The triple risk hypotheses in sudden infant death syndrome

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.

Revisiting the association of sudden infant death syndrome (SIDS) with polymorphisms of NHE3 and IL13

OBJECTIVES

Disturbances of the central nervous system and immune system are thought to play a role in sudden infant death syndrome (SIDS). Dysregulated expression of sodium (Na+)/hydrogen (H+) exchanger 3 (NHE3) in the brainstem and of interleukin 13 (IL13) in the lungs has been observed in SIDS. An association of single-nucleotide polymorphisms (SNPs) in NHE3 and IL13 with SIDS has been proposed, but controversial results were reported. Therefore, there is a need to revisit the association of SNPs in NHE3 and IL13 with SIDS.

METHODS

Genotyping of rs71597645 (G1131A) and rs2247114 (C2405T) in NHE3 and rs20541 (+ 4464A/G) in IL13 was performed in 201 SIDS cases and 338 controls. A meta-analysis was performed after merging our data with previously published data (all from European populations).

RESULTS

Polymorphisms rs2247114 (NHE3) and rs20541 (IL13) were significantly associated with SIDS overall and in multiple subgroups, but no association was found for rs71597645 (NHE3). After combining our data with previously published data, a fixed-effect meta-analysis showed that rs2247114 in NHE3 retained a significant association with SIDS under a recessive model (OR 2.78, 95%CI 1.53 to 5.06; p = 0.0008).

CONCLUSION

Our findings suggest an association of NHE3 variant rs2247114 (C2405T), though not rs71597645 (NHE3), with SIDS. A potential role of rs20541 (IL13) still has to be elucidated. Especially NHE3 seems to be an interesting topic for future SIDS research.

Correlation of gestational age and age at death in sudden infant death syndrome: another pointer to the role of critical developmental period?

BACKGROUND

Filiano and Kinney proposed a triple-risk model for the sudden infant death syndrome (SIDS) that involves the intersection of three risks: (1) a vulnerable infant, (2) a critical developmental period in homeostatic control, and (3) an exogenous stressor(s). The primary evidence for the role of a critical developmental period in SIDS etiology is the peak of cases around the third month of life. Independently, several studies pointed to correlation between gestational age and age at death in SIDS, but used that to assess the SIDS risk for preterm infants, ignoring further ramifications.

METHODS

We did a detailed analysis of CDC data spanning over two decades (1983-2011). We focused not only on the correlation between two age variables (gestational and age at death), but also on the possibility of misdiagnosis. Also, we attempted to account for potential biases in the data induced by the ICD-9/ICD-190 transition or the "Back to Sleep" campaign.

RESULTS

The peak of deaths in the third month of life, that was the main argument for the role of the critical development period, wasn't unique to SIDS. However, we confirmed an almost linear and negative correlation between gestational age and the week of death due to SIDS. This pattern (slope of correlation < 0 and significance of correlation p < 0.05) is characteristic of SIDS among all diseases analyzed in the study.

CONCLUSIONS

We interpret the results as the evidence of the role of the critical development period in SIDS etiology. Possibly more attention in the future research should be put to theories that are based on homeostatic control.

Age-related cytokine imbalance in the thymus in sudden infant death syndrome (SIDS)

BACKGROUND

Sudden infant death syndrome (SIDS) has been considered to be triggered by a combination of underlying immune dysregulation and infections. The thymus is a crucial lymphatic organ responsible for T cell development in infancy. We hypothesized that an altered thymic immune status may be detectable by intrathymic cytokine profiling in SIDS.

METHODS

27 cytokines in protein lysates of thymus tissue and thymus weights were assessed in 26 SIDS cases and 16 infants who died of other reasons.

RESULTS

Seventeen out of 27 cytokines were increased in thymic tissue of SIDS compared to controls without infections, and the most significant discrepancy was in infants younger than 20 weeks. The thymic cytokine profiles in SIDS cases were similar to those in controls with severe infection; however, the magnitude of the cytokine concentration elevation in SIDS was less pronounced, indicating sub-clinical infections in SIDS. In contrast to SIDS, intrathymic cytokine concentrations and thymus weight were increased with age in control children.

CONCLUSIONS

Elevated thymic cytokine expression and thymus weight, as well as impaired age-related alterations in SIDS, may be influenced by subclinical infection, which may play a role in initiating SIDS in infants with a compromised immune response.

IMPACT STATEMENT

Increased thymic weight and cytokine concentration may suggest possible subclinical infection in SIDS. Elevated thymic weight and cytokine concentration mainly in SIDS cases aged <20 weeks. Age-related impairment in the thymic weight and cytokine expression may be impaired by subclinical infection in SIDS.

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.

Current SIDS research: time to resolve conflicting research hypotheses and collaborate

From the earliest publications on cot death or sudden infant death syndrome (SIDS) through to this day, clinical pathology and epidemiology have strongly featured infection as a constant association. Despite mounting evidence of the role of viruses and common toxigenic bacteria in the pathogenesis of SIDS, a growing school of thought featuring a paradigm based on the triple risk hypothesis that encompasses vulnerability through deranged homoeostatic control of arousal and/or cardiorespiratory function has become the mainstream view and now dominates SIDS research. The mainstream hypothesis rarely acknowledges the role of infection despite its notional potential role as a cofactor in the triple hit idea. Decades of mainstream research that has focussed on central nervous system homoeostatic mechanisms of arousal, cardiorespiratory control and abnormal neurotransmission has not been able to provide consistent answers to the SIDS enigma. This paper examines the disparity between these two schools of thought and calls for a collaborative approach. IMPACT: The popular research hypothesis explaining sudden infant death syndrome features the triple risk hypothesis with central nervous system homoeostatic mechanisms controlling arousal and cardiorespiratory function. Intense investigation has not yielded convincing results. There is a necessity to consider other plausible hypotheses (e.g., common bacterial toxin hypothesis). The review scrutinises the triple risk hypothesis and CNS control of cardiorespiratory function and arousal and reveals its flaws. Infection-based hypotheses with their strong SIDS risk factor associations are reviewed in a new context.

