Sudden infant death syndrome and inherited cardiac conditions

Known pathogenic gene variants and new candidates detected in sudden unexpected infant death using whole genome sequencing

The purpose of this study is to gain insights into potential genetic factors contributing to the infant's vulnerability to Sudden Unexpected Infant Death (SUID). Whole Genome Sequencing (WGS) was performed on 144 infants that succumbed to SUID, and 573 healthy adults. Variants were filtered by gnomAD allele frequencies and predictions of functional consequences. Variants of interest were identified in 88 genes, in 64.6% of our cohort. Seventy-three of these have been previously associated with SIDS/SUID/SUDP. Forty-three can be characterized as cardiac genes and are related to cardiomyopathies, arrhythmias, and other conditions. Variants in 22 genes were associated with neurologic functions. Variants were also found in 13 genes reported to be pathogenic for various systemic disorders and in two genes associated with immunological function. Variants in eight genes are implicated in the response to hypoxia and the regulation of reactive oxygen species (ROS) and have not been previously described in SIDS/SUID/SUDP. Seventy-two infants met the triple risk hypothesis criteria. Our study confirms and further expands the list of genetic variants associated with SUID. The abundance of genes associated with heart disease and the discovery of variants associated with the redox metabolism have important mechanistic implications for the pathophysiology of SUID.

Investigating cardiac genetic background in sudden infant death syndrome (SIDS)

Sudden infant death syndrome (SIDS) is still the leading cause of death for newborns in developed countries. The pathophysiological mechanisms have not been fully clarified, but in some of SIDS cases variants of genes associated with inherited cardiac conditions are found. In this study, an analysis of SCD-related genes was performed to determine the prevalence of rare pathogenic (P) or likely pathogenic (LP) variants that could provide an unambiguous explanation for the fatal event. A cohort of 76 SIDS cases underwent Next-Generation Sequencing (NGS) analysis with a custom panel of SCD-related genes. Rare variants were classified according to the guidelines provided by the American College of Medical Genetics and Genomics (ACMG) and the specifications of the ClinGen association. Post-mortem genetic testing identified 50 (65.8%) carriers of at least one variant in SCD genes. 104 rare genetic variants were found, 65.4% in genes encoding structural proteins. Only 4 out of 76 cases (5.3%) hosted at least a P or LP variant found in genes with structural or structural/arrhythmogenic functions (SLC22A5, SCN5A, MYL3and TTN). 99 variants were classified as of uncertain significance (VUS). The difference in the distribution of variants between gene groups by function was not statistically significant (chi square, p = 0,219). Despite this, most of the variants concerned structural genes that were supposed to have a close interaction with ion channels, thus providing an explanation for the arrhythmic event. Segregation analysis, reclassification of VUS variants and identification of new associated genes could clarify the implications of the current findings.

Recurrent familial case of early childhood sudden death: Complex post mortem genetic investigations

INTRODUCTION

Sudden Unexplained Death in Childhood (SUDC) needs to be fully assessed considering its impact on the family, parents and siblings. Inborn Errors of Metabolism (IEM) such as Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCADD) should be taken into consideration when SUDC occurres. Our aim is to present a family with two successive SUDC and to discuss the post-mortem genetics investigations revealing an IEM implication.

CASES REPORT

A complete autopsy with genetic testing was performed when the proband, a 4-year-old girl, died. A few years previously, her older brother had died at the same age and off the same condition. Years later, his exhumation was necessary in order to perform a post-mortem diagnosis.The two siblings were revealed to have had the same pathogenic genotype of the ACADM gene, heterozygous substitutions in ACADM (NM_000016.5): c.985 A>G p.(Lys329Glu) and c.347 G>A p.(Cys116Tyr). In addition, they also both carried a VUS in TECRL, a gene implicated in Catecholaminergic Polymorphic Tachycardia Ventricular (CPVT) and SUDC.

CONCLUSION

We illustrate the importance of exome analyses for investigating unexplained sudden death, especially in children, with the possible impact for genetic counselling in the family. The finding of the implication of ACADM gene in this case, raises likely responsibility of the public health system in countries such as France, who delayed implementation of new born screening for these conditions. Exome analyses in this case detected unexpected complexity in interpretation linked to the identification of a second candidate gene for SUDC.

Autopsy of all young sudden death cases is important to increase survival in family members left behind

Sudden cardiac death (SCD) is an important public health problem worldwide, accounting for an estimated 6-20% of total mortality. A significant proportion of SCD is caused by inherited heart disease, especially among the young. An autopsy is crucial to establish a diagnosis of inherited heart disease, allowing for subsequent identification of family members who require cardiac evaluation. Autopsy of cases of unexplained sudden death in the young is recommended by both the European Society of Cardiology and the American Heart Association. Overall autopsy rates, however, have been declining in many countries across the globe, and there is a lack of skilled trained pathologists able to carry out full autopsies. Recent studies show that not all cases of sudden death in the young are autopsied, likely due to financial, administrative, and organizational limitations as well as awareness among police, legal authorities, and physicians. Consequently, diagnoses of inherited heart disease are likely missed, along with the opportunity for treatment and prevention among surviving relatives. This article reviews the evidence for the role of autopsy in sudden death, how the cardiologist should interpret the autopsy-record, and how this can be integrated and implemented in clinical practice. Finally, we identify areas for future research along with potential for healthcare reform aimed at increasing autopsy awareness and ultimately reducing mortality from SCD.

