Genetics of Hypertrophic Cardiomyopathy After 20 Years

Journal of the American College of Cardiology © 2012 by the American College of Cardiology Foundation Published by Elsevier Inc.

Vol. 60, No. 8, 2012 ISSN 0735-1097/$36.00 http://dx.doi.org/10.1016/j.jacc.2012.02.068

STATE-OF-THE-ART PAPER

Genetics of Hypertrophic Cardiomyopathy After 20 Years Clinical Perspectives Barry J. Maron, MD,* Martin S. Maron, MD,† Christopher Semsarian, MB, BS, PHD‡ Minneapolis, Minnesota; Boston, Massachusetts; and Sydney, New South Wales, Australia Hypertrophic cardiomyopathy (HCM) is the most common familial heart disease with vast genetic heterogeneity, demonstrated over the past 20 years. Mutations in 11 or more genes encoding proteins of the cardiac sarcomere (⬎1,400 variants) are responsible for (or associated with) HCM. Explosive progress achieved in understanding the rapidly evolving science underlying HCM genomics has resulted in fee-for-service testing, making genetic information widely available. The power of HCM mutational analysis, albeit a more limited role than initially envisioned, lies most prominently in screening family members at risk for developing disease and excluding unaffected relatives, which is information not achievable otherwise. Genetic testing also allows expansion of the broad HCM disease spectrum and diagnosis of HCM phenocopies with different natural history and treatment options, but is not a reliable strategy for predicting prognosis. Interfacing a heterogeneous disease such as HCM with the vast genetic variability of the human genome, and high frequency of novel mutations, has created unforeseen difficulties in translating complex science (and language) into the clinical arena. Indeed, proband diagnostic testing is often expressed on a probabilistic scale, which is frequently incompatible with clinical decision making. Major challenges rest with making reliable distinctions between pathogenic mutations and benign variants, and those judged to be of uncertain significance. Genotyping in HCM can be a powerful tool for family screening and diagnosis. However, wider adoption and future success of genetic testing in the practicing cardiovascular community depends on a standardized approach to mutation interpretation, and bridging the communication gap between basic scientists and clinicians. (J Am Coll Cardiol 2012;60:705–15) © 2012 by the American College of Cardiology Foundation

For over 50 years, hypertrophic cardiomyopathy (HCM) has been recognized as a familial cardiac disease with highly visible risk for sudden death and disease progression, characterized by heterogeneous phenotypic expression, natural history, and genetic profile (1– 6). HCM is the most common monogenic cardiovascular disease with a prevalence of 1:500 (7). For HCM, the molecular era emerged more than 20 years ago with identification of disease-causing mutations in genes coding for proteins of the cardiac sarcomere (5,8,9). These breakthrough observations defining the basic genetic substrate were accompanied by considerable optimism and expectation that mutational analysis would revolutionize

From the *Hypertrophic Cardiomyopathy Center, Minneapolis Heart Institute Foundation, Minneapolis, Minnesota; †Hypertrophic Cardiomyopathy Center, Tufts Medical Center, Boston, Massachusetts; and the ‡Agnes Ginges Centre for Molecular Cardiology; Centenary Institute; Sydney Medical School, University of Sydney; and Department of Cardiology, Royal Prince Alfred Hospital, Camperdown, Sydney, New South Wales, Australia. Dr. B. J. Maron is an advisor for GeneDx and a grantee of Medtronic. Dr. M. S. Maron has reported that he has no relationships relevant to the contents of this paper to disclose. Dr. Semsarian is the recipient of a Practitioner Fellowship from the National Health & Medical Research Council, Canberra, Australia. Manuscript received October 5, 2011; revised manuscript received January 20, 2012, accepted February 3, 2012.

HCM with regard to diagnosis and prediction of clinical course, as well as guiding management (10 –12). More recently, striking scientific advances in molecular genetics have resulted in availability of comprehensive commercial genetic testing to the practicing cardiovascular community, while paradoxically creating many unanswered questions, and communication gaps surrounding translation of genetic information to clinical decision making. Therefore, it is timely to place the benefits and challenges of genotyping in HCM into perspective, for a disease that epitomizes application of genetic science to cardiovascular medicine. Historical Perspectives HCM is inherited in an autosomal dominant Mendelian pattern with variable expressivity and age-related penetrance (3–5,9,11,13). Offspring of an affected individual have a 50% probability of inheriting a mutation and risk for disease; alternatively, sporadic cases may be due to de novo mutations in the proband but absent from the parents. For its first 25 years, diagnosis of HCM could only be made through integration of examination, electrocardiogram, and invasive angiographic/hemodynamic studies, dis-

