Potential asphyxia and brainstem abnormalities in sudden and unexpected death in infants

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.

The multiagency approach to Sudden Unexpected Infant Deaths (SUID): eleven years' experience in the Tuscany Region

Background

The Sudden Unexpected Infant Death Syndrome (SUID) is one of the leading causes of mortality in the first year of life. The aim of this work was the retrospective evaluation of the incidence of SUID and the effectiveness of the multiagency approach to this phenomenon in the Tuscany Region.

Methods

Data were obtained from the regional registry of SUID cases in the period 2009–2019. The registry contains both sudden unexpected deaths in the first week of life (Sudden Unexpected Early Neonatal Deaths - SUEND), and those occurring after the first week up to 1 year of age (SUID).

Results

In this timeframe a total of 73 sudden unexpected deaths occurred in our region; 32 were Unexplained (i.e. Sudden Infant Death Syndrome - SIDS), 24 Explained, 10 Undetermined, and 7 SUEND. Autopsies were performed in 91% of cases, and in 95% of these by three groups of selected pathologists according to our protocol.

We found a low incidence of SUID (0.21 ‰), and SIDS deaths accounted for 0.1‰ of live births (48% of cases) with a high prevalence of infants of non-Italian ethnicity (38% of cases). Bereaved families were able to receive psychological support from mental health professionals and have contact with the family association, Seeds for SIDS. Audits were organized when post-mortem examinations were not carried out or carried out incorrectly in procedural terms, and when the diagnosis was particularly uncertain.

Conclusions

This paper first provides data on SUID mortality based on complete post-mortems in an Italian region. According to these findings we can state that our approach is effective both in terms of correctly performed autopsies and support for bereaved families. Future efforts are necessary to further reduce the incidence of SUID especially among non- Italian infants. An improvement action is also recommended for ensuring a more accurate and consistent picture of the circumstances of death.

The final approval of the National Protocol for the management of SUID cases is therefore strongly advocated in order to improve surveillance in this specific field and abolish disparities among the Italian regions.

Multidisciplinary study of sudden unexpected infant death in Liguria (Italy): a nine-year report

INTRODUCTION

We conducted a retrospective analysis of cases of sudden unexpected infant death (SUID) referred to the SIDS-ALTE Center of the Liguria Region (Italy) from 2010 to 2018. In all cases, the death scene was inspected, and a multidisciplinary post-mortem evaluation was conducted. Our aim was to analyze the epidemiological data and etiological distribution.

EVIDENCE ACQUISITION

We examined 15 cases initially classified as sudden infant death.

EVIDENCE SYNTHESIS

In all cases, the death was initially unexplained. Seven cases involved males and eight involved females. Their mean age was 67.47 days; the youngest victim was 2 days old, while the oldest was 8.5 months (253 days). In 7 cases, the post-mortem analysis showed an infection of lung. In 4 cases, the prone position of the infant during sleep was identified as a risk factor. Only in one case the cause of death remains unexplained, and it was classified as sudden infant death syndrome II according to San Diego Classification.

CONCLUSIONS

In the forensic approach to cases of SUID, it is always important to conduct a thorough multidisciplinary investigation. In order to avoid procedural errors that might compromise the post-mortem investigation, it is necessary to consider the medical and social history of both mother and child, in addition to the circumstances of the death. Moreover, a complete pediatric post-mortem examination and multidisciplinary discussion are required in order to identify potentially important causative or contributory factors.

Take a deep breath and wake up: The protean role of serotonin preventing sudden death in infancy

Recordings from infants who died suddenly and unexpectedly demonstrate the occurrence of recurring apneas, ineffective gasping, and finally, failure to restore eupnea and arouse prior to death. Immunohistochemical and autoradiographic data demonstrate a constellation of serotonergic defects in the caudal raphe nuclei in infants who died of Sudden Infant Death Syndrome (SIDS). The purpose of this review is to synthesize what is known about adaptive responses of the infant to severely hypoxic conditions, which unleash a flood of neuromodulators that inhibit cardiorespiratory function, thermogenesis, and arousal and the emerging role of serotonin, which combats this cardiorespiratory inhibition to foster autoresuscitation, eupnea, and arousal to ensure survival following an hypoxic episode. The laryngeal and carotid body chemoreflexes are potent in newborns and infants, and both reflexes can induce apnea and bradycardia, which may be adaptive initially, but must be terminated if an infant is to survive. Serotonin has a unique ability to touch on each of the processes that may be required to recover from hypoxic reflex apnea: gasping, the restoration of heart rate and blood pressure, termination of apneas and, eventually, stimulation of eupnea and arousal. Recurrent apneic events, bradycardia, ineffective gasping and a failure to terminate apneas and restore eupnea are observed in animals harboring defects in the caudal serotonergic system models - all of these phenotypes are reminiscent of and compatible with the cardiorespiratory recordings made in infants who subsequently died of SIDS. The caudal serotonergic system provides an organized, multi-pronged defense against reflex cardiorespiratory inhibition and the hypoxia that accompanies prolonged apnea, bradycardia and hypotension, and any deficiency of caudal serotonergic function will increase the propensity for sudden unexplained infant death.

