Genetic Architecture of Dilated Cardiomyopathy in Individuals of African and European Ancestry.

Importance: Black patients with dilated cardiomyopathy (DCM) have increased familial risk and worse outcomes than White patients, but most DCM genetic data are from White patients. Objective: To compare the rare variant genetic architecture of DCM by genomic ancestry within a diverse population of patients with DCM. Design: Cross-sectional study enrolling patients with DCM who self-identified as non-Hispanic Black, Hispanic, or non-Hispanic White from June 7, 2016, to March 15, 2020, at 25 US advanced heart failure programs. Variants in 36 DCM genes were adjudicated as pathogenic, likely pathogenic, or of uncertain significance. Exposure: Presence of DCM. Main Outcomes and Measures: Variants in DCM genes classified as pathogenic/likely pathogenic/uncertain significance and clinically actionable (pathogenic/likely pathogenic). Results: A total of 505, 667, and 26 patients with DCM of predominantly African, European, or Native American genomic ancestry, respectively, were included. Compared with patients of European ancestry, a lower percentage of patients of African ancestry had clinically actionable variants (8.2% [95% CI, 5.2%-11.1%] vs 25.5% [95% CI, 21.3%-29.6%]), reflecting the lower odds of a clinically actionable variant for those with any pathogenic variant/likely pathogenic variant/variant of uncertain significance (odds ratio, 0.25 [95% CI, 0.17-0.37]). On average, patients of African ancestry had fewer clinically actionable variants in TTN (difference, -0.09 [95% CI, -0.14 to -0.05]) and other genes with predicted loss of function as a disease-causing mechanism (difference, -0.06 [95% CI, -0.11 to -0.02]). However, the number of pathogenic variants/likely pathogenic variants/variants of uncertain significance was more comparable between ancestry groups (difference, -0.07 [95% CI, -0.22 to 0.09]) due to a larger number of non-TTN non-predicted loss of function variants of uncertain significance, mostly missense, in patients of African ancestry (difference, 0.15 [95% CI, 0.00-0.30]). Published clinical case-based evidence supporting pathogenicity was less available for variants found only in patients of African ancestry (P < .001). Conclusion and Relevance: Patients of African ancestry with DCM were less likely to have clinically actionable variants in DCM genes than those of European ancestry due to differences in genetic architecture and a lack of representation of African ancestry in clinical data sets.

The Complex and Diverse Genetic Architecture of Dilated Cardiomyopathy.

Our insight into the diverse and complex nature of dilated cardiomyopathy (DCM) genetic architecture continues to evolve rapidly. The foundations of DCM genetics rest on marked locus and allelic heterogeneity. While DCM exhibits a Mendelian, monogenic architecture in some families, preliminary data from our studies and others suggests that at least 20% to 30% of DCM may have an oligogenic basis, meaning that multiple rare variants from different, unlinked loci, determine the DCM phenotype. It is also likely that low-frequency and common genetic variation contribute to DCM complexity, but neither has been examined within a rare variant context. Other types of genetic variation are also likely relevant for DCM, along with gene-by-environment interaction, now established for alcohol- and chemotherapy-related DCM. Collectively, this suggests that the genetic architecture of DCM is broader in scope and more complex than previously understood. All of this elevates the impact of DCM genetics research, as greater insight into the causes of DCM can lead to interventions to mitigate or even prevent it and thus avoid the morbid and mortal scourge of human heart failure.

SOS1 Gain-of-Function Variants in Dilated Cardiomyopathy.

