Diagnostic yield from cardiac gene testing for inherited cardiac conditions and re-evaluation of pre-ACMG variants of uncertain significance.

BACKGROUND: Inherited cardiomyopathies (HCM, DCM, ACM) and cardiac ion channelopathies (long QT/Brugada syndromes, CPVT) are associated with significant morbidity and mortality; however, diagnosis of a familial pathogenic variant in a proband allows for subsequent cascade screening of their at-risk relatives. AIMS: We investigated the diagnostic yield from cardiac gene panel testing and reviewed variants of uncertain significance from patients attending three specialist cardiogenetics services in Ireland in the years 2002 to 2020. RESULTS: Reviewing molecular genetic diagnostic reports of 834 patients from 820 families, the initial diagnostic yield of pathogenic/likely pathogenic variants was 237/834 patients (28.4%), increasing to 276/834 patients (33.1%) following re-evaluation of cases with variant(s) of uncertain significance. Altogether, 42/85 patients with VUS reviewed (49.4%) had a re-classification that could change their clinical management. Females were more likely to carry pathogenic/likely pathogenic variants than males (139/374, 37.2% vs 137/460, 29.8%, respectively, p = 0.03), and the diagnostic yields were highest in the 0 to < 2 years age group (6/12, 50.0%) and amongst those tested for cardiomyopathy gene panels (13/35, 37.1%). Variants in the MYBPC3/MYH7 (87/109, 79.8%) and KCNQ1/KCNH2 (91/100, 91.0%) genes were the predominant genetic causes for hypertrophic cardiomyopathy and long QT syndrome, respectively. CONCLUSION: Our study highlights the importance of collation and review of pre-ACMG genetic variants to increase diagnostic utility of genetic testing for inherited heart disease. Almost half of patients with pre-ACMG VUS reviewed had their variant re-classified to likely pathogenic/likely benign which resulted in a positive clinical impact for patients and their families.

Cardiac Rhabdomyomas Presenting with Critical Cardiac Obstruction in Neonates and Infants: Treatment Strategies and Outcome, A Single-Center Experience.

Cardiac rhabdomyomas are the most common benign pediatric heart tumor in infancy, which are commonly associated with tuberous sclerosis complex (TSC). Most rhabdomyomas are asymptomatic and spontaneously regress over time. However, some cases especially in neonates or small infants can present with hemodynamic instability. Surgical resection of the tumor, which has been the gold standard in alleviating obstruction, is not always possible and may be associated with significant morbidity and mortality. Recently, mammalian target of rapamycin inhibitors (mTORi) have been shown to be safe and effective in the treatment of TSC. We present the outcomes of neonates and an infant who received treatment for symptomatic rhabdomyomas at a tertiary cardiology center. Medical records were reviewed to obtain clinical, demographic, and outcome data. Six patients received interventions for symptomatic rhabdomyomas, median age at presentation was 1 day old (range from 1 to 121 days old), and 67% of the patients had a pathogenic mutation in TSC gene. One patient underwent surgical resection of solitary tumor at right ventricular outflow tract (RVOT) successfully. In the four patients with left ventricular outflow tract (LVOT) obstruction, two patients received combined therapy of surgical debulking of LVOT tumor, Stage I palliation procedure, and mTORi and two patients received mTORi therapy. One patient with RVOT obstruction underwent ductal stenting and received synergistic mTORi. Four of the five patients had good response to mTORi demonstrated by the rapid regression of rhabdomyoma size. 83% of patients are still alive at their latest follow-up, at two to eight years of age. One patient died on day 17 post-LVOT tumor resection and Hybrid stage one due to failure of hemostasis, in the background of familial factor VII deficiency. Treatment of symptomatic rhabdomyoma requires individualized treatment strategy based on the underlying pathophysiology, with involvement of multidisciplinary teams. mTORi is effective and safe in inducing rapid regression of rhabdomyomas. A standardized mTORi prescription and monitoring guide will ensure medication safety in neonates and infants with symptomatic cardiac rhabdomyoma. Although the majority of tumors responded to mTORi, some prove to be resistant. Further studies are warranted, ideally involving multiple international centers with a larger number of patients.