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proportionately identifying patients with left ventricular (LV) outflow obstruction (1) (Fig. 1). GINA ⴝ Genetic In the early 1970s, echocardiInformation Nonography afforded noninvasive viDiscrimination Act sualization of left ventricular hyHCM ⴝ hypertrophic cardiomyopathy pertrophy (LVH), and reliable identification of family members LV ⴝ left ventricle/ left ventricular with and without the HCM pheLVH ⴝ left ventricular notype (14). Introducing basic hypertrophy science to HCM, by interfacing VUS ⴝ variant of uncertain deoxyribonucleic acid (DNA)– significance based methodologies and classical segregation linkage analysis with echocardiography, allowed mapping HCM to a causative locus on chromosome 14 in 1989 (8). In 1990, sequence analysis of a candidate gene revealed a pathogenic missense mutation in the beta-myosin heavy chain gene (MYH7Arg 403 Gln) to be responsible for HCM (9). Abbreviations and Acronyms

Molecular Basis of HCM The substrate, 2011. Two decades of intensive investigation have defined the vast and daunting heterogeneity of the HCM substrate. The early report of 7 mutations in 1 gene (MYH7) (10) has now expanded to 11 or more causative genes (5,13,15–21) with ⬎1,400 mutations (Dr. H. Rehm, personal communication, August 2011), expressed primarily or exclusively in the heart. These genes encode thick and thin myofilament proteins of the sarcomere or contiguous Z-disc (Table 1). Mutations in several additional sarcomere (or calcium-handling) genes have been proposed, but with less evidence supporting pathogenicity (Table 1). Of those patients with positive genetic tests, about 70% are found to have mutations (of either definite or uncertain pathogenicity) in the 2 most common genes, MYH7 and myosinbinding protein C (MBPC3), while other genes including troponin T, troponin I, ␣-tropomyosin, and ␣-actin each account for a small proportion of patients (1% to 5%). Types of mutations. The vast majority (about 90%) of pathogenic mutations altering physical and functional properties of proteins are missense, in which a single normal amino acid is exchanged for another (e.g., replacement of arginine for glutamine). Alternatively, more radical muta-

Figure 1

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Molecular of Substrate HCM Table 1 Substrate Molecular of HCM Strongest evidence for pathogenicity Thick filament 1. ␤-myosin heavy chain

MYH7

2. Regulatory myosin light chain

MYL2

3. Essential myosin light chain

MYL3

Thin filament 4. Cardiac troponin T

TNNT2

5. Cardiac troponin I

TNNI3

6. Cardiac troponin C

TNNC1

7. ␣-tropomyosin

TPM1

8. ␣-cardiac actin

ACTC

Intermediate filament 9. Cardiac myosin-binding protein C

MYBPC3

Z-disc 10. ␣-actinin 2

ACTN2

11. Myozenin 2

MYOZ2

Lesser evidence for pathogenicity Thick filament 12. ␣-myosin heavy chain

MYH6

13. Titin

TTN

Z-disc 14. Muscle LIM protein

CSRP3

15. Telethonin

TCAP

16. Vinculin/metavinculin

VCL

Calcium handling 17. Calsequestrin

CASQ2

18. Junctophilin 2

JPH2

HCM ⫽ hypertrophic cardiomyopathy.

tions affect many amino acids in the protein, resulting in a very different product (i.e., frameshift), and are generally predicted to trigger more substantial clinical consequences. Frameshift mutations are caused by insertion or deletion of ⱖ1 nucleic acids in the coding region often resulting in shortened truncated proteins (frequently found in the MYBPC gene), or abnormal splicing of messenger ribonucleic acid (mRNA). Genetic Testing for HCM Background. HCM genetic testing was initially confined to the realm of a few research laboratories focused on enhancing a basic understanding of this disease. Testing results were unpredictable, as laboratories lacked sufficient

HCM Landmarks

Genetic and clinical advances over the ⬎50-year history of hypertrophic cardiomyopathy (HCM). ICD ⫽ implantable cardioverter-defibrillator; SD ⫽ sudden death.

*Testing also available abroad, including Norway (Rikshospitlet Medical Genetic Laboratory), Denmark (Statens Serum Institute), and the United Kingdom (National Health Service). †Usually includes metabolic phenocopies (e.g., LAMP2, PRKAG2, Fabry disease). ‡To assess mutational pathogenicity. §Courtesy interpretation and/or clarification of testing report by telephone/email. 储Systematic notification to physician/patient (“look back testing”) available. ¶Insurance program limits direct patient cost to $100, where this policy is permissible under local and state laws. #Testing company takes primary responsibility for establishing the insurance component of payment in conjunction with the commercial carrier. **Partners HealthCare Center for Personalized Genomic Medicine (Harvard University, Cambridge, Massachusetts). ††Also available as a pan-cardiomyopathy panel of 46 genes, including HCM (cost: $3,900). ‡Tests performed gratis for cosegregation to resolve VUS. §§When mutation is known in proband, and with generally shorter turnaround times of 2 to 4 weeks. HCM ⫽ hypertrophic cardiomyopathy; VUS ⫽ variant of uncertain significance.