Brainstem depolarization-induced lethal apnea associated with gain-of-function SCN1AL263V is prevented by sodium channel blockade

Apneic events are frightening but largely benign events that often occur in infants. Here, we report apparent life-threatening apneic events in an infant with the homozygous SCN1AL263V missense mutation, which causes familial hemiplegic migraine type 3 in heterozygous family members, in the absence of epilepsy. Observations consistent with the events in the infant were made in an Scn1aL263V knock-in mouse model, in which apnea was preceded by a large brainstem DC-shift, indicative of profound brainstem depolarization. The L263V mutation caused gain of NaV1.1 function effects in transfected HEK293 cells. Sodium channel blockade mitigated the gain-of-function characteristics, rescued lethal apnea in Scn1aL263V mice, and decreased the frequency of severe apneic events in the patient. Hence, this study shows that SCN1AL263V can cause life-threatening apneic events, which in a mouse model were caused by profound brainstem depolarization. In addition to being potentially relevant to sudden infant death syndrome pathophysiology, these data indicate that sodium channel blockers may be considered therapeutic for apneic events in patients with these and other gain-of-function SCN1A mutations.

Sudden cardiac arrest in infants and children: proposal for a diagnostic workup to identify the etiology. An 18-year multicenter evaluation in the Netherlands

Sudden cardiac arrest (SCA) studies are often population-based, limited to sudden cardiac death, and excluding infants. To guide prevention opportunities, it is essential to be informed of pediatric SCA etiologies. Unfortunately, etiologies frequently remain unresolved. The objectives of this study were to determine paediatric SCA etiology, and to evaluate the extent of post-SCA investigations and to assess the performance of previous cardiac evaluation in detecting conditions predisposing to SCA. In a retrospective cohort (2002-2019), all children 0-18 years with out-of-hospital cardiac arrest (OHCA) referred to Erasmus MC Sophia Children's Hospital or the Amsterdam UMC (tertiary-care university hospitals), with cardiac or unresolved etiologies were eligible for inclusion. SCA etiologies, cardiac and family history and etiologic investigations in unresolved cases were assessed. The etiology of arrest could be determined in 52% of 172 cases. Predominant etiologies in children ≥ 1 year (n = 99) were primary arrhythmogenic disorders (34%), cardiomyopathies (22%) and unresolved (32%). Events in children < 1 year (n = 73) were largely unresolved (70%) or caused by cardiomyopathy (8%), congenital heart anomaly (8%) or myocarditis (7%). Of 83 children with unresolved etiology a family history was performed in 51%, an autopsy in 51% and genetic testing in 15%. Pre-existing cardiac conditions presumably causative for SCA were diagnosed in 9%, and remained unrecognized despite prior evaluation in 13%.

CONCLUSION

SCA etiology remained unresolved in 83 of 172 cases (48%) and essential diagnostic investigations were often not performed. Over one-fifth of SCA patients underwent prior cardiac evaluation, which did not lead to recognition of a cardiac condition predisposing to SCA in all of them. The diagnostic post-SCA approach should be improved and the proposed standardized pediatric post-SCA diagnostics protocol may ensure a consistent and systematic evaluation process increasing the diagnostic yield.

WHAT IS KNOWN

• Arrests in infants remain unresolved in most cases. In children > 1 year, predominant etiologies are primary arrhythmia disorders, cardiomyopathy and myocarditis. • Studies investigating sudden cardiac arrest are often limited to sudden cardiac death (SCD) in 1 to 40 year old persons, excluding infants and successfully resuscitated children.

WHAT IS NEW

• In patients with unresolved SCA events, the diagnostic work up was often incompletely performed. • Over one fifth of victims had prior cardiac evaluation before the arrest, with either a diagnosed cardiac condition (9%) or an unrecognized cardiac condition (13%).

Known pathogenic gene variants and new candidates detected in Sudden Unexpected Infant Death using Whole Genome Sequencing

Purpose

To gain insights into potential genetic factors contributing to the infant's vulnerability to Sudden Unexpected Infant Death (SUID).

Methods

Whole Genome Sequencing (WGS) was performed on 145 infants that succumbed to SUID, and 576 healthy adults. Variants were filtered by gnomAD allele frequencies and predictions of functional consequences.

Results

Variants of interest were identified in 86 genes, 63.4% of our cohort. Seventy-one of these have been previously associated with SIDS/SUID/SUDP. Forty-three can be characterized as cardiac genes and are related to cardiomyopathies, arrhythmias, and other conditions. Variants in 22 genes were associated with neurologic functions. Variants were also found in 13 genes reported to be pathogenic for various systemic disorders. Variants in eight genes are implicated in the response to hypoxia and the regulation of reactive oxygen species (ROS) and have not been previously described in SIDS/SUID/SUDP. Seventy-two infants met the triple risk hypothesis criteria (Figure 1).

Conclusion

Our study confirms and further expands the list of genetic variants associated with SUID. The abundance of genes associated with heart disease and the discovery of variants associated with the redox metabolism have important mechanistic implications for the pathophysiology of SUID.