The fundamental need for unifying phenotypes in sudden unexpected pediatric deaths

A definitive, authoritative approach to evaluate the causes of unexpected, and ultimately unexplained, pediatric deaths remains elusive, relegating final conclusions to diagnoses of exclusion in the vast majority of cases. Research into unexplained pediatric deaths has focused primarily on sudden infant deaths (under 1 year of age) and led to the identification of several potential, albeit incompletely understood, contributory factors: nonspecific pathology findings, associations with sleep position and environment that may not be uniformly relevant, and the elucidation of a role for serotonin that is practically difficult to estimate in any individual case. Any assessment of progress in this field must also acknowledge the failure of current approaches to substantially decrease mortality rates in decades. Furthermore, potential commonalities with pediatric deaths across a broader age spectrum have not been widely considered. Recent epilepsy-related observations and genetic findings, identified post-mortem in both infants and children who died suddenly and unexpectedly, suggest a role for more intense and specific phenotyping efforts as well as an expanded role for genetic and genomic evaluation. We therefore present a new approach to reframe the phenotype in sudden unexplained deaths in the pediatric age range, collapsing many distinctions based on arbitrary factors (such as age) that have previously guided research in this area, and discuss its implications for the future of postmortem investigation.

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.

Sudden Infant Death Syndrome, Pulmonary Edema, and Sodium Toxicity: A Grounded Theory

Sudden Infant Death Syndrome (SIDS) occurs unexpectedly in an otherwise healthy infant with no identifiable cause of death following a thorough investigation. A general hypervolemic state has been identified in SIDS, and fluid in the lungs suggests the involvement of pulmonary edema and hypoxia as the cause of death. The present perspective paper reviews pathophysiological, epidemiological, and dietary evidence in SIDS. A grounded theory is presented that proposes an association of SIDS with sodium toxicity from excessive sodium chloride intake, mediated by noncardiogenic pulmonary edema, hypoxia, and alveolar damage. The peak of SIDS cases occurs in infants 2–4 months of age, who are less efficient in excreting excessive dietary sodium load. Evidence implicating sodium toxicity in SIDS includes increased levels of sodium associated with fever and with inflammatory/immune responses in the lungs. Conditions in near-miss SIDS cases are linked to dysregulated sodium, and increased sodium dietary intake suggests that sodium toxicity from a high-salt diet potentially mediates the association of seasonality and socioeconomic status with SIDS incidence. In addition, exposure to sodium toxicity meets three main criteria of the triple risk model of SIDS. The proposed pathophysiological effects of pulmonary edema related to sodium toxicity in SIDS merit further investigations.

Pulmonary immune profiling of SIDS: impaired immune maturation and age-related cytokine imbalance

BACKGROUND

For sudden infant death syndrome (SIDS), an impaired immunocompetence has been discussed for a long time. Cytokines and chemokines are soluble immune mediators (SIM) whose balance is essential for the immune status. We hypothesized that an imbalanced immune response might contribute to the etiology of SIDS.

METHODS

We investigated 27 cytokines, chemokines, and growth factors in protein lysates of lungs derived from 29 SIDS cases and 15 control children deceased for other reasons.

RESULTS

Except for the CCL5, no significant differences were detected in the lungs between SIDS cases with and without mild upper respiratory tract infections. In contrast, IL-1RA, IL-7, IL-13, and G-CSF were decreased in the merged SIDS cases compared to control cases without evidence of infection. Plotting SIM concentrations against infant age resulted in increasing concentrations in control but not in SIDS lungs, indicating a disturbed immune maturation. Moreover, an age-dependent shift towards a Th2-related pattern was observed in SIDS.

CONCLUSIONS

Our findings suggest that an impaired maturation of the immune system, an insufficient response to respiratory pathogens, and an immune response modulated by Th1/Th2 imbalance might play a possible role in triggering SIDS. These findings might in part be explained by chronic stress.

IMPACT

Maturation of the cytokine and chemokine network may be impaired in SIDS. An imbalance between Th1- and Th2-related cytokines, which may reflect a state of chronic stress causing a more Th2 shift. An impaired immune maturation, an insufficient response to respiratory pathogens, and an immune response modulated by Th1/Th2 imbalance might play a possible role in SIDS.

Variants in genes encoding the SUR1-TRPM4 non-selective cation channel and sudden infant death syndrome (SIDS): potentially increased risk for cerebral edema

Increasing evidence suggests that brain edema might play an important role in the pathogenesis of sudden infant death syndrome (SIDS) and that variants of genes for cerebral water channels might be associated with SIDS. The role of the sulfonylurea receptor 1 (SUR1)-transient receptor potential melastatin 4 (TRPM4) non-selective cation channel in cerebral edema was demonstrated by extensive studies. Therefore, we hypothesized that variants at genes of the SUR1-TRPM4 channel complex might be linked to SIDS. Twenty-four polymorphisms in candidate genes involved in the SUR1-TRPM4 non-selective cation channel were investigated in 185 SIDS cases and 339 controls. One (rs11667393 in TRPM4) of these analyzed SNPs reached nominal significance regarding an association with SIDS in the overall analysis (additive model: p = 0.015, OR = 1.438, 95% CI = 1.074-1.925; dominant model: p = 0.036; OR = 1.468, 95% CI = 1.024-2.106). In the stratified analysis, further 8 variants in ABCC8 (encoding SUR1) or TRPM4 showed pronounced associations. However, none of the results remained significant after correction for multiple testing. This preliminary study has provided the first evidence for a genetic role of the SUR1-TRPM4 complex in the etiology of SIDS, and we suggest that our initial results should be evaluated by further studies.

Hyperthermia and Heat Stress as Risk Factors for Sudden Infant Death Syndrome: A Narrative Review

BACKGROUND AND OBJECTIVES

Heat stress and hyperthermia are common findings in sudden infant death syndrome (SIDS) victims. It has been suggested that thermal stress can increase the risk of SIDS directly via lethal hyperthermia or indirectly by altering autonomic functions. Major changes in sleep, thermoregulation, cardiovascular function, and the emergence of circadian functions occur at the age at which the risk of SIDS peaks-explaining the greater vulnerability at this stage of development. Here, we review the literature data on (i) heat stress and hyperthermia as direct risk factors for SIDS, and (ii) the indirect effects of thermal loads on vital physiological functions.

