T. Thompson

A Prospective Study of Sudden Cardiac Death among Children and Young Adults

BACKGROUND Sudden cardiac death among children and young adults is a devastating event. We performed a prospective, population-based, clinical and genetic study of sudden cardiac death among children and young adults. METHODS We prospectively collected clinical, demographic, and autopsy information on all cases of sudden cardiac death among children and young adults 1 to 35 years of age in Australia and New Zealand from 2010 through 2012. In cases that had no cause identified after a comprehensive autopsy that included toxicologic and histologic studies (unexplained sudden cardiac death), at least 59 cardiac genes were analyzed for a clinically relevant cardiac gene mutation. RESULTS A total of 490 cases of sudden cardiac death were identified. The annual incidence was 1.3 cases per 100,000 persons 1 to 35 years of age; 72% of the cases involved boys or young men. Persons 31 to 35 years of age had the highest incidence of sudden cardiac death (3.2 cases per 100,000 persons per year), and persons 16 to 20 years of age had the highest incidence of unexplained sudden cardiac death (0.8 cases per 100,000 persons per year). The most common explained causes of sudden cardiac death were coronary artery disease (24% of cases) and inherited cardiomyopathies (16% of cases). Unexplained sudden cardiac death (40% of cases) was the predominant finding among persons in all age groups, except for those 31 to 35 years of age, for whom coronary artery disease was the most common finding. Younger age and death at night were independently associated with unexplained sudden cardiac death as compared with explained sudden cardiac death. A clinically relevant cardiac gene mutation was identified in 31 of 113 cases (27%) of unexplained sudden cardiac death in which genetic testing was performed. During follow-up, a clinical diagnosis of an inherited cardiovascular disease was identified in 13% of the families in which an unexplained sudden cardiac death occurred. CONCLUSIONS The addition of genetic testing to autopsy investigation substantially increased the identification of a possible cause of sudden cardiac death among children and young adults. (Funded by the National Health and Medical Research Council of Australia and others.).

R222Q SCN5A Mutation Is Associated With Reversible Ventricular Ectopy and Dilated Cardiomyopathy

OBJECTIVES The goal of this study was to characterize a variant in the SCN5A gene that encodes the alpha-subunit of the cardiac sodium channel, Nav1.5, which was identified in 1 large kindred with dilated cardiomyopathy (DCM) and multiple arrhythmias, including premature ventricular complexes (PVCs). BACKGROUND Treatment guidelines for familial DCM are based on conventional heart failure therapies, and no gene-based interventions have been established. METHODS Family members underwent clinical evaluation and screening of the SCN5A and LMNA genes. Cellular electrophysiology and computational modeling were used to determine the functional consequences of the mutant Nav1.5 protein. RESULTS An R222Q missense variant located in a Nav1.5 voltage-sensing domain was identified in affected family members. Patch-clamp studies showed that R222Q Nav1.5 did not alter sodium channel current density, but did left shift steady-state parameters of activation and inactivation. Using a voltage ramp protocol, normalized current responses of R222Q channels were of earlier onset and greater magnitude than wild-type channels. Action potential modeling using Purkinje fiber and ventricular cell models suggested that rate-dependent ectopy of Purkinje fiber origin is the predominant ventricular effect of the R222Q variant and a potential cause of DCM. In R222Q carriers, there were only modest responses to heart failure therapies, but PVCs and DCM were substantially reduced by amiodarone or flecainide, which are drugs that have sodium channel-blocking properties. CONCLUSIONS The R222Q SCN5A variant has an activating effect on sodium channel function and is associated with reversible ventricular ectopy and DCM. Elucidation of the genetic basis of familial DCM can enable effective gene-targeted therapy to be implemented.

Familial cardiological and targeted genetic evaluation: Low yield in sudden unexplained death and high yield in unexplained cardiac arrest syndromes

BACKGROUND It has been reported that cardiological screening and genetic evaluation in relatives of families with sudden unexplained death syndrome and unexplained cardiac arrest (UCA) may uncover a heritable etiology in a significant proportion of families. OBJECTIVE To evaluate the yield of a comprehensive evaluation protocol of a large unselected cohort of consecutive families with autopsy-negative sudden unexplained death syndrome (termed sudden arrhythmic death syndrome [SADS]) and UCA. METHODS We studied (1) 109 consecutive families (411 relatives) referred with 1 or more sudden deaths in the family and (2) 52 consecutive probands with UCA (91 relatives) referred by cardiologists between January 2007 and December 2012. A comprehensive cardiological screening was performed followed by targeted genetic evaluation if a clinical phenotype was proven or suspected. Diagnosis was made by a multidisciplinary team using published clinical criteria. RESULTS A diagnosis was made in 19 of 109 families with SADS (yield 18%), with the majority having long QT syndrome (LQTS). Diagnosis varied according to proband age, with LQTS most common in the very young (≤20 years) and Brugada syndrome in the older age probands (≥40 years) (P = .03). In contrast, a diagnosis was made in 32 of 52 families with UCA (yield 62%), the majority of which had LQTS and Brugada syndrome. No clinical or circumstantial factors increased the likelihood of diagnosis in families with either SADS or UCA. CONCLUSIONS In contrast to previously published series, a comprehensive strategy of cardiological evaluation and targeted genetic testing in more than 100 families with SADS was found to have a lower diagnostic yield (18%). Diagnostic yield in families with UCA was approximately 4 times higher (62%), which is consistent with the published literature.