Natural history and outcomes in paediatric RASopathy-associated hypertrophic cardiomyopathy.

AIMS: This study aimed to describe the natural history and predictors of all-cause mortality and sudden cardiac death (SCD)/equivalent events in children with a RASopathy syndrome and hypertrophic cardiomyopathy (HCM). METHODS AND RESULTS: This is a retrospective cohort study from 14 paediatric cardiology centres in the United Kingdom and Ireland. We included children <18 years with HCM and a clinical and/or genetic diagnosis of a RASopathy syndrome [Noonan syndrome (NS), NS with multiple lentigines (NSML), Costello syndrome (CS), cardiofaciocutaneous syndrome (CFCS), and NS with loose anagen hair (NS-LAH)]. One hundred forty-nine patients were recruited [111 (74.5%) NS, 12 (8.05%) NSML, 6 (4.03%) CS, 6 (4.03%) CFCS, 11 (7.4%) Noonan-like syndrome, and 3 (2%) NS-LAH]. NSML patients had higher left ventricular outflow tract (LVOT) gradient values [60 (36-80) mmHg, P = 0.004]. Over a median follow-up of 197.5 [inter-quartile range (IQR) 93.58-370] months, 23 patients (15.43%) died at a median age of 24.1 (IQR 5.6-175.9) months. Survival was 96.45% [95% confidence interval (CI) 91.69-98.51], 90.42% (95% CI 84.04-94.33), and 84.12% (95% CI 75.42-89.94) at 1, 5, and 10 years, respectively, but this varied by RASopathy syndrome. RASopathy syndrome, symptoms at baseline, congestive cardiac failure (CCF), non-sustained ventricular tachycardia (NSVT), and maximal left ventricular wall thickness were identified as predictors of all-cause mortality on univariate analysis, and CCF, NSVT, and LVOT gradient were predictors for SCD or equivalent event. CONCLUSIONS: These findings highlight a distinct category of patients with Noonan-like syndrome with a milder HCM phenotype but significantly worse survival and identify potential predictors of adverse outcome in patients with RASopathy-related HCM.

Sudden cardiac death in childhood RASopathy-associated hypertrophic cardiomyopathy: Validation of the HCM risk-kids model and predictors of events.

BACKGROUND: RASopathies account for nearly 20% of cases of childhood hypertrophic cardiomyopathy (HCM). Sudden cardiac death (SCD) occurs in patients with RASopathy-associated HCM, but the risk factors for SCD have not been systematically evaluated. AIM: To validate the HCM Risk-Kids SCD risk prediction model in children with RASopathy-associated HCM and investigate potential specific SCD predictors in this population. METHODS: Validation of HCM Risk-Kids was performed in a retrospective cohort of 169 patients with a RASopathy-associated HCM from 15 international paediatric cardiology centres. Multiple imputation by chained equations was used for missing values related to the HCM Risk-Kids parameters. RESULTS: Eleven patients (6.5%) experienced a SCD or equivalent event at a median age of 12.5 months (IQR 7.7-28.64). The calculated SCD/equivalent event incidence was 0.78 (95% CI 0.43-1.41) per 100 patient years. Six patients (54.54%) with an event were in the low-risk category according to the HCM Risk-Kids model. Harrell's C index was 0.60, with a sensitivity of 9.09%, specificity of 63.92%, positive predictive value of 1.72%, and negative predictive value of 91%; with a poor distinction between the different risk groups. Unexplained syncope (HR 42.17, 95% CI 10.49-169.56, p < 0.001) and non-sustained ventricular tachycardia (HR 5.48, 95% CI 1.58-19.03, p < 0.007) were predictors of SCD on univariate analysis. CONCLUSION: Unexplained syncope and the presence of NSVT emerge as predictors for SCD in children with RASopathy-associated HCM. The HCM Risk-Kids model may not be appropriate to use in this population, but larger multicentre collaborative studies are required to investigate this further.