RESULTS

Various situations leading to thermal stress (i.e., outdoors temperatures, thermal insulation from clothing and bedding, the prone position, bed-sharing, and head covering) have been analyzed. Hyperthermia mainly results from excessive clothing and bedding insulation with regard to the ambient thermal conditions. The appropriate amount of clothing and bedding thermal insulation for homeothermia requires further research. The prone position and bed-sharing do not have major thermal impacts; the elevated risk of SIDS in these situations cannot be explained solely by thermal factors. Special attention should be given to brain overheating because of the head's major role in body heat losses, heat production, and autonomic functions. Thermal stress can alter cardiovascular and respiratory functions, which in turn can lead to life-threatening events (e.g., bradycardia, apnea with blood desaturation, and glottal closure). Unfortunately, thermal load impairs the responses to these challenges by reducing chemosensitivity, arousability, and autoresuscitation. As a result, thermal load (even when not lethal directly) can interact detrimentally with vital physiological functions.

CONCLUSIONS

With the exception of excessive thermal insulation (which can lead to lethal hyperthermia), the major risk factors for SIDS appears to be associated with impairments of vital physiological functions when the infant is exposed to thermal stress.

A mouse zoonotic virus (LCMV): A possible candidate in the causation of SIDS

Lymphocytic choriomeningitis virus (LCMV) is a ubiquitous virus carried by rodents. It causes human disease through contact with infectious mouse faeces, urine or secretions. The virus initially infects the human respiratory tract and lungs and produces typical viral symptoms and signs. The infection is usually self-limiting and recovery is the norm. A small proportion of individuals may develop aseptic meningitis. It is hypothesised that in infancy the virus may cause respiratory tract infection through contact with mouse excreta. The infection could activate production of staphylococcal enterotoxin in babies who are colonised by Staphylococcus aureus. Indeed, a mouse animal model has shown that the combination of LCMV infection and introduction of enterotoxin B produces fatal haematogenous shock. Neither agent alone is lethal. Pathological (and physiological) evidence indicates shock could be the underlying terminal event in SIDS (the observed tissue damage seen in the heart and diaphragmatic muscles, and apoptosis observed in the brain and brainstem of SIDS cases). These features are consistent with a haematogenous shock event. The epidemiology of SIDS is entirely consistent with a mouse-related viral zoonosis. Moreover, rural cases of SIDS tend to feature more often than urban cases and their occurrence would be consistent with the dynamics of mouse populations. Low socioeconomic living conditions (a major risk factor for SIDS) is consistent with prevalence of mouse populations and poor hygienic conditions, with overcrowding. Prone sleeping would facilitate aspiration or ingestion of infectious material from contaminated surfaces. and poor hygienic conditions, with overcrowding, and prone sleeping would facilitate aspiration or ingestion of infectious material from contaminated surfaces. The epidemiology and pathology of SIDS and the dynamics and ubiquity of mouse populations together with human serological data would support the hypothesis that LCMV is a potential candidate as a key factor in the causation of SIDS.

Infection, Celestial Influences, and Sudden Infant Death Syndrome: A New Paradigm

The etiology of sudden infant death syndrome (SIDS) still remains unclear. This situation would seem unprecedented for 21st-century medical science. This article explores scientific fields that have not been largely considered in investigating the etiology of SIDS so far. In this study, we examined previously ignored studies on heliobiology, celestial influences, and SIDS in the non-medical literature in an attempt to answer the following questions: is there a relationship between sunspot/solar activity and the occurrence of SIDS? Could there be alternative reasons for the decline in SIDS incidences in the 1990s that were originally attributed to the “Back-to-Sleep” campaign? We note that the decline coincided with the ~11-year cyclical diminution in sunspot numbers (SSNs). The SSN/SIDS relationship does not necessarily imply causality; however, it supports published data regarding sunspots, Schumann resonance, and geomagnetic effects. How solar energy could adversely influence a baby’s existence remains conjectural. Observations in this respect suggest pathways involving melatonin and/or infection/inflammation.

Aquaporin 4 expression in the hippocampus in sudden infant death syndrome and sudden unexplained death in childhood

Aquaporin 4 (AQP4) is the main membrane water channel in the brain involved in regulating water homeostasis. The water distribution in neural tissue is often dysregulated after hypoxic neural injury. Previous research has indicated that victims of sudden infant death syndrome (SIDS) and sudden unexplained death in childhood (SUDC) have an underlying brain dysfunction that impairs their critical arousal response to hypoxic stress during sleep. The aim of this study was to determine the expression levels of AQP4 in the hippocampus in SIDS/SUDC cases and controls, and compare the findings with AQP4 genotypes that previously have been shown to be associated with SIDS. Immunochemical staining and morphometry were used to evaluate the density of AQP4-positive astrocytes in 30 SIDS/SUDC cases and 26 controls. AQP4-positive cells were counted in grids covering three layers in the hippocampus, which revealed that their count in any of the layers did not differ significantly between cases and controls. A decline in AQP4 expression was observed for infants older than 12 weeks. The AQP4 expression was lower in infants and children with the rs2075575 CT/TT genotype than in those with the CC genotype. This study indicates that AQP4 expression may be influenced by both age and genotype in infants. The role of AQP4 in the pathogenesis of SIDS remains to be elucidated.

Association between monoamine oxidase A promoter polymorphism and the risk of sudden infant death syndrome: a meta-analysis

Introduction

The etiology of sudden infant death syndrome (SIDS) remains an unsolved problem. The aim of this meta-analysis is to investigate the potential association between monoamine oxidase A (MAOA) promoter variable number tandem repeat (VNTR) polymorphism and SIDS risk.

Methods

A systematic review and meta-analysis were conducted on studies from accessible electronic databases. Each VNTR variant was examined in each gender independently by comparing with the pooled results of other alleles.

Results

A total of six independent case–control studies including 1022 SIDS cases and 1839 controls were enrolled in this meta-analysis. In both of the whole populations and Caucasian populations, male infants with the low-MAOA-expression alleles (2R+3R) were found to exhibit a statistically significant increased risk of SIDS, whereas those with a 4R allele exhibited a reduced risk of SIDS. Besides, an increased risk of SIDS was detected in male Caucasian infants with 2R or 3R alleles. However, none of the allele or genotype variants was associated with SIDS in female victims.

Conclusion

In male Caucasian infants, the low expression of MAOA promoter VNTR alleles (2R and 3R) is associated with an increased risk of SIDS, and the existence of the 4R allele could be regarded as a protective factor.