BACKGROUND: Dilated cardiomyopathy (DCM) is a genetically heterogeneous cardiac disease characterized by progressive ventricular enlargement and reduced systolic function. Here, we report genetic and functional analyses implicating the rat sarcoma signaling protein, SOS1 (Son of sevenless homolog 1), in DCM pathogenesis. METHODS: Exome sequencing was performed on 412 probands and family members from our DCM cohort, identifying several SOS1 variants with potential disease involvement. As several lines of evidence have implicated dysregulated rat sarcoma signaling in the pathogenesis of DCM, we assessed functional impact of each variant on the activation of ERK (extracellular signal-regulated kinase), AKT (protein kinase B), and JNK (c-Jun N-terminal kinase) pathways. Relative expression levels were determined by Western blot in HEK293T cells transfected with variant or wild-type human SOS1 expression constructs. RESULTS: A rare SOS1 variant [c.571G>A, p.(Glu191Lys)] was found to segregate alongside an A-band TTN truncating variant in a pedigree with aggressive, early-onset DCM. Reduced disease severity in the absence of the SOS1 variant suggested its potential involvement as a genetic risk factor for DCM in this family. Exome sequencing identified 5 additional SOS1 variants with potential disease involvement in 4 other families [c.1820T>C, p.(Ile607Thr); c.2156G>C, p.(Gly719Ala); c.2230A>G, p.(Arg744Gly); c.2728G>C, p.(Asp910His); c.3601C>T, p.(Arg1201Trp)]. Impacted amino acids occupied a number of functional domains relevant to SOS1 activity, including the N-terminal histone fold, as well as the C-terminal REM (rat sarcoma exchange motif), CDC25 (cell division cycle 25), and PR (proline-rich) tail domains. Increased phosphorylated ERK expression relative to wild-type levels was seen for all 6 SOS1 variants, paralleling known disease-relevant SOS1 signaling profiles. CONCLUSIONS: These data support gain-of-function variation in SOS1 as a contributing factor to isolated DCM.

Multigenic Disease and Bilineal Inheritance in Dilated Cardiomyopathy Is Illustrated in Nonsegregating LMNA Pedigrees.

BACKGROUND: We have previously described 19 pedigrees with apparent lamin (LMNA)-related dilated cardiomyopathy (DCM) manifesting in affected family members across multiple generations. In 6 of 19 families, at least 1 individual with idiopathic DCM did not carry the family's LMNA variant. We hypothesized that additional genetic cause may underlie DCM in these families. METHODS: Affected family members underwent exome sequencing to identify additional genetic cause of DCM in the 6 families with nonsegregating LMNA variants. RESULTS: In 5 of 6 pedigrees, we identified at least 1 additional rare variant in a known DCM gene that could plausibly contribute to disease in the LMNA variant-negative individuals. Bilineal inheritance was clear or presumed to be present in 3 of 5 families and was possible in the remaining 2. At least 1 individual with a LMNA variant also carried a variant in an additional identified DCM gene in each family. Using a multivariate linear mixed model for quantitative traits, we demonstrated that the presence of these additional variants was associated with a more severe phenotype after adjusting for sex, age, and the presence/absence of the family's nonsegregating LMNA variant. CONCLUSIONS: Our data support DCM as a genetically heterogeneous disease with, at times, multigene causation. Although the frequency of DCM resulting from multigenic cause is uncertain, our data suggest it may be higher than previously anticipated.

Copy number variation as a genetic basis for heterotaxy and heterotaxy-spectrum congenital heart defects.

Genomic disorders and rare copy number abnormalities are identified in 15-25% of patients with syndromic conditions, but their prevalence in individuals with isolated birth defects is less clear. A spectrum of congenital heart defects (CHDs) is seen in heterotaxy, a highly heritable and genetically heterogeneous multiple congenital anomaly syndrome resulting from failure to properly establish left-right (L-R) organ asymmetry during early embryonic development. To identify novel genetic causes of heterotaxy, we analysed copy number variants (CNVs) in 225 patients with heterotaxy and heterotaxy-spectrum CHDs using array-based genotyping methods. Clinically relevant CNVs were identified in approximately 20% of patients and encompassed both known and putative heterotaxy genes. Patients were carefully phenotyped, revealing a significant association of abdominal situs inversus with pathogenic or likely pathogenic CNVs, while d-transposition of the great arteries was more frequently associated with common CNVs. Identified cytogenetic abnormalities ranged from large unbalanced translocations to smaller, kilobase-scale CNVs, including a rare, single exon deletion in ZIC3, a gene known to cause X-linked heterotaxy. Morpholino loss-of-function experiments in Xenopus support a role for one of these novel candidates, the platelet isoform of phosphofructokinase-1 (PFKP) in heterotaxy. Collectively, our results confirm a high CNV yield for array-based testing in patients with heterotaxy, and support use of CNV analysis for identification of novel biological processes relevant to human laterality.This article is part of the themed issue 'Provocative questions in left-right asymmetry'.

Genetics and genetic testing in congenital heart disease.

Congenital heart defects (CHDs) are structural abnormalities of the heart and great vessels that are present from birth. The presence or absence of extracardiac anomalies has historically been used to identify patients with possible monogenic, chromosomal, or teratogenic CHD causes. These distinctions remain clinically relevant, but it is increasingly clear that nonsyndromic CHDs can also be genetic. This article discusses key morphologic, molecular, and signaling mechanisms relevant to heart development, summarizes overall progress in molecular genetic analyses of CHDs, and provides current recommendations for clinical application of genetic testing.