Using Ribonucleoprotein-based CRISPR/Cas9 to Edit Single Nucleotide on Human Induced Pluripotent Stem Cells to Model Type 3 Long QT Syndrome (SCN5A±).

Human induced pluripotent stem cells (hiPSCs) have been widely used in cardiac disease modelling, drug discovery, and regenerative medicine as they can be differentiated into patient-specific cardiomyocytes. Long QT syndrome type 3 (LQT3) is one of the more malignant congenital long QT syndrome (LQTS) variants with an SCN5A gain-of-function effect on the gated sodium channel. Moreover, the predominant pathogenic variants in LQTS genes are single nucleotide substitutions (missense) and small insertion/deletions (INDEL). CRISPR/Cas9 genome editing has been utilised to create isogenic hiPSCs to control for an identical genetic background and to isolate the pathogenicity of a single nucleotide change. In this study, we described an optimized and rapid protocol to introduce a heterozygous LQT3-specific variant into healthy control hiPSCs using ribonucleoprotein (RNP) and single-stranded oligonucleotide (ssODN). Based on this protocol, we successfully screened hiPSCs carrying a heterozygous LQT3 pathogenic variant (SCN5A±) with high efficiency (6 out of 69) and confirmed no off-target effect, normal karyotype, high alkaline phosphatase activity, unaffected pluripotency, and in vitro embryonic body formation capacity within 2 weeks. In addition, we also provide protocols to robustly differentiate hiPSCs into cardiomyocytes and evaluate the electrophysiological characteristics using Multi-electrode Array. This protocol is also applicable to introduce and/or correct other disease-specific variants into hiPSCs for future pharmacological screening and gene therapeutic development.

Planning Transition of Care for Adolescents Affected by Congenital Heart Disease: The Irish National Pathway.

At some point in their life, adolescent patients with a congenital heart disease (CHD) transition from paediatric services to adult care facilities. The process is not without any risks, as it is often linked with a significantly progressive deterioration in adolescents' health and loss of follow-up. In fact, transition patients often encounter troubles in finding a care giver who is comfortable managing their condition, or in re-establishing trust with the new care provider. Planning the rules of transition is pivotal in preventing these risks. Unfortunately, the American and European guidelines on CHD provide just generic statements about transition. In a recently published worldwide inter-societies consensus document, a hybrid model of transition, which should be adapted for use in high- and low- resource settings, has been suggested. Currently, in literature there are a few models of transition for CHD patients, but they are by far local models and cannot be generalized to other regions or countries. This paper describes the Irish model for transition of care of CHD patients. Due to the peculiarity of the healthcare organization in the Republic of Ireland, which is centralized with one main referral centre for paediatric cardiology (in Dublin, with a few smaller satellite centres all around, according to the "hub and spoke" model) and one centre for adult with CHD (in Dublin), the model can be considered as a national one and the first to be released in the old continent.

Severe Restriction of a VSD and Development of Pulmonary Atresia in a Patient with Transposition of the Great Arteries: Fetal Diagnosis.

Pulmonary atresia with an intact ventricular septum typically occurs in patients with concordant atrioventricular and ventriculoarterial connections. When it does occur in patients with discordant connections, it is most frequently seen in association with congenitally corrected transposition. We present a rare case of transposition of the great arteries with a ventricular septal defect (VSD) detected in fetal life which evolved throughout pregnancy resulting in the development of pulmonary atresia and severe restriction of the VSD.

Clinical Features and Natural History of Preadolescent Nonsyndromic Hypertrophic Cardiomyopathy.

