Jackie Crawford

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.).

Prospective, population-based long QT molecular autopsy study of postmortem negative sudden death in 1 to 40 year olds

BACKGROUND Retrospective investigation of sudden unexplained death in the young (SUDY) reveals that a high proportion is due to inherited heart disease. OBJECTIVE The purpose of this study was to ascertain the diagnostic value of postmortem long QT (LQT) genetic analysis in a prospective study of SUDY victims 1-40 years old. METHODS Denaturing high-performance liquid chromatography or direct sequencing of LQT genes 1, 2, 3, 5, and 6 was performed, in a National New Zealand protocol, in SUDY victims aged 1-40 years. RESULTS Over 26 months (2006-2008), DNA was stored at autopsy from 52 victims of sudden unexpected death. Further testing revealed a diagnosis in 19 cases (poisoning 4, dilated cardiomyopathy 3, myocarditis 3, other 9). The remaining 33 cases underwent genetic testing (age at death 18 months-40 years, median 25 years). Eighteen (55%) died during sleep or at rest, and 7 (21%) died during light activity. Rare missense variants in LQT genes were found in 5 (15%) cases (confidence interval 3%-27%): T96R in KCNQ1 (11-year-old male), P968L in KCNH2 (32-year-old female), P2006A in SCN5A (34-year-old female), and R67H and R98W in KCNE1 (17- and 38-year-old females, respectively). Evidence of pathogenicity was provided by in vitro evidence (T96R), family phenotype-genotype co-segregation (R98W, P2006A), and/or previous reports (R67H, P968L, P2006A, R98W). Family cardiac investigation was possible in 23 (70%) families and revealed probable cause of death for 5 (15%) other victims (confidence interval 3%-27%). CONCLUSION Most community SUDY occurs at rest or during light activity. A diagnostic rate of 15% supports the transition of LQT genetic autopsy, combined with family investigation, into routine medical practice.

Identification of large gene deletions and duplications in KCNQ1 and KCNH2 in patients with long QT syndrome

BACKGROUND Sequencing or denaturing high-performance liquid chromatography (dHPLC) analysis of the known genes associated with the long QT syndrome (LQTS) fails to identify mutations in approximately 25% of subjects with inherited LQTS. Large gene deletions and duplications can be missed with these methodologies. OBJECTIVE The purpose of this study was to determine whether deletions and/or duplications of one or more exons of the main LQTS genes were present in an LQTS mutation-negative cohort. METHODS Multiplex ligation-dependent probe amplification (MLPA), a quantitative fluorescent approach, was used to screen 26 mutation-negative probands with an unequivocal LQTS phenotype (Schwartz score >4). The appropriate MLPA kit contained probes for selected exons in LQTS genes KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2. Real-time polymerase chain reaction was used to validate the MLPA findings. RESULTS Altered exon copy number was detected in 3 (11.5%) patients: (1) an ex13-14del of the KCNQ1 gene in an 11-year-old boy with exercise-induced collapse (QTc 580 ms); (2) an ex6-14del of the KCNH2 gene in a 22-year-old woman misdiagnosed with epilepsy since age 9 years (QTc 560 ms) and a sibling with sudden death at age 13 years; and (3) an ex9-14dup of the KCNH2 gene in a 12 year-old boy (QTc 550 ms) following sudden nocturnal death of his 32-year-old mother. CONCLUSION If replicated, this study demonstrates that more than 10% of patients with LQTS and a negative current generation genetic test have large gene deletions or duplications among the major known LQTS susceptibility genes. As such, these findings suggest that sequencing-based mutation detection strategies should be followed by deletion/duplication screening in all LQTS mutation-negative patients.

Brugada Syndrome Masquerading as Febrile Seizures

Fever can precipitate ventricular tachycardia in adults with Brugada syndrome, but such a link has not been reported in children. A 21-month-old white girl presented repeatedly with decreased conscious level and seizures during fever. During a typical episode, rapid ventricular tachycardia was documented. The resting 12-lead electrocardiogram revealed a Brugada electrocardiogram signature. Resting electrocardiograms of the asymptomatic brother and mother were normal, but fever in the mother and pharmacologic stress with ajmaline in the brother revealed Brugada electrocardiogram features. Genetic testing revealed an SCN5A mutation in the affected family members.

