The Expansion of Genetic Testing in Cardiovascular Medicine: Preparing the Cardiology Community for the Changing Landscape.

PURPOSE OF REVIEW: Pathogenic DNA variants underlie many cardiovascular disease phenotypes. The most well-recognized of these include familial dyslipidemias, cardiomyopathies, arrhythmias, and aortopathies. The clinical presentations of monogenic forms of cardiovascular disease are often indistinguishable from those with complex genetic and non-genetic etiologies, making genetic testing an essential aid to precision diagnosis. RECENT FINDINGS: Precision diagnosis enables efficient management, appropriate use of emerging targeted therapies, and follow-up of at-risk family members. Genetic testing for these conditions is widely available but under-utilized. In this review, we summarize the potential benefits of genetic testing, highlighting the specific cardiovascular disease phenotypes in which genetic testing should be considered, and how clinicians can integrate guideline-directed genetic testing into their practice.

Genetic Testing Guidelines Impact Care in Newborns with Congenital Heart Defects.

OBJECTIVE: To evaluate genetic evaluation practices in newborns with the most common birth defect, congenital heart defects (CHD), we determined the prevalence and the yield of genetic evaluation across time and across patient subtypes, before and after implementation of institutional genetic testing guidelines. STUDY DESIGN: This was a retrospective, cross-sectional study of 664 hospitalized newborns with CHD using multivariate analyses of genetic evaluation practices across time and patient subtypes. RESULTS: Genetic testing guidelines for hospitalized newborns with CHD were implemented in 2014, and subsequently genetic testing increased (40% in 2013 and 75% in 2018, OR 5.02, 95% CI 2.84-8.88, P < .001) as did medical geneticists' involvement (24% in 2013 and 64% in 2018, P < .001). In 2018, there was an increased use of chromosomal microarray (P < .001), gene panels (P = .016), and exome sequencing (P = .001). The testing yield was high (42%) and consistent across years and patient subtypes analyzed. Increased testing prevalence (P < .001) concomitant with consistent testing yield (P = .139) added an estimated 10 additional genetic diagnoses per year, reflecting a 29% increase. CONCLUSIONS: In patients with CHD, yield of genetic testing was high. After implementing guidelines, genetic testing increased significantly and shifted to newer sequence-based methods. Increased use of genetic testing identified more patients with clinically important results with potential to impact patient care.

Importance of genetic testing in unexplained cardiac arrest.

AIMS: Genetic testing is recommended in specific inherited heart diseases but its role remains unclear and it is not currently recommended in unexplained cardiac arrest (UCA). We sought to assess the yield and clinical utility of genetic testing in UCA using whole-exome sequencing (WES). METHODS AND RESULTS: Survivors of UCA requiring external defibrillation were included from the Cardiac Arrest Survivor with Preserved Ejection fraction Registry. Whole-exome sequencing was performed, followed by assessment of rare variants in previously reported cardiovascular disease genes. A total of 228 UCA survivors (mean age at arrest 39 ± 13 years) were included. The majority were males (66%) and of European ancestry (81%). Following advanced clinical testing at baseline, the likely aetiology of cardiac arrest was determined in 21/228 (9%) cases. Whole-exome sequencing identified a pathogenic or likely pathogenic (P/LP) variant in 23/228 (10%) of UCA survivors overall, increasing the proportion of 'explained' cases from 9% only following phenotyping to 18% when combining phenotyping with WES. Notably, 13 (57%) of the 23 P/LP variants identified were located in genes associated with cardiomyopathy, in the absence of a diagnosis of cardiomyopathy at the time of arrest. CONCLUSIONS: Genetic testing identifies a disease-causing variant in 10% of apparent UCA survivors. The majority of disease-causing variants was located in cardiomyopathy-associated genes, highlighting the arrhythmogenic potential of such variants in the absence of an overt cardiomyopathy diagnosis. The present study supports the use of genetic testing including assessment of arrhythmia and cardiomyopathy genes in survivors of UCA.

Cascade testing for inherited arrhythmia conditions: Experiences and attitudes of family communication approaches for a Canadian cohort.