BACKGROUND: Up to one-half of childhood sarcomeric hypertrophic cardiomyopathy (HCM) presents before the age of 12 years, but this patient group has not been systematically characterized. OBJECTIVES: The aim of this study was to describe the clinical presentation and natural history of patients presenting with nonsyndromic HCM before the age of 12 years. METHODS: Data from the International Paediatric Hypertrophic Cardiomyopathy Consortium on 639 children diagnosed with HCM younger than 12 years were collected and compared with those from 568 children diagnosed between 12 and 16 years. RESULTS: At baseline, 339 patients (53.6%) had family histories of HCM, 132 (20.9%) had heart failure symptoms, and 250 (39.2%) were prescribed cardiac medications. The median maximal left ventricular wall thickness z-score was 8.7 (IQR: 5.3-14.4), and 145 patients (27.2%) had left ventricular outflow tract obstruction. Over a median follow-up period of 5.6 years (IQR: 2.3-10.0 years), 42 patients (6.6%) died, 21 (3.3%) underwent cardiac transplantation, and 69 (10.8%) had life-threatening arrhythmic events. Compared with those presenting after 12 years, a higher proportion of younger patients underwent myectomy (10.5% vs 7.2%; P = 0.045), but fewer received primary prevention implantable cardioverter-defibrillators (18.9% vs 30.1%; P = 0.041). The incidence of mortality or life-threatening arrhythmic events did not differ, but events occurred at a younger age. CONCLUSIONS: Early-onset childhood HCM is associated with a comparable symptom burden and cardiac phenotype as in patients presenting later in childhood. Long-term outcomes including mortality did not differ by age of presentation, but patients presenting at younger than 12 years experienced adverse events at younger ages.

Life-threatening cardiac arrhythmia and sudden death during electronic gaming: An international case series and systematic review.

BACKGROUND: Electronic gaming has recently been reported as a precipitant of life-threatening cardiac arrhythmia in susceptible individuals. OBJECTIVE: The purpose of this study was to describe the population at risk, the nature of cardiac events, and the type of game linked to cardiac arrhythmia associated with electronic gaming. METHODS: A multisite international case series of suspected or proven cardiac arrhythmia during electronic gaming in children and a systematic review of the literature were performed. RESULTS: Twenty-two patients (18 in the case series and 4 via systematic review; aged 7-16 years; 19 males [86%]) were identified as having experienced suspected or proven ventricular arrhythmia during electronic gaming; 6 (27%) had experienced cardiac arrest, and 4 (18%) died suddenly. A proarrhythmic cardiac diagnosis was known in 7 (31%) patients before their gaming event and was established afterward in 12 (54%). Ten patients (45%) had catecholaminergic polymorphic ventricular tachycardia, 4 (18%) had long QT syndrome, 2 (9%) were post-congenital cardiac surgery, 2 (9%) had "idiopathic" ventricular fibrillation, and 1 (after Kawasaki disease) had coronary ischemia. In 3 patients (14%), including 2 who died, the diagnosis remains unknown. In 13 (59%) patients for whom the electronic game details were known, 8 (62%) were war games. CONCLUSION: Electronic gaming can precipitate lethal cardiac arrhythmias in susceptible children. The incidence appears to be low, but syncope in this setting should be investigated thoroughly. In children with proarrhythmic cardiac conditions, electronic war games in particular are a potent arrhythmic trigger.

Generation and characterization of three induced pluripotent stem cell lines (NUIGi046-A, NUIGi046-B, NUIGi046-C) from a 51-year-old healthy individual.

Skin punch biopsy was donated by a healthy 51-year-old Caucasian male and the dermal fibroblasts were reprogrammed into human induced pluripotent stem cell (hiPSC) lines by using non-integrative Sendai viruses expressing OCT4, SOX2, KLF4 and c-MYC. Three iPSC lines (NUIGi046-A, NUIGi046-B, NUIGi046-C) highly expressed the pluripotent markers and were capable of differentiating into cells of endodermal, mesodermal, and ectodermal origin. These iPSCs can be offered as controls and in combination with genome-editing and three-dimensional (3D) system. They may be used for human disease modelling and drug screening.

Derivation and characterization of two human induced pluripotent stem cell lines (NUIGi004-A) and (NUIGi012-A) from two patients with LQT2 disease.