The genetic approach to stillbirth: A »systematic review«

Unexplained stillbirth is defined as a stillbirth with no known cause after the exclusion of common causes, including obstetric complications, infections, placental insufficiency or abruption, umbilical cord complications, and congenital abnormalities with or without known genetic cause. More than 60% of stillbirth cases remain unexplained. The aim of this systematic review was to investigate the known genetic causes of unexplained stillbirth cases and to evaluate the current position and future directions for the use of genetic and genomic testing in expanding the knowledge in this field. A systematic search through several databases was performed using the keywords genetics and stillbirths in humans. Different methods to detect various types of causal genetic aberrations have been used in the past decades, from standard karyotyping to novel methods such as chromosomal microarray analysis and next generation sequencing technologies. Apart from common chromosomal aneuploidies, a promising hypothesis about genetic causes included genes related to cardiomyopathies and channelopathies. However, these were tested in the research settings, since molecular karyotyping is currently the standard approach in the routine evaluation of genetic causes of stillbirth. Hereby, we provide evidence that expanding knowledge using novel genetic and genomic testing might uncover new genetic causes of unexplained stillbirth.

Risk of Sudden Infant Death Syndrome Among Siblings of Children Who Died of Sudden Infant Death Syndrome in Denmark

IMPORTANCE

Sudden infant death syndrome (SIDS) remains a leading cause of death during the first year of life. The etiology of SIDS is complex and remains largely unknown.

OBJECTIVE

To evaluate whether siblings of children who died of SIDS have a higher risk of SIDS compared with the general pediatric population.

DESIGN, SETTING, AND PARTICIPANTS

This register-based cohort study used Danish nationwide registers. Participants were all infants (<1 year) in Denmark between January 1, 1978, and December 31, 2016, including siblings of children who died of SIDS. Siblings were followed up from the index cases' date of SIDS, date of birth, or immigration, whichever came first, and until age 1 year, emigration, developing SIDS, death, or study end. The median (IQR) follow-up was 1 (1-1) year. Data analysis was conducted from January 2017 to October 2022.

MAIN OUTCOMES AND MEASURES

Standardized incidence ratios (SIRs) of SIDS were calculated with Poisson regression models relative to the general population.

RESULTS

In a population of 2 666 834 consecutive births (1 395 199 [52%] male), 1540 infants died of SIDS (median [IQR] age at SIDS, 3 [2-4] months) during a 39-year study period. A total of 2384 younger siblings (cases) to index cases (first sibling with SIDS) were identified. A higher rate of SIDS was observed among siblings compared with the general population, with SIRs of 4.27 (95% CI, 2.13-8.53) after adjustment for sex, age, and calendar year and of 3.50 (95% CI, 1.75-7.01) after further adjustment for mother's age (<29 years vs ≥29 years) and education (high school vs after high school).

CONCLUSIONS AND RELEVANCE

In this nationwide study, having a sibling who died of SIDS was associated with a 4-fold higher risk of SIDS compared with the general population. Shared genetic and/or environmental factors may contribute to the observed clustering of SIDS. The family history of SIDS should be considered when assessing SIDS risk in clinical settings. A multidisciplinary genetic evaluation of families with SIDS could provide additional evidence.

Machine Learning Model Based on Lipidomic Profile Information to Predict Sudden Infant Death Syndrome

Sudden infant death syndrome (SIDS) represents the leading cause of death in under one year of age in developing countries. Even in our century, its etiology is not clear, and there is no biomarker that is discriminative enough to predict the risk of suffering from it. Therefore, in this work, taking a public dataset on the lipidomic profile of babies who died from this syndrome compared to a control group, a univariate analysis was performed using the Mann–Whitney U test, with the aim of identifying the characteristics that enable discriminating between both groups. Those characteristics with a p-value less than or equal to 0.05 were taken; once these characteristics were obtained, classification models were implemented (random forests (RF), logistic regression (LR), support vector machine (SVM) and naive Bayes (NB)). We used seventy percent of the data for model training, subjecting it to a cross-validation (k = 5) and later submitting to validation in a blind test with 30% of the remaining data, which allows simulating the scenario in real life—that is, with an unknown population for the model. The model with the best performance was RF, since in the blind test, it obtained an AUC of 0.9, specificity of 1, and sensitivity of 0.8. The proposed model provides the basis for the construction of a SIDS risk prediction computer tool, which will contribute to prevention, and proposes lines of research to deal with this pathology.

Sudden Unexpected Death in Infancy [SUDI]: What the clinician, pathologist, coroner and researchers want to know

The loss of an apparently healthy infant is confronting for any family, puzzling for a clinician and challenging for the pathologist charged with the task of demonstrating a cause for death. The term "cot death" evolved to "sudden infant death syndrome" [SIDS] and now "sudden unexpected death in infancy [SUDI]" as the epidemiology and pathology of infant death changed. Community interventions were successful in changing sleep practices for young babies. The current research focus is on understanding genetic predispositions to unexpected death in early childhood. Whilst much has been achieved in reducing the infant mortality rate from SUDI by between 50%, and 80% in some countries, over the last 30 years, there remain challenges for improving rates of accurate diagnosis and reaching out to more vulnerable families with clearly modifiable risk factors for SUDI. These challenges directly involve the clinician through taking a systematic and detailed history and better standardised death scene evaluations with specifically accredited assessors. Better knowledge regarding circumstances of SUDI cases will help Coroners and researchers provide answers for grieving families now, and in the future contribute to further reductions in the rate of SUDI in communities across the world.