Prenatal intermittent hypoxia sensitizes the laryngeal chemoreflex, blocks serotoninergic shortening of the reflex, and reduces 5-HT3 receptor binding in the NTS in anesthetized rat pups

We tested the hypothesis that exposure to intermittent hypoxia (IH) during pregnancy would prolong the laryngeal chemoreflex (LCR) and diminish the capacity of serotonin (5-hydroxytryptamine; 5-HT) to terminate the LCR. Prenatal exposure to IH was associated with significant prolongation of the LCR in younger, anesthetized, postnatal day (P) rat pups age P8 to P16 compared to control, room air (RA)-exposed rat pups of the same age. Serotonin microinjected into the NTS shortened the LCR in rat pups exposed to RA during gestation, but 5-HT failed to shorten the LCR in rat pups exposed to prenatal IH. Given these observations, we tested the hypothesis that prenatal hypoxia would decrease binding to 5-HT3 receptors in the nucleus of the solitary tract (NTS) where 5-HT acts to shorten the LCR. Serotonin 3 receptor binding was reduced in younger rat pups exposed to IH compared to control, RA-exposed rat pups in the age range P8 to P12. Serotonin 3 receptor binding was similar in older animals (P18-P24) regardless of gas exposure during gestation. The failure of the 5-HT injected into the NTS to shorten the LCR was correlated with a developmental decrease in 5-HT3 receptor binding in the NTS associated with exposure to prenatal IH. In summary, prenatal IH sensitized reflex apnea and blunted processes that terminate reflex apneas in neonatal rat pups, processes that are essential to prevent death following apneas such as those seen in babies who died of SIDS.

Molecular mechanisms for nicotine intoxication

Nicotine, one of the more than 4700 ingredients in tobacco smoke, is a neurotoxin and once used as pesticides in agriculture. Although its use in agriculture is prohibited in many countries, nicotine intoxication is still a problem among the workers in tobacco farms, and young children as well as adults due to the accidental or suicidal ingestions of nicotine products. Understanding the mechanism of nicotine intoxication is important not only for the prevention and treatment but also for the appropriate regulatory approaches. Here, we review pharmacokinetics of nicotine and the molecular mechanisms for acute and chronic intoxication from nicotine that might be relevant to the central and the peripheral nervous system. We include green tobacco sickness, acute intoxication from popular nicotine products, circadian rhythm changes, chronic intoxication from nicotine through prenatal nicotine exposure, newborn behaviors, and sudden infant death syndrome.

Activation of serotonergic neurons in the medullary caudal raphe shortens the laryngeal chemoreflex in anaesthetized neonatal rats

NEW FINDINGS

What is the central question of this study? Does activation of serotonergic neurons in the caudal medullary raphe, some of which project to the nucleus of the solitary tract, shorten the laryngeal chemoreflex? What is the main finding and its importance? We found that serotonin originating from neurons in the caudal raphe acts through a 5-HT₃ receptor located in the nucleus of the solitary tract to terminate reflex apnoea. Failure or deficiency of this arousal-related process is likely to be relevant to the pathogenesis of sudden infant death syndrome. Failure to terminate apnoea and arouse is likely to contribute to sudden infant death syndrome (SIDS). Serotonin is deficient in the brainstems of babies who have died of SIDS. We tested the hypothesis that activation of serotoninergic neurons in the caudal medullary raphe, some of which project to the nucleus of the solitary tract (NTS), would shorten the laryngeal chemoreflex (LCR). We studied anaesthetized neonatal rat pups between postnatal days 9 and 17. We injected 5-40 μl of water into the larynx to elicit the LCR and measured the duration of respiratory disruption. Microinjection of 50 nl of 100 μm AMPA into the caudal medullary raphe shortened the apnoeas (P < 0.001) and respiratory inhibition (P < 0.005) associated with the LCR. When 50 nl of 30 mm ondansetron, a 5-HT₃ antagonist, was microinjected bilaterally into the NTS, AMPA microinjected into the caudal raphe no longer shortened the LCR. After bilateral microinjection of vehicle into the NTS, AMPA microinjection into the caudal raphe significantly shortened the LCR. AMPA, a glutamate receptor agonist, may activate many neurons within the caudal raphe, but blocking the 5-HT₃ receptor-dependent responses in the NTS prevented the shortening of the LCR associated with AMPA microinjections into the caudal raphe. Thus, serotonin originating from neurons in the caudal raphe acts through a 5-HT₃ receptor located in the NTS to terminate or shorten the LCR. Serotonin is deficient in the brainstems of babies who have died of SIDS, and deficient serotonergic termination of apnoea is likely to be relevant to the pathogenesis of SIDS.