Risk Factors for Sudden Infant Death in North Carolina

Background: Sudden infant death syndrome (SIDS) is the sudden, unexplained death of infants <1 year old. SIDS remains a leading cause of death in US infants. We aim to identify associations between SIDS and race/ethnicity, birth weight/gestational age, and socioeconomic/environmental factors in North Carolina (NC) to help identify infants at risk for SIDS. Methods and Results: In this IRB-approved study, infant mortality 2007-2016 and death certificate-linked natality 2007-2014 were obtained from the NC Department of Health and Human Services. General, NC natality statistics 2007-2016 were obtained from CDC Wonder. Association between SIDS/total infant death and covariates (below) were calculated. Total infant mortality decreased 2007-2016 by an average of 14 deaths/100,000 live births per year, while SIDS incidence remained constant. Risk ratios of SIDS/total infant deaths, standardized to Non-Hispanic White, were 1.76/2.41 for Non-Hispanic Black and 0.49/0.97 for Hispanic infants. Increased SIDS risk was significantly and independently associated with male infant sex, Non-Hispanic Black maternal race/ethnicity, young maternal age, low prenatal care, gestational age <39 weeks, birthweight <2500 g, low maternal education, and maternal tobacco use (p < 0.01). Maternal previous children now deceased also trended toward association with increased SIDS risk. Conclusions: A thorough SIDS risk assessment should include maternal, socioeconomic, and environmental risk factors as these are associated with SIDS in our population.

A Nursing Perspective on Infant Bed-Sharing Using Multidisciplinary Theory Integration

The American Academy of Pediatrics recommends against bed-sharing between infants and caregivers due to an association with suffocation. Caregivers continue to share a bed with their infant despite these recommendations for a multitude of reasons. A close examination of the bed-sharing literature reveals that the debate is fundamentally about theoretical differences. The major theories used to frame this problem include the triple risk model of bed-sharing and evolutionary theories. Nurses are masters of multidisciplinary collaboration and are well positioned to unify the triple risk and evolutionary views of infant bed-sharing to guide future innovations in health care practice and research.

SIDS, prone sleep position and infection: An overlooked epidemiological link in current SIDS research? Key evidence for the "Infection Hypothesis"

Mainstream researchers explain the etiology of SIDS with the cardiorespiratory paradigm. This has been the focus of intense study for many decades without providing consistent supporting data to link CNS findings to epidemiological risk factors or to the usual clinicopathological findings. Despite this, and the apparent oversight of the link between prone sleep position and respiratory infection, papers citing CNS, cardiac and sleep arousal findings continue to be published. Discovery of the prone sleep position risk factor provided tangential support for the cardiorespiratory control hypothesis which defines the mainstream approach. Despite many decades of research and huge expenditure, no aetiological answer has been forthcoming. In asking why?This paper exposes some of the shortcomings regarding this apparent oversight by mainstream SIDS researchers and examines the role of respiratory infection and puts the case for the “Infection Hypothesis.” In addition, the paper provides encouragement to neuropathologists to examine the potential link between CNS findings and cardiac function (as opposed to respiratory function) in relation to infection and to examine possible correlates between CNS findings and established risk factors such as recent infection, contaminated sleeping surfaces, maternal/obstetric/higher birth, ethnicity, non-breast-feeding, male gender, etc. or with the usual gross pathological findings of SIDS (intrathoracic petechial hemorrhages, liquid blood, congested lungs). The shortcomings exposed through this review invite questions over current research directions and hopefully encourage research into other more plausible hypotheses, such as the infection paradigm.•

Mainstream SIDS researchers appear to have overlooked the key relationship between prone sleep position and infection.

•

This omission has major implications for current and future SIDS research.

Ambient Air Pollution and Sudden Infant Death Syndrome in Korea: A Time-Stratified Case-Crossover Study

Sudden infant death syndrome (SIDS) is an occasional cause of unexpected mortality in infancy. While various etiological factors have been hypothesized, air pollution has been consistently presented as an environmental factor. In this study, we aimed to estimate the risk of SIDS in relation to exposure to air pollution and the effects of its modifying factors. A mortality dataset with supplementary infant mortality survey data from Statistics Korea was used and combined the concentration of ambient air pollution data from AirKorea based on the date of death and residential addresses of the SIDS cases. Odds ratios (ORs) were estimated according to birthweight, gestational age, maternal age, and infant age using a time-stratified case-crossover study design. The risk of exposure to particulate matter of less than 10 μm in diameter (PM₁₀), nitrogen dioxide (NO₂), carbon monoxide (CO), and sulfur dioxide was estimated. The number of deaths due to SIDS was 454 (253 males and 201 females). The OR per 27.8 µg/m³ increment of PM₁₀ was 1.14 (95% confidence interval [CI]: 1.03–1.25) and that per 215.8 ppb of CO was 1.20 (95% CI: 1.03–1.40) in all infants. In females, an increase in NO₂ and CO levels was associated with a higher risk of SIDS in low-birthweight and preterm infants. The OR per 15.7 ppb increment in NO₂ was highest among preterm infants, with a value of 5.12 (95% CI: 1.27–20.63), and low-birthweight individuals, with a value of 4.11 (95% CI: 1.74–9.72), at a moving average of 0 to 3 days. In males, however, no significant association was found. In the present study, exposure to air pollution was associated with an increased risk of SIDS. This association was more evident in susceptible infants with a low-birthweight or in cases of preterm birth.

Location of arrest and survival from out-of-hospital cardiac arrest among children in the public-access defibrillation era in Japan

BACKGROUND

Our objective was to assess the characteristics such as public-access defibrillation (PAD) by laypersons and the outcomes after pediatric out-of-hospital cardiac arrest by location in the PAD era.

METHODS

From a nationwide, prospective, population-based registry of out-of-hospital cardiac arrest patients in Japan, we enrolled consecutive pediatric patients aged ≤17 years before emergency medical service (EMS) arrival between 2013 and 2015. The primary outcome measure was 1-month survival, with favorable neurologic outcome defined as cerebral performance category 1 or 2. Factors associated with favorable neurologic outcome were assessed using multivariable logistic regression analysis.