Genetic and functional analyses of ZIC3 variants in congenital heart disease.

Mutations in zinc-finger in cerebellum 3 (ZIC3) result in heterotaxy or isolated congenital heart disease (CHD). The majority of reported mutations cluster in zinc-finger domains. We previously demonstrated that many of these lead to aberrant ZIC3 subcellular trafficking. A relative paucity of N- and C-terminal mutations has, however, prevented similar analyses in these regions. Notably, an N-terminal polyalanine expansion was recently identified in a patient with VACTERL, suggesting a potentially distinct function for this domain. Here we report ZIC3 sequencing results from 440 unrelated patients with heterotaxy and CHD, the largest cohort yet examined. Variants were identified in 5.2% of sporadic male cases. This rate exceeds previous estimates of 1% and has important clinical implications for genetic testing and risk-based counseling. Eight of 11 were novel, including 5 N-terminal variants. Subsequent functional analyses included four additional reported but untested variants. Aberrant cytoplasmic localization and decreased luciferase transactivation were observed for all zinc-finger variants, but not for downstream or in-frame upstream variants, including both analyzed polyalanine expansions. Collectively, these results expand the ZIC3 mutational spectrum, support a higher than expected prevalence in sporadic cases, and suggest alternative functions for terminal mutations, highlighting a need for further study of these domains.

Return of genetic results in the familial dilated cardiomyopathy research project.

The goal of the Familial Dilated Cardiomyopathy (FDC) Research Project, initiated in 1993, has been to identify and characterize FDC genetic cause. All participating individuals have been consented for the return of genetic results, an important but challenging undertaking. Since the inception of the Project we have enrolled 606 probands, and 269 of these had 1670 family members also enrolled. Each subject was evaluated for idiopathic dilated cardiomyopathy (IDC) and pedigrees were categorized as familial or sporadic. The coding regions of 14 genes were resequenced in 311 to 324 probands in five studies. Ninety-two probands were found to carry nonsynonymous rare variants absent in controls, and with Clinical Laboratory Improvement Amendment of 1988 (CLIA) compliant protocols, relevant genetic results were returned to these probands and their consented relatives by study genetic counselors and physicians in 353 letters. In 10 of the 51 families that received results >1 year ago, at least 23 individuals underwent CLIA confirmation testing for their family's rare variant. Return of genetic results has been successfully undertaken in the FDC Research Project. This report describes the methods utilized in the process of returning research results. We use this information as a springboard for providing guidance to other genetic research groups and proposing future directions in this arena.

Maternal smoking at first prenatal visit as a marker of risk for adverse pregnancy outcomes in the Qikiqtaaluk (Baffin) Region.

INTRODUCTION: In Nunavut, 60-80% of pregnant women report smoking in pregnancy, a rate five times the Canadian average. Nunavut also has the highest rates of preterm birth and low birth weight infants in Canada. The present study assessed whether the number of cigarettes smoked per day, as recorded in the first trimester, influenced birth outcomes. METHODS: Maternal-newborn charts were reviewed for infants born between 1 January 2003 and 31 December 2005 to at least one Inuit parent in the Qikiqtaaluk (Baffin) region of Nunavut. Smoking data, as reported by the mother at an early prenatal visit, were extracted from the prenatal record. Birth outcomes including birth weights (for term births), low birth weight, small for gestational age births and rates of preterm birth, were analysed according to category of reported number of cigarettes smoked (0, 1-5, 6-10, and >10 per day). Maternal age, alcohol and street drug use were also assessed for each category of smokers. Statistical analysis among groups was carried out. RESULTS: Of 918 births meeting the study criteria, more than 80% of women reported smoking. For 80% of those, the amount smoked per day was available. Non-smokers and women smoking less than 5 cigarettes daily had perinatal outcomes equal to or better than Canadian averages for low birth weight, small for gestational age, and preterm birth. Furthermore, average birth weights at term significantly decreased from 3681 g for non smokers to 3310 g for those smoking more than 10 cigarettes per day. Compared with non-smokers, women in the highest smoking category (>10 cigarettes daily) had a six-fold increase in low birth weight infants (OR 6.7, 95% CI 2.3-19.6), almost a four-fold increase for small for gestational age births (OR 3.7, 95% CI 1.6-8.8) and twice the chance of a premature birth compared with non-smokers (OR 2.14, 95% CI 1.1-4.2). Those in the highest smoking category were also most likely to report alcohol and other substance use. CONCLUSIONS: Inuit women who reported not smoking, or smoking less than 5 cigarettes per day had birth outcomes equal or superior to average Canadian outcomes in each category evaluated. Those women reporting smoking more than 10 cigarettes daily had significantly increased risk for preterm birth, low birth weight and small for gestational age infants. Because those in the highest smoking category also reported the highest rates of alcohol and other substance use, it is likely that a combination of factors assessed in this study influenced the outcomes. Along with public health preventative measures to reduce smoking directed to this high risk group, other contributing factors for adverse birth outcomes need to be assessed more fully to understand the complex interactions that lead to increased smoking, substance use and, therefore, adverse birth outcomes. Furthermore, evidence from this study suggests that smoking more than 10 cigarettes per day, reported at first prenatal visit, may provide a marker for those women at highest risk of poor outcomes, which could provide direction for focused public health efforts.

