SHA24/086004

Page 1

Role of Genetic Testing in Inherited Arrhythmia Diagnosis and Management

Li Zhang, MD Lankenau Medical Center, Lankenau Institute for Medical Research Jefferson Medical College, Philadelphia, PA, USA

Approximately 50% Sudden Unexplained Deaths (SUDs) are caused by Cardiac Channelopathies and Cardiomyopathies Diagnoses in SUDS

Adapted from Behr ER, et al. Eur Heart J. 2008;29:1670-1680.

• 1/3 of SUDs are attributable to a cardiac channelopathies, while another 10-15% are attributable to cardiomyopathies.1,2 • Accurate identification is vital for appropriate prophylaxis among relatives who should undergo comprehensive cardiology evaluation, guided and confirmed by mutation analysis. Reference: 1. Behr ER, Dalageorgou C, Christiansen M, et al. Sudden arrhythmic death syndrome: familial evaluation identifies inheritable heart disease in the majority of families. Eur Heart J. 2008;29:1670-80. 2. Tan HL, Hofman N,van Langen IM, et al. Sudden unexplained death: heritability and diagnostic yield of cardiological and genetic examination in surviving relatives. Circulation. 2005;112:207-13.

Sudden Infant Death Syndrome (SIDS) San Diego Definition • Sudden unexpected death of an infant <1 year of age, with onset of the fatal episode apparently occurring during sleep, that remains unexplained after a thorough investigation, including performance of a complete autopsy and review of the circumstances of death and the clinical history. Pediatrics, vol. 114, no. 1, pp. 234–238, 2004

Code in death certificate

Back-to-Sleep Campaign

(approved by WHO in Oct 2009)

• R95.0 SIDS with mention of autopsy • R95.9 SIDS without mention of autopsy Prevalence in the US • 1.5/1000 births in 80’s, 0.5/1000 births in 20’s. However, SIDS is still a major cause of infant mortality in the US (6 SIDS/day) and developing countries. The congenital cause • It is estimated that 1 out of 5 SIDS victims carries a mutation in a cardiac ion channel-related gene and that the majority of these mutations are of a known malignant phenotype.

Sudden Infant Death Syndrome (SIDS)

•

Genetic predisposition and risks during development create a vulnerable infant. If this vulnerable infant encounters environmental triggers during a critical developmental period, it may become an SIDS victim.

Sudden Death in Young Athletes

•

Among 1,866 young US athletes (19±6 years of age) who died suddenly (or survived cardiac arrest) in 38 diverse sports, more than half (56%) were due to cardiovascular disease.1 – The most common cardiovascular cause was hypertrophic cardiomyopathy (36%).1 – Cardiac channelopathies (long QT syndromeLQTS, Brugada syndrome, etc) and arrhythmogenic right ventricular displasia (ARVD) account for 8% of the cardiovascular causes.1

Reference: 1. Maron BJ, Doerer JJ, Haas TS, et al. Sudden deaths in young competitive athletes: analysis of 1866 deaths in the United States, 1980-2006. Circulation. 2009;119:1085-92. 5

Role of Genetic Testing • Over the last two decades, we have witnessed a revolution in the understanding of primary cardiac arrhythmia syndromes. • These remarkable advances stemmed from the discovery of mutations, primarily in ion channel genes, underlying a number of these disorders. • The availability of a genetic diagnostic test has added an important diagnostic tool, providing new opportunities for patient management such as early (presymptomatic) identification and treatment of individuals at risk of developing fatal arrhythmias.

Role of Genetic Testing • Several cardiac arrhythmia syndromes that for long were considered idiopathic are now known to have a genetic basis. They are caused by mutations in genes primarily encoding ion channels. • The genetic basis for most arrhythmia syndromes is heterogeneous—that is, a given disorder may be caused by mutations in different genes, and evidence for further genetic heterogeneity exists.

Role of Genetic Testing • Studies into genotype–phenotype relationships, carried out mostly for LQTS, have uncovered important gene specific aspects of disease and indicated that patient management must take the nature of the gene affected into consideration. • The recognition of the genetic substrate underlying the inherited arrhythmia syndromes has provided remarkable insight into the molecular basis of cardiac electrophysiology, including the role of the various ion channels and mechanisms of arrhythmias.

Role of Genetic Testing • It is becoming increasingly clear that treatment should take the type of gene affected into consideration (gene specific therapy). • The identification of a proband with a primary cardiac arrhythmia should trigger screening of family members to identify all affected relatives (presymptomatically). • In LQTS, information on ECG morphology and triggers for arrhythmia (to be sought in the proband as well as family members) can indicate the gene likely affected, enabling initiation of the most appropriate treatment even before results from the genetic test become available.

SCD: What Genetics Have Taught Us? • Considerable heterogeneity may exist in disease manifestation (both in severity as well as differences in disease features) among family members carrying the same mutation. In this respect, a genetic test is vital in uncovering all carriers of the genetic defect within a family.

The FAMILION Genetic Tests for Inherited Cardiac Syndromes

*Large deletion/duplication testing available.