RESULTS

Among 3991 eligible pediatric out-of-hospital cardiac arrests, the proportion of PAD was 0.2% (5/2888) at residence, 1.6% (2/125) in public areas, 0.9% (3/321) on streets/highways, 21.6% (11/51) at recreation/sports event areas, 46.1% (82/178) at education institutions, and 1.2% (5/428) in others. In the multivariable analysis, arrest witnessed by family members (adjusted odds ratio [AOR], 5.25; 95% confidence interval [CI], 3.22-8.58) and nonfamily members (AOR, 2.45; 95% CI, 1.26-4.77), first documented ventricular fibrillation (AOR, 12.29; 95% CI, 7.08-21.35), PAD (AOR, 2.63; 95% CI, 1.23-5.62), and earlier EMS response time (AOR for 1-min increment, 0.88; 95% CI, 0.81-0.94) were associated with improving outcome. As for locations, recreation/sports event areas (AOR, 3.43; 95% CI, 1.17-10.07) and education institutions (AOR, 3.03; 95% CI, 1.39-6.63) were also associated with favorable neurologic outcome.

CONCLUSIONS

In Japan, where public-access automated external defibrillators are well disseminated, characteristics such as PAD and outcomes for pediatric out-of-hospital cardiac arrest before EMS arrival differed substantially by location.

Sudden unexpected infant death characteristics in the French region of West Provence-Alpes-Côte d'Azur

Background: Although the incidence of sudden unexpected infant death (SUID) has decreased since the 'Back to Sleep' campaign in English-speaking countries and other preventive campaigns, the circumstances of such deaths remain unclear. Aim: To analyse infant deaths recorded at the referral centre for sudden infant death of the West Provence-Alpes-Côte d'Azur region of France (West PACA) and the forensic medicine department of Marseille University Hospital. Methods: Information on all SUID cases from 2000 to 2017 was extracted from the referral centre for sudden infant deaths in West PACA and the forensic medicine department of Marseille. Results: The study included 130 infants over the 17 years with a very similar distribution. There was a marked male preponderance, with 61.6% of boys whatever the age at death (sex ratio 1.6). Half of the deaths occurred in the first 6 months of life and the majority (61%) of infants died during autumn and winter. Nearly one-third (33.2%) had presented with minor infections and 21% had been seen by a doctor or had been admitted to hospital. Most deaths (86.4%) occurred during sleep (night or day). Nearly half of the infants (47.7%) were discovered in a prone position. A large majority of parents (90.7%) agreed to a post-mortem examination. Only 6.2% of deaths led to legal proceedings. Nearly 16.9% remained unexplained after compiling all the data included in the protocol and 9.2% remained unexplained because of incomplete investigation, including refusal of post-mortem examination. Abuse was involved in 2.3% of cases. Conclusions: Asymptomatic infectious conditions were associated with a high proportion of SUID cases. Non-supine sleep positions were still practised. There is a need to increase SUID prevention campaigns. Abbreviations: HAS, Haute Autorité de Santé: French National Health Authority; NICHD, National Institute of Child Health and Human Development; PACA, Provence-Alpes-Côte d'Azur region of France; SUID, sudden unexpected infant death; SIDS, sudden infant death syndrome; CépiDc, Centre d'Epidémiologie sur les Causes Médicales de Décès/Center for Epidemiology on the Medical Causes of Death.

Mechanisms underlying a critical period of respiratory development in the rat

Twenty-five years ago, Filiano and Kinney (1994) proposed that a critical period of postnatal development constitutes one of the three risk factors for sudden infant death syndrome (SIDS). The underlying mechanism was poorly understood. In the last 17 years, much has been uncovered on this period in the rat. Against several expected trends of development, abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur in the respiratory system at P12-13. This results in a transient synaptic imbalance with suppressed excitation and enhanced inhibition, and the response to acute hypoxia is the weakest at this time, both at the cellular and system's levels. The basis for the synaptic imbalance is likely to be contributed by a reduced expression of brain-derived neurotrophic factor (BDNF) and its TrkB receptors in multiple brain stem respiratory-related nuclei during the critical period. Exogenous BDNF or a TrkB agonist partially reverses the synaptic imbalance, whereas a TrkB antagonist accentuates the imbalance. A transient down-regulation of pituitary adenylate cyclase-activating polypeptide (PACAP) at P12 in respiratory-related nuclei also contributes to the vulnerability of this period. Carotid body denervation during this time or perinatal hyperoxia merely delays and sometimes prolongs, but not eliminate the critical period. The rationale for the necessity of the critical period in postnatal development is discussed.

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.

The Sudden Infant Death Syndrome mechanism of death may be a non-septic hyper-dynamic shock

BACKGROUND

Sudden Infant Death Syndrome (SIDS) mechanisms of death remains obscured. SIDS' Triple Risk Model assumed coexistence of individual subtle vulnerability, critical developmental period and stressors. Prone sleeping is a major risk factor but provide no clues regarding the mechanism of death. The leading assumed mechanisms of death are either an acute respiratory crisis or arrhythmias but neither one is supported with evidence, hence both are eventually speculations. Postmortem findings do exist but are inconclusive to identify the mechanism of death. WHAT DOES THE PROPOSED HYPOTHESIS BASED ON?: 1. The stressors (suggested by the triple risk model) share a unified compensatory physiological response of decrease in systemic vascular resistant (SVR) to facilitate a compensatory increase in cardiac output (CO). 2. The cardiovascular/cardiorespiratory control of the vulnerable infant during a critical developmental period may be impaired. 3. A severe decrease in SVR is associated with hyper-dynamic state, high output failure and distributive shock.

THE HYPOTHESIS

Infant who is exposed to one or more stressors responds normally by decrease in SVR which increases CO. In normal circumstances once the needs are met both SVR and CO are stabilized on a new steady state. The incompetent cardiovascular control of the vulnerable infant fails to stabilize SVR which decreases in an uncontrolled manner. Accordingly CO increases above the needs to hyper-dynamic state, high output heart failure and hyper-dynamic shock.

CONCLUSIONS

The proposed hypothesis provides an appropriate alternative to either respiratory crises or arrhythmia though both speculations cannot be entirely excluded.

Influence of prenatal alcohol and smoke exposure on neonatal vagal tone in response to head-up tilt

This paper investigates differences in the parasympathetically mediated heart rate response to head-up tilt in two populations of newborns. One group was unexposed to any drug during pregnancy, the other was exposed to both alcohol and smoking in utero. Four different estimates of vagal tone were calculated. These indexes quantify vagal tone magnitude in four different domains: time, frequency, complexity and phase. Control group (CG) results across all parameters show a consistent physiological response to an orthostatic tilt consistent with vagal withdrawal. On the other hand, infants in the exposed group (EG) did not express a decrease in vagal measures following tilt.