SCN1A Mutation-Beyond Dravet Syndrome: A Systematic Review and Narrative Synthesis

Background:SCN1A is one of the most common epilepsy genes. About 80% of SCN1A gene mutations cause Dravet syndrome (DS), which is a severe and catastrophic epileptic encephalopathy. More than 1,800 mutations have been identified in SCN1A. Although it is known that SCN1A is the main cause of DS and genetic epilepsy with febrile seizures plus (GEFS+), there is a dearth of information on the other related diseases caused by mutations of SCN1A.

Objective: The aim of this study is to systematically review the literature associated with SCN1A and other non-DS-related disorders.

Methods: We searched PubMed and SCOPUS for all the published cases related to gene mutations of SCN1A until October 20, 2021. The results reported by each study were summarized narratively.

Results: The PubMed and SCOPUS search yielded 2,889 items. A total of 453 studies published between 2005 and 2020 met the final inclusion criteria. Overall, 303 studies on DS, 93 on GEFS+, three on Doose syndrome, nine on the epilepsy of infancy with migrating focal seizures (EIMFS), six on the West syndrome, two on the Lennox–Gastaut syndrome (LGS), one on the Rett syndrome, seven on the nonsyndromic epileptic encephalopathy (NEE), 19 on hemiplegia migraine, six on autism spectrum disorder (ASD), two on nonepileptic SCN1A-related sudden deaths, and two on the arthrogryposis multiplex congenital were included.

Conclusion: Aside from DS, SCN1A also causes other epileptic encephalopathies, such as GEFS+, Doose syndrome, EIMFS, West syndrome, LGS, Rett syndrome, and NEE. In addition to epilepsy, hemiplegic migraine, ASD, sudden death, and arthrogryposis multiplex congenital can also be caused by mutations of SCN1A.

Epidemiology of sudden infant death syndrome in Mexico, 2005-2020

BACKGROUND

Sudden Infant Death Syndrome (SIDS) constitutes one of the main causes of mortality in children under one year of age in developed countries; it's frequency to varies geographically. In Mexico the real incidence of SIDS is not known.

METHODS

National databases of deaths in children under one year of age, from 2005 to 2020, were analyzed, due to Sudden Unexpected Infant Death (SUID) [SIDS (R95), accidental suffocation in a sleeping environment (W75), and other ill-defined and unspecified causes of mortality (R99), according to the International Classification of Diseases, tenth revision (ICD 10)]. Mortality rates per year of occurrence due to SUID and their subcategories were calculated. Simple frequencies of SIDS were obtained per year and month of occurrence, state of residence, age, place of death, and access to social security services.

RESULTS

In the study period 473,545 infant deaths occurred; 7,714 (1.62%) deaths were due to SUID; of these, 6,489 (84%) were due to SIDS, which is among the 10 leading causes of infant death in Mexico. The average mortality rate for SUID was 22.4/100,000 live births, for SIDS was 18.8/100,000 live births. Mortality rates within the states were variable, ranging from 2.4/100,000 to 105.1/100,000 live births. In 81% of SIDS records there was no autopsy; 38% of deaths due to SIDS occurred in infants under one month of age, up to 87% of deaths occurred in families without social security services or it was unknown, and 76.2% of deaths occurred at home. Deaths were more frequent during the last months of autumn and during winter.

CONCLUSION

In Mexico there is an underregistry of SIDS as cause of death, along with other SUID categories. Health workers need to be trained to improve diagnosis and data registration, including the practice of autopsies; additionally, it is necessary to implement a public health campaign.

De novo mutations in childhood cases of sudden unexplained death that disrupt intracellular Ca2+ regulation

Approximately 400 United States children 1 y of age and older die suddenly from unexplained causes annually. We studied whole-exome sequence data from 124 “trios” (decedent child and living parents) to identify genetic risk factors. Nonsynonymous mutations, mostly de novo (present in child but absent in both biological parents), were highly enriched in genes associated with cardiac and seizure disorders relative to controls, and contributed to 9% of deaths. We found significant overtransmission of loss-of-function or pathogenic missense variants in cardiac and seizure disorder genes. Most pathogenic variants were de novo in origin, highlighting the importance of trio studies. Many of these pathogenic de novo mutations altered a protein network regulating calcium-related excitability at submembrane junctions in cardiomyocytes and neurons.