Posthumous diagnosis of long QT syndrome from neonatal screening cards

BACKGROUND Molecular autopsy in sudden unexplained death in the young (SUDY) victims cannot usually be performed if tissue suitable for DNA extraction is not retained at autopsy. OBJECTIVE The purpose of this study was to assess the feasibility and clinical value of posthumous genetic testing for long QT syndrome (LQTS) using residual material from the neonatal screening (Guthrie) card in SUDY victims. METHODS Twenty-one cases were investigated up to 13 years after death. Deaths occurred at <1 year in one, 1-18 years in 18, and 19-35 years in two patients. Guthrie cards were 3-39 years old. DNA was extracted, and amplicons corresponding to the coding regions of the LQTS genes 1, 2, 3, 5, and 6 underwent either denaturing high-performance liquid chromatography screening or direct DNA sequencing. RESULTS Adequate DNA was extracted in every case, although repeated purification and amplification was often required. Rare variants were detected in six of 19 cases undergoing diagnostic screening. Four (21%) are considered to be pathological and have been used for family screening: R243C and H455Y in KCNQ1 in 12-year-old and 13-year-old boys, respectively, and Q81H and S621R in KCNH2 in 21-month and 28-year-old females, respectively. Variants of uncertain significance were R1047L in KCNH2 in a 2-year-old girl and S38G in KCNE1 in a 19-month-old boy. Point mutation tests for previously identified familial LQTS mutations revealed a positive result in both cases: E146K in KCNQ1 and exon 6-4del in KCNH2. CONCLUSION Residual material from Guthrie cards collected for newborn metabolic screening can be used as a reliable source of DNA for the posthumous diagnosis of LQTS decades after SUDY, although purification and amplification of DNA is time intensive.

Community detection of long QT syndrome with a clinical registry: An alternative to ECG screening programs?

BACKGROUND Long QT syndrome (LQTS) prevalence is estimated at 4 of 10,000 based on community electrocardiogram (ECG) screening, about which there is disagreement regarding efficacy, accuracy, cost-effectiveness, and practicality. Family studies of autosomal dominant conditions such as LQTS have revealed 8-9 gene-positive family members per proband. OBJECTIVE To evaluate a cardiac/genetic registry and family screening program as a tool to identify LQTS in the community. METHODS Possible LQTS probands were referred to the New Zealand Cardiac Inherited Disease service. The registry was first established in the northern region (population 2.03 million), including central Auckland (population 0.46 million). After clinical evaluation, genetic testing and family cascade screening were initiated. Genotype-positive individuals were classified as definite LQTS, and others were classified as definite or probable LQTS by clinical and ECG criteria. RESULTS One hundred twelve probands were identified (presentation: 7 sudden death, 82 cardiac event, 16 ECG abnormality, and 7 sudden death of a family member). Following cascade screening, 309 patients with LQTS were identified (248 definite and 61 probable). Two hundred twenty patients had LQTS-causing mutations identified (120 [55%] LQT1, 78 [35%] LQT2, 19 [9%] LQT3, 1 [0.5%] LQT 5, and 2 [1%] LQT7). Thus far, an average of 2.1 definitely or probably affected family members have been identified per proband. The community detection rate is 1.5 of 10,000 for the whole region and 2.2 of 10,000 in Auckland. CONCLUSIONS A high level of community detection of LQTS is possible using a clinical registry. With adequate resourcing, this has the potential to be an effective alternative to community ECG screening.

Biophysical Properties of 9 KCNQ1 Mutations Associated With Long-QT Syndrome

Background—Inherited long-QT syndrome is characterized by prolonged QT interval on the ECG, syncope, and sudden death caused by ventricular arrhythmia. Causative mutations occur mostly in cardiac potassium and sodium channel subunit genes. Confidence in mutation pathogenicity is usually reached through family genotype-phenotype tracking, control population studies, molecular modeling, and phylogenetic alignments; however, biophysical testing offers a higher degree of validating evidence. Methods and Results—By using in vitro electrophysiological testing of transfected mutant and wild-type long-QT syndrome constructs into Chinese hamster ovary cells, we investigated the biophysical properties of 9 KCNQ1 missense mutations (A46T, T265I, F269S, A302V, G316E, F339S, R360G, H455Y, and S546L) identified in a New Zealand–based long-QT syndrome screening program. We demonstrate through electrophysiology and molecular modeling that 7 of the missense mutations have profound pathological dominant-negative loss-of-function properties, confirming their likely disease-causing nature. This supports the use of these mutations in diagnostic family screening. Two mutations (A46T, T265I) show suggestive evidence of pathogenicity within the experimental limits of biophysical testing, indicating that these variants are disease-causing via delayed- or fast-activation kinetics. Further investigation of the A46T family has revealed an inconsistent cosegregation of the variant with the clinical phenotype. Conclusions—Electrophysiological characterization should be used to validate long-QT syndrome pathogenicity of novel missense channelopathies. When such results are inconclusive, great care should be taken with genetic counseling and screening of such families, and alternative disease-causing mechanisms should be considered.