100 $400 ⫹ 2003 Partners** (Cambridge, Massachusetts)

www.pcpgm.partners.org

617-768-8500

18††

5

5

⫹

$3,200‡

40 $250 ⫹ 2007 Correlagen Diagnostics (Waltham, Massachusetts)

www.correlagen.com

866-647-0735

16

6–8

7

⫹

$3,975

10 $900

$350

⫹ ⫹

$5,400#

⫹ ⫹

3 4–6

8 18

12 877-274-9432

301-519-2100 www.genedx.com

Transgenomic-FAMILION (New Haven, Connecticut)

www.familion.com

2008

2008

GeneDx (Gaithersburg, Maryland)

Telephone Website Company

5

Variant Reclassification储

$3.375#¶

No. of Other Genetic Diseases Tested Cost (Other Family Members) Cost (Proband Testing) Genetic Consultation Available§ No. of Probability Categories‡ Turnaround Time (Weeks)§§ No. of HCM Genes in Panel† Began HCM Testing (Year)

Commercial Genetic Testing Services in the UnitedinStates for HCM* Table 2 Commercial Genetic Testing Services the United States for HCM*

resources to accommodate all clinical requests. In 2003, genetic testing entered the mainstream of the healthcare system with automated DNA sequencing providing rapid, reliable, and comprehensive molecular diagnosis on a feefor-service basis. DNA testing typically requires transporting 5 to 10 ml of whole blood to institutional or commercial laboratories (Table 2), all offering similar panels, including established HCM causative genes, phenocopies, and possibly other genes with lesser evidence for pathogenicity. U.S. proband testing may be associated with significant cost and economic burden, but also with a variety of insurance and billing strategies available. Pathogenic versus nonpathogenic mutations. A mutation can be considered pathogenic (or likely pathogenic) on the basis of the preponderance of evidence from the following criteria (15,22) (Table 3): 1) cosegregates with the HCM phenotype (i.e., LV hypertrophy) in family members, i.e., the only criterion that relies on data obtained directly from the patients; 2) previously reported or identified as a cause of HCM; 3) absent from unrelated and ethnic-matched normal controls; 4) protein structure and function is importantly altered (e.g., frameshift with truncation); and 5) amino acid sequence change in a region of the protein otherwise highly conserved through evolution with virtually no variation observed among species, suggesting its importance to basic cellular function. On the other hand, many amino acid substitutions in DNA sequence do not cause disease and are regarded as benign polymorphisms (i.e., variants not generally expected to be deleterious), by convention occurring in ⬎0.5% to 1.0% of ethnic-specific normal control populations. Nevertheless, the relevance for causing disease attached to a significant minority of such identified variants remains unclear, even after applying all criteria for pathogenicity. As a result, these mutations are assigned by genetic test reports into an ambiguous category (i.e., variants of uncertain significance [VUS or VOUS]) (15,21,22) with virtually no clinical utility for family screening. Indeed, distinguishing pathogenic mutations from VUS, or rare nonpathogenic variants, has increasingly emerged as a dilemma for interpreting testing results in HCM, and has been regarded as the “Achilles heel” of this diagnostic strategy (15). This issue has become particularly challenging as the reduced cost of technology now allows comprehensive DNA sequencing of the exome and even the whole genome (23,24,25). Although affording scientific insights, this development also substantially increases the recognition of VUS, potentially creating only further ambiguity in test reports. That VUS occur more commonly in human control populations than previously appreciated (genetic variation referred to collectively as “background noise”) underscores the need for more definitive criteria to differentiate pathogenic mutations from benign genetic “noise.” Notably, generally accepted guidelines for interpreting VUS are currently lacking, with estimated frequencies varying dramatically from 5% to 50%, largely dependent on the number of pathogenicity classes used to categorize mutations and the

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Current UsedCriteria to Determine Pathogenicity of an HCM Mutation* Table 3Criteria Current Used toProbability Determinefor Probability for Pathogenicity of an HCM Mutation* Pathogenicity Criterion

Description

Potential Limitations for Interpretation

Cosegregation

Determine whether mutation is present in relatives with LVH and absent in those without LVH