Sudden unexplained death in childhood (SUDC) is an understudied problem. Whole-exome sequence data from 124 “trios” (decedent child, living parents) was used to test for excessive de novo mutations (DNMs) in genes involved in cardiac arrhythmias, epilepsy, and other disorders. Among decedents, nonsynonymous DNMs were enriched in genes associated with cardiac and seizure disorders relative to controls (odds ratio = 9.76, P = 2.15 × 10⁻⁴). We also found evidence for overtransmission of loss-of-function (LoF) or previously reported pathogenic variants in these same genes from heterozygous carrier parents (11 of 14 transmitted, P = 0.03). We identified a total of 11 SUDC proband genotypes (7 de novo, 1 transmitted parental mosaic, 2 transmitted parental heterozygous, and 1 compound heterozygous) as pathogenic and likely contributory to death, a genetic finding in 8.9% of our cohort. Two genes had recurrent missense DNMs, RYR2 and CACNA1C. Both RYR2 mutations are pathogenic (P = 1.7 × 10⁻⁷) and were previously studied in mouse models. Both CACNA1C mutations lie within a 104-nt exon (P = 1.0 × 10⁻⁷) and result in slowed L-type calcium channel inactivation and lower current density. In total, six pathogenic DNMs can alter calcium-related regulation of cardiomyocyte and neuronal excitability at a submembrane junction, suggesting a pathway conferring susceptibility to sudden death. There was a trend for excess LoF mutations in LoF intolerant genes, where ≥1 nonhealthy sample in denovo-db has a similar variant (odds ratio = 6.73, P = 0.02); additional uncharacterized genetic causes of sudden death in children might be discovered with larger cohorts.

Massively Parallel Sequencing of 43 Arrhythmia Genes in a Selected SUDI Cohort from Cape Town

Sudden unexpected death in infants (SUDI) is a devastating event, and unfortunately occurs frequently in developing countries. The emerging molecular autopsy has added value to post-mortem investigations, where genetic variants were able to explain the unexpected demise. Many of these variants have been found in genes involved in arrythmia pathways. The aim of this study was to sequence 43 genes previously associated with cardiac arrhythmia in a selected cohort of SUDI cases (n = 19) in South Africa. A total of 335 variants were found among the 19 infants, of which four were novel. The variants were classified as “likely pathogenic” (n = 1), “variant of unknown significance” (n = 54), “likely benign” (n = 56) or “benign” (n = 224). The likely pathogenic variant was LMNA NM_170707.2:c.1279C > T (p.Arg427Cys) and was found in a 3-week-old male infant of African ancestry. Variants in LMNA have previously been associated with dilated cardiomyopathy, with a typical age of onset in adulthood; therefore, this may be the first report in an infant. The yield of pathogenic or likely pathogenic variants in the classic genes typically associated with channelopathies and sudden death, was less in this study compared with other settings. This finding highlights the importance of population-specific research to develop a molecular autopsy which is locally relevant.

Seizure-related deaths in children: The expanding spectrum

Although seizures are common in children, they are often overlooked as a potential cause of death. Febrile and nonfebrile seizures can be fatal in children with or without an epilepsy diagnosis and may go unrecognized by parents or physicians. Sudden unexpected infant deaths, sudden unexplained death in childhood, and sudden unexpected death in epilepsy share clinical, neuropathological, and genetic features, including male predominance, unwitnessed deaths, death during sleep, discovery in the prone position, hippocampal abnormalities, and variants in genes regulating cardiac and neuronal excitability. Additionally, epidemiological studies reveal that miscarriages are more common among individuals with a personal or family history of epilepsy, suggesting that some fetal losses may result from epileptic factors. The spectrum of seizure-related deaths in pediatrics is wide and underappreciated; accurately estimating this mortality and understanding its mechanism in children is critical to developing effective education and interventions to prevent these tragedies.

The role of sodium channels in sudden unexpected death in pediatrics

BACKGROUND

Sudden Unexpected Death in Pediatrics (SUDP) is a tragic event, likely caused by the complex interaction of multiple factors. The presence of hippocampal abnormalities in many children with SUDP suggests that epilepsy-related mechanisms may contribute to death, similar to Sudden Unexplained Death in Epilepsy. Because of known associations between the genes SCN1A and SCN5A and sudden death, and shared mechanisms and patterns of expression in genes encoding many voltage-gated sodium channels (VGSCs), we hypothesized that individuals dying from SUDP have pathogenic variants across the entire family of cardiac arrhythmia- and epilepsy-associated VGSC genes.

METHODS

To address this hypothesis, we evaluated whole-exome sequencing data from infants and children with SUDP for variants in VGSC genes, reviewed the literature for all SUDP-associated variants in VGSCs, applied a novel paralog analysis to all variants, and evaluated all variants according to American College of Medical Genetics and Genomics (ACMG) guidelines.

RESULTS

In our cohort of 73 cases of SUDP, we assessed 11 variants as pathogenic in SCN1A, SCN1B, and SCN10A, genes with long-standing disease associations, and in SCN3A, SCN4A, and SCN9A, VGSC gene paralogs with more recent disease associations. From the literature, we identified 82 VGSC variants in SUDP cases. Pathogenic variants clustered at conserved amino acid sites intolerant to variation across the VGSC genes, which is unlikely to occur in the general population (p < .0001). For 54% of variants previously reported in literature, we identified conflicting evidence regarding pathogenicity when applying ACMG criteria and modern population data.

CONCLUSION

We report variants in several VGSC genes in cases with SUDP, involving both arrhythmia- and epilepsy-associated genes. Accurate variant assessment as well as future studies are essential for an improved understanding of the contribution of sodium channel-related variants to SUDP.

