Cardiogenetics 2020; volume 10:8860

Sudden cardiac death in young vent many disorders, including cardiovas- athletes: Literature review of cular risk factors, obesity, depression, anxi- Correspondence: Giulia Frisso and Cristina ety, musculoskeletal problems and stress.1-3 Mazzaccara, Department of Molecular molecular basis Numerous epidemiological studies have Medicine and Medical Biotechnology/ shown an association between moderate CEINGE- Advanced Biotechnologies, Via Pansini 5, 80131 Naples, Italy. Cristina Mazzaccara,1,2 Bruno Mirra,1,2 aerobic exercise and decreased risk of coro- 1,2 4-6 Tel.: +39.081.7462405; +39.081.7462422 - Ferdinando Barretta, nary disease, reduced risk of ven- Fax: +39.081.7462404. Barbara Lombardo,1,2 Olga Scudiero,1,2 tricular fibrillation in patients affected by a E-mail: [email protected]; 7,8 Giulia Frisso1,2 first myocardial infarction, as well as a [email protected] reduction of overall death and cardiovascu- 1Department of Molecular Medicine and lar mortality in cardiac patients subjected to Key words: Sudden cardiac death; cardiomy- Medical Biotechnology, University of 9,10 opathy; genetic testing; athletes. 2 adequate training programs. Furthermore Naples Federico II; CEINGE Advanced the use of biochemical and haematological Biotechnologies, Naples, Italy Contributions: GF, CM, BM; wrote the manu- tests to evaluate risk factors in athlete is of script and approved the final version; FB, BL, relevance and interest at the amateur, com- OS; involved in literature data collection. All 11 petitive and elite level. authors critically reviewed the manuscript. However, for a small number of indi- Abstract viduals physical exercise can increase the Funding: the authors declare that no sources of risk of sudden cardiac death (SCD).12,13 In funding were used in the preparation of this Intense athletic training and competi- particular, vigorous activity can transiently review. tion can rarely result in sudden cardiac increase the risk of SCD in asymptomatic death (SCD). Despite the introduction of Conflict of interest: the authors declare no young athletes carrying genetic pre-participation cardiovascular screening, conflict of interests. predisposing to arrhythmic diseases.14,15 especially among young competitive ath- Sudden cardiac death is the most fre- letes, sport-related SCD remains a debated Received for publication: 31 January 2020. quent medical cause of sudden death in ath- Revision received: 24 March 2020. issue among medical personnel, sports com- only letes. Estimates vary widely based on the Accepted for publication: 27 March 2020. munities and laypersons alike, and gener- analyzed population, sports-associated SCD ates significant media attention. The most represents about 6% of the overall SCD bur- This work is licensed under a Creative frequent cause of SCD is a hidden inherited Commons Attribution NonCommercial 4.0 den.16,17 In Europe and North America the , the athletes may not even License (CC BY-NC 4.0). incidence of SCD is 2 athletes of use100,000 be aware of. Predictive medicine, by per year.18 In the Veneto region of Northern © searching the presence of pathogenic alter- Copyright: the Author(s), 2020 Italy, where >110,000 athletes were evaluat- ations in cardiac , may be an integra- Licensee PAGEPress, Italy ed over a 21-year follow-up period, the inci- Cardiogenetics 2020; 10:8860 tive tool, besides the conventional ones dence of SCD was 2.6/100,000 person- doi:10.4081/cardiogenetics.2020.8860 used in cardiology (mainly electro and years in male athletes and 1.1/100,000 per- echocardiogram), to reach a definitive diag- son-years in their female counterparts.13 nosis in athletes showing signs/symptoms, The incidence varied by sex, the risk of even borderline, of inherited cardiomyopa- relevant role for the early identification of SCD being higher in men than in women.15 thy/channelopathy, and in athletes present- molecular alterations that can be causative Some athlete subgroups, specifically 21 ing family history of SCD and/or of heredi- or con-causative of SCD in athletes. It is African Americans, male basketball and tary cardiac disease. In this review, we important to identify the specific DNA football players, appear to be at higher risk revised the molecular basis of the major