Postmortem genetic screening of SNPs in RyR2 gene in sudden unexplained nocturnal death syndrome in the southern Chinese Han population

The Role of Ryanodine Receptor 2 Polymorphisms in Oral Squamous Cell Carcinoma Susceptibility and Clinicopathological Features

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignancy worldwide, and oral squamous cell carcinoma (OSCC) is one of the most common types. There is strong evidence that ryanodine receptor 2 (RYR2) plays an important role in different types of cancer according to previous studies. Its expression is associated with survival in patients with HNSCC, but it is unknown whether altered RYR2 expression contributes to tumorigenesis. Therefore, we examined how RYR2 polymorphisms affect OSCC susceptibility and clinicopathological characteristics. Five single nucleotide polymorphisms (SNPs) of RYR2, rs12594, rs16835904, rs2779359, rs3765097, and rs3820216, were analyzed in 562 cases of OSCC and 332 healthy controls using real-time PCR. We demonstrated that RYR2 SNP rs12594 was significantly different between the case and control groups, but this difference was not significant after adjusting for personal habits. In contrast, we found that different genotypes of SNP rs2779359 were significantly associated with the characteristics of clinical stage and tumor size in OSCC patients, according to the odds ratios and the adjusted odds ratios; specifically, patients with the T genotype had 1.477-fold (95% CI, 1.043 to 2.091; p = 0.028) and 1.533-fold (95% CI, 1.087-2.162; p = 0.015) increases in clinical stage and tumor size, respectively, compared with patients with the C allele. The results of our study, in which RYR2 SNPs associated with OSCC progression and development were examined for the first time, suggest that clinicopathological characteristics may alter OSCC susceptibility. Finally, RYR2 SNP rs2779359 not only plays a role in both the prognosis and diagnosis of oral cancer but is also likely an important predictive factor for recurrence, response to treatment, and medication toxicity.

Sudden Unexpected Death after a mild trauma: The complex forensic interpretation of cardiac and genetic findings

A 55-year-old man affected by a psychotic disorder suddenly died during a quarrel with his father. The autopsy excluded traumatic causes of death, and the cardiac examination identified a severe cardiomegaly with biventricular dilatation of very likely multifactorial origin. Toxicological and pharmacogenetic analyses excluded a fatal intoxication and identified the presence of the antipsychotic drug fluphenazine in the therapeutic range in a normal metabolizer. The screening for genetic variations highlighted a novel heterozygous single-nucleotide variant in the exon 36: c 0.4750C>A (p.Pro1584Thr) of the Ryanodine Receptor Type 2 (RYR2) gene. The mutation detected can be classified as Likely Pathogenic according to the American College of Medical Genetics and Genomics (ACMG) criteria. RYR2 variation has been associated to catecholaminergic polymorphic ventricular tachycardia (CPVT), a disease currently recognized as one of the most malignant cardiac channelopathies, expressed mostly in young patients, normally in the absence of structural heart disease. The victim late middle age, compared to juvenile onset of CPVT reported in literature, his clinical history, his structurally altered heart, circumstances at death and the absence of phenotype-related variations of dilated cardiomyopathy genes, suggested that the fatal arrhythmia could have been caused by an acquired form of dilated cardiopathy/cardiomyopathy. However, the contribution of the genetic variant to death cannot be completely ruled out, since the significance of a VUS or of a novel variant depends on the data available at the time of investigation, and should be periodically evaluated. We discuss the contribution of the structural alteration and of the variant detected, as well as the role of the molecular autopsy in forensic examination, which can make a significant contribution for inferring both cause and manner of death.