Genetic innovations and our understanding of stillbirth

Stillbirth after 20 weeks gestation happens in 1 in 200 pregnancies and occurs more commonly than neonatal loss and sudden infant death syndrome (SIDs) combined. The stillbirth rate is several times greater in low as opposed to high-resource countries. However, among high-resource countries, although a lower overall stillbirth rate exists, there has been little change for several decades. Molecular genetic technologies are emerging as important contributors to our understanding of stillbirth. Initially, genetic etiologies included alterations in chromosome number or structure such as aneuploidy and microduplications and deletions. More recently, next-generation sequencing analysis in two genetic conditions, Smith Lemli Optiz Syndrome (SLOs) and the channelopathy disorders (such as long QT syndrome (LQTS)) provide examples into the association of pathogenic gene variants with stillbirth. Although these specific conditions individually account for only a small number of stillbirths, investigating these disorders provides a new and innovative approach for further understanding genetic contributors to adverse pregnancy outcomes. Our knowledge of the role of genetic disease as an etiology for stillbirth is elementary. Genomic interrogation of maternal-fetal genotypes, gene-gene, and genotype-environment interaction is lacking in stillbirth research. At the DNA sequence level, further investigation of variants of unknown significance is an opportunity for exploration of biologic pathways of importance to pregnancy loss. This review concentrates on SLO as an example of a single gene disorder with a high carrier but low affected liveborn proband rate. The channelopathy disorders are included as initial examples of genetic conditions with variable presentation including an association with sudden infant death syndrome. Highlighted are the challenges when numerous genes and variants are involved, and the task of assigning pathogenicity. The advantages and limitations of genetic evaluations are presented and avenues for further research considered.

A standardized postmortem protocol to assess the real burden of sudden infant death syndrome

Sudden unexpected infant death (SUID) is a major cause of death in infants < 1 year of age. Sudden infant death syndrome (SIDS) is a SUID still unexplained after post-mortem examination. In 2014, a protocol of post-mortem investigation was introduced to assess both the prevalence and the etiopathogenesis of SUID. Our aim was to compare SUID data before and after the application of a standardized autopsy protocol of investigation. In the time interval 2004-2018, SUID cases occurring in the Veneto Region, North-East Italy, were referred to our Core Lab. Since 2014, a complete autopsy was performed, including gross and histological study with toxicologic and molecular analysis carried out at the referral center. A total of 36 SUIDs (22 M, mean age 95.5 ± 80 days), 17 before (group A) and 19 after (group B) 2014, were collected. In group A, only 1 (6%) resulted as explained SUID, due to lymphocytic myocarditis and 16 (94%) were SIDS. In group B, 8 were SIDS (42%) and 11 (58%) explained SUID cases (p < 0.01), consisting of interstitial pneumonia and bronchiolitis in 9 and lymphocytic myocarditis in 2 cases. Molecular analysis was positive for viruses in 8 of them (73%). In conclusion, since the application of a standardized protocol of post-mortem investigation, inflammatory, mostly infective, cardio-pulmonary diseases have been identified as the most common cause of SUID, with SIDS falling from 94 to 42% of SUID. Efforts must be made to implement a uniform autopsy protocol to provide reliable epidemiological data on SIDS.

Potential Role of Febrile Seizures and Other Risk Factors Associated With Sudden Deaths in Children

IMPORTANCE

Sudden unexplained death in childhood (SUDC) is the fifth leading category of death among toddlers but remains underrecognized and inadequately studied.

OBJECTIVE

To assess the potential role of febrile seizures (FS) and other risk factors associated with SUDC and describe the epidemiology, mechanisms, and prevention of SUDC.

DESIGN, SETTING, AND PARTICIPANTS

This case series study reviewed 622 consecutive sudden child death cases aged 1 to 17 years from 2001 to 2017 from 18 countries. Data were collected from family members of children who died suddenly; these families voluntarily registered with the SUDC Foundation. Data analysis was conducted from November 2017 to February 2019.

MAIN OUTCOME MEASURES

Certified manner of death characterized as accident, natural, or undetermined.

RESULTS

A total of 391 families with decedents aged 1 to 6 years completed a comprehensive interview on medical and social histories, and circumstances of death with forensic evaluations revealing a cause of death (sudden explained death in childhood [SEDC]) or no cause of death (SUDC). Of these children, 231 (59.1%) were male, the mean (SD) age at death was 24.9 (12.8) months, and 104 (26.6%) had a history of FS. Compared with the general population FS prevalence (2%-5%), FS prevalence among SUDC (28.8%; 95% CI, 23.3%-34.2%) and SEDC (22.1%; 95% CI, 14.8%-29.3%) were elevated. The odds of death during sleep was 4.6-fold higher in SUDC than in SEDC cases (odds ratio, 4.61; 95% CI, 1.92-11.09; adjusted P = .008). The siblings of SUDC cases were followed up for 3144 life-years, and none died prematurely from SUDC.

CONCLUSIONS AND RELEVANCE

This analysis of the largest SUDC cohort confirmed an increased FS rate and found significantly increased rates of FS among SEDC. This study suggests that seizures may contribute to some SUDC and SEDC deaths. The risk of sudden death in a sibling was low. To develop and assess preventive strategies, population-based studies are needed to define the epidemiology and spectrum of risk factors and identify biomarkers of patients with FS at high risk of sudden death.