car- defect associated with a clinically manifest in the United States, whereas male soccer diac diseases associated to sudden cardiac heart disease in an athlete, and, above all, to players had a higher incidence of SCD than death and the clinical molecular biology recognize the possible individual predispo- other athletes in Europe.18,19 This observa- approach that can be used to perform risk sition to develop a latent heart disease, tion suggests that individuals participating assessment at DNA level of sudden cardiac before the disease can manifest itself with in sports of high dynamic and low isometric death, contributing to the early implementa-Non-commercial the fatal event of SCD. intensity are at higher risk of death. tion of adequate therapy. Alterations can In this review we will discuss genetic Few studies report prevalence of sports- occur in genes, in genes encod- causes of sudden cardiac death in athletes, related sudden death in the general popula- ing desmosomal and junctional , with particular emphasis on challenges in tion. Of note, paper of Marijon et al. sarcomeric and Z-disc proteins, proteins for molecular diagnostics of inherited cardiac showed that only 6% of sports-related sud- the and the . disease, like channelopathy and cardiomy- den death in the general population occur in The advent of next generation sequencing opathy. young competitive athletes, the remaining (NGS) technology has provided the means involving amateur athletes.20 to search for mutations in all these genes, at Though SCD is rare, its occurrence in the same time. Therefore, this molecular athletes who are often young and presum- approach should be the preferred methodol- ably healthy has a large emotional and Cardiac diseases in young athletes ogy for the aforementioned purpose. social impact on the surrounding communi- Cardiac diseases associated with SCD ty. Therefore, considerable effort has been differ in young vs older athletes, the SCD made to better understand the causes of cause being elusive even after autopsy in SCD in athletes and to discover optimal young subjects. Guidelines of the European Introduction strategies for prevention. Society of Cardiology (ESC) encouraged Regular physical activity is a powerful To this aim, the clinical molecular biol- molecular autopsy22 in addition to the stan- tool for improving health and helps to pre- ogy laboratory has acquired an increasingly dard autopsy, as it may allow the post-

[Cardiogenetics 2020; 10:8860] [page 1] Review mortem diagnosis of cardiac chan- Inherited are char- nelopathies, which explain 15–25% of sud- acterized by both allelic heterogeneity, Cardiac channelopathies den arrhythmic deaths. The most common which occurs when mutations within the Cardiac channelopathies are rare inher- causes of sport-related SCD in adolescents same can produce different pheno- ited primary electrical disorders, without and young adults are inherited cardiomy- types, and genetic heterogeneity, occur- evidence of structural cardiomyopathy, 18,23-31 opathies, a clinically heterogeneous ring when mutations within different resulting from dysfunction of cardiac ion group of heart muscle disorders, character- genes produce the same phenotype. channels. This alteration impairs cardiac ized by the presence of abnormal myocar- For example, SCN5A gene mutations or intracellular dial structure and/or function, in the are associated with distinct chan- handling and results in electrical instabili- absence of ischemic heart disease or abnor- nelopathies, such as long QT syndrome, ty,50 leading to life-threatening cardiac 32 mal loading conditions. Brugada syndrome, and also to HCM or , including ventricular tachycar- 51 Arrhythmogenic cardiomyopathy DCM. Instead, DCM may be caused by dia or fibrillation (VT/VF) predisposing to (ACM) has been reported to account for mutations in sarcomeric, cytoskeletal, gap SCD. Channelopathies are usually transmit- approximately 25% in Italy, whereas it junction and even ion channel genes. ted as an autosomal dominant trait and accounts for only 6% of cases in the Variable penetrance and incomplete show variable clinical penetrance and 13,25,33,34 USA. By contrast, hypertrophic car- expression are common in all cardiomy- expressivity. The main clinical features diomyopathy (HCM) is one of the leading opathies, even among related subjects include and SCD; however, most 52,53 causes of SCD among athletes in the USA, sharing the same pathogenic allele, and patients remain asymptomatic throughout where it has been reported to accounting for may reflect the action of modifier genes, life and symptoms may be triggered by more than 30% of fatal cases,9,22,28 while in epigenetic changes, environmental fac- physical activity (light, moderate and European studies HCM is reported to cause tors, or other factors such as age, gender, heavy), sexual activity, emotions and sleep. less than 10% of SCDs.29 These divergences ethnicity or physical activity. To establish Early diagnosis of genetic carriers is war- are attributable to the heterogeneity of rela- the diagnosis of inherited cardiomyopa- ranted, being the SCD in apparently healthy tive frequencies in various countries, to the thy, the elucidation of family history and young people the potential presenting different diagnostic and autopsy procedures comprehensive assessment of pedigree is symptom;only therefore, genetic testing has used18 and probably they are mainly due to the foremost necessity, but it may not be been progressively introduced in clinical the different protocols of sports activity pre- sufficient. Electrocardio graphy, echocar- practice. participation screening. Electrocardio - diography and cardiac magnetic resonance The most frequent inherited cardiac graphy (ECG) screening is a common prac- imaging may not reveal subclinic anoma-usechannelopathies are long QT syndrome tice in most European countries and is com- lies present in asymptomatic subjects har- (LQTS), Brugada syndrome (BrS), and cat- 54 pulsory in Italy and Israeli,18,35 but it is not bouring mutations. Thus, genetic test in echolaminergic polymorphic ventricular routinely performed in the USA. The ECG the proband and cascade family screening tachycardia (CPVT). Other rare inherited inclusion into the athlete screening protocol is a valuable tool to exactly diagnose an arrhythmogenic diseases are short QT syn- improves efficacy to identify asympto matic inherited cardiomyopathy and to identify drome (SQTS), sick sinus syndrome (SSS), athletes who have a potentially lethal car- family members at disease-risk in preclin- familial progressive cardiac conduction 55 diomyopathy, ECG findings being abnor- ical stage. Furthermore, bioinformatics defect (PCCD), Haïssaguerre syndrome or mal in 90% of HCM patients,36 and protect approach and functional studies can help early repolarization syndrome.47-49 To date, them from the risk of SCD through restric- to predict the pathogenicity of new vari- more than 40 genes are implicated in cardiac 56,57 tion from competitive sports. ants found during genetic screening. channelopathies47,64 (Appendix Table 1): the However, as reported in recent litera- In this regard, ESC and American most common genes encode the cardiac ture21,27,37,38 the most common cardiomy- Heart Association (AHA)/American and potassium voltage-gated chan- 58- opathies related to SCD, are the inherited College of Cardiology (ACC) guidelines nels (NaV1.5, KV7.1 and KV11.1), the L-type 61 ion channel diseases, followed by ACM, recommend molecular testing to calcium channel (CaV1.2), the cardiac recep- HCM and (DCM). improve the diagnosis and management of tor of ryanodine (RyR2). Mutations in these patients and at-risk family members. genes may cause loss or gain of channel Non-commercialBy these considerations, in 2013 the function, although mixed effects on ion new cardiomyopathy classification system channels are also reported.65-67 32,62,63 Genetic basis of cardiac diseases MOGE(S) has become necessary. LQTS is a cardiac channelopathy, char- MOGE(S) can assist in the diagnosis and acterized by abnormally prolonged QT in athletes management of each cardiomyopathy interval.68-71 To the best of our knowledge, In the last two decades the knowledge patient, classified following five pathogenic variants associated with LQTS of molecular basis of cardiomyopathies attributes: Morpho-functional characteris- have been identified in the following genes: has progressively increased: actually tic (M); Organ involvement (O); Genetic AKAP9, ANK2, CACNA1C, CALM1, mutations in more than 200 genes