Genetic Testing of Familial Cardiomyopathies and Cardiac Ion Channel Diseases

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1 Genetic Testing of Familial Cardiomyopathies and Cardiac Ion Channel Diseases Dr YUEN Yuet Ping Liz Chemical Pathology, Prince of Wales Hospital 29 Nov 2015

2 Marked genetic heterogeneity Overlapping disease genes for different phenotypes Autosomal dominant with age-related penetrance and variable expressivity A small proportion carry 2 mutations in the same gene (biallelic) or in 2 different genes (digenic) Kimura et al. 2015

3 Family member screening Recommended Recommended Recommended Recommended Recommended Recommended Recommended Recommended Impact of genetic testing for index case regarding the contribution of the genetic test result for diagnosis, prognosis and guiding therapy (+++ strong, - negligible) Genetic testing for symptomatic patients recommended for LQTS, CPVT, HCM and DCM+CCD High yield of genetic test Provides diagnostic and prognostic information Influence therapeutic choices Recommended Recommended Ackerman MJ et al. HRS/EHRA Consensus Statement Europace 2011;13:

4 Hypertrophic Cardiomyopathy Gene Protein 1 MYH7 Myosin-7 2 MYBPC3 Myosin-binding protein C, cardiac type 3 TNNT2 Troponin T, cardiac muscle 4 TNNI3 Troponin I, cardiac muscle 5 TPM1 Tropomyosin alpha-1 chain 6 MYL2 Myosin regulatory light chain 2, ventricular/cardiac muscle isoform 7 MYL3 Myosin light chain 3 8 ACTC1 Actin, alpha cardiac muscle 1 9 CSRP3 Cysteine and glycine-rich protein 3 10 ACTN2 Alpha-actinin-2 11 MYH6 Myosin-6 12 TCAP Telethonin 13 TNNC1 Troponin C, slow skeletal and cardiac muscles 14 PLN Cardiac phospholamban 15 MYOZ2 Myozenin-2 16 NEXN Nexilin

5 Sarcomere gene mutations Mutation detection rate MYH7: 20 30% MYBPC3: 20 30% TNNT2: 3 5% TNNI3: 3 5% TPM1: 1 3% Total 56% : 100 unrelated Chinese patients Familial HCM 61% (31/51) MYH7 (41%) MYBPC3 (18%) TNNT2 (2%) Sporadic HCM 6% (3/49) Song et al. Clin Chim Acta 2005

6 Case 1 Clinical role of genetic testing Genetic testing approaches Possible outcome

7 I Sudden F/54 F/45 M/38 II LV noncompaction, end-stage heart failure III M/20 Hypertrophic F/6 Normal heart by echocardiogram F/1

8 II:3 and II:4 50% risk III:2 50% risk III:3 25% risk Require life-long follow-up and avoidance of risk I Sudden F/54 F/45 M/38 II LV noncompaction, end-stage heart failure M/20 F/6 F/1 III Hypertrophic

9 Family members - Clinical vs Genetics Dx Clinical Screening History, physical exam, echocardiography, ECG, etc. A normal baseline echocardiogram and ECG does not rule out HCM in asymptomatic relatives, particularly in children or young adults. Require screening and longitudinal FU throughout life. Genetic Diagnosis Testing of at-risk asymptomatic relatives is possible if the disease-causing mutation in the proband is known. Negative not at increased risk of developing HCM and thus obviate unnecessary screening. Positive result regular clinical assessment and surveillance.

10 Genetic testing strategies Septal contour and location and extent of hypertrophy Sigmoidal Reverse Apical Neutral Gene-by-gene approach Which gene(s) should be tested? Prevalence may be ethnic-specific Phenotype-guided genetic testing Bos JM et al unrelated patients with HCM Genetic testing for 9 myofilaments genes Overall yield 34% (359/1053) Positive predictor markers (80% with all 5 markers): 1. Reverse curve morphological subtype 2. Age at diagnosis younger than 45 yrs 3. Maximum left ventricular all thickness of 20mm or greater 4. Family history of HCM 5. Family history of sudden cardiac death Negative predictor marker: hypertension Binder et al sarcomere genes tested in 382 unrelated patients with HCM. Theis JL et al /239 patients +ve for mutations in Z- disc proteins. 11/13 sigmoidal contour 2/13 apical contour

11 Scenario 1: Sequencing results Target 1: MYH7 Beta heavy chain subunit of myosin Account for ~40% familial HCM in Chinese 38 coding exons > 600 mutations reported MYH7 heterozygous p.r719w

12 I Sudden F/54 F/45 M/38 II -/- p.r719w/- M/20 F/6 F/1 III p.r719w/- p.r719w/- Not tested Not tested

13 Before genetic screening II:3 50% risk II:4 50% risk III:2 50% risk III:3 25% risk After genetic screening II:3 not at increased risk II:4 Dx confirmed III:2 50% risk III:3 50% risk Genotype-phenotype correlation? Prognosis? Age of onset? Severity? Treatment of choice? I II p.r719w/- -/- p.r719w/- Limited prognostic value F/6 F/1 III p.r719w/- Not tested Genetic test for guiding therapy remains controversial Not tested

