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

Genetic Background and Clinical Phenotype in an Italian Cohort with Inherited Arrhythmia Syndromes and Arrhythmogenic Cardiomyopathy (ACM): A Whole-Exome Sequencing Study

Inherited arrhythmia syndromes include several different diseases, as well as Brugada syndrome (BrS), long QT syndrome (LQTS), catecholaminergic polymorphic ventricular tachycardia (CPVT), and short QT syndrome (SQTS). They represent, together with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C), an important cause of sudden cardiac death in the young. Most arrhythmia syndromes are inherited in an autosomal dominant manner, and genetic studies are suggested.: to report the spectrum of genetic variations and clinical phenotype in an Italian cohort with confirmed inherited arrhythmia syndromes and arrhythmogenic cardiomyopathy using whole-exome sequencing (WES). Patients with confirmed inherited arrhythmia syndromes and hereditary cardiomyopathy were recruited at the Cardiology Unit, University Polyclinic Hospital of Foggia, Italy and were included in this study. Genomic DNA samples were extracted from peripheral blood and conducted for WES. The variants were annotated using BaseSpace Variant Interpreter Annotation Engine 3.15.0.0 (Illumina). Reported variants were investigated using ClinVar, VarSome Franklin and a literature review. They were categorised agreeing to the criteria of the American College of Medical Genetics and Genomics. Overall, 62 patients were enrolled. Most of them had a clinical diagnosis of BrS (n 48, 77%). The remaining patients included in the present study had diagnosis of confirmed LQT (n 7, 11%), AR-DCM (n 4, 6.5%), ARVD (n 2, 3%), and SQT (n 1, 1.6%). Using the WES technique, 22 variants in 15 genes associated with Brugada syndrome were identified in 21 patients (34%). Among these, the SCN5A gene had the highest number of variants (6 variants, 27%), followed by KCNJ5 and CASQ2 (2 variants). Only one variant was identified in the remaining genes. In 27 patients with a clinical diagnosis of BrS, no gene variant was detected. In patients with confirmed LQT, SQT, 10 variants in 9 genes were identified. Among patients with ARVD and AR-DCM, 6 variants in 5 genes were found. Variants found in our cohort were classified as pathogenic (6), likely pathogenic (3), of uncertain significance (26), and benign (1). Two additional gene variants were classified as risk factors. In this study, 13 novel genetic variations were recognized to be associated with inherited arrhythmogenic cardiomyopathies. Our understanding of inherited arrhythmia syndromes continues to progress. The era of next-generation sequencing has advanced quickly, given new genetic evidence including pathogenicity, background genetic noise, and increased discovery of variants of uncertain significance. Although NGS study has some limits in finding the full genetic data of probands, large-scale gene sequencing can promptly be applied in real clinical practices, especially in inherited and possibly fatal arrhythmia syndromes.

Case Report: Comprehensive evaluation of ECG phenotypes and genotypes in a family with Brugada syndrome carrying SCN5A-R376H

Background

Brugada syndrome (BrS) is a channelopathy that can lead to sudden cardiac death in the absence of structural heart disease. Patients with BrS can be asymptomatic or present with symptoms secondary to polymorphic ventricular tachycardia or ventricular fibrillation. Even though BrS can exhibit autosomal dominant inheritance, it is not easy to identify the phenotype and genotype in a family thoroughly.

Case

We report the case of a 20-year-old man with variants in SCN5A and RyR2 genes who was resuscitated from sudden cardiac death during sleep due to a ventricular fibrillation. The patient did not have underlying diseases. The routine laboratory results, imaging study, coronary angiogram, and echocardiogram (ECG) were normal. A type 1 BrS pattern was identified in one resting ECG. Furthermore, prominent J wave accentuation with PR interval prolongation was identified during therapeutic hypothermia. Therefore, we were easily able to diagnose BrS. For secondary prevention, the patient underwent implantable cardioverter defibrillator implantation. Before discharge, a genetic study was performed using next-generation sequencing. Genotyping was performed in the first-degree relatives, and ECG evaluations of almost all maternal and paternal family members were conducted. The proband and his mother showed SCN5A-R376H and RyR2-D4038Y variants. However, his mother did not show the BrS phenotype on an ECG. One maternal aunt and uncle showed BrS phenotypes.

Conclusion

Genetics alone cannotdiagnose BrS. However, genetics could supply evidence or direction for evaluating ECG phenotypes in family groups. This case report shows how family evaluation using ECGs along with a genetic study can be used in BrS diagnosis.