Often impractical Family size may be small/relatives unavailable Family compliance unpredictable Requires resources for imaging/DNA studies in ⱖ3 relatives (other than proband) including ⱖ1 with HCM phenotype†

Prior evidence of pathogenicity

Documentation that mutation is HCM disease–causing in ⱖ1 patient in published literature, or in the individual experience of a testing laboratory

Absence of established comprehensive, curated, and cooperative database tabulating mutations‡ High rate of novel (de novo; “private”) mutations in 65% of probands Interpretation of pathogenicity can be inconsistent among testing laboratories

Control population

Confidence for pathogenicity increased when mutation absent from large, ethnicity-matched ostensibly healthy population

Often insufficient size§ Control subjects should be unrelated, ethnicity-specific and free of the disease in question Potentially pathogenic variants can occur in subjects judged clinically normal Many rare benign (missense) variants in normals, termed “background noise”

Major disruption protein structure, and function

Mutant proteins are judged to have substantially altered physical properties储

Inferred from evidence obtained from in nonhuman sources¶

*Presented in approximate order of the power for establishing disease-causing status for a given mutation, although meeting any 1 of the criteria can be sufficient to assign pathogenicity. †In clinical family screening the threshold burden of evidence for a gene already known to cause HCM is lower than for a new gene in a research setting requiring linkage analysis over 3 generations with LOD (logarithm of odds) score ⬍3. ‡Databases proposed to systematically assemble genetic data from all clinical and research laboratories include MutaDATABASE and Clin-Var; currently each clinical laboratory has assembled its own control group. §ⱖ100 subjects (200 alleles) considered the minimum; control groups of up to 400 subjects are in use. 储Includes: 1) Frameshift with profoundly altered amino acid sequence, associated with insertions/deletions, or resulting in truncated (shortened) protein; 2) occurring in amino acids otherwise highly conserved through evolution in humans and across species; 3) location in a functionally important site in genetic sequence leading to dysfunction. ¶Includes: 1) in vivo mutated mouse or rabbit models of HCM; 2) in vitro basic metabolic cell culture assay experiments using extracted protein of various species; 3) predictive software program models. HCM ⫽ hypertrophic cardiomyopathy; LVH ⫽ left ventricular hypertrophy.

number of genes comprising the testing panel (Fig. 2). Laboratory commercial testing strategies vary widely, employing from 3 to 7 descriptive pathogenicity classes to construct formal reports, thereby creating the distinct possibility that different interpretations of pathogenicity may emanate from different laboratories for the same mutation (Table 2). Indeed, it is not universally appreciated in the clinical cardiovascular community that molecular diagnosis and assign-

Figure 2

ment of mutations to pathogenic status is often made on a probabilistic basis, and not necessarily as a definitive binary (“yes” [positive] or “no” [negative]) test result. Certainly, the expectation threshold may have been set too high for genotyping initially, given the relatively few definitive scenarios that emerge in HCM, with the pathogenicity of sequence variants often difficult to establish with certainty. This principle is often difficult to merge with clinical practice decision making, and

Pathogenicity in Probands

Genetic testing interpretation categories are depicted with respect to the relative strength of each for clinical practice, and independent of the frequency with which these test results occur. These variant classifications are those commonly used by testing laboratories in formatting reports, to express the probability of pathogenicity. Benign and likely benign variants are not responsible for disease (polymorphisms). Variants of uncertain significance (VUS) are single nucleotide variants the significance of which are currently unresolved in terms of disease pathogenesis or causation. Absence of a mutation (in proband), is considered indeterminate, and of no clinical significance. Such category assignments are made largely on the basis of expert professional judgment by clinical laboratory geneticists using currently available data.