14 Scenario 2: Sequencing results MYH7 no pathogenic variants identified Gene-by-gene approach: MYBPC3 TNNT2 TNNI3 TPM1 Genomic approach Test all known genes associated with HCM and phenocopies in one test Next generation sequencing (NGS) much cheaper cost per base than Sanger sequencing Remarkable genetic heterogeneity Mutations in more than one gene poorer prognosis

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16 Scenario 3: Sequencing results MYH7 a variant of uncertain significance (VUS) identified A variant that could be disease-causing or benign. Additional information is necessary to understand the significance. Ackerman MJ et al. HRS/EHRA Consensus Statement Europace 2011;13:

17 Evidence Predicted effect on protein structure and function Reported previously and what evidence was available to establish pathogenicity Prevalence in ethnic-matched normal controls Cosegregation with phenotype Pathogenic classification of variants can change over time as new relevant information becomes available.

18 Ruan Y et al. Nat Rev Cardiol 2009

19 Defects in one gene result in different phenotypes I ks Potassium channel α-subunit KCNQ1 β- subunit KCNE1 Expressed in cardiac muscles and inner ear A-kinase anchor protein 9 AKAP9 (I ks Potassium channel interacting protein) KCNQ1 KCNE1 AKAP9 Loss of function repolarization plateau phase Long QT LQT1 / JNL1 LQT5 / JLN2 LQT11 KCNQ1 Gain of function repolarization plateau phase Short QT Familial AF SQT2 ATBF3

20 Long QT syndrome Autosomal dominant with reduced penetrance (Romano Ward syndrome) Autosomal recessive (Jervell and Lange-Nielsen syndrome), associated with sensorineural hearing loss ~ 4 10% biallelic or digenic (longer QTc, earlier age of onset, higher risk of cardiac events)

21 1 KCNQ1 LQTS type 1 / JLNS % 70 75% 2 KCNH2 LQT2 type % 3 SCN5A LQTS type % 4 ANK2 LQTS type 4 <1% Around 20% no detectable mutations in these genes 5 KCNE1 LQTS type 5 / JLN2 <1% 6 KCNE2 LQTS type 6 <1% 7 KCNJ2 LQTS type 7 (Andersen-Tawil syndrome) <1% 8 CACNA1C LQTS type 8 (Timothy syndrome) <1% 9 CAV3 LQTS type 9 <1% 10 SCN4B LQTS type 10 Rare (2 cases) 11 AKAP9 LQTS type 11 Rare (1 case) 12 SNTA1 LQTS type 12 Rare (3 cases) 13 KCNJ5 LQTS type 13 Rare (2 cases) 14 CALM1 LQTS type 14 <1% 15 CALM2 LQTS type 15 <1%

22 LQT1 LQT2 LQT3 Gene KCNQ1 KCNH2 SCN5A Arrhythmogenic triggers Exercise, Swimming Auditory stimuli Post-partum period Sleeping / rest T-wave morphology Broad-based Low amplitude notched Normal-appearing after a prolonged isoelectric ST segment Incidence of cardiac events 63% 46% 18% Sudden death risk 4 6% 4 6% 4 6% Treatment β-blocker (90% remained symptom-free; mortality rate 1%) Na channel blockers Wilde AAM and Behr ER. Nat Rev Cardiol Priori SG et al. Europace 2013; 15(10):

23 Case 2 Cardiac arrhythmia misdiagnosed as epilepsy Difficulty in interpretation of genetic testing results

24 M/4 Born in mainland China Frequent seizures since 16mo, triggered by crying or emotional instability Severe sensorineural hearing loss P/E - NAD Repeated EEG NAD Ix - NAD

25 Admitted after road traffic accident with Rt keg laceration In OT, uprolling of eyeballs, apnoea Pulseless VT for 1 min with evidence of TdP QTc 470ms 2 nd episode of VT while in PICU Jervell and Lange-Nielsen syndrome Autosomal recessive KCNQ1 or KCNE1

26 Echocardiogram NAD ICD placement Oral metoprolol Parents normal ECG

27 Before 2009 KCNQ1 Exon 16 NM_ : c.1831g>a (p.asp611asn) p.asp611tyr mild alteration of KCNQ1 electrophysiological properties in in vitro expression study. 6/11 carriers had prolonged QTc Penetrance ~ 54.5% KCNQ1 Exon 15 NM_ : c.1762a>t (p.ile588phe) Novel

28 M/70+ Normal ECG p.i588f p.d611n / - F/30+ Normal ECG -/- Father has the same genotype as the son Both mutations located on the same allele (not compound heterozygous) Mutation analysis of KCNE1 ve Clinically JLNS p.i588f p.d611n / - Careful in result interpretation. Additional analysis to confirm mutation analysis results in the proband. Mutation in other regions of the gene that were not covered by sequencing? Gross deletion / insertion / rearrangement that were not detected by sequencing?

29 Genetic analysis benefits and limitations Benefits Provides confirmation of clinical diagnosis More definitive identification of atrisk family members Provides insight into the underlying disease biology Limitations Results may be ambiguous. Interpretation of pathogenicity may change over time Testing cannot detect all disease-causing variants Test results are unlikely to directly affect the management Due to reduced penetrance and variable expressivity, results cannot be used predict age of onset or clinical outcomes

30 Thank you