Multiallelic rare variants support an oligogenic origin of sudden cardiac death in the young

Unexplained sudden death in the young is cardiovascular in most cases. Structural and conduction defects in cardiac-related genes can conspire to underlie sudden cardiac death. Here we report a clinical investigation and an extensive genetic assessment of a Tunisian family with sudden cardiac death in young members. In order to identify the family-genetic basis of sudden cardiac death, we performed Whole Exome Sequencing (WES), read depth copy-number-variation (CNV) screening and segregation analysis. We identify 6 ultra-rare pathogenic heterozygous variants in OBSCN, RYR2, DSC2, AKAP9, CACNA1C and RBM20 genes, and one homozygous splicing variant in TECRL gene consistent with an oligogenic model of inheritance. CNV analysis did not reveal any causative CNV consistent with the family phenotype. Overall, our results are highly suggestive for a cumulative effect of heterozygous missense variants as disease causation and to account for a greater disease severity among offspring. Our study further confirms the complexity of the inheritance of sudden cardiac death and highlights the utility of family-based WES and segregation analysis in the identification of family specific mutations within different cardiac genes pathways.

Identification of RyR2-PBmice and the effects of transposon insertional mutagenesis of the RyR2 gene on cardiac function in mice

Ryanodine receptor 2 (RyR2) plays an important role in maintaining the normal heart function, and mutantions can lead to arrhythmia, heart failure and other heart diseases. In this study, we successfully identified a piggyBac translocated RyR2 gene heterozygous mouse model (RyR2-PBmice) by tracking red fluorescent protein (RFP) and genotyping PCR. Cardiac function tests showed that there was no significant difference between the RyR2-PBmice and corresponding wild-type mice (WTmice), regardless of whether they were in the basal state or injected with epinephrine and caffeine. However, the sarcoplasmic reticulum Ca²⁺ content was significantly reduced in the cardiomyocytes of RyR2-PBmice as assessed by measuring caffeine-induced [Ca²⁺]_i transients; the cardiac muscle tissue of RyR2-PBmice displayed significant mitochondrial swelling and focal dissolution of mitochondrial cristae, and the tissue ATP content in the RyR2-PBmice heart was significantly reduced. To further analyze the molecular mechanism behind these changes, we tested the expression levels of related proteins using RT-PCR and Western blot analyses. The mRNA level of RyR2 in RyR2-PBmice cardiac tissue decreased significantly compared with the WTmice, and the protein expression associated with the respiratory chain was also downregulated. These results suggested that the piggyBac transposon inserted into the RyR2 gene substantively affected the structure and function of mitochondria in the mouse cardiomyocytes, leading to disorders of energy metabolism.

HCN4 Gene Variations in Sudden Unexplained Nocturnal Death Syndrome in the Southern Han Chinese Population

Sudden unexplained nocturnal death syndrome (SUNDS) is widely considered to be related to hereditary fatal arrhythmias. Hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) channels are widely distributed in sinus myocytes and play a profound role in generating pacemaker electro-activity in cardiomyocytes. In the present study, the potential correlation between HCN4 gene variations and the occurrence of SUNDS was investigated. Genomic DNA was extracted from blood samples of both 119 unrelated SUNDS patients and 184 healthy individuals and screened for candidate HCN4 gene variants. One missense heterozygous variant c.1578C>T (Ala195Val) and four synonymous heterozygous variants c.1552C>T, c.2833C>T, c.3823C>T, and c.4189C>A were discovered in the SUNDS cases. The missense variant c.1578C>T (Ala195Val) was absent in 163 recruited controls and 105 persons of the Southern Han Chinese population, had in-silico prediction indications as damaging, and was reported prevalent in sudden infant death, and is thus likely to be involved in SUNDS.

Associations between common ion channel single nucleotide polymorphisms and sudden cardiac death in adults: A MOOSE-compliant meta-analysis

BACKGROUND

We sought to identify common ion channel single nucleotide polymorphisms (SNPs) associated with the occurrence of sudden cardiac death (SCD) to predict the incidence of SCD in clinical settings.

METHODS

This study involved a systematic review and meta-analysis of ion channel SNPs and risk of SCD in adults. We searched public databases for studies published up to September 19, 2017. We examined relationships between SNPs in common ion channel genes and the incidence of SCD.

