Emily Tu

Post‐Mortem Review and Genetic Analysis of Sudden Unexpected Death in Epilepsy (SUDEP) Cases

Sudden unexpected death in epilepsy (SUDEP) is the most frequent epilepsy‐related cause of death and is characterized by an absence of any identifiable cause of death at post‐mortem, suggesting an underlying arrhythmogenic predisposition. This study sought to identify SUDEP cases in a review of post‐mortem records and to undertake genetic studies in key familial long QT syndrome (LQTS) genes. All autopsies performed from 1993‐2009 at a forensic centre in Sydney, Australia were reviewed and SUDEP cases identified. DNA was extracted from post‐mortem blood and the three most common LQTS genes, ie, KCNQ1, KCNH2 (HERG) and SCN5A, were amplified and analyzed. Sixty‐eight SUDEP cases were identified (mean age of 40 ± 16 years). Genetic analysis revealed 6 (13%) non‐synonymous (amino acid changing) variants in KCNH2 (n = 2) and SCN5A (n = 4), all previously reported in LQTS patients. Specifically, KCNH2 Arg176Trp and SCN5A Pro1090Leu were identified once in SUDEP cases and absent in control alleles. Both DNA variants have been previously identified in the pathogenesis of LQTS. The cause of SUDEP is currently unknown. Our results indicate that investigation of key ion channel genes should be pursued in the investigation of the relationship between epilepsy and sudden death.

Severe Heart Failure and Early Mortality in a Double-Mutation Mouse Model of Familial Hypertrophic Cardiomyopathy

Background— Familial hypertrophic cardiomyopathy (FHC) is characterized by genetic and clinical heterogeneity. Five percent of FHC families have 2 FHC-causing mutations, which results in earlier disease onset, increased cardiac dysfunction, and a higher incidence of sudden death events. These observations suggest a relationship between the number of gene mutations and phenotype severity in FHC. Methods and Results— We sought to develop, characterize, and investigate the pathogenic mechanisms in a double-mutant murine model of FHC. This model (designated TnI-203/MHC-403) was generated by crossbreeding mice with the Gly203Ser cardiac troponin I (TnI-203) and Arg403Gln α-myosin heavy chain (MHC-403) FHC-causing mutations. The mortality rate in TnI-203/MHC-403 mice was 100% by age 21 days. At age 14 days, TnI-203/MHC-403 mice developed a significantly increased ratio of heart weight to body weight, marked interstitial myocardial fibrosis, and increased expression of atrial natriuretic factor and brain natriuretic peptide compared with nontransgenic, TnI-203, and MHC-403 littermates. By age 16 to 18 days, TnI-203/MHC-403 mice rapidly developed a severe dilated cardiomyopathy and heart failure, with inducibility of ventricular arrhythmias, which led to death by 21 days. Downregulation of mRNA levels of key regulators of Ca2+ homeostasis in TnI-203/MHC-403 mice was observed. Increased levels of phosphorylated STAT3 were observed in TnI-203/MHC-403 mice and corresponded with the onset of disease, which suggests a possible cardioprotective response. Conclusions— TnI-203/MHC-403 double-mutant mice develop a severe cardiac phenotype characterized by heart failure and early death. The presence of 2 disease-causing mutations may predispose individuals to a greater risk of developing severe heart failure than human FHC caused by a single gene mutation.

Sudden death in type 1 diabetes: The mystery of the ‘dead in bed’ syndrome

Sudden cardiac death is an unpredictable and devastating event, particularly in the young. A significant proportion of sudden deaths in the young are unexplained-no cause is identified either during life or at post-mortem. This is seen in a subgroup of young patients with type 1 diabetes who have dead in bed syndrome, where these victims are in good health, retire to bed, only to be found dead the following morning in a bed which is undisturbed, suggesting no terminal struggle or seizure. The underlying cause of dead in bed syndrome remains unknown, but is likely to be due to a terminal malignant arrhythmia. A plausible hypothesis is that it may be secondary to QT interval prolongation (followed by a degenerate ventricular tachycardia), caused by a number of factors including acute hypoglycaemia, on a background of cardiac autonomic neuropathy, and possible genetic influences. It is envisaged that understanding the causes and triggers of dead in bed syndrome will allow appropriate therapeutic interventions to be initiated in high-risk patients with type 1 diabetes, with the ultimate goal to prevent sudden death.