Sudden Unexpected Death and the Mammalian Dive Response: Catastrophic Failure of a Complex Tightly Coupled System

In tightly coupled complex systems, when two or more factors or events interact in unanticipated ways, catastrophic failures of high-risk technical systems happen rarely, but quickly. Safety features are commonly built into complex systems to avoid disasters but are often part of the problem. The human body may be considered as a complex tightly coupled system at risk of rare catastrophic failure (sudden unexpected death, SUD) when certain factors or events interact. The mammalian dive response (MDR) is a built-in safety feature of the body that normally conserves oxygen during acute hypoxia. Activation of the MDR is the final pathway to sudden cardiac (SCD) in some cases of sudden infant death syndrome (SIDS), sudden unexpected death in epilepsy (SUDEP), and sudden cardiac death in water (SCDIW, fatal drowning). There is no single cause in any of these death scenarios, but an array of, unanticipated, often unknown, factors or events that activate or interact with the mammalian dive reflex. In any particular case, the relevant risk factors or events might include a combination of genetic, developmental, metabolic, disease, environmental, or operational influences. Determination of a single cause in any of these death scenarios is unlikely. The common thread among these seemingly different death scenarios is activation of the mammalian dive response. The human body is a complex tightly coupled system at risk of rare catastrophic failure when that "safety feature" is activated.

Electrocardiographic Assessment and Genetic Analysis in Neonates: a Current Topic of Discussion

Background:

Sudden death of a newborn is a rare entity, which may be caused by genetic cardiac arrhythmias. Among these diseases, Long QT syndrome is the most prevalent arrhythmia in neonates, but other diseases such as Brugada syndrome, Short QT syndrome and Catecholaminergic Polymorphic Ventricular Tachycardia also cause sudden death in infants. All these entities are charac-terized by well-known alterations in the electrocardiogram and the first symptom of the disease may be an unexpected death. Despite the low prevalence of these diseases, the performance of an electro-cardiogram in the first hours or days after birth could help identify these electrical disruptions and adopt preventive measures. In recent years, there has been an important impulse by some experts in the scientific community towards the initiation of a newborn electrocardiogram-screening program, for the detection of these electrocardiographic abnormalities. In addition, the use of genetic analysis in neonates could identify the cause of these heart alterations. Identification of relatives carrying the ge-netic alteration associated with the disease allows adoption of measures to prevent lethal episodes.

Conclusion:

Recent technological advances enable a comprehensive genetic screening of a large number of genes in a cost-effective way. However, the interpretation of genetic data and its translation into clinical practice are the main challenges for cardiologists and geneticists. However, there is im-portant controversy as to the clinical value, and cost-effectiveness of the use of electrocardiogram as well as of genetic testing to detect these cases. Our review focuses on these current matters of argue.

Whole-Exome Sequencing Identifies a Novel Mutation (p.L320R) of Alpha-Actinin 2 in a Chinese Family with Dilated Cardiomyopathy and Ventricular Tachycardia

Dilated cardiomyopathy (DCM) is a severe cardiovascular disease which can lead to heart failure and sudden cardiac death (SCD). The typical feature of DCM is left ventricular enlargement or dilatation. In some conditions, DCM and arrhythmia can occur concurrently, apparently promoting the prevalence of SCD. According to previous studies, mutations in more than 100 genes have been detected in DCM and/or arrhythmia patients. Here, we report a Chinese family with typical DCM, ventricular tachycardia, syncope, and SCD. Using whole-exome sequencing, a novel, likely pathogenic mutation (c.959T>G/p.L320R) of actinin alpha 2 (ACTN2) was identified in all affected family members. This novel mutation was also predicted to be disease-causing by MutationTaster, SIFT, and Polyphen-2. Our study not only expands the spectrum of ACTN2 mutations and contributes to the genetic diagnosis and counseling of the family, but also provides a new case with overlap phenotype that may be caused by the ACTN2 variant.

Evidence for an association of interferon gene variants with sudden infant death syndrome

BACKGROUND

There is evidence that inflammation plays a role in the etiology of sudden infant death syndrome (SIDS). Immune system dysregulation seems to be the background of higher infection susceptibility in SIDS infants. This phenotype is possibly determined by genetic factors.

METHODS

Twenty-three single nucleotide polymorphisms (SNPs) in the following 13 candidate genes governing the immune system were successfully genotyped in 251 Caucasian SIDS cases and 336 controls from Germany: ADAR1, CSF2RB, DDX58, IFNA1, IFNA21, IFNA8, IFNAR2, IFNG, IL6, MX2, OAS1, OAS3, and TNFA. Associations between genotypes and SIDS were then statistically evaluated using logistic regression analyses.

RESULTS

Overall analysis revealed statistically significant results for two variants in interferon gamma (IFNG) (rs2069705: OR 1.40 (1.07; 1.83), p = 0.01; and rs2069727: OR 0.75 (0.59; 0.96), p = 0.02) and for one variant in interferon alpha 8 (IFNA8) (rs1330321: OR 1.85 (1.06; 3.21), p = 0.03). Haplotype analyses identified a three-marker risk IFNG haplotype rs2069727-rs2069718-rs2069705 associated with SIDS (OR = 1.62, 95% CI 1.23-2.13; p = 0.0003). Subgroup associations were found for variants in adenosine deaminase acting on RNA1 (ADAR1), 2',5'-oligoadenylate synthetase-1 (OAS1) and colony stimulating factor 2 receptor beta common subunit (CSF2RB).