RESULTS

We collected data for 22 trials that included a total of 4149 patients who experienced SCD or had a high risk of SCD and assessed these data in our meta-analysis. An allelic model showed that rs11720524 in SCN5A clearly protected against SCD (odds ratio [OR]: 0.76; 95% confidence interval [95% CI]: 0.67-0.85; P < .001). Subgroup analysis showed that rs11720524 in SCN5A protected against SCD in Europeans and Caucasians but not in Koreans. The allelic model indicated that rs12296050 in KCNQ1 also had significant protective effects against SCD (OR: 0.85; 95% CI: 0.76-0.96; P = .007). Moreover, this model demonstrated that rs2283222 in KCNQ1 had a significant negative relationship with SCD (OR: 0.73; 95% CI: 0.62-0.85; P < .001). Rs12296050 in KCNQ1 protected against SCD in Koreans and Americans. Our results also showed that rs790896 in RYR2 was negatively associated with SCD in a dominant model (OR: 0.66; 95% CI: 0.45-0.97; P = .033).

CONCLUSIONS

Rs11720524 in SCN5A is negatively related to SCD in Europeans and Caucasians, and rs12296050 and rs2283222 in KCNQ1 and rs790896 in RYR2 clearly have protective effects against SCD.

Critical Roles of Xirp Proteins in Cardiac Conduction and Their Rare Variants Identified in Sudden Unexplained Nocturnal Death Syndrome and Brugada Syndrome in Chinese Han Population

BACKGROUND

Sudden unexplained nocturnal death syndrome (SUNDS) remains an autopsy negative entity with unclear etiology. Arrhythmia has been implicated in SUNDS. Mutations/deficiencies in intercalated disc components have been shown to cause arrhythmias. Human cardiomyopathy-associated 1 (XIRP1) and 3 (XIRP2) are intercalated disc-associated, Xin repeats-containing proteins. Mouse Xirp1 is necessary for the integrity of intercalated disc and for the surface expression of transient outward and delayed rectifier K+ channels, whereas mouse Xirp2 is required for Xirp1 intercalated disc localization. Thus, XIRP1 and XIRP2 may be potentially causal genes for SUNDS.

METHODS AND RESULTS

We genetically screened XIRP genes in 134 sporadic SUNDS victims and 22 Brugada syndrome (BrS) cases in a Chinese Han population. We identified 16 rare variants (6 were in silico predicted as deleterious) in SUNDS victims, including a novel variant, XIRP2-E215K. There were also four rare variants (2 were in silico predicted as deleterious) detected in BrS cases, including a novel variant, XIRP2-L2718P. Interestingly, among these 20 variants, we detected 2 likely pathogenic variants: a nonsense variant (XIRP2-Q2875*) and a frameshift variant (XIRP2-T2238QfsX7). Analyzing available Xirp2 knockout mice, we further found that mouse hearts without Xirp2 exhibited prolonged PR and QT intervals, slow conduction velocity, atrioventricular conduction block, and an abnormal infranodal ventricular conduction system. Whole-cell patch-clamp detected altered ionic currents in Xirp2-/- cardiomyocytes, consistent with the observed association between Xirp2 and Nav1.5/Kv1.5 in co-immunoprecipitation.

CONCLUSIONS

This is the first report identifying likely pathogenic XIRP rare variants in arrhythmogenic disorders such as SUNDS and Brugada syndrome, and showing critical roles of Xirp2 in cardiac conduction.

Molecular investigation by whole exome sequencing revealed a high proportion of pathogenic variants among Thai victims of sudden unexpected death syndrome

Introduction

Sudden unexpected death syndrome (SUDS) is an important cause of death in young healthy adults with a high incident rate in Southeast Asia; however, there are no molecular autopsy reports about these victims. We performed a combination of both a detailed autopsy and a molecular autopsy by whole exome sequencing (WES) to investigate the cause of SUDS in Thai sudden death victims.