Long QT syndrome type 2 (LQT2) is associated with KCNH2, which encodes the α subunit of the ion channel that controls the K+ current in the heart. Mutations of KCNH2 cause loss of Kv11.1 channel function by disrupting subunit folding, assembly, or trafficking of the channel to the cell surface. Here we generated two induced pluripotent stem cell (iPSC) lines from two patients carrying mutation in KCNH2 gene. These iPSCs express the pluripotent markers and have the capacity of differentiation into other cell types. These patient-derived iPSCs are useful for investigating the disease pathology and identifying the therapeutic target.

Generation and characterization of three induced pluripotent stem cell lines (NUIGi047-A, NUIGi047-B, NUIGi047-C) from a 7-year-old healthy Caucasian male.

We report the generation of three human induced pluripotent stem cell (hiPSC) lines (NUIGi047-A, NUIGi047-B, NUIGi047-C) from a healthy 7-year-old boy using non-integrational Sendai re-programming method expressing OCT4, SOX2, KLF4 and C-MYC. Stem cell characterization was confirmed through morphology, immunofluorescence staining and RT-qPCR. Differentiation potential in vitro was demonstrated to all three germ layers with STR lineage verification and normal molecular karyotyping through the process of re-programming.

Generation and characterization of an induced pluripotent stem cell (iPSC) line (NUIGi003-A) from a long QT syndrome type 2 (LQT2) patient harbouring the KCNH2 c.2464G>A pathogenic variant.

Long QT syndrome (LQTS), an inherited cardiac ion channelopathy, is associated with ventricular arrhythmias and risk of sudden death. LQTS sub-type 2 (LQT2) is caused by pathogenic variants in KCNH2 encoding the α-subunit of Kv11.1, thus affecting the rapid component of delayed rectifier K+ current (IKr) channel during the action potential. In this study, non-integrational Sendai reprogramming method was used to generate an induced-pluripotent-stem-cell (iPSC) line carrying the KCNH2 c.2464G>A (p.Val822Met) pathogenic variant from a LQT2 patient. This patient-specific iPSC line NUIGi003-A harbouring the c.2464G>A variant expressed pluripotency markers and demonstrated the differentiation potential to all three germ layers.

Generation and characterization of two induced pluripotent stem cell lines (NUIGi038-A, NUIGi038-B) from dermal fibroblasts of a healthy individual.

Two human induced pluripotent stem cell (hiPSC) lines (NUIGi038-A, NUIGi038-B) were generated from dermal fibroblasts of a healthy 47 year old female using non-integrational Sendai reprogramming method expressing OCT4, SOX2, KLF4 and C-MYC. Characterization of both hiPSC lines was confirmed by the expression of typical pluripotency markers and differentiation potential in vitro.

Generation and characterization of twelve human induced pluripotent stem cell (iPSC) lines from four familial long QT syndrome type 1 (LQT1) patients carrying KCNQ1 c.1201dupC mutation.

In this study, we describe the generation and characterization of induced pluripotent stem cell (iPSC) lines from familial long QT syndrome type 1 (LQT1) patients carrying the KCNQ1 c.1201dupC (p.Arg401fs) frame shift mutation by using non-integrational Sendai reprogramming method. The patient-specific iPSC lines harboring the c.1201dupC mutation on KCNQ1 gene expressed pluripotency markers and had the capacity to differentiate into three germ layers.

Long QT Syndrome: Genetics and Future Perspective.