Autonomic Function and QT Interval During Night-Time Sleep in Infant Long QT Syndrome

BACKGROUND

Sudden infant death syndrome mainly occurs during night-time sleep. Approximately 10% of cases are thought to involve infants with long QT syndrome (LQTS). Autonomic function and QT interval in night-time sleep in early infancy in LQTS infants, however, remain controversial.Methods and Results:Holter electrocardiography was performed in 11 LQTS infants before medication in early infancy, and in 11 age-matched control infants. Control infants were re-evaluated in late infancy. The power spectral density was calculated and parasympathetic activity and sympathovagal balance were obtained. Electrocardiograms of a representative hour during night-time sleep, daytime sleep, and daytime activity, were chosen and QT/RR intervals were manually measured. LQTS infants had significantly lower parasympathetic activity and higher sympathovagal balance during night-time sleep than control infants in early infancy. These autonomic conditions in early infancy were significantly depressed compared with late infancy. Corrected QT interval (QTc) during night-time sleep (490±20 ms) was significantly longer than that in daytime sleep (477±21 ms, P=0.04) or daytime activity (458±18 ms, P=0.003) in LQTS infants, and significantly longer than that during night-time sleep in controls.

CONCLUSIONS

A combination of the longest QTc and autonomic imbalance during night-time sleep in early infancy may be responsible for development of life-threatening arrhythmia in LQTS infants. Critical cases should be included in future studies.

Ambient Temperature and Sudden Infant Death Syndrome in the United States

BACKGROUND

Sudden infant death syndrome (SIDS) is a leading cause of infant mortality in the United States. While thermal stress is implicated in many risk factors for SIDS, the association between ambient temperature and SIDS remains unclear.

METHODS

We obtained daily individual-level infant mortality data and outdoor temperature data from 1972 to 2006 for 210 US cities. We applied a time-stratified case-crossover analysis to determine the effect of ambient temperature on the risk of SIDS by season. We stratified the analysis by race, infant age, and climate.

RESULTS

There were a total of 60,364 SIDS cases during our study period. A 5.6°C (10°F) higher daily temperature on the same day was associated with an increased SIDS risk of 8.6% (95% confidence interval [CI] = 3.6%, 13.8%) in the summer, compared with a 3.1% decrease (95% CI = -5.0%, -1.3%) in the winter. Summer risks were greater among black infants (18.5%; 95% CI = 9.3%, 28.5%) than white infants (3.6%; 95% CI = -2.3%, 9.9%), and among infants 3-11 months old (16.9%; 95% CI = 8.9%, 25.5%) than infants 0-2 months old (2.7%; 95% CI = -3.5%, 9.2%). The temperature-SIDS association was stronger in climate clusters in the Midwest and surrounding northern regions.

CONCLUSIONS

Temperature increases were associated with an elevated risk of SIDS in the summer, particularly among infants who were black, 3 months old and older, and living in the Midwest and surrounding northern regions.

Neonatal Outcomes Associated With Placental Abruption

Placental abruption (early separation of the placenta) is associated with preterm birth and perinatal mortality, but associations with other neonatal morbidities remain understudied. We examined the association between abruption and newborn outcomes. We analyzed 223,341 singleton deliveries from the Consortium on Safe Labor study, a retrospective, multisite, observational study (2002-2008) of electronic medical records in the United States. Adjusted relative risks, incidence rate ratios, and 99% confidence intervals were estimated. Direct effects attributable to abruption were examined by conditioning on intermediates (preterm birth and small for gestational age) with sensitivity analyses. Incidence of abruption was 1.6% (n = 3,619). Abruption was associated with an elevated risk of newborn resuscitation (relative risk (RR) = 1.5, 99% confidence interval (CI): 1.5, 1.6), apnea (RR = 5.8, 99% CI: 5.1, 6.5), asphyxia (RR = 8.5, 99% CI: 5.7, 11.3), respiratory distress syndrome (RR = 6.5, 99% CI: 5.9, 7.1), neonatal intensive care unit admission (RR = 3.4, 99% CI: 3.2, 3.6), longer intensive care length of stay (incidence rate ratio = 2.0, 99% CI: 1.9, 2.2), stillbirth (RR = 6.3, 99% CI: 4.7, 7.9), and neonatal mortality (RR = 7.6, 99% CI: 5.2, 10.1). In sensitivity analyses, there was a direct effect of abruption associated with increased neonatal risks. These findings expand our knowledge of the association between abruption and perinatal and neonatal outcomes.

Intestinal Microbiota Composition in Sudden Infant Death Syndrome and Age-Matched Controls

OBJECTIVE

To assess whether features of the infant intestinal microbiome, including the carriage of toxigenic bacteria, are associated with sudden infant death syndrome (SIDS).

STUDY DESIGN

We undertook a case-controlled analysis of fecal microbiology in SIDS. Fecal material was obtained from 44 cases and 44 aged-matched controls. Microbiota composition was determined by 16S ribosomal RNA gene amplicon sequencing and comparisons between cases and controls made based on both bacterial alpha diversity measures and unconstrained ordination. Specific quantitative polymerase chain reaction assays were used to determine intestinal carriage of Staphylococcus aureus, toxigenic Clostridium difficile, and pathogenic and nonpathogenic Escherichia coli.

RESULTS

The microbial composition for the study population as a whole was consistent with previous studies of infants <12 months of age, with a correlation between alpha diversity and age (r² = 0.08; P = .007). However, no difference was observed in alpha diversity between SIDS cases and controls (P > .4). Nonmetric multidimensional scaling also revealed no evidence of differences in microbiota dispersal between SIDS cases and controls (P = .4, permutational multivariate ANOVA test; Pseudo-F = 0.9), nor was a difference observed in microbiota dispersion (P = .19, PERMDISP test; F = 1.9). There were no significant intergroup differences in the carriage of S aureus, toxigenic C difficile, total E coli, or pathogenic E coli.

CONCLUSIONS

We found no evidence of an association between altered intestinal microbiology and SIDS, or to support the development of strategies to reduce the incidence of SIDS that target intestinal microbiology.