are or familial inheritance pattern (G); CALM2, CALM3, CAV3, KCNE2, KCNH2, associated to cardiomyopathies, such as Etiological description (E) of genetic KCNJ2, KCNJ5, RYR2, SCN1B, SCN4B, sarcomeric and cytoskeleton genes (par- defect or nongenetic underlying cause; SCN5A and SNTA1, showing an autosomal- ticularly related to HCM and DCM), and functional Status (S), using the dominant inheritance; TRDN, resulting in desmosomal genes (involved in ACM), ACC/AHA stage (A to D) and the New an autosomal-recessive pattern, and ion channel genes (channelopathies).39-49 York Heart Association (I to IV) function- KCNQ1 and KCNE1 with both autosomal- Mutations are mainly inherited in an auto- al classes. The “S” notation is especially dominant and -recessive hereditary72 somal dominant pattern, although X- useful when carriers are healthy, (Appendix Table 1). In particular, the three linked, autosomal recessive, or matrilineal or if they demonstrate imaging-verified major LQTS-susceptibility genes are inheritance may also occur in a minority early abnormalities suggestive of car- KCNQ1, KCNH2 and SCN5A, encoding the 32,50 of cases. diomyopathy. α-subunit of the voltage-dependent KV7.1,

[page 2] [Cardiogenetics 2020; 10:8860] Review

73- KV11.1 and Nav1.5 channels, respectively. the diagnostic sensibility of genetic test for the desmosomal adhesion molecules is 75 Generally, gain of function mutations of SQTS is low (15-25%).89,91-93 mediated by and the armadillo or loss of function muta- Globally, the diagnostic sensibility of proteins and . Thus, tions of potassium channels prolong cardiac genetic test for channelopathies is variable, desmosomes contain desmoplakin, action potential, producing a prolonged ranging from 70-85% in LQTS to 15-25% plakoglobin and at least one isoform each of repolarization in cardiac cells and pro- in SQTS; therefore, genetic screening in plakophilin and the desmosomal cadherins longed QT interval on the ECG. These three genes known to cause cardiac chan- desmocollin and desmoglein. A number of genes, together, explain up to 75% of LQTS nelopathies might result unsuccessful in other accessory proteins are associated with clinical diagnosed patients, while the around 15-30% of patients with LQTS, 40% desmosomes. Desmosomal genes related to remaining genes contribute up to an addi- of patients with CPVT, and 60-85% of ACM (Appendix Table 1) include PKP2, tional 5-10% of LQTS cases.72,76,77 Of note, patients with BrS or SQTS. DSG2, DSC2, JUP and DSP, encoding subjects carrying mutations in KCNQ1 In the last decade it has become evident plakophilin-2, desmoglein, desmocollin, gene are at high risk to develop VT/VF dur- that hereditary channelopathies can also be plakoglobin, desmoplakin, respectively. ing physical activity. caused by mutations in genes encoding car- PKP2 is the most frequently mutated gene About 20-25% of Brugada patients diac ion channels regulatory proteins, such in ACM patients, associated with about 30- 114,115 carry loss of function mutations in the as transcription factors and proteins 40% of cases. exhibit dual SCN5A gene. In addition, CACNA1C, involved in the expression, intracellular localization, in the desmosomes as well as SCN10A, CACNB2, ABCC9 genes, among transport and subsequent subcellular local- in the nucleus, where they can trigger about 30 other associated genes, are each izations of ion channels.94 For example, fibroadipocytic replacement of cardiac responsible for just over 5% of positive- pathogenic variants in myocytes by suppression of Wnt/beta- 116 genotype patients, while the remaining (CASQ2), encoding the calsequestrin 2 pro- pathway. genes are very rare72,78,79 (Appendix Table tein, and genes (CALM1, Of note, mutations in desmosomal 1). Overall, known susceptibility BrS genes CALM2 and CALM3) are involved in the genes are founded in about 5% of DCM explain about 40% of cases, indicating that intracellular calcium homeostasis and are cases, suggesting that there are little differ- about 60% of BrS patients remain geneti- associated with LQTS and/or CPVT.95-98 Of ences, in some cases, between ACM and only108,117 cally unresolved. Furthermore, genome- note, CASQ2 mutations trigger SCD with a DCM. wide association studies (GWAS) have frequency higher than RYR2 mutations.99 Mutations