Utility of Post-Mortem Genetic Testing in Cases of Sudden Arrhythmic Death Syndrome

Background Sudden arrhythmic death syndrome (SADS) describes a sudden death with negative autopsy and toxicological analysis. Cardiac genetic disease is a likely etiology. Objectives This study investigated the clinical utility and combined yield of post-mortem genetic testing (molecular autopsy) in cases of SADS and comprehensive clinical evaluation of surviving relatives. Methods We evaluated 302 expertly validated SADS cases with suitable DNA (median age: 24 years; 65% males) who underwent next-generation sequencing using an extended panel of 77 primary electrical disorder and cardiomyopathy genes. Pathogenic and likely pathogenic variants were classified using American College of Medical Genetics (ACMG) consensus guidelines. The yield of combined molecular autopsy and clinical evaluation in 82 surviving families was evaluated. A gene-level rare variant association analysis was conducted in SADS cases versus controls. Results A clinically actionable pathogenic or likely pathogenic variant was identified in 40 of 302 cases (13%). The main etiologies established were catecholaminergic polymorphic ventricular tachycardia and long QT syndrome (17 [6%] and 11 [4%], respectively). Gene-based rare variants association analysis showed enrichment of rare predicted deleterious variants in RYR2 (p = 5 × 10-5). Combining molecular autopsy with clinical evaluation in surviving families increased diagnostic yield from 26% to 39%. Conclusions Molecular autopsy for electrical disorder and cardiomyopathy genes, using ACMG guidelines for variant classification, identified a modest but realistic yield in SADS. Our data highlighted the predominant role of catecholaminergic polymorphic ventricular tachycardia and long QT syndrome, especially the RYR2 gene, as well as the minimal yield from other genes. Furthermore, we showed the enhanced utility of combined clinical and genetic evaluation.

Single nucleotide polymorphisms in arrhythmia genes modify the risk of cardiac events and sudden death in long QT syndrome

BACKGROUND Disease-modifying single nucleotide polymorphisms (SNPs) can help explain incomplete penetrance and variable expressivity in congenital long QT syndrome (LQTS) by altering susceptibility to arrhythmias. OBJECTIVE The purpose of this study was to assess multiple arrhythmia SNPs (in 16 genes) in a distinct cohort of LQTS patients to identify modifier SNPs influencing the risk of sudden death. METHODS This study included 273 patients with LQTS from the New Zealand Cardiac Inherited Disease Registry (154 long QT type 1, 96 long QT type 2, and 23 long QT type 3), including 31 patients who had experienced death or resuscitated sudden cardiac death (RSCD). Patients were genotyped for 29 SNPs and tested for associations with clinical events and QTc length. Caucasian (n = 220) and Pacific Islander/New Zealand Maori (n = 53) ethnic groups were analyzed separately. This subgroup of Polynesian ancestry has not been previously studied for LQTS in either presentation or outcome. RESULTS In Caucasians, four SNPs at two risk loci (NOS1AP: rs12143842 and rs16847548; and KCNQ1: rs10798 and rs8234) were significantly associated with clinical events after correction for multiple testing. Patients homozygous for the risk allele of rs12143842 had an increased risk of death/RSCD [hazard ratio 10.15, 95% confidence interval (2.38, 43.34), q = 0.045). Several other SNPs showed trends toward association with QTc length and clinical events. CONCLUSION This study demonstrates that SNPs in NOS1AP and KCNQ1 are associated with an increased risk of cardiac events in LQTS patients, with the hazard ratio suggesting they have significant potential in clinical risk stratification.

Long QT molecular autopsy in sudden infant death syndrome

Objective To describe experience of long QT (LQT) molecular autopsy in sudden infant death syndrome (SIDS). Design Descriptive audit from two distinct periods: (1) A prospective, population-based series between 2006 and 2008 (‘unselected’). (2) Before and after 2006–2008, with testing guided by a cardiac genetic service (‘selected’). LQT genes 1, 2, 3, 5, 6 and 7 were sequenced. Next of kin were offered cardiac evaluation. Setting New Zealand. Patients 102 SIDS cases. Interventions Nil. Main outcome measures Detection of genetic variants. Results Maori 49 (47%), and Pacific island 24 (23%), infants were over-represented. Risk factors were common; bed sharing was reported in 49%. Rare genetic variants were commoner within the selected than unselected populations (5 of 31 infants (16%) vs 3 of 71 infants (4%) p < 0.05). In the selected population two infants had variants of definite or probable pathogenicity (KCNQ1, E146K; KCNH2, R1047L), two had novel variants of possible pathogenicity in SCN5A (I795F, F1522Y) and one had R1193Q in SCN5A, of doubtful pathogenicity. R1193Q was also the only variant in the three cases from the unselected population and occurred as a second variant with R1047L. Engaging families proved challenging. Only 3 of 8 (38%) variant-positive cases and 18 of 94 (19%) of variant-negative families participated in cardiac/genetic screening. Conclusions LQT molecular autopsy has a very low diagnostic yield among unselected SIDS cases where risk factors are common. Diagnostic yield can be higher with case selection. Engagement of the family prior to genetic testing is essential to counsel for the possible uncertainty of the results and to permit family genotype-phenotype cosegregation studies.