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translating complex molecular science to patient care has proved more challenging than initially anticipated. In addition, not generally recognized by clinicians is the possibility that pathogenic classifications of variants can change over time as new relevant information becomes accessible (e.g., a VUS can be reassigned to pathogenic [or alternatively, mutations regarded as disease-causing may be downgraded], scenarios that could be considered a second “Achilles heel” of genetic testing). Responsibility for notification of such reassignments to physicians and patients has unavoidably been assumed by genetic testing laboratories. However, the optimal strategies for this process are unclear and standard procedures have not been established to resolve these unique circumstances. Clinical Applications of Genetic Testing Mutation-specific screening of family members for HCM. A common question asked by cardiologists is “Should my HCM patient have genetic testing?” and it reflects the persistent confusion regarding molecular strategies in this disease (Figs. 3 and 4). Some form of family screening for HCM is universally recommended (26), with the preferred first option usually clinical testing with cardiac imaging and electrocardiography to identify phenotype-positive relatives (27) (Table 4). Screening of family members is also the predominant role for genetic testing (i.e., to identify those at risk for developing disease who do not have LV hypertrophy) (26). This strategy is initiated by successfully genotyping the proband with clinically expressed HCM. Failure to identify the causative mutation in the proband is an indeterminate result that provides no useful information and precludes predictive testing in family members. It should be underscored that the likelihood of obtaining a positive test in the proband is only about 50%, as all genes causing HCM have not yet been identified, and are absent from testing panels (19,20,26) (Fig. 5). Furthermore, many of the detected mutations will not be judged pathogenic, thereby eliminating substantially ⬎50% of families from the option of genotyping for identification of relatives at risk for HCM. Therefore, in only a minority of HCM probands will the result of the genetic test be actionable for family screening. If a pathogenic mutation is identified in a proband, it becomes a tool for screening at-risk relatives, with several possible diagnostic scenarios (26) (Figs. 3 and 4). In the most robust application of genetic testing, relatives testing negative for the known family mutation are considered unaffected. This result largely alleviates the psychological and economic burden of further cardiovascular surveillance, imaging tests or lifestyle and competitive sports restrictions (28). However, extraordinarily rare (but possible) scenarios can impact the use of genetic testing to definitively exclude the risk of developing HCM and make it imprudent to permanently forgo imaging tests: 1) reassignment of a mutation from likely pathogenic to VUS; 2) proband with 1 diseasecausing mutation in fact has a second mutation (unknown

Figure 3

Predictive Cascade (Generational) Testing

(A) A 45-year-old proband with a pathogenic MYH7 mutation. Genetic testing provided 3 diagnostic scenarios in third-generation offspring: age 10 years, unaffected status is virtually certain by absence of the mutation (reassuring to the family given multiple HCM-SCDs); age 14 years, gene positive but phenotype negative is at risk for developing disease, requiring continued clinical surveillance and imaging; age 22 years, diagnosis in patient with phenotypically expressed HCM (but only mild LVH) is confirmed. (B) A 33-year-old mother with clinical HCM diagnosis (probable pathogenic MYBPC mutation); 3 offspring tested negative for that mutation, with risk to develop HCM virtually excluded. Circles ⫽ females, squares ⫽ males; plus sign ⫽ present, zero ⫽ absent; solid symbols ⫽ clinical HCM diagnosis; and slash ⫽ deceased. CMR ⫽ cardiovascular magnetic resonance; HCM ⫽ hypertrophic cardiomyopathy; LVH ⫽ left ventricular hypertrophy; SCD ⫽ sudden cardiac death.

and undetected), which is transmitted to an offspring; 3) laboratory or human error in processing/reporting a mutation; and 4) de novo mutation, not accounted for in initial proband testing, occurs in subsequent generations. Genotype positive-phenotype negative. Penetration of genetic testing into clinical practice has created an important legacy, evident as a new and rapidly expanding patient subset within the HCM spectrum, i.e., genetically affected family members (usually MYH7 or MYBPC3 mutations) without LVH (29), although often with other markers such as myocardial crypts or scarring, elongated mitral leaflets, or diastolic dysfunction (11,30 –32) (Figs. 3 and 4). Such individuals have generated clinical decision-making dilemmas: which (if any) should be disqualified from

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Genetic Family Screening Strategies in HCM

*First option for assessment of family members would be a clinical screening evaluation with imaging tests and ECG; the option of genetic testing is triggered largely for those relatives with negative or indeterminate clinical testing (for the HCM phenotype). †Genetic testing may potentially lead to definitive diagnosis of HCM in patients with coexisting conditions (e.g., systemic hypertension or physiologic athlete’s heart). ‡Genetic screening often not productive; cosegregation, while an option, has practical obstacles including limited family size or patient compliance. ECG ⫽ electrocardiography; ICD ⫽ implantable cardioverter-defibrillator; PGD ⫽ pre-implantation genetic diagnosis; VUS ⫽ variant of uncertain significance; other abbreviations as in Figure 3.

intense competitive sports to reduce risk, or be considered for prophylactic implantable cardioverterdefibrillator therapy (28,29)? While Bethesda Conference #36 consensus recommendations do not exclude genotype positive-phenotype negative (G⫹ P⫺) from sports (28), the paucity of evidence that the nonhypertrophied LV is in fact electrically unstable (33) can make clinical decisions difficult (29). Given the relatively short period of time that genetic testing has been available, the precise proportion of the G⫹ P⫺ population that will develop overt disease expression remains uncertain, although believed to be low. Until rigorous penetrance data are available, it is prudent to extend standard HCM surveillance with cardiac imaging at least through midlife to detect development of the phenotype. On the basis of mutated HCM mouse and rabbit models, there is emerging interest in drug strategies (antioxidants, calcium-channel blockers, statins) to prevent development of the phenotype and disease progression in G⫹ P⫺ individuals (34,35). While there are no data that support this hypothesis, studies are in progress assessing pharmacologic prevention strategies in patients.