11

Interpretation Genetic Data •

Class I mutations: considered disease-causing

• Class II: Unclassified variant (UV, VUS) -association with disease is uncertain; generally < 1% • Class III: Polymorphism ≥ 1% population; may have an effect SNP: single nucleotide polymorphism -often in non-coding DNA -in regulatory sequences/introns: may have effects

Demo 2. Class I mutation identified in Type-1 LQTS (LQT1) LQT1 ECG Phenotype

Non-pause Dependent Torsade de Pointes (TdP) Competitive sports Triggers

• QTc 500 ms

Sudden death

KCNQ1-V254M a missence mutation is co-segregated with LQT1 phenotype in this family. To date >333 mutations have been reported to cause LQT1 and JLNS. References: Wang et al., 1996,Donger et al., 1997: Paulussen et al 2003; Choi et al 2004; Struijk et al 2006; Zhang, et al 2000*

From clinical perspective: • LQTS ≠ sudden cardiac death! • >95% of TdP in LQTS will convert to sinus rhythm. • On average, the mortality is 4% in the common LQTS genotypes LQT1-3. For Class I and and some of Class II mutations:  It is important to remember that positive genetic testing results have no absolute governing in many clinical situations. The final judgment regarding care of a particular patient must be made by health care provider and patient in light of all relevant circumstances. Reference: Ackerman, et al. HRS/EHRA Expert Consensus Statement on the State of Genetic Teting for the Channelopathies and cardiomyopathies Heart Rhythm, 2011;8:1308-1338

Aborted Sudden Unexplained Death Case Demo 1

VF

Class II Variant Case Demo 1

VF

To follow-up on Case 1 demonstrated previously, DSG2 Val56Met, a class II variant, was identified in the proband. Nevertheless, family genotyping revealed that DSG2 Val56Met does not co-segregated with the disease phenotype.

Class III mutations

• In most cases they are not deleterious therefore not diseasecausing mutations. • Negative test results does not always exclude the presence of the disease.

Cataloging Normal Genetic Variation is Critical for Accurate Variant Interpretation •

Mutations that cause cardiac channelopathies and cardiomyopathies are frequently novel and “family-specific”.

•

In the same disease-causing genes, healthy individuals often harbor rare, benign genetic variation.

– This fact complicates assigning clinical significance to novel variants observed in patients.*

•

Cataloging rare, benign variation in large control populations helps reduce the number of Class II mutations (VUSs) reported.

– Rare variants that would otherwise be interpreted as VUSs, if instead are seen in a control population would be interpreted as Class III variants (polymorphisms). * Holst, et al: Sodium current and potassium transient outward genes in Brugada syndrome: screening and bioinformatics. Can J Cardiol 2010 (in press)

Spectrum and Prevalence Of Genetic Variation in HCM Genes Among Ostensibly Healthy Adults •

In 2010, the Mayo Clinic and Transgenomic described the spectrum and prevalence of genetic variation in more than 400 ostensibly healthy adults in 9 sarcomeric HCM-susceptibility genes.1

– 52 distinct missense variants were identified among healthy controls, 32 (62%) of which were observed only once and had not been identified previously in healthy adults.

– 11 variants (21%) found in Famillion HCM control population had been previously published as HCM-associated.

•

These observations highlight the importance of large control populations for accurately interpreting the clinical significance of variants detected in patients. Reference: 1. Kapplinger J, Landstrom AP; Bos JM, et al. Spectrum And Prevalence Of Genetic Variation In Hypertrophic CardiomyopathySusceptibility Genes Among Ostensibly Healthy Adults. American Heart Association 2010, Abstract 19436.

Healthy and Ethnically Diverse Reference Population •

Complete reference DNA sequences from private and published healthy “control” subjects

•

Over 400 controls for every gene that could cause SCD ~100 European ~100 African ~100 East Asian ~100 Hispanic, Native American, South Asian and other

•

Over 1300 subjects for major LQTS & BrS genes* ~600 European ~350 African ~150 East Asian ~150 Hispanic ~85 Native American, South Asian, Middle Eastern, and other * KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2 used in Famililon tests

20

Distinguishing Pathogenic Mutations from Benign Variants in LQTS

•

In this large case-control study, the type, frequency, and location of mutations across KCNQ1 (LQT1), KCNH2 (LQT2), and SCN5A (LQT3) were compared between 388 unrelated “definite” LQTS cases and 1300 healthy controls for each gene.

Reference: 1. Kapa S, Tester DJ, Salisbury BA, et al. Genetic testing for long-QT syndrome. Distinguishing pathogenic mutations from benign variants. Circulation. 2009;120:1752-60.

Distinguishing Pathogenic Mutations from Benign Variants in LQTS Topological depiction of all protein-altering mutations

•

In total, 248 mutations (180 distinct: 129 missense mutations, 51 radical) were found among 224 of the 388 LQTS cases (58%).

•

In contrast, only 79 unique mutations (77 missense) were found among the 1300 diverse controls (6%). The “background” mutation rate in non-white controls (8%) was substantially higher than in white controls (4%; P<0.01).

•

From these data, estimated predictive values (EPVs % mutations found in definite cases that would cause LQTS) were determined according to mutation type and location.