Inherited arrhythmia conditions (IAC) can lead to sudden cardiac death at any age, and relatives of an affected person have up to a 50% chance of inheriting the condition and are at risk for developing features. Cascade testing is a stepwise approach for identifying relatives at risk for IACs through clinical screening and genetic testing. Early detection can reduce morbidity and mortality for affected individuals and determine potential risk mitigation strategies for relatives. However, cardiovascular genetic studies have reported an incomplete uptake of cascade testing in at-risk relatives. We explored patient perspectives on cascade testing for IACs and alternative approaches to family communication. Twelve semi-structured phone interviews were conducted with probands of the British Columbia Inherited Arrhythmia Program confirmed to carry a pathogenic or likely pathogenic variant in a gene associated with an IAC. Thematic analysis of transcripts through an iterative coding process revealed five main themes: (a) a stepwise approach is followed in disclosing risk to relatives, (b) relatives' autonomy in cascade testing is supported, (c) lived experience with the condition influences disclosure and uptake of cascade testing, (d) collaborative approach to informing relatives reduces negative impact of disclosure, and (e) direct contact from a healthcare provider is viewed as acceptable. The findings highlight this patient cohort's experiences and opinions with approaches to disclosure and demonstrate their understanding and acceptance of their relatives' approaches to cascade testing. In addition, while the notion of direct contact was generally accepted, a collaborative approach to contacting relatives between the proband and provider may be most effective.

Insights Into Genetics and Pathophysiology of Arrhythmogenic Cardiomyopathy.

PURPOSE OF REVIEW: Arrhythmogenic cardiomyopathy (ACM) is a genetic disease characterized by life-threatening ventricular arrhythmias and sudden cardiac death (SCD) in apparently healthy young adults. Mutations in genes encoding for cellular junctions can be found in about half of the patients. However, disease onset and severity, risk of arrhythmias, and outcome are highly variable and drug-targeted treatment is currently unavailable. RECENT FINDINGS: This review focuses on advances in clinical risk stratification, genetic etiology, and pathophysiological concepts. The desmosome is the central part of the disease, but other intercalated disc and associated structural proteins not only broaden the genetic spectrum but also provide novel molecular and cellular insights into the pathogenesis of ACM. Signaling pathways and the role of inflammation will be discussed and targets for novel therapeutic approaches outlined. Genetic discoveries and experimental-driven preclinical research contributed significantly to the understanding of ACM towards mutation- and pathway-specific personalized medicine.

The role of genetics in cardiovascular disease: arrhythmogenic cardiomyopathy.

Arrhythmogenic cardiomyopathy (ACM) is a heritable cardiomyopathy characterized by frequent ventricular arrhythmias and progressive ventricular dysfunction. Risk of sudden cardiac death is elevated in ACM patients and can be the presenting symptom particularly in younger individuals and athletes. This review describes current understanding of the genetic architecture of ACM and molecular mechanisms of ACM pathogenesis. We consider an emerging threshold model for ACM inheritance in which multiple factors including pathogenic variants in known ACM genes, genetic modifiers, and environmental exposures, particularly exercise, are required to reach a threshold for disease expression. We also review best practices for integrating genetics-including recent discoveries-in caring for ACM families and emphasize the utility of genotype for both management of affected individuals and predictive testing in family members.

The Double Mutation DSG2-p.S363X and TBX20-p.D278X Is Associated with Left Ventricular Non-Compaction Cardiomyopathy: Case Report.

Left ventricular non-compaction cardiomyopathy (LVNC) is a rare heart disease, with or without left ventricular dysfunction, which is characterized by a two-layer structure of the myocardium and an increased number of trabeculae. The study of familial forms of LVNC is helpful for risk prediction and genetic counseling of relatives. Here, we present a family consisting of three members with LVNC. Using a next-generation sequencing approach a combination of two (likely) pathogenic nonsense mutations DSG2-p.S363X and TBX20-p.D278X was identified in all three patients. TBX20 encodes the cardiac T-box transcription factor 20. DSG2 encodes desmoglein-2, which is part of the cardiac desmosomes and belongs to the cadherin family. Since the identified nonsense variant (DSG2-p.S363X) is localized in the extracellular domain of DSG2, we performed in vitro cell transfection experiments. These experiments revealed the absence of truncated DSG2 at the plasma membrane, supporting the pathogenic relevance of DSG2-p.S363X. In conclusion, we suggest that in the future, these findings might be helpful for genetic screening and counseling of patients with LVNC.

A Comprehensive Clinical Genetics Approach to Critical Congenital Heart Disease in Infancy.

