of the biology of these collagens and the mechanisms by which mutations therein cause disease. Novel insights into pathomolecular disease mechanisms and cellular responses to these mutations has been exploited to develop proof-of-concept treatment strategies in animal models. Combined, these studies have also highlighted the complexity of the disease mechanisms and the need to obtain a more complete understanding of these mechanisms. The identification of pathomolecular mechanisms of collagen mutations shared between different disorders represent an attractive prospect for treatments that may be effective across phenotypically distinct disorders.

Exploring genetic modifiers of Gaucher disease: The next horizon

Gaucher disease is an autosomal recessive lysosomal storage disorder resulting from mutations in the gene GBA1 that lead to a deficiency in the enzyme glucocerebrosidase. Accumulation of the enzyme's substrates, glucosylceramide and glucosylsphingosine, results in symptoms ranging from skeletal and visceral involvement to neurological manifestations. Nonetheless, there is significant variability in clinical presentations amongst patients, with limited correlation between genotype and phenotype. Contributing to this clinical variation are genetic modifiers that influence the phenotypic outcome of the disorder. In this review, we explore the role of genetic modifiers in Mendelian disorders and describe methods to facilitate their discovery. In addition, we provide examples of candidate modifiers of Gaucher disease, explore their relevance in the development of potential therapeutics, and discuss the impact of GBA1 and modifying mutations on other more common diseases like Parkinson disease. Identifying these important modulators of Gaucher phenotype may ultimately unravel the complex relationship between genotype and phenotype and lead to improved counseling and treatments.

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.

Genes Associated with Thoracic Aortic Aneurysm and Dissection: 2018 Update and Clinical Implications

Thoracic aortic aneurysms, with an estimated prevalence in the general population of 1%, are potentially lethal, via rupture or dissection. Over the prior two decades, there has been an exponential increase in our understanding of the genetics of thoracic aortic aneurysm and/or dissection (TAAD). To date, 30 genes have been shown to be associated with the development of TAAD and ∼30% of individuals with nonsyndromic familial TAAD have a pathogenic mutation in one of these genes. This review represents the authors' yearly update summarizing the genes associated with TAAD, including implications for the surgical treatment of TAAD. Molecular genetics will continue to revolutionize the approach to patients afflicted with this devastating disease, permitting the application of genetically personalized aortic care.