Materials and methods

A detailed forensic autopsy was performed to identify the cause of death, followed by a molecular autopsy, in 42 sudden death victims who died between January 2015 and August 2015. The coding sequences of 98 SUDS-related genes were sequenced using WES. Potentially causative variants were filtered based on the variant functions annotated in the dbNSFP database. Variants with inconclusive clinical significance evidence in ClinVar were resolved with a variant prediction algorithm, metaSVM, and the frequency data of the variants found in public databases, such as the 1000 Genome Project, ESP6500 project, and the Exome Aggregation Consortium (ExAc) project.

Results

Combining both autopsy and molecular autopsy enabled the potential identification of cause of death in 81% of the cases. Among the 25 victims with WES data, 72% (18/25) were found to have potentially causative SUDS mutations. The majority of the victims had at a mutation in the TTN gene (8/18 = 44%), and only one victim had an SCN5A mutation.

Conclusions

WES can help to identify the genetic causes in victims of SUDS and may help to further guide investigations into their relatives to prevent additional SUDS victims.

Abnormal autonomic nervous system function in rural Thai men: A potential contributor to their high risk of sudden unexplained nocturnal death syndrome

BACKGROUND

Rural compared to urban Thai populations have a higher incidence of sudden unexplained nocturnal death syndrome (SUNDS). This study tests the hypothesis that compared to young urban Thai men, the young rural northeast Thai men display autonomic system dysfunction that may contribute to their relatively high risk to develop SUNDS.

METHODS

Forty-seven healthy second and third year students from Khon Kaen University (20-22years old) were divided into central, urban northeastern, and rural northeastern groups, based on the locality in which they had grown up and in which their parents had lived prior to their birth.

RESULTS

Body weight, body height, serum sodium, serum potassium, fasting blood sugar, glucose tolerance, resting mean arterial pressure, resting heart rate, ulnar nerve conduction velocity, and sympathetic and parasympathetic nervous system activity were not significantly different among the three groups. In contrast, compared to urban northeasterners and central Thais, rural northeasterners displayed low sympathetic and high parasympathetic responses to cold stress and oral saline load; however, baroreflex sensitivity and the autonomic nervous system responses to upright tilt were not significantly different among the three groups. In addition, respiratory rates at rest and in response to upright tilt, cold stress, and oral saline load were not significantly different among the three groups.

CONCLUSIONS

These data indicate that compared to central or urban, individuals from rural origin display decreased sympathetic and increased parasympathetic responses to stresses. These altered responses could predispose the individuals to inappropriate autonomic control during the stresses, including those resulting in SUNDS.

GJA1 gene variations in sudden unexplained nocturnal death syndrome in the Chinese Han population

Sudden unexplained nocturnal death syndrome (SUNDS) is a conundrum to both forensic pathologists and physicians, more than 80% of which the molecular pathogenesis remains unclear. Reported studies on both clinical and genetic phenotypes suggest SUNDS is related to congenital and acquired arrhythmias. Recent researches have linked the mutations of gene gap junction alpha 1 (GJA1) with arrhythmogenic cardiac disorders. In the present study, we investigate the potential correlation between GJA1 gene variations and the occurrence of SUNDS. Genomic DNA was extracted from the blood samples of both 124 sporadic SUNDS patients and 125 healthy controls to screen GJA1 gene for candidate variants using polymerase chain reaction (PCR) and direct DNA sequencing. One novel homozygous variant c.169C>T and one heterozygous SNP c.624C>T (rs530633057) were determined in 124 SUNDS cases (one case for each detected variant) and none of the 125 healthy controls. Base C>T transition at nucleotide position 169 led to termination of protein production after glutamine (Q) at codon 57 which is very likely to result in decreased expression of Cx43 gap junction channels and cause arrhythmic sudden death. This is the first report of GJA1 gene variations in SUNDS in the Chinese Han population, which suggests a novel susceptibility gene for Chinese SUNDS.