in αT-catenin (CTNNA3) and demonstrated that common genetic variants N-cadherin (CDH2) are also associated Mutations in genes encoding other ion- 118,119 increase susceptibility to Brugada syn- channel associated proteins, such use as cave- with ACM. Both proteins are present in drome, suggesting a polygenic way of olin (CAV3), (ANK3, ANK2), syn- the area composita at the cardiac intercalat- 80 inheritance, also. trophin (SNTA1), and yotiao (AKAP-9) are ed discs. Alpha-T-catenin binds Physical activity, increasing parasym- now implicated in the genesis of the cardiac plakophilins contributing to the formation pathetic tone and body temperatures, may channelopathies, although they affect only a of the area composita, which strengthens precipitate fatal arrhythmias in BrS asymp- very small proportion of arrhythmic cell-cell adhesion in contractile cardiomy- 94,100-107 ocytes. This involvement shows that the tomatic subjects. patients. CPVT is a rare channelopathy with both pathogenesis of ACM extends beyond autosomal-dominant and, less commonly, desmosomes. Area composite is a mixed- autosomal-recessive inheritance,81,82 show- type junctional structure composed of both desmosomal and adherents junctional pro- ing polymorphic ventricular tachyarrhyth- Arrhythmogenic ventricular car- mia, which can lead to syncope or SCD teins. Physiologically, important interac- under physical stress or emotional condi- diomyopathy tions exist between the cardiac desmosome tions. Clinical symptoms and higher risk of Arrhythmogenic ventricular cardiomy- and gap and adherents junctions, with the cardiac events occur in youth particularly in opathy is an inherited heart muscle disease, resulting integrity of the males.83,84 CPVT is, generally, caused by showing typically ECG abnormalities and and its important role in both mechanical gain of function mutations in RYR2 gene, ventricular arrhythmias.108 and electrical cellular stability dependent on coding the ionic channel for theNon-commercial release of ACM is characterized by a progressive adequate functioning of all three subunits. calcium from the , loss of myocytes and fibro-fatty replace- Rare mutations in TMEM43, transmem- which plays a crucial role in regulating ment; biventricular involvement is often brane 43, located in nucleus inner intracellular calcium concentrations. RYR2 observed in later stages. membrane, are associated with severe ACM phenotypes,120 high penetrance and high gene is mutated in about 60% of CPTV ACM is reported to cause 0,08-3,6% of 111,121,122 patients, while only a small percentage of SCDs/year;109 however patients with known SCD risk. This gene contains a subjects carry mutations in other genes genotype are characterized by mortality response element for PPARγ (an adipogenic (Appendix Table 1).85-88 <1%, as reported in recent literature.110 transcription factor), which may explain the SQTS is a very rare cardiac channelopa- Mutations in desmosomal genes are fibrofatty replacement of the myocardium, a thy, characterized by peculiarly short QT found in about 50-60% of ACM patients, characteristic pathological finding in ACM.123 intervals and increased susceptibility to defining desmosomes as major factors in develop atrial and ventricular tachyarrhyth- ACM pathogenesis.111-113 Desmosomes are mia, which may arise later on physical intercellular junctions that provide strong activity.89 The main symptom is the cardiac adhesion between cells and link, intracellu- arrest (up to 40%).90 Mutations (generally larly, to the intermediate cytoskeleton fila- Hypertrophic cardiomyopathy of the gain of function type) in KCNQ1, ment. They are found in tissue that experi- Hypertrophic Cardiomyopathy is a KCNH2, KCNJ2, CACNA1C, CACNB2, ence intense mechanical stress, such as car- myocardial disease, characterized by thick- CACNA2D1, SCN5A and SLC4A3 genes diac and epidermis. The link- ening of the interventricular septum and left are involved in disease (Table 1), although age between the intermediate filaments and ventricular wall, in the absence of clinically