Suspected HCM phenocopies. An application of genetic testing is a disease-specific diagnosis in patients with LVH, due to mutations in genes distinct from those that encode sarcomere proteins. Metabolic myocardial storage cardiomyopathies, often misdiagnosed clinically, comprise an important but small fraction of patients genotyped for suspicion of HCM (ⱕ1%): regulatory subunit of adenosine monophosphate-activated protein kinase (PRKAG2) glycogen storage disease; lysosme-associated membrane protein (LAMP2; Danon disease), an X-linked dominant lyosomal storage disorder; Fabry, an X-linked recessive disease due to mutations in the galactosidase alpha (GLA) gene, and ␣-galactosidase A deficiency leading to multiorgan intracellular glycosphingolipid deposition (36 – 40). Diagnostic distinction between sarcomeric HCM and its phenocopies is crucial, given differences in natural history and management strategies. For example, mutations in LAMP2 are usually associated with rapid and potentially lethal clinical course within the first 3 decades, requiring early consideration for heart transplant (37,38). In Fabry disease, clinical benefits have been attributed to enzyme replacement therapy with recombinant ␣-galactosidase A,

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Proposed Clinical Echocardiography Resonance Detection of(and HCM12-Lead With Family or Cardiovascular Left Electrocardiography) Screening Ventricular Magnetic Hypertrophy*† forStrategies With Proposed Clinical Family Strategies Screening With Echocardiography or Cardiovascular Magnetic Table 4 Resonance (and 12-Lead Electrocardiography) for Detection of HCM With Left Ventricular Hypertrophy*† Age ⬍12 yrs Optional unless: Malignant family history of premature death from HCM, or other adverse complications Competitive athlete in an intense training program Onset of symptoms Other clinical suspicion of early left ventricular hypertrophy Age 12–21 yrs‡ Every 12–18 months Age ⬎21 yrs Imaging at onset of symptoms, or possibly at 5-year intervals at least through midlife; more frequent intervals for imaging are appropriate in families with malignant clinical course, or history of late-onset HCM *In family members who had not undergone genetic testing, or in whom testing was unresolved or indeterminate. †Modified from Maron et al. (27). ‡Age range takes into consideration individual variability in achieving physical maturity, and in some patients may justify screening at an earlier age; initial evaluation should occur no later than early pubescence. HCM ⫽ hypertrophic cardiomyopathy.

including regression of LVH and improved myocardial function and exercise capacity (39,40). Clinical suspicion sufficient to trigger genetic testing can be raised by: Wolff-Parkinson-White pattern in PRKAG2 and LAMP2, or greatly increased precordial voltages and massive LVH in patients with LAMP2 mutations (36 –38). Fabry disease can be suspected by symmetric LVH and late gadolinium enhancement in the posterobasal LV (39,40) (Fig. 6). Genotype–phenotype relationships/differential diagnosis. A positive genetic test in phenotypically expressed HCM is only confirmatory, but often useful when morphologic features are mild, equivocal, or atypical. Genetic testing can potentially resolve ambiguous clinical diagnoses such as HCM versus athlete’s heart or systemic hypertension; however, in this setting anticipated mutational yield is very low, and a negative test is indeterminate and does not exclude HCM (26). Availability of genetic testing has defined and expanded the HCM clinical spectrum showing a variety of sarcomere mutations to be responsible for diverse disease expressions and new patient subgroups (Fig. 7). Patterns of LVH vary greatly in closely related individuals (41) with phenotypes as dissimilar as apical aneurysms, end-stage, and massive or unusual patterns of hypertrophy, including wall thickening confined to the apex, are all part of this heterogeneous genetic disease (3,4,6,31,32,42,43). These observations dispel the notion that HCM is many similar but unrelated conditions, and create the unifying principle of a single but heterogeneous disease of the sarcomere.