Morphological analysis of 13 LMNA variants identified in a cohort of 324 unrelated patients with idiopathic or familial dilated cardiomyopathy.

BACKGROUND: Mutations in the LMNA gene, encoding lamins A/C, represent a significant cause of dilated cardiomyopathy. We recently identified 18 protein-altering LMNA variants in a cohort of 324 unrelated patients with dilated cardiomyopathy. However, at least one family member with dilated cardiomyopathy in each of 6 pedigrees lacked the LMNA mutation (nonsegregation), whereas small sizes of 5 additional families precluded definitive determinations of segregation, raising questions regarding contributions by those variants to disease. METHODS AND RESULTS: We have consequently expressed, in COS7 cells, GFP-prelamin A (GFPLaA) fusion constructs incorporating the 6 variants in pedigrees with nonsegregation (R101P, A318T, R388H, R399C, S437Hfsx1, and R654X), the 4 variants in pedigrees with unknown segregation (R89L, R166P [in 2 families], I210S, R471H), and 3 additional missense variants (R190Q, E203K, and L215P) that segregated with disease. Confocal immunofluorescence microscopy was used to characterize GFP-lamin A localization and nuclear morphology. Abnormal phenotypes were observed for 10 of 13 (77%) variants (R89L, R101P, R166P, R190Q, E203K, I210S, L215P, R388H, S437Hfsx1, and R654X), including 4 of 6 showing nonsegregation and 3 of 4 with uncertain segregation. All 7 variants affecting coil 1B and the lamin A-only mutation, R654X, exhibited membrane-bound GFP-lamin A aggregates and nuclear shape abnormalities. Unexpectedly, R388H largely restricted GFP-lamin A to the cytoplasm. Equally unexpected were unique streaked aggregates with S437Hfsx1 and giant aggregates with both S437Hfsx1 and R654X. CONCLUSIONS: This work expands the recognized spectrum of lamin A localization abnormalities in dilated cardiomyopathy. It also provides evidence supporting pathogenicity of 10 of 13 tested LMNA variants, including some with uncertain or nonsegregation.

Clinical and functional characterization of TNNT2 mutations identified in patients with dilated cardiomyopathy.

BACKGROUND: A key issue for cardiovascular genetic medicine is ascertaining if a putative mutation indeed causes dilated cardiomyopathy (DCM). This is critically important as genetic DCM, usually presenting with advanced, life-threatening disease, may be preventable with early intervention in relatives known to carry the mutation. METHODS AND RESULTS: We recently undertook bidirectional resequencing of TNNT2, the cardiac troponin T gene, in 313 probands with DCM. We identified 6 TNNT2 protein-altering variants in 9 probands, all who had early onset, aggressive disease. Additional family members of mutation carriers were then studied when available. Four of the 9 probands had DCM without a family history, and 5 probands had familial DCM. Only 1 mutation (Lys210del) could be attributed as definitively causative from previous reports. Four of the 5 missense mutations were novel (Arg134Gly, Arg151Cys, Arg159Gln, and Arg205Trp), and one was previously reported with hypertrophic cardiomyopathy (Glu244Asp). Based on the clinical, pedigree, and molecular genetic data, these 5 mutations were considered possibly or likely disease causing. To further clarify their potential pathophysiologic impact, we undertook functional studies of these mutations in cardiac myocytes reconstituted with mutant troponin T proteins. We observed decreased Ca(2+) sensitivity of force development, a hallmark of DCM, in support of the conclusion that these mutations are disease causing. CONCLUSIONS: We conclude that the combination of clinical, pedigree, molecular genetic, and functional data strengthen the interpretation of TNNT2 mutations in DCM.