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.

Metabolomic profiling of brain from infants who died from Sudden Infant Death Syndrome reveals novel predictive biomarkers

OBJECTIVE

Sudden Infant Death Syndrome (SIDS) is defined as the sudden death of an infant <1 year of age that cannot be explained following a thorough investigation. Currently, no reliable clinical biomarkers are available for the prediction of infants who will die of SIDS.

STUDY DESIGN

This study aimed to profile the medulla oblongata from postmortem human brain from SIDS victims (n=16) and compare their profiles with that of age-matched controls (n=7).

RESULTS

Using LC-Orbitrap-MS, we detected 12 710 features in electrospray ionization positive (ESI+) mode and 8243 in ESI- mode from polar extracts of brain. Five features acquired in ESI+ mode produced a predictive model for SIDS with an area under the receiver operating characteristic curve (AUC) of 1 (confidence interval (CI): 0.995-1) and a predictive power of 97.4%. Three biomarkers acquired in ESI- mode produced a predictive model with an AUC of 0.866 (CI: 0.767-0.942) and a predictive power of 77.6%. We confidently identified 5 of these features (l-(+)-ergothioneine, nicotinic acid, succinic acid, adenosine monophosphate and azelaic acid) and putatively identify another 4 out of the 15 in total.

CONCLUSIONS

This study underscores the potential value of metabolomics for studying SIDS. Further characterization of the metabolome of postmortem SIDS brains could lead to the identification of potential antemortem biomarkers for novel prevention strategies for SIDS.

Hypothesis on supine sleep, sudden infant death syndrome reduction and association with increasing autism incidence

AIM: To identify a hypothesis on: Supine sleep, sudden infant death syndrome (SIDS) reduction and association with increasing autism incidence.

METHODS: Literature was searched for autism spectrum disorder incidence time trends, with correlation of change-points matching supine sleep campaigns. A mechanistic model expanding the hypothesis was constructed based on further review of epidemiological and other literature on autism.

RESULTS: In five countries (Denmark, United Kingdom, Australia, Israel, United States) with published time trends of autism, change-points coinciding with supine sleep campaigns were identified. The model proposes that supine sleep does not directly cause autism, but increases the likelihood of expression of a subset of autistic criteria in individuals with genetic susceptibility, thereby specifically increasing the incidence of autism without intellectual disability.

CONCLUSION: Supine sleep is likely a physiological stressor, that does reduce SIDS, but at the cost of impact on emotional and social development in the population, a portion of which will be susceptible to, and consequently express autism. A re-evaluation of all benefits and harms of supine sleep is warranted. If the SIDS mechanism proposed and autism model presented can be verified, the research agenda may be better directed, in order to further decrease SIDS, and reduce autism incidence.

Proteomic MALDI-TOF/TOF-IMS examination of peptide expression in the formalin fixed brainstem and changes in sudden infant death syndrome infants

Matrix assisted laser desorption/ionisation imaging mass spectrometry (MALDI-IMS) has not previously been utilised to examine sudden infant death syndrome (SIDS). This study aimed to optimise MALDI IMS for use on archived formalin-fixed-paraffin-embedded human infant medulla tissue (n=6, controls; n=6, SIDS) to evaluate differences between multiple nuclei of the medulla by using high resolution IMS. Profiles were compared between SIDS and age/sex matched controls. LC-MALDI identified 55 proteins based on 321 peptides across all samples; 286 peaks were found using IMS, corresponding to these 55 proteins that were directly compared between controls and SIDS. Control samples were used to identify common peptides for neuronal/non-neuronal structures allowing identification of medullary regions. In SIDS, abnormal expression patterns of 41 peptides (p≤0.05) corresponding to 9 proteins were observed; these changes were confirmed with immunohistochemistry. The protein abnormalities varied amongst nuclei, with the majority of variations in the raphe nuclei, hypoglossal and pyramids. The abnormal proteins are not related to a previously identified neurological disease pathway but consist of developmental neuronal/glial/axonal growth, cell metabolism, cyto-architecture and apoptosis components. This suggests that SIDS infants have abnormal neurological development in the raphe nuclei, hypoglossal and pyramids of the brainstem, which may contribute to the pathogenesis of SIDS.