Proteins in urine - Possible biomarkers of endometriosis

In the pathogenesis of endometriosis, a number of pathological reactions occur. Proteins secreted in the urine are thought to interact with each other and stimulate the pathological processes in endometriosis. Identifying one or more proteins that are specific enough and could serve as biomarkers for endometriosis is both a challenge and a necessity that would facilitate diagnosis. The urine of patients treated in a tertiary university hospital between July 1, 2020 and June 30, 2021 was analyzed. The studied group consists of patients who were treated surgically for endometriosis and in whom the diagnosis was confirmed by pathohistological analysis. The control group consists of patients who were operated for functional ovarian cysts. Urinary proteins were analyzed by chromatography and mass spectrometry (LC-MS/MS). We identified 17 proteins in urine whose concentrations were statistically significantly different in the group with endometriosis (N = 16) compared with the control groups (N = 16). The detected proteins were classified into groups according to their function in invasion, migration and proliferation, proteolysis, immune system, cell adhesion and vascular system. For all mentioned proteins the difference in concentration is statistically significant p < 0.005. Proteins are secreted in the urine of patients with endometriosis that may be involved in the pathogenesis of the disease and are possible biomarkers for endometriosis.

Research Progress on Molecular Markers Related to Unexplained Sudden Cardiac Death and Its Forensic Application

Routine pathological examination of unexplained sudden cardiac death (USCD) lacks significant morphological characteristics. In the field of forensic medicine, molecular biology methods have been used to find the cause of death by detecting genes and research related to the mechanism of sudden cardiac death has been carried out. From the molecular pathology point of view, the application of multiple levels of biomarkers to resolve the causes of USCD has already shown potential and provides an important path for forensic identification of USCD. This article reviews the latest research progress on USCD-related genes, RNA, proteins and USCD, and summarizes forensic application.

Desmosomal COP9 regulates proteome degradation in arrhythmogenic right ventricular dysplasia/cardiomyopathy

Dysregulated protein degradative pathways are increasingly recognized as mediators of human disease. This mechanism may have particular relevance to desmosomal proteins that play critical structural roles in both tissue architecture and cell-cell communication, as destabilization/breakdown of the desmosomal proteome is a hallmark of genetic-based desmosomal-targeted diseases, such as the cardiac disease arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C). However, no information exists on whether there are resident proteins that regulate desmosomal proteome homeostasis. Here, we uncovered a cardiac constitutive photomorphogenesis 9 (COP9) desmosomal resident protein complex, composed of subunit 6 of the COP9 signalosome (CSN6), that enzymatically restricted neddylation and targeted desmosomal proteome degradation. CSN6 binding, localization, levels, and function were affected in hearts of classic mouse and human models of ARVD/C affected by desmosomal loss and mutations, respectively. Loss of desmosomal proteome degradation control due to junctional reduction/loss of CSN6 and human desmosomal mutations destabilizing junctional CSN6 were also sufficient to trigger ARVD/C in mice. We identified a desmosomal resident regulatory complex that restricted desmosomal proteome degradation and disease.

Post-operative Brugada electrocardiographic pattern, polymorphic ventricular tachycardia, and sudden death in a child after administration of propofol anaesthesia

A 9-year-old African-American girl presented with sudden cardiac arrest a few hours after adenotonsillectomy. She received anaesthesia which included propofol during the procedure. Her electrocardiogram (EKG) showed type 1 Brugada pattern, and genetic testing revealed a variant of unknown significance in desmoplakin (DSP) gene. We discuss the association between propofol, Brugada EKG pattern, and malignant ventricular arrhythmias.

Sudden Cardiac Death (SCD) - risk stratification and prediction with molecular biomarkers

Sudden cardiac death (SCD) is a sudden, unexpected death that is caused by the loss of heart function. While SCD affects many patients suffering from coronary artery diseases (CAD) and heart failure (HF), a considerable number of SCD events occur in asymptomatic individuals. Certain risk factors for SCD have been identified and incorporated in different clinical scores, however, risk stratification using such algorithms is only useful for health management rather than for early detection and prediction of future SCD events in high-risk individuals. In this review, we discuss different molecular biomarkers that are used for early detection of SCD. This includes genetic biomarkers, where the majority of them are genomic variants for genes that encode for ion channels. Meanwhile, protein biomarkers often denote proteins that play roles in pathophysiological processes that lead to CAD and HF, notably (i) atherosclerosis that involves oxidative stress and inflammation, as well as (ii) cardiac tissue damage that involves neurohormonal and hemodynamic regulation and myocardial stress. Finally, we outline existing challenges and future directions including the use of OMICS strategy for biomarker discovery and the multimarker panels.

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.