Long QT syndrome (LQTS) is an inherited primary arrhythmia syndrome that may present with malignant arrhythmia and, rarely, risk of sudden death. The clinical symptoms include palpitations, syncope, and anoxic seizures secondary to ventricular arrhythmia, classically torsade de pointes. This predisposition to malignant arrhythmia is from a cardiac ion channelopathy that results in delayed repolarization of the cardiomyocyte action potential. The QT interval on the surface electrocardiogram is a summation of the individual cellular ventricular action potential durations, and hence is a surrogate marker of the abnormal cellular membrane repolarization. Severely affected phenotypes administered current standard of care therapies may not be fully protected from the occurrence of cardiac arrhythmias. There are 17 different subtypes of LQTS associated with monogenic mutations of 15 autosomal dominant genes. It is now possible to model the various LQTS phenotypes through the generation of patient-specific induced pluripotent stem cell-derived cardiomyocytes. RNA interference can silence or suppress the expression of mutant genes. Thus, RNA interference can be a potential therapeutic intervention that may be employed in LQTS to knock out mutant mRNAs which code for the defective proteins. CRISPR/Cas9 is a genome editing technology that offers great potential in elucidating gene function and a potential therapeutic strategy for monogenic disease. Further studies are required to determine whether CRISPR/Cas9 can be employed as an efficacious and safe rescue of the LQTS phenotype. Current progress has raised opportunities to generate in vitro human cardiomyocyte models for drug screening and to explore gene therapy through genome editing.

Development of a Novel Risk Prediction Model for Sudden Cardiac Death in Childhood Hypertrophic Cardiomyopathy (HCM Risk-Kids).

Importance: Sudden cardiac death (SCD) is the most common mode of death in childhood hypertrophic cardiomyopathy (HCM), but there is no validated algorithm to identify those at highest risk. Objective: To develop and validate an SCD risk prediction model that provides individualized risk estimates. Design, Setting, and Participants: A prognostic model was developed from a retrospective, multicenter, longitudinal cohort study of 1024 consecutively evaluated patients aged 16 years or younger with HCM. The study was conducted from January 1, 1970, to December 31, 2017. Exposures: The model was developed using preselected predictor variables (unexplained syncope, maximal left-ventricular wall thickness, left atrial diameter, left-ventricular outflow tract gradient, and nonsustained ventricular tachycardia) identified from the literature and internally validated using bootstrapping. Main Outcomes and Measures: A composite outcome of SCD or an equivalent event (aborted cardiac arrest, appropriate implantable cardioverter defibrillator therapy, or sustained ventricular tachycardia associated with hemodynamic compromise). Results: Of the 1024 patients included in the study, 699 were boys (68.3%); mean (interquartile range [IQR]) age was 11 (7-14) years. Over a median follow-up of 5.3 years (IQR, 2.6-8.3; total patient years, 5984), 89 patients (8.7%) died suddenly or had an equivalent event (annual event rate, 1.49; 95% CI, 1.15-1.92). The pediatric model was developed using preselected variables to predict the risk of SCD. The model's ability to predict risk at 5 years was validated; the C statistic was 0.69 (95% CI, 0.66-0.72), and the calibration slope was 0.98 (95% CI, 0.59-1.38). For every 10 implantable cardioverter defibrillators implanted in patients with 6% or more of a 5-year SCD risk, 1 patient may potentially be saved from SCD at 5 years. Conclusions and Relevance: This new, validated risk stratification model for SCD in childhood HCM may provide individualized estimates of risk at 5 years using readily obtained clinical risk factors. External validation studies are required to demonstrate the accuracy of this model's predictions in diverse patient populations.

Generation of eight human induced pluripotent stem cell (iPSC) lines from familial Long QT Syndrome type 1 (LQT1) patients carrying KCNQ1 c.1697C>A mutation (NUIGi005-A, NUIGi005-B, NUIGi005-C, NUIGi006-A, NUIGi006-B, NUIGi006-C, NUIGi007-A, and NUIGi007-B).

Long QT Syndrome type 1 (LQT1), an inherited cardiac ion channelopathy associated with arrhythmias and risk of sudden death, is caused by mutations in KCNQ1 encoding the α-subunit of Kv7.1, that affects the slow component of delayed rectifier K+ current (IKs) channel. In this study, the non-integrational Sendai reprogramming method was used to express four Yamanaka factors and to generate induced pluripotent stem cell (iPSC) lines carrying the KCNQ1 c.1697C>A (p.S566Y) mutation from familial LQT1 patients. The patient-specific iPSC lines harbouring the c.1697C>A mutation expressed pluripotency markers and had the capacity to differentiate into three germ layers.