BIOLOGICAL SIGNIFICANCE

This study is the first to perform an imaging mass spectrometry investigation in the human brainstem and also within sudden infant death syndrome (SIDS). LC MALDI and MALDI IMS identified 55 proteins based on 285 peptides in both control and SIDS tissue; with abnormal expression patterns present for 41/285 and 9/55 proteins in SIDS using IMS. The abnormal proteins are critical for neurological development; with the impairment supporting the hypothesis that SIDS may be due to delayed neurological maturation. The brainstem regions mostly affected included the raphe nuclei, hypoglossal and pyramids. This study highlights that basic cyto-architectural proteins are affected in SIDS and that abnormal expression of these proteins in other CNS disorders should be examined.

KEY SENTENCES

LC MALDI and MALDI IMS identified 55 proteins based on 285 peptides in both control and SIDS tissue. Abnormal expression patterns were present for 41/285 and 9/55 proteins in SIDS using IMS. Brainstem regions mostly affected included the raphe nuclei, hypoglossal and pyramids.

Supporting SIDS Families: The Public Health Nurse SIDS Home Visit

Sudden infant death syndrome (SIDS) death has a devastating effect on parents. There is no known cause, so parents experience guilt about what they might have done or not done to contribute to the death. Although some SIDS parents may receive support from family and friends, the public health nurse (PHN) has an important professional role in providing grief support, SIDS education, and offering SIDS resources and referrals. Based on years of clinical practice, we recommend the following: Perform the home visit as soon as possible. Show care and compassion. Personalize the baby by using his or her name and asking to see photographs. Reassure the parents that grief is a process which takes time. Educate about what SIDS is and what it is not. Increasingly, SIDS deaths occur in the presence of risk factors. Explain that risk factors are not causes of death. As an authority in health care, reassuring families that they did not cause their baby's death has a tremendous impact on relieving guilt. Putting newly bereaved SIDS parents in contact with other SIDS parents is one of the most helpful actions a PHN can take to help families.

Decreased orexin (hypocretin) immunoreactivity in the hypothalamus and pontine nuclei in sudden infant death syndrome

Infants at risk of sudden infant death syndrome (SIDS) have been shown to have dysfunctional sleep and poor arousal thresholds. In animal studies, both these attributes have been linked to impaired signalling of the neuropeptide orexin. This study examined the immunoreactivity of orexin (OxA and OxB) in the tuberal hypothalamus (n = 27) and the pons (n = 15) of infants (1-10 months) who died from SIDS compared to age-matched non-SIDS infants. The percentage of orexin immunoreactive neurons and the total number of neurons were quantified in the dorsomedial, perifornical and lateral hypothalamus at three levels of the tuberal hypothalamus. In the pons, the area of orexin immunoreactive fibres were quantified in the locus coeruleus (LC), dorsal raphe (DR), laterodorsal tegmental (LDT), medial parabrachial, dorsal tegmental (DTg) and pontine nuclei (Pn) using automated methods. OxA and OxB were co-expressed in all hypothalamic and pontine nuclei examined. In SIDS infants, orexin immunoreactivity was decreased by up to 21 % within each of the three levels of the hypothalamus compared to non-SIDS (p ≤ 0.050). In the pons, a 40-50 % decrease in OxA occurred in the all pontine nuclei, while a similar decrease in OxB immunoreactivity was observed in the LC, LDT, DTg and Pn (p ≤ 0.025). No correlations were found between the decreased orexin immunoreactivity and previously identified risk factors for SIDS, including prone sleeping position and cigarette smoke exposure. This finding of reduced orexin immunoreactivity in SIDS infants may be associated with sleep dysfunction and impaired arousal.

Proposal for mechanisms of protection of supine sleep against sudden infant death syndrome: an integrated mechanism review

Supine sleep decreases sudden infant death syndrome (SIDS) incidence, however the mechanisms for this are unclear. The triple risk model for SIDS requires that one or more underlying abnormalities of breathing or autonomic control are present; these are rare, but brainstem defects are found in most SIDS cases. Supine sleep increases sympathetic nervous system tone, and level of state organization, and may therefore act as a stressor. This is evidenced by physiological arousal, and by delayed neurodevelopment in supine compared to prone sleepers. It is argued here that prone sleep position is the biological normative standard in healthy infants, supporting autonomic regulation. During rapid eye movement (REM) sleep (and other circumstances), a parasympathetic-mediated adverse autonomic event (AAE) may be spontaneously triggered. In healthy infants, gasping initiates autoresuscitation and recovery.