Genetic diagnosis of acute aortic dissection in South China Han population using next-generation sequencing

Acute aortic dissection (AAD) is a clinically "silent," but emergent and life-threatening cardiovascular disease, and hereditary factors play an important etiologic role in the development of AAD. The purposes of this study are to definitize the diagnostic yield of 59 AAD patients, investigate the molecular pathological spectrum of AAD by NGS, and explore the future preclinical prospects of genetic diagnosis on AAD high-risk groups. We performed next-generation sequencing (NGS) based on screening of the 69 currently aortic dissections/aneurysms-associated genes on 59 sporadic AAD samples from South China. A Kaplan-Meier survival curve was constructed to compare the event-free survival depending on variant number. Overall, 67 variants were detected in 39 patients, among which 4 patients were identified with pathogenic variants and 13 patients were diagnosed with likely pathogenic variants. Seventeen genotype positive patients were identified in aggregate, and the diagnostic yield of our study is 28.8%. All genotype-positive variants were distributed in 11 genes, FBN1 variants were in the largest number among genotype-positive variants, which were detected for 4 times, ACTA2 for 3 times, ABCC6 and TGFBR1 twice, and NOS3, MYLK, XYLT1, TIMP4, TGFBR2, CNTN3, and PON1 once. Individuals with three or more variants showed shorter mean event-free survival than patients with fewer variants. Our observations broaden the genetic pathological spectrum of AAD. Furthermore, our research uncovered two susceptibility genes FBN1 and ACTA2 for Stanford type A AAD patients. Finally, our study concluded that the number of variants an individual harbored was an important consideration in risk stratification for individualized prediction and disease diagnosis.

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.

A compendium and functional characterization of mammalian genes involved in adaptation to Arctic or Antarctic environments

Background

Many mammals are well adapted to surviving in extremely cold environments. These species have likely accumulated genetic changes that help them efficiently cope with low temperatures. It is not known whether the same genes related to cold adaptation in one species would be under selection in another species. The aims of this study therefore were: to create a compendium of mammalian genes related to adaptations to a low temperature environment; to identify genes related to cold tolerance that have been subjected to independent positive selection in several species; to determine promising candidate genes/pathways/organs for further empirical research on cold adaptation in mammals.

Results

After a search for publications containing keywords: “whole genome”, “transcriptome or exome sequencing data”, and “genome-wide genotyping array data” authors looked for information related to genetic signatures ascribable to positive selection in Arctic or Antarctic mammalian species. Publications related to Human, Arctic fox, Yakut horse, Mammoth, Polar bear, and Minke whale were chosen. The compendium of genes that potentially underwent positive selection in >1 of these six species consisted of 416 genes. Twelve of them showed traces of positive selection in three species. Gene ontology term enrichment analysis of 416 genes from the compendium has revealed 13 terms relevant to the scope of this study. We found that enriched terms were relevant to three major groups: terms associated with collagen proteins and the extracellular matrix; terms associated with the anatomy and physiology of cilium; terms associated with docking. We further revealed that genes from compendium were over-represented in the lists of genes expressed in the lung and liver.

Conclusions

A compendium combining mammalian genes involved in adaptation to cold environment was designed, based on the intersection of positively selected genes from six Arctic and Antarctic species. The compendium contained 416 genes that have been positively selected in at least two species. However, we did not reveal any positively selected genes that would be related to cold adaptation in all species from our list. But, our work points to several strong candidate genes involved in mechanisms and biochemical pathways related to cold adaptation response in different species.

Electronic supplementary material

The online version of this article (10.1186/s12863-017-0580-9) contains supplementary material, which is available to authorized users.

The Promise of Molecular Autopsy in Forensic Pathology Practice

Molecular autopsy is changing the practice of forensic pathology. Under some circumstances, one must contemplate the involvement of genetic factors to help explain why someone has died unexpectedly. Such considerations most commonly occur when a young person dies by natural means. However, there are deaths that occur by nonnatural means that the forensic pathologist will be asked to investigate, which could involve natural disease that has a significant genetic underpinning. Elucidation of genetic mutations may not only further an understanding of the pathophysiology at hand, but also speak to underlying susceptibilities in an individual who dies that may not have been recognized. In addition, one may occasionally identify pathological findings that are confused for trauma that may actually be better explained by an underlying disease process. Using molecular medicine as a tool to explore such possibilities can improve the quality of death investigations and provide a new lens to probe challenging and contentious forensic cases that have proved resistant to traditional methods.

An East Asian Common Variant Vinculin P.Asp841His Was Associated With Sudden Unexplained Nocturnal Death Syndrome in the Chinese Han Population

Background

We have identified the cardiomyopathy‐susceptibility gene vinculin (VCL) mutation M94I may account for a sudden unexplained nocturnal death syndrome (SUNDS) case. We addressed whether VCL common variant D841H is associated with SUNDS.