Sudden unexpected death, epilepsy and familial cardiac pathology.

We evaluated the prevalence of epilepsy in a cohort of patients who suffered a sudden unexpected death (SUDEP), and determined the proportion of the deaths that were related to an identifiable underlying familial cardiac pathology. Epilepsy is common in people who experience a sudden unexpected death, with approximately a quarter having identifiable familial electrophysiological abnormalities. Familial cardiac pathology may be an important cause of SUDEP. A retrospective evaluation was performed of 74 families that were referred to the Royal Melbourne Hospital Cardiac Genetic Clinic over a 5 year period for investigation following a family members sudden, presumed cardiac, death. This state-wide referral clinic includes all patients who have died from a sudden unexpected death in whom the cause of death is unascertained. An epilepsy diagnosis was categorised as either definite, probable, possible or unlikely. The family members underwent comprehensive clinical evaluations and investigations in an attempt to identify a familial cardiac cause for the sudden unexpected death. Our findings suggest that systematic referral to a cardiac genetics service is warranted for the first degree relatives of people with epilepsy who experience a sudden unexplained death, for further evaluation and to identify those who are at higher risk for sudden death. Interventions may then be instituted to potentially reduce this risk.

The Cardiac Genetics Clinic: a model for multidisciplinary genomic medicine

Objectives: To describe patient characteristics, standard operating procedure, and uptake of genetic testing at the multidisciplinary Cardiac Genetics Clinic (CGC) at the Royal Melbourne Hospital during its first 6 years.

Lynch syndrome and cervical cancer.

Carriers of germline mutations in DNA mismatch repair (MMR) genes are at increased risk of several cancers including colorectal and gynecologic cancers (Lynch syndrome). There is no substantial evidence that these mutations are associated with an increased risk of cervical cancer. A total of 369 families with at least one carrier of a mutation in a MMR gene (133 MLH1, 174 MSH2, 35 MSH6 and 27 PMS2) were ascertained via population cancer registries or via family cancer clinics in Australia, New Zealand, Canada, and USA. Personal and family histories of cancer were obtained from participant interviews. Modified segregation analysis was used to estimate the hazard ratio (incidence rates for carriers relative to those for the general population), and age‐specific cumulative risks of cervical cancer for carriers. A total of 65 cases of cervical cancer were reported (including 10 verified by pathology reports). The estimated incidence was 5.6 fold (95% CI: 2.3–13.8; p = 0.001) higher for carriers than for the general population with a corresponding cumulative risk to 80 years of 4.5% (95% CI: 1.9–10.7%) compared with 0.8% for the general population. The mean age at diagnosis was 43.1 years (95% CI: 40.0–46.2), 3.9 years younger than the reported USA population mean of 47.0 years (p = 0.02). Women with MMR gene mutations were found to have an increased risk of cervical cancer. Due to limited pathology verification we cannot be certain that a proportion of these cases were not lower uterine segment endometrial cancers involving the endocervix, a recognized cancer of Lynch syndrome.

Arrhythmogenic Right Ventricular Cardiomyopathy: A Review of Living and Deceased Probands

BACKGROUND Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a potentially life-threatening genetic cardiomyopathy with a spectrum of clinical presentations including sudden cardiac death (SCD). METHODS Clinical and genetic data of 44 probands referred to a cardiac genetics clinic (2007-2017) who met 2010 Task Force Criteria (TFC) for ARVC diagnosis were included. RESULTS Thirty-three (33) (75%) male, 20 (45%) were referred by the Victorian Institute of Forensic Medicine. Presentation that lead to diagnosis included ARVC-related SCD (n=19), SCD due to alternate cause of death (n=1), aborted cardiac arrest (n=6), stable symptomatic ventricular tachycardia (n=14), palpitations (n=3) and presyncope (n=1). Left ventricular involvement (50%) was more common in the SCD subgroup (84% vs 21%, p<0.001). Genetic testing (n=39) revealed a pathogenic mutation in 16 (commonest: plakophillin-2 (n=9)), a variant of uncertain significance (VUS) in 15, with no abnormality in eight. In the SCD subgroup, median age at death was 44.7 years and 74% were male. Genetic testing (n=16) in this subgroup revealed a pathogenic mutation in six patients (commonest: desmoplakin (n=4)). Comparison of the two commonest mutations (PKP2 and desmoplakin [DSP]) showed DSP mutation was more frequently associated with SCD (p<0.01) and LV involvement (p<0.001). Screening of 117 relatives has lead to ARVC diagnosis in 29 patients. CONCLUSIONS Arrhythmogenic right ventricular cardiomyopathy has a heterogeneous and often severe clinical presentation. Sudden cardiac death and aborted cardiac arrest (ACA) are common, demonstrating electrical abnormalities appear early in the ARVC phenotype. Left ventricular involvement was common and may reflect a worse prognosis. Genetic testing is essential in family screening and may be helpful in risk assessment. Desmoplakin mutation is associated with LV involvement and may be indicative of worse prognosis and increased risk of SCD. Genetic screening of proband family members in a specialised multidisciplinary clinic is essential in early diagnosis of affected family members.