[Cardiogenetics 2020; 10:8860] [page 3] Review important abnormal loading conditions or ladin, , , , DCM.145 About 10% of DCM patients,146,147 primary valve disease. The most specific . However, mutations in Z-disc show mutations in LMNA gene.148 A histological features include myocyte genes give rise to heterogenous diseases and C are nuclear hypertrophy and disarray, as well as intersti- encompassing various cardiomyopathies envelope proteins, encoded by the LMNA tial fibrosis. such as DCM, HCM, ACM.132,133 gene, implicated in DNA replication, cell- HCM is the most common cause of sud- Although the utilization of next-genera- cycle regulation, chromatin organization, den death,25 particularly in adolescents and tion sequencing methods has increased the differentiation maintenance, nuclear stabili- young adults, and the most common cause spectrum of the putative HCM related ty, pore positioning, and of SCD in athletes, in the United States.25,124 genes, recent studies have suggested that signal transduction. Through alternative Nonsustained ventricular tachycardia, syn- mutations in non sarcomeric genes are very splicing, a single transcript generates four cope, family history of sudden cardiac rare cause of HCM.134,135 products, collectively known as A/C. death, and severe cardiac hypertrophy are Lamin A/C is associated with the LInker of the major risk factors for sudden cardiac Nucleoskeleton and Cytoskeleton (LINC) death.125 Furthermore, the presence of bridge complex, which links the nucleus to underlying but undiagnosed HCM in ath- Dilated cardiomyopathy the cytoskeleton. The major compo- letes is among the main causes of SCD, Dilated cardiomyopathy, characterized nents of the LINC complex are: lamin A/C with the majority (60%) of cases occurring by left ventricular enlargement and systolic (LMNA), (EMD), nesprins-1 (SYNE- during exercise.27 1) and nesprins-2 (SYNE-2) and SUN- dysfunction, is a heterogeneous heart dis- 146 Hypertrophic Cardiomyopathy is a ease leading to progressive systolic heart domain containing proteins (SUN1/2). genetic disease, generally transmitted as failure and sudden cardiac death. When Mutations in all these genes are involved in autosomal dominant trait and characterized DCM as well as in rare cases of ACM.148-151 61,126 DCM occurs, in the absence of an identifi- by marked genetic heterogeneity. able cause, the disease is referred to as idio- Other cytoskeletal proteins involved in Mutations in about 100 different genes have pathic DCM (IDCM). Familial DCM DCM are (DES), been described associated to HCM; howev- (FDCM) demonstrates marked genetic het- (DMD), alpha- (DAG1), dys- er, mutations in eight sarcomeric genes are erogeneity and age-dependent penetrance, trobrevinonly (DTNA), (SGCD), responsible for approximately 60-70% of with disease developing in childhood, ado- (SNTA1), 61,126 cases of HMC. Typically, the most lescence and middle age, but rarely in the (PLN), caveolin (CAV3). commonly genes involved in HCM are elderly. More than 40 genes have been iden- Desminopathy is one of the most com- MYBPC3 (-binding protein C3), tified in association with non-syndromicusemon intermediate filament disorders MYH7 (myosin heavy chain 7), TNNT2 FDCM, the majority demonstrating autoso- associated with mutations in desmin and (cardiac T), TNNI (cardiac tro- mal dominant inheritance.136 They encode alphaB-crystallin proteins. Desmin links ponin I), ACTC1 (actin alpha cardiac mus- cytoskeletal, sarcomeric, nuclear proteins desmosomes with the Z disk, helping to cle 1), TPM1 ( 1), MYL2 and act through different pathogenetic connect together. This allows the ( 2), MYL3 (myosin light mechanisms, such as disruption of sarcom- formation of a continuous cytoskeletal net- chain 3); other six sarcomeric genes are ere-cytoskeletal interactions or myocyte work that maintains a spatial relationship 41,127,128 involved in less than 10% of cases architecture; amyloid deposition; abnormal- between the contractile apparatus and other (Appendix Table 1). Most muta- ities of desmosomal, calcium handling, ion structural elements of the cell, providing tions result in a single substitu- channel function; alterations of mitochon- maintenance of cellular integrity, force tion, with the exception of mutations in the drial energy dynamics or nuclear mem- transmission and mechanochemical signal- MYBPC3 gene, which are most frequently brane-cytoskeletal integrity. ing. Desminopathy-associated diseases may 151,152 frameshift mutations, and create a prema- TTN