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mutations are linked to prognosis (5,10,11) have been unrealized, in part by initial underappreciation of HCM as an exceedingly complex biological entity with vast genetic heterogeneity (11,15,21). While in the past some HCM genes and variants have been judged to convey more severe disease consequences than others (5,10 –12,44,45), there is now consensus on the basis of studies in large cohorts of unrelated patients that routine screening for specific mutations (each exceedingly uncommon in a genotyped population) cannot be designated either “benign” or “malignant” or reliably predict clinical outcome (17,18,21,26,46,47) (Fig. 4). Indeed, risk stratification with conventional clinical markers (e.g., history-taking or echocardiography) has served HCM well as a more rigorous prediction model for identifying highrisk patients who benefit from implantable cardioverterdefibrillator therapy (48). Multiple mutations. Through large-scale gene sequencing, data have emerged in HCM suggesting that double (or triple) or compound pathogenic mutations can be associated with more severe disease expression and adverse prognosis (e.g., advanced heart failure or sudden death, even in the absence of conventional risk markers [49–51]) (Fig. 8). While it is possible that multiple mutations will prove to be prognostic markers or arbitrators of ambiguous risk profiles, current evidence is preliminary and prospective long-term studies in large populations are required.

Figure 5

Prevalence of HCM Genes in Probands

Predicting Prognosis With Mutations Single mutations. The early period of HCM genetics was characterized by substantial optimism and, in retrospect, the unrealistic expectation that the discipline of molecular genetics would lead to a new paradigm in predicting the outcome of individual patients (5,12). Early notions that specific missense

Distribution of genes encoding proteins of cardiac sarcomere in hypertrophic cardiomyopathy (HCM) probands who undergo clinical genetic testing. A variety of laboratories report a wide range in mutational yield (24% to 63%), leaving a significant proportion of the HCM population genotype negative. Highest yields are in HCM probands with multiple affected family members, while lower rates are expected in probands without other affected family members (19,20).

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Genetic Diagnosis of Sarcomeric HCM Phenocopies

(A) LAMP2 (Tyr109Ter mutation, resulting in truncated protein) in 12-year-old boy who died suddenly with massive hypertrophy (septal thickness 65 mm, heart weight 1,425 g). (B) Histopathology showing marked scarring (stained blue) containing clusters of distorted myocytes with distinctive vacuolated sarcoplasm (arrows); inclusions are granular degraded lysosome material (Maron et al. [37], with permission of the American Medical Association). (C) Explanted heart from 24-year-old woman with LAMP2 (IVS6-2A-G splice site mutation), showing marked LV cavity dilatation and wall thinning due to diffuse transmural and subepicardial scarring (white areas) (Maron et al. [38], with permission of Elsevier). (D and E) CMR from 57-year-old woman with Fabry disease and typical modest/symmetric LVH. Ao ⫽ aorta; FW ⫽ free wall (of left ventricle); HCM ⫽ hypertrophic cardiomyopathy; LA ⫽ left atrium; LV ⫽ left ventricle; RV ⫽ right ventricle; VS ⫽ ventricular septum.

Consideration for Other Initiatives Assisted reproduction. Pre-implantation genetic diagnosis allows couples with an increased risk for transmitting a severe or potentially lethal genetic disease the opportunity to conceive a child who will not inherit the pathogenic mutation (52) (Fig. 4). After in vitro fertilization of harvested ova, a single cell is removed from each embryo (8 cells; 3-day stage) and tested for the specific mutation; only embryos free of the mutation are transferred into the uterus. Gene therapy. There is no established role for widespread experimental genetic engineering in HCM, a disease often associated with normal longevity. Gene therapy is also most applicable to recessively inherited defects caused by mutations associated with decreased or absent enzyme function. Genetic Counseling All HCM patients and relatives should be fully informed by virtue of some form of genetic counseling. Those who undergo genetic testing should receive specific pre- and post-test counseling, including discussion of risks, benefits, and options available (26,53). Certified genetic counselors play an important role by collecting detailed family history data to facilitate cosegregation studies and clarifying the pathogenicity of mutations, as well as discussing family planning, and mitigating the psychosocial impact of inher-

iting a potentially deleterious disorder (53). While the multidisciplinary approach has considerable merit in bringing together diverse expertise into 1 program (e.g., cardiologist, counselor, nurse), in the United States many HCM patients are evaluated outside of academic hospital settings, often making this model difficult to follow. As a consequence, cardiologists and nursing staffs assume a greater role in genetic counseling. In addition, all testing vendors have clinical geneticists available for post-test consultation.

Legal Implications Some patients are hesitant to contemplate genetic analysis for a variety of reasons, most often confidentiality concerns. However, in the United States, there is legislative protection from genetic discriminatory practices. Since 2008, Genetic Information Non-Discrimination Act (GINA) (54) has been a federal law for which most employers and health insurance providers are prohibited from denying or terminating insurance, employment, or promotion based solely on a mutation or family history of genetic disease. GINA does not protect against discrimination in the military, for life, disability, or long-term care insurance, or when there is a documented medical condition. GINA is a major advantage in promoting the dissemination of genetic testing.