HYPOTHESIS

The underlying vulnerability to SIDS is specific to autoresuscitation from an AAE, the initial serotonin-dependent gasp is commonly compromised. Serotonin metabolism defects also influence sleep architecture, increasing the likelihood of AAE. The mechanism whereby supine sleep decreases SIDS may therefore be a stressor effect, disturbing sleep architecture to decrease REM and AAEs, and increasing sympathetic tone, which may prevent and counteract the purely parasympathetic-mediated AAE, thereby decreasing the risk of SIDS.

Complex brain malformations associated with chromosome 6q27 gain that includes THBS2, which encodes thrombospondin 2, an astrocyte-derived protein of the extracellular matrix

This case describes the autopsy findings of a 2-month-old male infant with extensive and severe developmental brain abnormalities, including microcephaly, neocortical neuronal layering abnormalities, leptomeningeal heterotopias, commissural agenesis, and cerebellar and brainstem hypoplasia. Microarray analysis identified a gain in chromosome band 6q27, which includes the entire coding region of THBS2. THSB2 encodes thrombospondin 2 (TSP2), an astrocyte secreted protein of the extracellular matrix that promotes synaptogenesis, neurite outgrowth, and cerebellar granule cell migration. Thrombospondin 2 is not a matrix structural protein; instead it serves as an extracellular modulator of cell function, so it is considered a matricellular protein. The neuropathological findings at autopsy are compatible with perturbations in several known functions of TSP2 and demonstrate that TSP2 dysregulation can have a significant negative impact on human brain development. Furthermore, this case demonstrates the important role of astrocytes in human brain development.

Sudden unexpected death in infancy: a historical perspective

Epidemiological, developmental and pathological research over the last 40 years has done much to unravel the enigma of sudden unexpected death in infancy (SUDI) and sudden infant death syndrome (SIDS) that has afflicted the human condition for millennia. Modifications in infant care practices based on the avoidance of risk factors identified from a consistent epidemiological profile across time and multiple locations have resulted in dramatic reductions in the incidence of SUDI and SIDS in particular. The definition of SIDS (or unexplained SUDI) has been continually refined allowing enhanced multidisciplinary research, results of which can be more reliably compared between investigators. These latter expanded definitions mandating death scene investigations, evaluation of the circumstances of death and more comprehensive autopsies including additional ancillary testing have illuminated the importance of life-threatening sleep environments. The triple-risk hypothesis for SIDS has been increasingly validated and formulates an inextricable relationship between an infant's state of development, underlying pathological vulnerability and an unsafe sleep environment for sudden infant death to occur. Today, the major risk factors for SUDI are maternal smoking and bed sharing, and the challenge is to implement effective strategies that will reduce the exposure to such risks as was done with prone sleeping position. The challenges ahead include development of clinical methods and/or laboratory testing that will accurately identify which infants are at particularly high risk of SIDS but also means by which their deaths can be prevented.

Classification system for the Sudden Unexpected Infant Death Case Registry and its application

Sudden unexpected infant deaths (SUID) accounted for 1 in 3 postneonatal deaths in 2010. Sudden infant death syndrome and accidental sleep-related suffocation are among the most frequently reported types of SUID. The causes of these SUID usually are not obvious before a medico-legal investigation and may remain unexplained even after investigation. Lack of consistent investigation practices and an autopsy marker make it difficult to distinguish sudden infant death syndrome from other SUID. Standardized categories might assist in differentiating SUID subtypes and allow for more accurate monitoring of the magnitude of SUID, as well as an enhanced ability to characterize the highest risk groups. To capture information about the extent to which cases are thoroughly investigated and how factors like unsafe sleep may contribute to deaths, CDC created a multistate SUID Case Registry in 2009. As part of the registry, the Centers for Disease Control and Prevention developed a classification system that recognizes the uncertainty about how suffocation or asphyxiation may contribute to death and that accounts for unknown and incomplete information about the death scene and autopsy. This report describes the classification system, including its definitions and decision-making algorithm, and applies the system to 436 US SUID cases that occurred in 2011 and were reported to the registry. These categories, although not replacing official cause-of-death determinations, allow local and state programs to track SUID subtypes, creating a valuable tool to identify gaps in investigation and inform SUID reduction strategies.