gene, encoding the protein, is be associated with DCM, ACM and 153 ture-termination codon. Allelic balance the most frequently mutated gene in DCM restrictive cardiomyopathy. between mutant and wild-type sarcomere patients (up to 25% of cases, Appendix Among the rare DCM genes, SCN5A, proteins is variable and mutation-specific, Table 1).137,138 Titin is an elastic protein, FLNC and PLN genes, deserve particular reflecting differential stability or efficiency which passively stretched during the dias- attention. FLNC codes the C pro- of sarcomere incorporation of mutatedNon-commercial pro- tole and then returns to its initial state. tein, an actin cross-linking molecule, which tein compared to the wild-type. However, it is also a biomolecular scaffold contributes to the sarcomeric architecture; About 5% of HCM patients carry multi- and mediates multiple protein interactions PLN gene encodes phospholamban protein, ple sarcomeric mutations: these patients and intracellular signalling cascades, which a key regulator of the sarcoplasmic reticu- present with more severe disease at an ear- may exert regulatory functions on muscular lum Ca2+ATPase pump (SERCA2a), which, lier age.128-131 As a result, more extensive activity. The TTN mutations are generally in turn, is responsible for the calcium home- genetic evaluation may be warranted in nonsense, splice variants or deletion/inser- ostasis.154-156 probands presenting with early or severe tions mutations, producing a truncated pro- DCM patients carrying mutations in disease. tein. Also mutations in genes encoding for SCN5A, FLNC or PLN genes, as well as in More rarely (less than 1% of cases) sarcomeric thin and thick filaments LMNA, had a prominent arrhythmogenic HCM patients present mutations in genes (MYPBC3, MYH7, TNNT2, TNNI3, ACTC1, phenotype and a higher risk for life-threat- encoding Z-disc or calcium-handling pro- TPM1, MYL2, MYL3),32,139 and other pro- ening ventricular arrhythmias and SCD. teins. The sarcomeric Z-disc defines the lat- teins interacting with titin [myomesin 1 Therefore, early identification of patients eral borders of the sarcomere and is impor- (MYOM1), cardiac repeat protein 1 carrying mutations in these genes is partic- tant not only for mechanical stability and (ANKRD1) and telethonin (TCAP)] have ular imperative.108 force transmission but also for signalling, been found in up to 5-10% of DCM The great genetic heterogeneity associ- mechanosensation, mechanotransduction, patients137,140-144 indicating that a complex ated to DCM demonstrates a central rele- apoptosis and cell survival. It is composed network of proteins organized around the vance for cytoskeletal integrity and biome- of numerous proteins, such as titin, myopal- central scaffold titin may be defective in chanical coupling of elastic and contractile

[page 4] [Cardiogenetics 2020; 10:8860] Review elements. Mutations in cytoskeletal proteins approach to identify DNA mutations associ- to hidden cardiovascular disease, can sud- critically diminish force generation and ated with genetically heterogeneous denly affect even high-value athletes. interfere with mechanical transduction with- pathologies, such as cardiomyopathies and SCD related to the practice of sports in the contractile apparatus of the myocardi- channelopathies. This approach not only accounts for about 6% of the total SCDs17, um, thereby ultimately leading to impaired allows to analyze a large number of genes both in competitive and amateur young systolic function.157 In addition, cytoskeletal simultaneously in several patients, but, athletes.25 In fact, athletes, also asymp- alterations can affect ion channel anchoring through the identification of further variants tomatic, may be at risk of SCD while and trafficking, causing an imbalance in car- associated with the disease phenotype, they’re training or competing, due to car- diac ionic homeostasis with subsequent allows to obtain information also on possi- diovascular defects they may not even be action potential and conduction alterations ble additional genetic factors that can act as aware of. To date, pre-participation car- that will trigger arrhythmogenesis.158,159 phenotype modifiers or predict the patient’s diovascular screening of athletes is a life- prognosis. Recent evidence supports