Open circles represent case mutations; solid circles, rare (each observed only once) genetic variants observed among the >1300 healthy volunteers; and solid squares, the genetic variants/ polymorphisms observed more than once among controls.

Reference: 1. Kapa S, Tester DJ, Salisbury BA, et al. Genetic testing for long-QT syndrome. Distinguishing pathogenic mutations from benign variants. Circulation. 2009;120:1752-60.

EPVs for Missense Mutations in the Major LQTS Genes are Location Dependent KCNQ1 LQT1

KCNH2 LQT2

SCN5A LQT3 *The presence of a radical mutation (splice-site, nonsense, frame-shift, or in-frame insertions/deletions in KCNQ1 and KCNH2; in-frame insertions/deletions in SCN5A) confers an EPV >99% regardless of gene or gene region. Reference: 1. Kapa S, Tester DJ, Salisbury BA, et al. Genetic testing for long-QT syndrome. Distinguishing pathogenic mutations from benign variants. Circulation. 2009;120:1752-60.

Distinguishing Pathogenic Mutations from Benign Variants ARVD

•

This large case-control study compared the genetic variation identified in 175 high probability ARVD cases of Caucasian ancestry with the variation found in a collection of over 400 ostensibly healthy volunteers of diverse ancestry.

Reference: 1. Kapplinger JD, Landstrom AP, Salisbury BA, et al. Distinguishing arrhythmogenic right ventricular cardiomyopathy/dysplasia-associated mutations from background genetic noise. J Am Coll Cardiol. 2011;57:2317-27.

Distinguishing Pathogenic Mutations from Benign Variants ARVD

•

While only 0.5% of controls had radical mutations, such mutations were present in 43% of ARVD cases, indicating that radical mutations in ARVD cases are high-probability disease-causing mutations.

•

In contrast, missense mutations were found in 21% of ARVD cases but also in 16% of controls (6% of Caucasians and 19% of non-Caucasians).

•

Missense variants localizing to N-terminal regions of DSP or DSG2 or affecting highly conserved residues, particularly within PKP2 and DSG2, more likely to be deleterious.

Mutation “Hot Spots” Within the Cardiomyocyte Desmosome Reference: 1. Kapplinger JD, Landstrom AP, Salisbury BA, et al. Distinguishing arrhythmogenic right ventricular cardiomyopathy/dysplasia-associated mutations from background genetic noise. J Am Coll Cardiol. 2011;57:2317-27.

When is a mutation pathogenic? -Absence in control group -Amino-acid properties -Evolutionary conservation -Functionally important domain -Functional data -Co-segregation -Nonsense/affecting splicing -In silico predictions Not every -Described before as... published -De novo variant/mutation is pathogenic Awad et al. Nature CV Practice 2008

Distinguishing Pathogenic Mutations from Benign Variants

•

The results of these studies aid physicians in estimating the clinical significance of rare, novel variants identified in disease-susceptibility and underscore the importance of evaluating a large, ethnically-diverse control population to help guide interpretation as is done proactively for every gene.

•

These studies also demonstrate why many potential disease-causing mutations are necessarily labeled Class II variants of uncertain significance.

Reference: 1. Kapa S, Tester DJ, Salisbury BA, et al. Genetic testing for long-QT syndrome. Distinguishing pathogenic mutations from benign variants. Circulation. 2009;120:1752-60. 2. Kapplinger JD, Landstrom AP, Salisbury BA, et al. Distinguishing arrhythmogenic right ventricular cardiomyopathy/dysplasia-associated mutations from background genetic noise. J Am Coll Cardiol. 2011;57:2317-27. 2. Kapplinger JD, Landstrom AP, Salisbury BA, et al. Distinguishing arrhythmogenic right ventricular cardiomyopathy/dysplasia-associated mutations from background genetic noise. J Am Coll Cardiol. 2011;57:2317-27.

Future Implications • With recent advances in genotyping technology, comprehensive screening of multiple genes in different pathways is now feasible. Moreover, the availability of a high resolution genome-wide map of polymorphisms and the evolving technology for whole exome sequencing, and related bioinformatics, are also expected to facilitate the study of genetics of common acquired arrhythmias. This is likely to provide novel tools for risk stratification and open new opportunities for prevention and therapy of lethal arrhythmias in the common pathologies.

Acknowledgement •

Tom Callis, PhD FAMILION Genetic Tests, Transgenomic, Inc, USA

•

J. Peter van Tintelen, MD PhD University Medical Center Groningen, the Netherlands

•

•

Sheila Zuniga, PhD Sistemas Genomicos, SL, Spain Yuxin Fan, MD, PhD Texas Children's Hospital, Baylor College of Medicine

•

William Wikoff Smith Charitable Trust

•

AHA0735474N

SHA24-GHA10 Joint Scientific Conference

Riyadh, Kingdom of Saudi Arabia, February 13-16, 2013

Turn static files into dynamic content formats.

Create a flipbook
Issuu converts static files into: digital portfolios, online yearbooks, online catalogs, digital photo albums and more. Sign up and create your flipbook.