OBJECTIVE: To investigate the frequency of genetic diagnoses among infants with critical congenital heart disease (CHD) using a comprehensive cardiovascular genetics approach and to identify genotype-phenotype correlations. STUDY DESIGN: A retrospective chart review of patients evaluated by cardiovascular genetics in a pediatric cardiac intensive care unit from 2010 to 2015 was performed. Infants with CHD who were <1 month of age were included. CHD was classified using structured phenotype definitions. Cardiac and noncardiac phenotypes were tested for associations with abnormal genetic testing using χ1 and Fisher exact tests. RESULTS: Genetic evaluation was completed in 293 infants with CHD, of whom 213 had isolated congenital heart disease (iCHD) and 80 had multiple congenital anomalies. Overall, the yield of abnormal genetic testing was 26%. The multiple congenital anomalies cohort had a greater yield of genetic testing (39%) than the iCHD cohort (20%) (OR 2.7). Using a non-hierarchical CHD classification and excluding 22q11.2 deletion and common aneuploidies, right ventricular obstructive defects were associated with abnormal genetic testing (P = .0005). Extracardiac features associated with abnormal genetic testing included ear, nose, and throat (P = .003) and brain (P = .0001) abnormalities. A diagnosis of small for gestational age or intrauterine growth retardation also was associated with abnormal genetic testing (P = .0061), as was presence of dysmorphic features (P = .0033, OR 3.5). Infants without dysmorphia with iCHD or multiple congenital anomalies had similar frequencies of abnormal genetic testing. CONCLUSIONS: The present study provides evidence to support a comprehensive cardiovascular genetics approach in evaluating infants with critical CHD while also identifying important genotype-phenotype considerations.

In vitro analysis of arrhythmogenic cardiomyopathy associated desmoglein-2 (DSG2) mutations reveals diverse glycosylation patterns.

Arrhythmogenic right ventricular cardiomyopathy is a heritable cardiac disease causing severe ventricular arrhythmias, heart failure and sudden cardiac death. It is mainly caused by mutations in genes encoding several structural proteins of the cardiac desmosomes including the DSG2 gene encoding the desmosomal cadherin desmoglein-2. Although the molecular structure of the extracellular domain of desmoglein-2 is known, it remains an open question, how mutations in DSG2 contribute to the pathogenesis of arrhythmogenic right ventricular cardiomyopathy. In the present study, we analyzed the impact of different DSG2 mutations on the glycosylation pattern using de-glycosylation assays, lectin blot analysis and genetic inhibition studies. Remarkably, wildtype and mutant desmoglein-2 displayed different glycosylation patterns, although the investigated DSG2 mutations do not directly affect the consensus sequences of the N-glycosylation sites. Our study reveals complex molecular interactions between DSG2 mutations and N-glycosylations of desmoglein-2, which may contribute to the molecular understanding of the patho-mechanisms associated with arrhythmogenic right ventricular cardiomyopathy.

An examination of the factors contributing to the expansion of subspecialty genetic counseling.

In recent years, genetic counselors have moved into increasingly varied areas of patient care. Yet limited information is known about how these genetic counselors transitioned from more general clinical practice to subspecialized practice. This study was designed to answer three research questions: (1) What common factors establish a need for a genetic counselor in a subspecialty setting? (2) How do genetic counselors in subspecialties establish their positions? (3) Once established, how do the positions of these genetic counselors evolve as the subspecialty expands? Phone interviews with subspecialized genetic counselors led to the development of an online survey distributed through the National Society of Genetic Counselors ListServ. Sixty-eight of the 144 initial participants met eligibility criteria for participation as subspecialty genetic counselors in a clinical role. Physician interest in hiring a genetic counselor, clinical need, genetic counselor interest in subspecialty area, and available genetic testing were commonly reported as contributing factors to position creation. Most subspecialty genetic counseling positions were created as new positions, rather than evolved from a previous position. Over time, subspecialty positions drew more departmental funding and included increased clinical coordination or administrative responsibilities. The results of this study can encourage genetic counselors to collaborate with their medical institutions to utilize their skill-set in diverse areas of patient care.

Human Induced Pluripotent Stem-Cell-Derived Cardiomyocytes as Models for Genetic Cardiomyopathies.