Methods and Results

In 8 of 120 SUNDS cases, we detected an East Asian common VCL variant p.Asp841His (D841H). Comparing the H841 allele frequency of the general population in the local database (15 of 1818) with SUNDS victims (10 of 240) gives an odds ratio for SUNDS of 5.226 (95% CI, 2.321, 11.769). The VCL‐D841H variant was engineered and either coexpressed with cardiac sodium channel (SCN5A) in HEK293 cells or overexpressed in human induced pluripotent stem‐cell–derived cardiomyocytes to examine its effects on sodium channel function using the whole‐cell patch‐clamp method. In HEK293 cells, under physiological pH conditions (pH 7.4), D841H caused a 29% decrease in peak I_Na amplitude compared to wild type (WT), whereas under acidotic conditions (pH 7.0), D841H decreased further to 43% along with significant negative shift in inactivation compared to WT at pH 7.4. In induced pluripotent stem‐cell‐derived cardiomyocytes, similar effects of D841H on I_Na were observed. VCL colocalized with SCN5A at the intercalated disk in human cardiomyocytes. VCL was also confirmed to directly interact with SCN5A, and VCL‐D841H did not disrupt the association of VCL and SCN5A.

Conclusions

A VCL common variant was genetically and biophysically associated with Chinese SUNDS. The aggravation of loss of function of SCN5A caused by VCL‐D841H under acidosis supports that nocturnal sleep respiratory disorders with acidosis may play a key role in the pathogenesis of SUNDS.

Vinculin variant M94I identified in sudden unexplained nocturnal death syndrome decreases cardiac sodium current

Sudden unexplained nocturnal death syndrome (SUNDS) remains an autopsy negative disorder with unclear etiology. Vinculin (VCL) was linked to sudden arrhythmia death in VCL knockout mice prior to the appearance of cardiomyopathy. We hypothesized VCL mutations underlie risk for SUNDS. A rare heterozygous variant VCL-M94I was found in a SUNDS victim who suffered sudden nocturnal tachypnea and lacked pathogenic variants in known arrhythmia-causing genes. VCL was identified to interact with SCN5A in vitro/vivo. The VCL-M94I was co-expressed with the cardiac sodium channel in HEK293 cells and also overexpressed in induced pluripotent stem cells derived cardiomyocytes (iPSCs-CM). In HEK293 cells with pH 7.4, VCL-M94I caused ~30% decrease in peak sodium current (I_Na) amplitude compared to WT; under acidotic conditions (pH 7.0) typically found with hypoxia during sleep apnea, M94I resulted in 37% reduction in peak I_Na compared to WT and the combination of VCL-M94I and pH 7.0 decreased peak I_Na by ~56% compared to WT at pH 7.4. In iPSCs-CM, similar effects of M94I on reduction of peak I_Na were observed. This study initially shows both physical and functional interaction between VCL and cardiac sodium channel, and suggests an important role for respiratory acidosis in triggering the fatal arrhythmia underlying SUNDS.

Molecular pathological study on LRRC10 in sudden unexplained nocturnal death syndrome in the Chinese Han population

Sudden unexplained nocturnal death syndrome (SUNDS) is a perplexing disorder to both forensic pathologists and clinic physicians. Clinical features of SUNDS survivors suggested that SUNDS is similar to Brugada syndrome (BrS). Leucine-rich repeat containing 10 (LRRC10) gene was a newly identified gene linked to dilated cardiomyopathy, a disease associated with sudden cardiac death. To investigate the prevalence and spectrum of genetic variants of LRRC10 gene in SUNDS and BrS, the coding regions of LRRC10 were genetically screened in 113 sporadic SUNDS victims (from January 2005 to December 2015, 30.7 ± 7.5 years) and ten BrS patients (during January 2010 to December 2014, 38.7 ± 10.3 years) using direct Sanger sequencing. Afterwards, LRRC10 missense variant carriers were screened for a panel of 80 genes known to be associated with inherited cardiac arrhythmia/cardiomyopathy using target-captured next-generation sequencing. In this study, an in silico-predicted malignant LRRC10 mutation p.E129K was detected in one SUNDS victim without pathogenic rare variant in a panel of 80 arrhythmia/cardiomyopathy-related genes. We also provided evidence to show that rare variant p.P69L might contribute to the genetic cause for one SUNDS victim and two BrS family members. This is the first report of genetic screening of LRRC10 in Chinese SUNDS victims and BrS patients. LRRC10 may be a new susceptible gene for SUNDS, and LRRC10 variant was initially and genetically linked to BrS-associated arrhythmia.

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.