Genetic analysis of hyperpolarization-activated cyclic nucleotide-gated cation channels in sudden unexpected death in epilepsy cases.

Sudden unexpected death in epilepsy (SUDEP) is the most common epilepsy‐related cause of death, yet the cause is unknown. Our previous studies suggest a role for arrhythmia‐related ion channel genes in the pathogenesis of SUDEP. Hyperpolarization‐activated cyclic nucleotide‐gated cation (HCN1–4) channels are ion channels involved in generating spontaneous rhythmic activity in cardiac pacemaker and neuronal cells. This study sought to determine the role of pathogenic DNA variants in the HCN1–4 genes in a large SUDEP cohort collected from 1993 to 2009. Post‐mortem DNA samples were amplified and analyzed for each HCN exon. Genetic analysis in 48 SUDEP cases (age range 12–82 years) identified six novel and three previously reported nonsynonymous (amino acid changing) variants in HCN1 (n = 1), HCN2 (n = 2), HCN3 (n = 2) and HCN4 (n = 4). The Phe738Cys and Pro802Ser variants in HCN2, and Gly973Arg in HCN4 were absent in control alleles and affecting highly conserved residues in the carboxyl‐cytoplasmic tail region. Our results support a pathogenic link between the heart and brain in SUDEP, mediated by the HCN neuro‐cardiac ion channel genes.

Genetic analysis of hyperpolarization-activated cyclic nucleotide-gated cation channels in sudden unexpected in epilepsy cases

Sudden unexpected death in epilepsy (SUDEP) is the most common epilepsy‐related cause of death, yet the cause is unknown. Our previous studies suggest a role for arrhythmia‐related ion channel genes in the pathogenesis of SUDEP. Hyperpolarization‐activated cyclic nucleotide‐gated cation (HCN1–4) channels are ion channels involved in generating spontaneous rhythmic activity in cardiac pacemaker and neuronal cells. This study sought to determine the role of pathogenic DNA variants in the HCN1–4 genes in a large SUDEP cohort collected from 1993 to 2009. Post‐mortem DNA samples were amplified and analyzed for each HCN exon. Genetic analysis in 48 SUDEP cases (age range 12–82 years) identified six novel and three previously reported nonsynonymous (amino acid changing) variants in HCN1 (n = 1), HCN2 (n = 2), HCN3 (n = 2) and HCN4 (n = 4). The Phe738Cys and Pro802Ser variants in HCN2, and Gly973Arg in HCN4 were absent in control alleles and affecting highly conserved residues in the carboxyl‐cytoplasmic tail region. Our results support a pathogenic link between the heart and brain in SUDEP, mediated by the HCN neuro‐cardiac ion channel genes.

Post-mortem pathologic and genetic studies in "dead in bed syndrome" cases in type 1 diabetes mellitus.

Dead in bed syndrome is a poorly understood cause of sudden death in young people with type 1 diabetes. The underlying cause remains unknown. One possible explanation may involve prolongation of the QT interval followed by a terminal malignant arrhythmia. Risk factors associated with QT interval prolongation include hypoglycemia and cardiac autonomic neuropathy. We sought to identify myocardial cellular changes and genetic influences that may contribute to the pathogenesis of dead in bed syndrome. Post-mortem reports between 1994 and 2006 from the 2 largest Departments of Forensic Medicine in Australia were reviewed for dead in bed syndrome cases. Post-mortem heart sections were immunohistochemically stained for collagen types I and III and connective tissue growth factor (CTGF). Genomic DNA was prepared from post-mortem samples, and genetic analysis was performed in the SCN5A, G6PC, PHOX2B, and CTGF genes. Twenty-two dead in bed syndrome cases were identified and staining of heart sections for collagen I and III, and CTGF showed no differences between dead in bed syndrome cases and controls. Genetic screening of SCN5A revealed 3 silent polymorphisms A29A, E1061E, and D1819D and 1 protein-changing variant H558R. No genetic variants were found in G6PC, PHOX2B, and CTGF, and dead in bed syndrome cases were not associated with the G-945C CTGF promoter polymorphism. In conclusion, this study is the first to investigate potential pathogenic mechanisms underlying the dead in bed syndrome in type 1 diabetes with the results substantially adding to knowledge of this condition. Understanding the causes and triggers of dead in bed syndrome will be critical in facilitating the identification of patients with type 1 diabetes at highest risk of developing sudden death.