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Figure 7

Utility of Genotyping for Defining Diverse HCM Phenotypes Within the Clinical Spectrum

(A) LV apical aneurysms (arrowheads) with mid cavity muscular obstruction (Maron et al. [32], with permission of the American Heart Association); (B) “endstage” remodeling with enlargement of LV (and atria) and wall thinning, associated with systolic dysfunction; (C) massive hypertrophy (wall thickness 34 mm) in anterolateral LV free wall (ALFW) (Maron et al. [42], with permission of Elsevier). (D to F) Morphologic abnormalities in absence of LVH: (D) primary elongation of anterior mitral leaflet (arrows) (Maron et al. [31], with permission of the American Heart Association); (E) multiple LV myocardial crypts (arrows); (F) late gadolinium enhancement indicative of replacement myocardial fibrosis (arrows). (G and G1) De novo phenotypic conversion at advanced age: (G) LVH absent at age 46 years; (G1) apical HCM (*) evident at age 51 years (Maron et al. [43], with permission of Elsevier). D ⫽ distal cavity; P ⫽ proximal cavity; other abbreviations as in Figure 6.

Promise and Cautionary Notes The science underlying HCM genotyping has become exceedingly complex, given the interfacing of a highly heterogeneous

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genetic disease with an increasing appreciation for the fundamentally complex nature of normal human genetic variability (i.e., with about 4 million largely benign nucleotide variants unique to each person). Nevertheless, novel and rapidly evolving strategies for generating genetic data, using nextgeneration technology, have emerged that will allow exome and whole-genome sequencing, leading to even greater amounts of genetic information. This opens up the possibility of defining new genes responsible for HCM (55), but also a multitude of novel variants and VUS for which clinical relevance is uncertain. Therefore, the application of genomics to HCM stands at a crossroads. If genetic testing is to evolve and have a more substantial role in the management of patients with HCM, future efforts should focus on clarifying pathogenicity more precisely for the substantial number of novel variants presently recognized and those that will inevitably be identified by new molecular techniques. Consequently, it is timely to create clinically advantageous collaborations among the commercial and academic testing laboratories to promote the exchange of genetic information and development of standardized mutational classification schemes that can be more easily translated into patient care. Databases that have been proposed for systematic assembly of genetic data from clinical laboratories include MutaDATABASE and Clin-Var. Such an initiative would almost certainly improve the quality of genetic test reports by reducing ambiguity in terminology and interpretation. Current genetic testing reports, which are both the window to this science and a potential guide to patient care, often seem too nuanced for the expectations of clinical cardiovascular medicine. As a result, clinical decisions are sometimes made in the context of rapidly evolving but often imprecise science, underscoring the role of clinical correlation and judgment for integrating diagnostic genetic testing into patient care. Another transforming question is, given the complex and probabilistic nature of genetic testing and the imperfect state of knowledge, how (or by whom) should the results and implications of genetic testing be adjudicated? Should this responsibility be confined to those elite (“master”) clinical geneticists harboring a higher level of expertise? (15). Perhaps, more realistically, genetic test reports could be modeled with more clinically relevant language so that patient-specific interpretations do not require special knowledge or teaching.

Conclusions Closing this communication gap currently separating clinicians from basic scientists is paramount. To this purpose it would be important to work toward greater standardization and less ambiguity in reporting mutations, hopefully enabling such testing to achieve the confidence of the clinical community and ultimately its full potential for translating basic genetic information into HCM decision making and patient management.

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JACC Vol. 60, No. 8, 2012 August 21, 2012:705–15

Family T

A

73y/F

77y/M

B VS

C

37y/M

MYBPC3 Gln998Glu TNNI3 Arg145Trp

Figure 8

Double Mutations as a Potential Risk Factor in HCM

Asymptomatic proband (arrow) with 2 disease-causing mutations, MYBPC3 and TNN13, experienced resuscitated cardiac arrest (RCA) at age 37 years, but without conventional risk factors. Both parents have HCM, and each contributed 1 mutation to their offspring. Electropherograms show identified mutations. From Maron et al. (51), with permission of the Heart Rhythm Society. Solid symbols are those clinically affected with HCM. N ⫽ normal on clinical screening with imaging; ⫹ ⫽ heterozygote for mutation; ⫺ ⫽ without mutation; other symbols and abbreviations as in Figure 3.

Reprint requests and correspondence: Dr. Barry J. Maron, Hypertrophic Cardiomyopathy Center, Minneapolis Heart Institute Foundation, 920 East 28th Street, Suite 620, Minneapolis, Minnesota 55407. E-mail: [email protected].

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