An insertion/deletion polymorphism within 3'UTR of RYR2 modulates sudden unexplained death risk in Chinese populations

Sudden unexplained death (SUD) constitutes a part of the overall sudden death that can not be underestimated. Over the last years, genetic testing on SUD has revealed that inherited channelopathies might play important roles in the pathophysiology of this disease. Ryanodine receptor type-2 (RYR2) is a kind of ion channel extensively distributed in the sarcoplasmic reticulum (SR) of myocardium. Studies on RYR2 have suggested that either dysfunction or abnormal expression of it could lead to arrhythmia, which may cause cardiac arrest. In this study, we conducted a case-control study to evaluate the association of a 4-base pair (4-bp) Indel polymorphism (rs10692285) in the 3'UTR of RYR2 with the risk of SUD and sudden cardiac death induced by coronary heart disease (SCD-AS) in a Chinese population. Logistic regression analysis showed that the insertion allele of rs10692285 had significantly increased the risk of SUD [OR=2.03; 95% confidence interval (CI)=1.08-3.77; P=0.0161; statistical power=0.743]. No relevance was observed between rs10692285 and SCD-AS. Further genotype-phenotype association analysis suggested that the expression level of RYR2 in human myocardium tissues with the insertion allele was higher than that with the deletion allele at both mRNA and protein levels. Dual-Luciferase activity assay system was used to detect the effect of rs10692285 on the transcription activity of RYR2. As expected, the result indicated that the transcription activity of RYR2 with the ins/ins genotype was higher than that with the del/del genotype. Finally, in-silico prediction revealed that different alleles of rs10692285 could alter the local structure of RYR2 mRNA and microRNA (miRNA) binding. In summary, our findings provided evidence that rs10692285 might contribute to SUD susceptibility through affecting the expression of RYR2, which suggest that abnormal ion channel activity is very likely to be the underlying mechanism of SUD, but not for SCD-AS. Thus, rs10692285 may become a potential marker for molecular diagnosis and genetic counseling of SUD.

Does Sudden Unexplained Nocturnal Death Syndrome Remain the Autopsy-Negative Disorder: A Gross, Microscopic, and Molecular Autopsy Investigation in Southern China

OBJECTIVE

To look for previously unrecognized cardiac structural abnormalities and address the genetic cause for sudden unexplained nocturnal death syndrome (SUNDS).

METHODS

Data for 148 SUNDS victims and 444 controls (matched 1:3 on sex, race, and age of death within 1 year) were collected from Sun Yat-sen University from January 1, 1998, to December 31, 2014, to search morphological changes. An additional 17 patients with Brugada syndrome (BrS) collected from January 1, 2006, to December 31, 2014, served as a comparative disease cohort. Target-captured next-generation sequencing for 80 genes associated with arrhythmia/cardiomyopathy was performed in 44 SUNDS victims and 17 patients with BrS to characterize the molecular spectrum.

RESULTS

The SUNDS victims had slight but statistically significant increased heart weight and valve circumference compared with controls. Twelve of 44 SUNDS victims (SCN5A, SCN1B, CACNB2, CACNA1C, AKAP9, KCNQ1, KCNH2, KCNJ5, GATA4, NUP155, ABCC9) and 6 of 17 patients with BrS (SCN5A, CACNA1C; P>.05) carried rare variants in primary arrhythmia-susceptibility genes. Only 2 of 44 SUNDS cases compared with 5 of 17 patients with BrS hosted a rare variant in the most common BrS-causing gene, SCN5A (P=.01). Using the strict American College of Medical Genetics guideline-based definition, it was found that only 2 of 44 (KCNQ1) SUNDS and 3 of 17 (SCN5A) patients with BrS hosted a "(likely) pathogenic" variant. Fourteen of 44 SUNDS cases with cardiomyopathy-related variants had a subtle but significantly decreased circumference of cardiac valves, and tended to die on average 5 to 6 years younger compared with the remaining 30 cases (P=.02).