In the last few decades, many pathogenic or likely pathogenic genetic mutations in over hundred different genes have been described for non-ischemic, genetic cardiomyopathies. However, the functional knowledge about most of these mutations is still limited because the generation of adequate animal models is time-consuming and challenging. Therefore, human induced pluripotent stem cells (iPSCs) carrying specific cardiomyopathy-associated mutations are a promising alternative. Since the original discovery that pluripotency can be artificially induced by the expression of different transcription factors, various patient-specific-induced pluripotent stem cell lines have been generated to model non-ischemic, genetic cardiomyopathies in vitro. In this review, we describe the genetic landscape of non-ischemic, genetic cardiomyopathies and give an overview about different human iPSC lines, which have been developed for the disease modeling of inherited cardiomyopathies. We summarize different methods and protocols for the general differentiation of human iPSCs into cardiomyocytes. In addition, we describe methods and technologies to investigate functionally human iPSC-derived cardiomyocytes. Furthermore, we summarize novel genome editing approaches for the genetic manipulation of human iPSCs. This review provides an overview about the genetic landscape of inherited cardiomyopathies with a focus on iPSC technology, which might be of interest for clinicians and basic scientists interested in genetic cardiomyopathies.

Deleterious protein-altering mutations in the SCN10A voltage-gated sodium channel gene are associated with prolonged QT.

BACKGROUND: Long QT syndrome (LQT) is a pro-arrhythmogenic condition with life-threatening complications. Fifteen genes have been associated with congenital LQT, however, the genetic causes remain unknown in more than 20% of cases. MATERIALS AND METHODS: Eighteen patients with history of palpitations, pre-syncope, syncope and prolonged QT were referred to the Yale Cardiovascular Genetics Program. All subjects underwent whole-exome sequencing (WES) followed by confirmatory Sanger sequencing. Mutation burden analysis was carried out using WES data from 16 subjects with no identifiable cause of LQT. RESULTS: Deleterious and novel SCN10A mutations were identified in 3 of the 16 patients (19%) with idiopathic LQT. These included 2 frameshifts and 1 missense variants (p.G810fs, p.R1259Q, and p.P1877fs). Further analysis identified 2 damaging SCN10A mutations with allele frequencies of approximately 0.2% (p.R14L and p.R1268Q) in 2 independent cases. None of the SCN10A mutation carriers had mutations in known arrhythmia genes. Damaging SCN10A mutations (p.R209H and p.R485C) were also identified in the 2 subjects on QT prolonging medications. CONCLUSION: Our findings implicate SCN10A in LQT. The presence of frameshift mutations suggests loss-of-function as the underlying disease mechanism. The common association with atrial fibrillation suggests a unique mechanism of disease for this LQT gene.

All Along the Watchtower: a Case of Long QT Syndrome Misdiagnosis Secondary to Genetic Testing Misinterpretation.

Clinical genetics services continue to expand into diverse medical specialties. An ever-increasing number of non-genetics providers are independently ordering genetic tests, interpreting results, and at times, making diagnoses leading to patient care recommendations. Non-genetics healthcare providers can help increase patient access to these services, but a potential pitfall occurs when these providers either do not have adequate expertise with genetic variant interpretation or do not have access to multi-disciplinary teams including genetic counselors or clinical geneticists for advanced review. In the cardiology setting, variant misinterpretation can lead to misattribution of disease risk, unnecessary treatments or management, and potentially adverse psychosocial and financial effects. To address this, case reports and series are needed to highlight variant misinterpretation and misdiagnoses, including discussion of possible solutions and best practices for avoidance. This report details a child previously diagnosed with long QT syndrome type 4 by chromosomal microarray who was then subsequently managed for this disease by cardiac providers with insufficient expertise to critically review and question the genetic testing results. The patient was eventually referred to a pediatric electrophysiology team as part of a larger multidisciplinary cardiovascular genetics program, composed of specialist genetic counselors, cardiologists, and clinical geneticists. Advanced review and clinical evaluation raised concern about the initial genetic testing result and diagnosis. Complementary testing with a different modality to confirm or disconfirm the chromosome microarray result was performed, providing evidence that the original result reflected analytic error in the laboratory as well as interpretive error by the clinical geneticist and that the patient was misdiagnosed, and treated over the course of years, for long QT syndrome. This case shows the value of multidisciplinary teams caring for patients with inherited cardiovascular diseases.

At the Heart of the Pregnancy: What Prenatal and Cardiovascular Genetic Counselors Need to Know about Maternal Heart Disease.

In the last decade, an increasing number of cardiac conditions have been shown to have a genetic basis. Cardiovascular genetic counseling has emerged as a subspecialty aiming to identify unaffected at-risk individuals. An important sector of this at-risk population also includes expectant mothers, in whom unique clinical challenges may arise. Genetic counselors, especially those in cardiovascular and prenatal settings, have an opportunity to identify and assist women who may benefit from cardiovascular care during pregnancy. This paper provides basic management and genetic evaluation principles for affected women, as well as guidance on identifying those who are at risk. We provide considerations for cardiac surveillance in pregnancy and the post-partum period. Finally, key psychosocial issues that appraise how to best provide support to at risk women as they make informed decisions are discussed. We propose that a team approach including cardiology, maternal fetal medicine, and genetic counseling best serves this patient population. Ongoing questions addressing an evidence based approach to cardiovascular genetic conditions in pregnancy still remain. Thus, well-designed research protocols are essential to mark progress in this area.

