Precision Medicine in Cardiovascular Disease: Genetics and Impact on Phenotypes: JACC Focus Seminar 1/5.

Our understanding of the genetic basis of cardiovascular diseases (CVDs) has evolved rapidly. This has resulted from a combination of dedicated research in well phenotyped CVD patients, the sequencing of the human genome, and the ready accessibility and decreasing cost of next-generation sequencing technologies. This increased knowledge of the genetic basis of CVDs has heralded the era of precision medicine. This encompasses many elements including improved diagnosis, family screening, assistance with reproductive decisions, targeted therapeutics guided by both phenotype and genotype, and providing important insights into risk stratification and prognosis. Furthermore, novel insights into genetic mechanisms, clinical rollout of polygenic risk scores for common CVDs, and the promise of genome editing approaches to effectively cure disease represent some of the exciting future endeavors that will change established clinical approaches. This Part 1 of a 5-part series focuses on the underpinnings and fundamental aspects of precision medicine.

Genetic architecture of left ventricular noncompaction in adults.

The genetic etiology and heritability of left ventricular noncompaction (LVNC) in adults is unclear. This study sought to assess the value of genetic testing in adults with LVNC. Adults diagnosed with LVNC while undergoing screening in the context of a family history of cardiomyopathy were excluded. Clinical data for 35 unrelated patients diagnosed with LVNC at ≥18 years of age were retrospectively analyzed. Left ventricular (LV) dysfunction, electrocardiogram (ECG) abnormalities, cardiac malformations or syndromic features were identified in 25 patients; 10 patients had isolated LVNC in the absence of cardiac dysfunction or syndromic features. Exome sequencing was performed, and analysis using commercial panels targeted 193 nuclear and mitochondrial genes. Nucleotide variants in coding regions or in intron-exon boundaries with predicted impacts on splicing were assessed. Fifty-four rare variants were identified in 35 nuclear genes. Across all 35 LVNC patients, the clinically meaningful genetic diagnostic yield was 9% (3/35), with heterozygous likely pathogenic or pathogenic variants identified in the NKX2-5 and TBX5 genes encoding cardiac transcription factors. No pathogenic variants were identified in patients with isolated LVNC in the absence of cardiac dysfunction or syndromic features. In conclusion, the diagnostic yield of genetic testing in adult index patients with LVNC is low. Genetic testing is most beneficial in LVNC associated with other cardiac and syndromic features, in which it can facilitate correct diagnoses, and least useful in adults with only isolated LVNC without a family history. Cardiac transcription factors are important in the development of LVNC and should be included in genetic testing panels.

Development of induced pluripotent stem cells from a patient with hypertrophic cardiomyopathy who carries the pathogenic myosin heavy chain 7 mutation p.Arg403Gln.

Hypertrophic cardiomyopathy (HCM) is an inherited cardiomyopathy characterized by left ventricular hypertrophy ≥15 mm in the absence of loading conditions. HCM has a prevalence of up to one in 200, and can result in significant adverse outcomes including heart failure and sudden cardiac death. An induced pluripotent stem cell (iPSC) line was generated from peripheral blood mononuclear cells obtained from the whole blood of a 38-year-old female patient with HCM in which genetic testing identified the well-known pathogenic p.Arg403Gln mutation in myosin heavy chain 7. iPSCs express pluripotency markers, demonstrate trilineage differentiation capacity, and display a normal 46,XX female karyotype. This resource will allow further assessment of the pathophysiological development of HCM.

Generation of an induced pluripotent stem cell line from a hypertrophic cardiomyopathy patient with a pathogenic myosin binding protein C (MYBPC3) p.Arg502Trp mutation.

Hypertrophic cardiomyopathy is an inherited cardiomyopathy with a prevalence of up to 1 in 200, which can result in significant morbidity and mortality. An iPSC line was generated from peripheral blood mononuclear cells obtained from the whole blood of a 58-year-old male with hypertrophic cardiomyopathy who carries the heterozygous pathogenic myosin binding protein C mutation p.Arg502Trp. Induced pluripotent stem cells express pluripotency markers, demonstrate trilineage differentiation potential, and display a normal karyotype. This line is a useful resource for studying and modeling hypertrophic cardiomyopathy. Resource table.

Whole Genome Sequencing Improves Outcomes of Genetic Testing in Patients With Hypertrophic Cardiomyopathy.

BACKGROUND: Whole genome sequencing (WGS) is a comprehensive genetic testing approach that reports most types of nucleotide variants. OBJECTIVES: This study sought to assess WGS for hypertrophic cardiomyopathy (HCM) in which prior genetic testing did not establish a molecular diagnosis, and as a first-line genetic test. METHODS: WGS was performed on 58 unrelated patients with HCM, 14 affected family members, and 2 unaffected parents of a severely affected proband. The authors searched for nucleotide variants in coding regions of 184 candidate cardiac hypertrophy genes. They also searched for nucleotide variants in deep intronic regions that alter RNA splicing, large genomic rearrangements, and mitochondrial genome variants. RNA analysis was performed to validate splice-altering variants. RESULTS: The authors found a pathogenic or likely pathogenic variant in 9 of 46 families (20%) for which prior genetic testing was inconclusive. Three families had variants in genes not included in prior genetic testing. One family had a pathogenic variant that was filtered out with prior exome sequencing. Five families had pathogenic variants in noncoding regions, including 4 with deep intronic variants that activate novel splicing, and 1 mitochondrial genome variant. As a first-line genetic test, WGS identified a pathogenic variant in 5 of 12 families (42%) that had never received prior genetic testing. CONCLUSIONS: WGS identified additional genetic causes of HCM over targeted gene sequencing approaches. Extending genetic screening to deep intronic regions identified pathogenic variants in 9% of gene-elusive HCM. These findings translate to more accurate diagnosis and management in HCM families.