Sudden infant death syndrome and inherited cardiac conditions

Sudden infant death syndrome (SIDS) is the leading cause of post-neonatal infant mortality in developed countries, characterized by the death of infants for no obvious reason and without prior warning. The complex interaction of multiple factors in the pathogenesis of SIDS is illustrated by the 'triple risk hypothesis', which proposed that SIDS results from a convergence of three overlapping risk factors: a critical developmental period, an exogenous stressor, and underlying genetic and/or nongenetic vulnerability in the infant. Rare variants in genes associated with inherited arrhythmia syndromes and cardiomyopathies have been proposed as the substrate for an infant's critical vulnerability in a small subset of SIDS cases. Given the potential risk of inherited cardiac disease, current guidelines recommend post-mortem genetic testing (molecular autopsy) and cardiological investigation of the surviving family, complemented by targeted genetic testing if appropriate. In this Review, we highlight the latest developments in understanding the spectrum and prevalence of cardiac-mediated SIDS, and discuss the clinical implications of SIDS in the surviving family and the general population.

Towards Better Understanding of the Pathogenesis of Neuronal Respiratory Network in Sudden Perinatal Death

Sudden perinatal death that includes the victims of sudden infant death syndrome, sudden intrauterine death syndrome, and stillbirth are heartbreaking events in the life of parents. Most of the studies about sudden perinatal death were reported from Italy, highlighting two main etiological factors: prone sleeping position and smoking. Other probable contributory factors are prematurity, male gender, lack of breastfeeding, respiratory tract infections, use of pacifiers, infant botulism, extensive use of pesticides and insecticides, etc. However, extensive studies across the world are required to establish the role of these factors in a different subset of populations. Previous studies confirmed the widely accepted hypothesis that neuropathology of the brainstem is one of the main cause of sudden perinatal death. This study is an effort to summarize the neuropathological evaluation of the brainstems and their association to sudden perinatal death. Brainstem nuclei in vulnerable infants undergo certain changes that may alter the sleep arousal cycle, cardiorespiratory control, and ultimately culminate in death. This review focuses on the roles of different brainstem nuclei, their pathologies, and the established facts in this regard in terms of it's link to such deaths. This study will also help to understand the role of brainstem nuclei in controlling the cardiorespiratory cycles in sudden perinatal death and may provide a better understanding to resolve the mystery of these deaths in future. It is also found that a global initiative to deal with perinatal death is required to facilitate the diagnosis and prevention in developed and as well as developing countries.

Long QT syndrome and sudden unexpected infant death

Long QT syndrome (LQTS) is an inheritable primary electric disease of the heart characterised by abnormally long QT intervals and a propensity to develop atrial and ventricular tachyarrhythmias. It is caused by an inherited channelopathy responsible for sudden cardiac death in individuals with structurally normal hearts. Long QT syndrome can present early in life, and some studies suggest that it may be associated with up to 20% of sudden unexplained infant death (SUID), particularly when associated with external stressors such as asphyxia, which is commonly seen in many infant death scenes. With an understanding of the genetic defects, it has now been possible to retrospectively analyse samples from infants who have presented to forensic pathology services with a history of unexplained sudden death, which may, in turn, enable the implementation of preventative treatment for siblings previously not known to have pathogenic genetic variations. In this viewpoint article, we will discuss SUID, LQTS and postmortem genetic analysis.

Targeted Metabolic Profiling of Post-Mortem Brain from Infants Who Died from Sudden Infant Death Syndrome

Currently little is known about the underlying pathophysiology associated with SIDS, and no objective biomarkers exist for the accurate identification of those at greatest risk of dying from SIDS. Using targeted metabolomics, we aim to profile the medulla oblongata of infants who have died from SIDS (n = 16) and directly compare their biochemical profile with age matched controls. Combining data acquired using ¹H NMR and targeted DI-LC-MS/MS, we have identified fatty acid oxidation as a pivotal biochemical pathway perturbed in the brains of those infants who have from SIDS (p = 0.0016). Further we have identified a potential central biomarker with an AUC (95% CI) = 0.933 (0.845-1.000) having high sensitivity (0.933) and specificity (0.875) values for discriminating between control and SIDS brains. This is the first reported study to use targeted metabolomics for the study of PM brain from infants who have died from SIDS. We have identified pathways associated with the disease and central biomarkers for early screening/diagnosis.

Sudden infant death syndrome due to long QT syndrome: a brief review of the genetic substrate and prevalence

The pathophysiological mechanisms which lead to sudden infant death syndrome (SIDS) are not completely understood. Cardiac channelopathies are a well-established causative factor with long QT syndrome (LQTS) being the most frequent one, accounting for approximately 12% of SIDS cases. The genetic substrate of the above arrhythmogenic syndrome has been thoroughly described but only specific gene mutations or polymorphisms have been identified as SIDS causative. The review will focus on the prevalence of LQTS-induced SIDS or near-SIDS cases and the mutations held responsible. A literature search was performed in PubMed and Scopus electronic databases. Search terms used were: long QT syndrome, channelopathies, QT prolongation, cardiac ion channels. The above-mentioned search terms were always combined with the term: sudden infant death syndrome. Study types considered eligible were: case–control, family pedigree analysis, case reports. The prevalence of LQTS-induced SIDS according to six broad genetic studies ranges from 3.9 to 20.6%, with an average of 12%. Since LQTS can be effectively managed, LQTS-related SIDS cases could be prevented, provided that a screening method is efficient enough to detect all the affected infants.

Evolution and significance of the triple risk model in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is a leading cause of death in infants, although the mechanisms leading to death remain unclear. Multiple theories have emerged over time, with one of the most influential hypotheses being the triple risk model. This model, first devised in 1972 and later revised in 1994 by Filiano and Kinney, is still widely used in assisting with conceptualising and understanding sudden death in infancy. This model has evolved over time, with each version stressing that SIDS is likely to occur when certain risk factors coincide, suggesting that the lethal mechanisms in SIDS are likely to be multifactorial. All versions of the triple risk model from 1972 to the present have emphasised the complexity of SIDS and serve as useful guides for current and future research into the enigma of sudden and unexpected death in infancy.

Forensic clinical anatomy: A new field of study with application to medicolegal issues

Forensic clinical anatomy is a new practical application of the discipline of Clinical Anatomy for ascertaining and evaluating medicolegal questions. In particular, individual anatomy (normal anatomy, anatomical variations, age-, disease-, or surgery-related modifications) can acquire significant relevance in various fields of legal medicine such as child abuse, sudden death, medical responsibility and/or liability, personal injury and damage. Anatomical data of forensic interest frequently arise from the correct application of methods of ascertainment; anatomical methods may then be required for further comprehensive analysis. The rigorous interpretation of anatomical data, derived from the ascertainment phase and analyzed on the basis of pertinent literature, can be pivotal for the correct application of evaluation criteria in various forensic contexts. Clin. Anat. 30:2-5, 2017. © 2016 Wiley Periodicals, Inc.