CONCLUSION

In summary, this large study of 251 SIDS cases for common variants in 13 candidate genes governing the immune system has provided first evidence for a role of IFNG in the etiology of SIDS and should stimulate further research into the clinicopathological relevance of immunomodulatory genes for this fatal syndrome.

Peri-mortem evaluation of infants who die without a diagnosis: focus on advances in genomic technology

Infants who die within the first weeks to months of life may have genetic disorders, though many die without a confirmed diagnosis. Non-genetic conditions may also be responsible for unexplained infant deaths, and the diagnosis may be reliant upon studies performed in the peri-mortem period. Neonatologists, obstetricians, or pediatricians caring for these children and their families may be unsure of which investigations can and should be performed in the setting of a newborn or infant who is dying or has died. Recent advances in genomic sequencing technology may provide additional diagnostic options, though the interpretation of genetic variants discovered by this technique may be contingent upon clinical phenotype information that is obtained peri-mortem or upon autopsy. We have reviewed the current literature concerning the evaluation of an unexplained neonatal or infantile demise and synthesized a diagnostic approach, with a focus on the contribution of new and emerging genomic technologies.

A Systematic Review of Molecular Autopsy Studies in Sudden Infant Death Cases

Sudden unexpected death is an upsetting event, which can remain unexplained even after post-mortem investigation. Internationally, molecular autopsies have shown to resolve up to 44% of unexplained cases; however, it is currently unclear how many of these were infants. This systematic literature review showed that significantly fewer infant cases were resolved (median: 4%) compared with cohorts of 1 to 45 years old (median: 32%). Further, no study involving indigenous African participants has yet been published. Overall, molecular autopsies hold immense value to living family members and is motivation to explore new avenues in infant cohorts.

Retrospective Genetic Analysis of 200 Cases of Sudden Infant Death Syndrome and Its Relationship with Long QT Syndrome in Korea

BACKGROUND

There has been a campaign by the National Education on Sleeping Habits and Living Environment, to reduce the incidence of sudden infant death syndrome (SIDS). However, more than 100 infants die suddenly and unexplainably before the age of 1 year in Korea. Long QT syndrome (LQTS), an inheritable cardiac disease, has been reported to likely be associated with up to 14% of SIDS cases. However, genetic studies of the association between SIDS and LQTS have not yet been conducted in Korea.

METHODS

We conducted genetic analysis using genomic DNA extracted from paraffin-embedded tissue blocks from 200 SIDS cases autopsied between 2005 and 2013. We analyzed the following genetic mutations associated with LQTS, KCNQ1, SCN5A, KCNE1, KCNE2, KCNJ2, and CAV3.

RESULTS

Of the 200 SIDS cases, 58% involved male infants (116 male and 84 female infants, respectively), the mean age was 140 days (median, 107 days; range, 24-270 days), and they were all of Asian-Korean ethnicity. SIDS IA category criteria comprised 45 cases (22.5%) while the rest were SIDS IB. Fifteen infants (7.5%) had R1193Q in SCN5A, of doubtful pathogenicity, and no pathogenic LQTS variants were observed.

CONCLUSION

This genetic investigation of LQTS in SIDS showed a low diagnostic yield. These findings suggest that LQTS molecular autopsy could be cautiously conducted in selected cases with family involvement to improve the available genetic counseling information. Meanwhile, a national SIDS registry should be established to document and evaluate the genetic risk of SIDS in Korea.

Association between histological alterations in the thymus and sudden infant death syndrome

INTRODUCTION

Sudden infant death syndrome (SIDS) involves the death of an infant during the first year of life and it is among the leading causes of infant mortality worldwide. One hypothesis regarding the pathogenesis of SIDS is that it results from a combination of three independent factors: endogenous vulnerability, a critical time window during postnatal development, and exogenous stressors. This hypothesis is known as the "triple-risk model".

METHODS

In this study, we used an immunohistological approach to compare the cellular microenvironments of thymuses from 19 infants whose sudden death was classified as SIDS and a control group, which consisted of thymuses from age-matched children undergoing surgery for various congenital heart defects. We hypothesized that morphological signs of stress-related thymic involution would be present.

RESULTS

Based on our observations, we found evidence that the proliferation and maturation of T-lymphocytes in the thymuses of infants with SIDS were suppressed. We observed enhanced macrophage activity, suggesting an increase in the apoptosis of lymphocytes and decrease in number of thymic dendritic cells and myoid cells. Significant apoptosis of thymic lymphocytes without cell regeneration typically leads to atrophy of the thymus. All cellular events we observed resemble the initial stage of stress-related thymic involution.

CONCLUSION

These results support the "triple-risk model," suggesting that certain exogenous stressors might be involved in the pathogenesis of SIDS. This was probably not recognized during the autopsies of infants who died suddenly.

H. R, Thamleena A. H, Joseph A, Ben A, V. U. K. Roles of different amino-acid residues towards binding and selective transport of K+ through KcsA K+-ion channel

Each amino acid in the selectivity filter plays a distinct role towards binding and transport of K⁺ ion through KcsA.

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.