Induced pluripotent stem cell technology and inherited arrhythmia syndromes.

Inherited arrhythmia syndromes, including familial long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, and Brugada syndrome, can cause life-threatening arrhythmias and are responsible for a significant proportion of sudden deaths in the young. Identification of genetic mutations and pathophysiological changes that underlie disease development can inform clinical practice and guide novel drug development. However, disease mechanisms in a large number of patients remain elusive and pharmacologic treatment is suboptimal, so many patients rely on implantable cardioverter-defibrillator therapy. Induced pluripotent stem cell models of disease facilitate analysis of disease mechanisms in patient-specific cardiomyocytes, overcoming limitations of animal models and human tissue restrictions. This review outlines how studies using induced pluripotent stem cell-derived cardiomyocytes are contributing to our understanding of the mechanisms that underpin disease pathogenesis and their potential to facilitate new pharmacologic therapies and personalized medicine.

Burden of Recurrent and Ancestral Mutations in Families With Hypertrophic Cardiomyopathy.

BACKGROUND: Hypertrophic cardiomyopathy is a genetically heterogeneous myocardial disease with >1000 causal variants identified. Nonunique variants account for disease in many families. We sought to characterize nonunique variants in Australian families and determine whether they arise from common ancestral mutations or recurrent mutation events. METHODS AND RESULTS: Genetic test results of 467 index patients from apparently unrelated families with hypertrophic cardiomyopathy were evaluated. Causal variants were found in 185 of 467 (40%) families. Nonunique variants accounted for 122 of 185 (66%) families. The most common single genetic cause of hypertrophic cardiomyopathy is the recurrent MYBPC3 (myosin-binding protein-C) variant c.1504C>T, p.Arg502Trp, which was found in 13 of 185 (7%) families with a causal variant identified. Thirteen variants in MYBPC3 and MYH7 (myosin heavy chain 7) were each identified >3 times and accounted for 78 of 185 (42%) hypertrophic cardiomyopathy families with a causal variant. Haplotype analysis of these 13 variants was performed on 126 individuals from 70 Australian families, and 11 variants arose through recurrent mutation events. Two variants, MYBPC3 c.1928-2A>G and MYH7 c.2681A>G, p.Glu894Gly, were found on 1 haplotype in 6 families each, supportive of a single mutation event inherited from a common ancestor. CONCLUSIONS: The majority of families with a causal variant identified have a nonunique variant. Discovery of the genetic origins of human disease forms a fundamental basis for improved understanding of disease pathogenesis and phenotype development.

Peripheral blood derived induced pluripotent stem cells (iPSCs) from a female with familial hypertrophic cardiomyopathy.

Induced pluripotent stem cells (iPSCs) were generated from peripheral blood mononuclear cells (PBMCs) obtained from a 62-year-old female with familial hypertrophic cardiomyopathy (HCM). PBMCs were reprogrammed to a pluripotent state following transfection with non-integrative episomal vectors carrying reprogramming factors OCT4, SOX2, LIN28, KLF4 and L-MYC. iPSCs were shown to express pluripotency markers, possess trilineage differentiation potential, carry rare variants identified in DNA isolated directly from the patient's whole blood, have a normal karyotype and no longer carry episomal vectors for reprogramming. This line is a useful resource for identifying unknown genetic causes of HCM.

Generation of induced pluripotent stem cells (iPSCs) from a hypertrophic cardiomyopathy patient with the pathogenic variant p.Val698Ala in beta-myosin heavy chain (MYH7) gene.

Induced pluripotent stem cells (iPSCs) were generated from peripheral blood mononuclear cells (PBMCs) isolated from the whole blood of a 43-year-old male with hypertrophic cardiomyopathy (HCM) who carries the pathogenic variant p.Val698Ala in beta-myosin heavy chain (MYH7). Patient-derived PBMCs were reprogrammed using non-integrative episomal vectors containing reprogramming factors OCT4, SOX2, LIN28, KLF4 and L-MYC. iPSCs were shown to express pluripotent markers, have trilineage differentiation potential, carry the pathogenic MYH7 variant p.Val698Ala, have a normal karyotype and no longer carry the episomal reprogramming vector. This line is useful for studying the link between variants in MYH7 and the pathogenesis of HCM.

Induced pluripotent stem cells in the inherited cardiomyopathies: From disease mechanisms to novel therapies.

Inherited cardiomyopathies lead to diverse clinical outcomes including heart failure, arrhythmias, and sudden death. Mutations in over 100 genes have been implicated in the pathogenesis of genetic heart diseases, including the main inherited cardiomyopathies, such as hypertrophic, dilated, and arrhythmogenic right ventricular cardiomyopathies. Understanding how these gene mutations lead to clinical disease and the various secondary genetic and environmental factors, which may modify the clinical phenotype, are key areas of research ultimately influencing diagnosis and management of patients. The emergence of patient-derived induced pluripotent stem cells (iPSCs), which can be differentiated into functional cardiomyocytes (CMs) in vitro, may provide an exciting new approach to understand disease mechanisms underpinning inherited heart diseases. This review will focus specifically on the key role of iPSC-based studies in the inherited cardiomyopathies, both in their potential utility as well as the significant challenges they present.