An Acute Respiratory Infection of a Physiologically Anemic Infant is a More Likely Cause of SIDS than Neurological Prematurity

Introduction

The cause of the sudden infant death syndrome (SIDS) is perhaps the oldest of unsolved mysteries of medicine, possibly dating back to Exodus in Biblical times when Egyptian children died in their sleep as if from a plague. It occurs when infants die unexpectedly with no sufficient cause of death found in a forensic autopsy, including death scene investigation and review of medical history. That SIDS is an X-linked recessive death from infectious respiratory disease of a physiologically anemic infant and not a simple anomalous cardiac or neurological condition is an extraordinary claim that requires extraordinary evidence. If it were by a simple cause, it would have already been solved, with over 11,000 papers on SIDS listed now in PubMed. Our aim is to use mathematical models of SIDS to explain: (1) its 50% excess male death rate; (2) its 4-parameter lognormal distribution of ages at death; (3) its winter maxima and summer minima; and (4) its increasing rate with live-birth order.

Methods

From extensive SIDS vital statistics data and published epidemiologic studies, we developed probability models to explain the mathematical behavior of SIDS meeting the four constraints mentioned above. We, then, compare these SIDS properties to infant death from acute respiratory infection (ARI), and infant death from encephalopathy, unspecified (EU).

Results

Comparisons show that SIDS are congruent with ARI and are not consistent with EU and that these probability models not only fit the SIDS data but they also predict and fit the male fraction of all infant and child mortality from birth through the first 5 years of their life.

Conclusion

SIDS are not rejected as an X-linked disease involving ARI and are not explained by a triple risk model that has been commonly accepted by the SIDS medical community, as implicating a neurological causation process in a subset of SIDS.

Novel heart rate parameters for the assessment of autonomic nervous system function in premature infants

Autonomic nervous system (ANS) balance is a key factor in homeostatic control of cardiac activity, breathing and certain reflex reactions such as coughing, sneezing and swallowing and thus plays a crucial role for survival. ANS impairment has been related to many neonatal pathologies, including sudden infant death syndrome (SIDS). Moreover, some conditions have been identified as risk factors for SIDS, such as prone sleep position. There is an urgent need for timely and non-invasive assessment of ANS function in at-risk infants. Systematic measurement of heart rate variability (HRV) offers an optimal approach to access indirectly both sympathetic and parasympathetic influences on ANS functioning. In this paper, data from premature infants collected in a sleep physiology laboratory in the NICU are presented: traditional and novel approaches to HRV analyses are applied and compared in order to evaluate their relative merits in the assessment of ANS activity and the influence of sleep position. Indices from time domain and nonlinear approaches contributed as markers of physiological development in premature infants. Moreover, significant differences were observed as a function of sleep position.

Sudden Unexpected Postnatal Collapse of the Newborn

Sudden unexpected postnatal collapse is a rare but devastating neonatal event. A well-appearing, full-term newborn with Agpar scores of eight or more suddenly crashes, often with full respiratory and cardiac arrest. Up to half of newborns with sudden unexpected postnatal collapse die, with many survivors suffering serious neurological damage. The first 2 hours of life are the hours of greatest risk, coinciding with the time frame when nurses encourage breastfeeding and uninterrupted skin-to-skin contact between women and newborns. Nursing assessments and measures to promote neonates' optimal transition to extrauterine life through skin-to-skin contact and early breastfeeding while decreasing the risk of this catastrophic event are described. Nursing surveillance to promote optimal transition in a safe environment is essential, and birth facilities should allocate staffing resources accordingly.

Sudden infant death syndrome caused by cardiac arrhythmias: only a matter of genes encoding ion channels?

Sudden infant death syndrome is the unexpected demise of a child younger than 1 year of age which remains unexplained after a complete autopsy investigation. Usually, it occurs during sleep, in males, and during the first 12 weeks of life. The pathophysiological mechanism underlying the death is unknown, and the lethal episode is considered multifactorial. However, in cases without a conclusive post-mortem diagnosis, suspicious of cardiac arrhythmias may also be considered as a cause of death, especially in families suffering from any cardiac disease associated with sudden cardiac death. Here, we review current understanding of sudden infant death, focusing on genetic causes leading to lethal cardiac arrhythmias, considering both genes encoding ion channels as well as structural proteins due to recent association of channelopathies and desmosomal genes. We support a comprehensive analysis of all genes associated with sudden cardiac death in families suffering of infant death. It allows the identification of the most plausible cause of death but also of family members at risk, providing cardiologists with essential data to adopt therapeutic preventive measures in families affected with this lethal entity.

Sudden infant death syndrome: an unrecognized killer in developing countries

Sudden infant death syndrome (SIDS) is defined as the sudden unexpected death of an infant <1 year of age, with onset of the fatal episode apparently occurring during sleep, that remains unexplained after a thorough investigation including performance of a complete autopsy and review of the circumstances of death and the clinical history. SIDS contributes to infant mortality and resulted in ∼15,000 deaths globally in 2013. Most of the risk factors of SIDS are common in developing countries; yet, there has been little interest in SIDS by researchers in Africa. This review looks at the extent of the attention given to SIDS in a developing country like Nigeria, and factors responsible for the scarce data concerning this significant cause of mortality.

Influence of sleep state and position on cardio-respiratory regulation in newborn babies

The paper presents results of a sleep study on 60 newborn infants and 22 one-month infants, in quiet and active sleep and in prone and supine position. During the study, HRV and respiration were acquired and then analyzed with a multi-parametric approach. Time, Frequency Domain and Non-Linear parameters were calculated, also encompassing indices from the adult and fetal field. The novelty of this study is the introduction of innovative measurements in a thorough investigation to characterize the effect of sleep state and position on the cardio-respiratory control in newborns. Results show that most parameters succeed in classifying different sleep states, while differences between positions were found in the one-month population only. This study comes as a continuation of previous analysis with the addition of respiratory signal. These results are encouraging for the aim of defining a set of parameters that could help characterizing the autonomic control of infants and early detect the onset of distress or particular pathologies.