CONCLUSION

We present the first comprehensive autopsy evidence that SUNDS victims may have concealed cardiac morphological changes. SUNDS and BrS may result from different molecular pathological underpinnings. The distinct association between cardiomyopathy-related rare variants and SUNDS warrants further investigation.

The biophysical characterization of the first SCN5A mutation R1512W identified in Chinese sudden unexplained nocturnal death syndrome

Increasing evidence observed in clinical phenotypes show that abrupt breathing disorders during sleep may play an important role in the pathogenesis of sudden unexplained nocturnal death syndrome (SUNDS). The reported Brugada syndrome causing mutation R1512W in cardiac sodium channel α subunit encoded gene SCN5A, without obvious loss of function of cardiac sodium channel in previous in vitro study, was identified as the first genetic cause of Chinese SUNDS by us. The R1512W carrier was a 38-year-old male SUNDS victim who died suddenly after tachypnea in nocturnal sleep without any structural heart disease. To test our hypothesis that slight acidosis conditions may contribute to the significant loss of function of mutant cardiac sodium channels underlying SUNDS, the biophysical characterization of SCN5A mutation R1512W was performed under both extracellular and intracellular slight acidosis at pH 7.0. The cDNA of R1512W was created using site-directed mutagenesis methods in the pcDNA3 plasmid vector. The wild type (WT) or mutant cardiac sodium channel R1512W was transiently transfected into HEK293 cells. Macroscopic voltage-gated sodium current (INa) was measured 24 hours after transfection with the whole-cell patch clamp method at room temperature in the HEK293 cells. Under the baseline conditions at pH 7.4, R1512W (-175 ± 15 pA/pF) showed about 30% of reduction in peak INa compared to WT (-254 ± 23 pA/pF, P < 0.05). Under the acidosis condition at pH 7.0, R1512W (-130 ± 17 pA/pF) significantly decreased the peak INa by nearly 50% compared to WT (-243 ± 23 pA/pF, P < 0.005). Compared to baseline condition at pH 7.4, the acidosis at pH 7.0 did not affect the peak INa in WT (P > 0.05) but decreased peak INa in R1512W (P < 0.05). This initial functional study for SCN5A mutation in the Chinese SUNDS victim revealed that the acidosis aggravated the loss of function of mutant channel R1512W and suggested that nocturnal sleep disorders-associated slight acidosis may trigger the lethal arrhythmia underlying the sudden death of SUNDS cases in the setting of genetic defect.

Identification of rare variants of DSP gene in sudden unexplained nocturnal death syndrome in the southern Chinese Han population

Sudden unexplained nocturnal death syndrome (SUNDS) is a perplexing disorder to both forensic pathologists and clinic physicians. Desmoplakin (DSP) gene was the first desmosomal gene linked to arrhythmogenic right ventricular cardiomyopathy (ARVC) which was associated with sudden death. To identify the genetic variants of the DSP gene in SUNDS in the southern Chinese Han population, we genetically screened the DSP gene in 40 sporadic SUNDS victims, 16 Brugada syndrome (BrS) patients, and 2 early repolarization syndrome (ERS) patients using next generation sequencing (NSG) and direct Sanger sequencing. A total of 10 genetic variants of the DSP gene were detected in 11 cases, comprised of two novel missense mutations (p.I125F and p.D521A) and eight previously reported rare variants. Of eight reported variants, two were previously considered pathogenic (p.Q90R and p.R2639Q), three were predicted in silico to be pathogenic (p.R315C, p.E1357D and p.D2579H), and the rest three were predicted to be benign (p.N1234S, p.R1308Q, and p.T2267S). This is the first report of DSP genetic screening in Chinese SUNDS and Brugada syndrome. Our results imply that DSP mutations contribute to the genetic cause of some SUNDS victims and maybe a new susceptible gene for Brugada syndrome.