Influence of Smoking Status and Intensity on Discovery of Blood Pressure Loci Through Gene-Smoking Interactions.

BACKGROUND: Genetic variation accounts for approximately 30% of blood pressure (BP) variability but most of that variability has not been attributed to specific variants. Interactions between genes and BP-associated factors may explain some "missing heritability." Cigarette smoking increases BP after short-term exposure and decreases BP with longer exposure. Gene-smoking interactions have discovered novel BP loci, but the contribution of smoking status and intensity to gene discovery is unknown. METHODS: We analyzed gene-smoking intensity interactions for association with systolic BP (SBP) in three subgroups from the Framingham Heart Study: current smokers only (N = 1,057), current and former smokers ("ever smokers," N = 3,374), and all subjects (N = 6,710). We used three smoking intensity variables defined at cutoffs of 10, 15, and 20 cigarettes per day (CPD). We evaluated the 1 degree-of-freedom (df) interaction and 2df joint test using generalized estimating equations. RESULTS: Analysis of current smokers using a CPD cutoff of 10 produced two loci associated with SBP. The rs9399633 minor allele was associated with increased SBP (5 mmHg) in heavy smokers (CPD > 10) but decreased SBP (7 mmHg) in light smokers (CPD ≤ 10). The rs11717948 minor allele was associated with decreased SBP (8 mmHg) in light smokers but decreased SBP (2 mmHg) in heavy smokers. Across all nine analyses, 19 additional loci reached P < 1 × 10(-6). DISCUSSION: Analysis of current smokers may have the highest power to detect gene-smoking interactions, despite the reduced sample size. Associations of loci near SASH1 and KLHL6/KLHL24 with SBP may be modulated by tobacco smoking.

Analysis of TGFBR1*6A variant in individuals evaluated for Marfan syndrome.

Marfan syndrome (MFS) and Loeys-Dietz syndrome (LDS) are genetic disorders that affect connective tissue as a result of dysregulated TGF-ß signaling. MFS is most frequently caused by mutations in FBN1 whereas Loeys-Dietz syndrome results from mutations in TGFBR1 or TGFBR2. There is substantial inter- and intra-familial phenotypic variability among these disorders, suggesting the presence of genetic modifiers. Previously, a polymorphism in the TGFßR1 protein termed the TFGBR1*6A allele was found to be overrepresented in patients with MFS and was identified as a low penetrance allele with suggestion as a possible modifier. To further investigate the importance of this variant, a retrospective review of genetic and phenotypic findings was conducted for 335 patients evaluated for suspicion of MFS or related disorders. In patients with a diagnosis of MFS, the presence of the TFGBR1*6A allele was not associated with phenotypic differences. Similarly, careful phenotyping of patients who carried the TFGBR1*6A allele but did not have MFS did not identify an altered frequency of specific connective tissue features. In this small cohort, the results did not reach significance to identify the TFGBR1*6A allele as a major modifier for aortic dilation, ectopia lentis, or systemic features associated with MFS or other connective tissue disorders. © 2016 Wiley Periodicals, Inc.

Coronary Artery Disease: Why We should Consider the Y Chromosome.

Coronary artery disease (CAD) is one of the leading causes of morbidity and mortality globally. In the last few years our understanding of the genetic and molecular mechanisms that promote CAD in individuals has increased with the advent of the genome era. This complex inflammatory disease has well-defined environmental risk factors. However, in the last 10 years, studies including genome-wide association studies (GWAS) have clearly demonstrated a genetic influence on CAD. Recently, studies on the human Y chromosome have also demonstrated that genetic variation within the male-specific region of the Y chromosome (MSY) could play a part in determining cardiovascular risk in men, confirming the notion that the increased risk for CAD in men cannot be fully explained through common CAD risk factors. Here, we review the literature about the pathophysiology of CAD, its potential causes and environmental risk factors known so far. Furthermore, we review the genetics of CAD, especially the latest discoveries regarding the implication of the Y chromosome, the most underexplored portion of the human genome to date, highlighting methods and difficulties arising in this research field, and discussing the importance of considering the Y chromosome in CAD research.