the saving and cost-effective strategy in ath- importance of a sensible molecular analysis letes in whom SCD can be caused by heart also in athletes showing a reasonable index muscle diseases and is recommended by High-throughput sequencing of suspicion for an inherited cardiomyopa- both the AHA and ESC. The AHA recom- technology: Next Generation thy or channelopathy, in order to early iden- mends screening competitive athletes by tify or prevent serious complications, up to means of family/personal history and Sequencing (NGS) 54,163,164 the risk of sudden death. The use of physical examination.165 In Italy, a manda- The correct molecular diagnostic frame- genetic test by NGS methodologies could tory state-sponsored screening program work of inherited cardiomyopathies is often be taken as a useful implementation in the exists for all competitive athletes, includ- very complex, because of high clinical and path of cardiological prevention for ath- ing symptoms evaluation, family history, 160 genetic heterogeneity (Figure 1). letes, when the pre-participation screening physical examination and 12-lead ECG. The sequencing with the traditional shows a family history of SCD, cardiomy- This protocol was acknowledged by the techniques such as Sanger sequencing of a opathy/channelopathy or, symptoms and/or ESC to propose for a common European lot number of genes requires long execution instrumental signs, even borderline, of car- conduct.only166 times and involves a lower diagnostic and diac dysfunction. The integrated diagnostic A recent study by the Institute of analytical sensitivity. These limitations path may result in an exhaustive precise Sports Medicine of Italian National have been overcome by the development of characterization of the underlying cardiac Olympic Committee (CONI), conducted highly productive nucleic acid sequencing inherited disease. on more than 2,300 athletes who had taken techniques (“Next Generation Sequencing”, use 161 part in the Olympic Games from 2004 NGS). These methods allow the analysis (Athens) to 2014 (Sochi), confirms the of a large number of nucleotides, from a opportunity to subject athletes to pre-par- single exon or gene, up to the analysis of Conclusions ticipation cardiovascular screening and gene panels, or of the whole exome or other examinations when necessary.167 127,162 Subjects practicing routine sports, genome, accurately and at extremely About 0,2% of these athletes were found both at a competitive and amateur level, competitive costs compared to traditional to have inherited cardiomyopathies, and have a lifestyle characterized by a vigor- methods. globally about 4% showed cardiovascular ous and continuous physical effort. The analysis of gene panels by NGS abnormalities (coronary heart disease, However, sudden cardiac death, often due sequencing represents the ideal analytical high blood pressure, heart rhythm disor- ders) all equally asymptomatic. The main aim of this review is to pro- vide genetic support to prevent sudden cardiac death in young athletes, a highly visible tragedy that generates significant media attention and discussion among Non-commercial medical personnel, sports communities and laypersons alike. We think that genet- ic cardiomyopathy testing in athletes may be an integrative tool to reach a definitive diagnosis when the pre-participation screening shows personal symptoms (i.e. syncope, arrhythmias) or instrumental signs of heart dysfunction, even border- line, suggesting the presence of an inherit- ed cardiomyopathy/ channelopathy.168 Moreover, the genetic test may also be indicated in athletes with a family history of SCD or when a his/her family member is affected by cardiomyopathy/chan- Figure 1. Schematic representation of cardiomyopathies and genes involved in Sudden nelopathy and carries a disease-causing Cardiac Death, can reflect our work and be used as a cover image. Diagram shows the mutation. In this setting, the identification overlap between the genes associated with Channelopathies, Dilated Cardiomyopathy of athletes carrying a pathogenic mutation (DCM), Hypertrophic Cardiomyopathy (HCM), Arrhythmogenic Cardiomyopathy (ACM). allows to detect individuals at risk in the pre-clinical or asymptomatic phase.

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