Progress with genetic cardiomyopathies: screening, counseling, and testing in dilated, hypertrophic, and arrhythmogenic right ventricular dysplasia/cardiomyopathy.

This review focuses on the genetic cardiomyopathies: principally dilated cardiomyopathy, with salient features of hypertrophic cardiomyopathy and arrhythmogenic right ventricular dysplasia/cardiomyopathy, regarding genetic etiology, genetic testing, and genetic counseling. Enormous progress has recently been made in identifying genetic causes for each cardiomyopathy, and key phenotype and genotype information is reviewed. Clinical genetic testing is rapidly emerging with a principal rationale of identifying at-risk asymptomatic or disease-free relatives. Knowledge of a disease-causing mutation can guide clinical surveillance for disease onset, thereby enhancing preventive and treatment interventions. Genetic counseling is also indicated for patients and their family members regarding the symptoms of their cardiomyopathy, its inheritance pattern, family screening recommendations, and genetic testing options and possible results.

Genetic testing and genetic counseling in cardiovascular genetic medicine: overview and preliminary recommendations.

In this emerging era of cardiovascular genetic medicine, increasing responsibility will be placed on cardiovascular practitioners to be aware of the latest clinical genetic testing methods and the knowledge base needed to interpret genetic test results. Some cardiovascular specialists will develop the expertise within the field to order genetic testing and interpret results, while other practitioners will refer patients to centers of excellence in cardiovascular genetic medicine. A previous article in the Cardiovascular Genetic Medicine: Clinical Perspectives and Future Applications series(1) highlighted an increasing recognition of the cardiomyopathies (hypertrophic [HCM], dilated [DCM], arrhythmogenic right ventricular dysplasia [ARVD]) and channelopathies (long QT syndrome [LQTS] and others) as genetic diseases, and focused on the importance of a targeted family history as a critical part of patient evaluation. The goal of this article, second in the series, is to provide a general framework for understanding the principles of genetic testing and genetic counseling. We review the growing number of genetic tests currently available to cardiac specialists, the selection of an appropriate test, and the numerous genetic counseling issues raised by the testing process. We also provide our preliminary recommendations for genetic testing in cardiovascular genetic medicine.

Family history: an essential tool for cardiovascular genetic medicine.

We are pleased to provide a new section devoted to topics in cardiovascular genetic medicine. An emerging field, cardiovascular genetic medicine is devoted to the identification and understanding of cardiac conditions resulting from genetic mechanisms and to the development and validation of treatment algorithms and guidelines. Cardiovascular genetic medicine is rapidly enlarging, and we anticipate a broad range of comprehensive reviews. We will first focus on the most tractable diagnoses to apply the principles of cardiovascular genetic medicine: the cardiomyopathies such as dilated, hypertrophic, arrhythmogenic right ventricular dysplasia/cardiomyopathy and the channelopathies such as long QT syndrome and related disorders. These conditions follow classical or Mendelian genetics, otherwise known as the single gene disorders. As greater numbers of disease genes and their specific mutations are identified, and as large clinical cohorts of affected probands and their at-risk family members become available for study, clinical recommendations, and then guidelines, will follow. Progress is also evident for those conditions considered to be complex or multigenic diseases, such as coronary disease and hypertension, which affect large segments of the population. Risk alleles are now being identified that may rapidly lead to genetic testing to assess risk for these conditions. Cardiovascular genetic medicine must also be responsive to public concerns regarding confidentiality, and it must also demonstrate clinical integrity and utility for genetic testing. Our first topic features the role of family history in cardiovascular genetic medicine. Assisted by my clinical and research group -- genetic counselors and nursing personnel devoted to the field -- we have provided a glossary with explanations of genetic terminology, as illustrated in this first article, and will continue to do so for the series. We will prepare additional topics and others will be solicited from experts in the field. I also invite any potential contributors to propose and submit topics that are both of interest to you and relevant to the field. Please also give us your feedback, especially to improve the clarity, diversity, and timeliness of the genetic concepts presented. So, away we go.