Infant gender, shared sleeping and sudden death

Death from Failed Protection? An Evolutionary-Developmental Theory of Sudden Infant Death Syndrome

Sudden infant death syndrome (SIDS) has been mainly described from a risk perspective, with a focus on endogenous, exogenous, and temporal risk factors that can interact to facilitate lethal outcomes. Here we discuss the limitations that this risk-based paradigm may have, using two of the major risk factors for SIDS, prone sleep position and bed-sharing, as examples. Based on a multipronged theoretical model encompassing evolutionary theory, developmental biology, and cultural mismatch theory, we conceptualize the vulnerability to SIDS as an imbalance between current physiologic-regulatory demands and current protective abilities on the part of the infant. From this understanding, SIDS appears as a developmental condition in which competencies relevant to self-protection fail to develop appropriately in the future victims. Since all of the protective resources in question are bound to emerge during normal infant development, we contend that SIDS may reflect an evolutionary mismatch situation-a constellation in which certain modern developmental influences may overextend the child's adaptive (evolutionary) repertoire. We thus argue that SIDS may be better understood if the focus on risk factors is complemented by a deeper appreciation of the protective resources that human infants acquire during their normal development. We extensively analyze this evolutionary-developmental theory against the body of epidemiological and experimental evidence in SIDS research and thereby also address the as-of-yet unresolved question of why breastfeeding may be protective against SIDS.

Investigating genetic variants in microRNA regulators of Neurokinin-1 receptor in sudden infant death syndrome

Sudden infant death syndrome (SIDS) occurs more often in male than in female infants, suggesting involvement of the X-chromosome. Histopathological studies have suggested that altered expression of the Neurokinin-1 receptor may also play a role in the pathogenesis of SIDS. It was hypothesised that genetic variants in three X-chromosome-encoded microRNA (miRNA/miR), known to down-regulate expression of the Neurokinin-1 receptor, may contribute to SIDS.

AIM

To identify sequence variants in the miRNAs within a study cohort (27 cases of SIDS and 28 controls) and determine if there was a difference in the frequencies in male and female SIDS infants.

METHODS

Genomic DNA prepared from stored blood spots was amplified and sequenced to identify genetic variants in miR500A, miR500B and miR320D2.

RESULTS

No novel variants in the miRNAs were identified in our study cohort. We identified one known single-nucleotide polymorphism (SNP) in miR320D2: rs5907732 G/T, in both cases and controls. No significant difference in the SNP frequency was observed between male and female SIDS cases.

CONCLUSION

This pilot study suggests that sequence variants in three miRNAs do not contribute to the reported higher prevalence of SIDS in male infants and do not contribute to the pathogenesis of SIDS in our cohort.

Medullary Astrogliosis in Sudden Infant Death Syndrome Varies With Sleeping Environment: Evidence for Different Mechanisms of Death in Alone Versus Co-sleepers?

Sudden infant death syndrome remains the leading cause of death in infants under 1 year, and underlying pathophysiological mechanisms are poorly understood. The current study investigated the hypothesis that co-sleepers die more rapidly from causes such as suffocation from overlaying by comparing levels of reactive astrogliosis in the medulla of infants who died sleeping alone to those who died co-sleeping. The amount of glial fibrillary acidic protein (GFAP) staining in alone sleepers was significantly higher than shared sleepers in 3 specific areas of the medulla, the inferior vestibular nucleus, the medial vestibular nucleus and the cochlear nucleus. Given that glial fibrillary acidic protein elevations follow a delayed time course, this suggests that death in co-sleepers was more rapid, not allowing for reactive gliosis to occur. This provides evidence of pathological differences in mechanisms of death in infants who are classified as having died from sudden infant death syndrome, suggesting potential need for refinement of categorization of these cases.

Why is a prone sleeping position dangerous for certain infants?

The prone (face down) sleeping position is known to be associated with a significantly increased risk of sudden and unexpected death in infancy (sudden infant death syndrome or SIDS), however, the reasons for this are unclear. Suggested mechanisms have involved suffocation from occlusion of the external airways by soft bedding/pillows or from flattening of the nose with backward displacement of the tongue, rebreathing of carbon dioxide, blunting of arousal responses with decreased cardiac responses to auditory stimulation, diaphragmatic splinting or fatigue, lowering of vasomotor tone with tachycardia, nasopharyngeal bacterial overgrowth, overheating, alteration of sleep patterns, compromise of cerebral blood flow and upper airway obstruction from distortion of nasal cartilages. Recent studies have, however, shown a significant reduction in substance P in the inferior portion of the olivo-cerebellar complex in SIDS infants which is crucial for the integration of motor and sensory information for the control of head and neck movement. This deficit may explain why some infants are not able to move their faces away from potentially dangerous sleeping environments.

Sleep-Related Infant Deaths in Victoria: A Retrospective Case Series Study

BACKGROUND

There is general agreement that in some circumstances, sharing a sleep surface of any kind with an infant increases the risk of sudden unexpected death in infancy. There is a paucity of research conducted in Australia examining this issue. This study examines the frequency and distribution of sleep-related infant deaths in a defined population, and reports the proportion that occurred in the context of bed-sharing.

METHODS

A retrospective population-based case series study was conducted of infants (≤365 days) who died in a sleeping context during the period 1 January 2008 to 31 December 2010 in the state of Victoria, Australia. Information about the infant, caregiver, sleeping environment and bed-sharing was collected from a review of the coroner's death investigation record.

RESULTS

During the 3-year study period, 72 infant deaths occurred in a sleeping context. Of these, 33 (45.8 %) occurred in the context of bed-sharing: n = 7 in 2008; n = 11 in 2009; and n = 15 in 2010. Further analysis of the 33 deaths occurring in the context of bed-sharing showed that in this group, bed-sharing was largely intentional, habitual and most often involved the mother as one of the parties.

CONCLUSIONS

Given the case series nature of the study design, a causal relationship between bed-sharing and infant death could not be inferred. However the fact that nearly half of all sleep-related deaths occurred in the context of bed-sharing, provides strong support for the need to undertake definitive analytic studies in Australia so that evidence-based advice can be provided to families regarding the safety of bed-sharing practices.

Infants dying suddenly and unexpectedly share demographic features with infants who die with retinal and dural bleeding: a review of neural mechanisms

The cause of death in infants who die suddenly and unexpectedly (sudden unexpected death in infancy [SUDI]) remains a diagnostic challenge. Some infants have identified diseases (explained SUDI); those without explanation are called sudden infant death syndrome (SIDS). Demographic data indicate subgroups among SUDI and SIDS cases, such as unsafe sleeping and apparent life-threatening events. Infants dying suddenly with retinal and dural bleeding are often classified as abused, but in many there is no evidence of trauma. Demographic features suggest that they may represent a further subgroup of SUDI. This review examines the neuropathological hypotheses to explain SIDS and highlights the interaction of infant oxygen-conserving reflexes with the brainstem networks considered responsible for SIDS. We consider sex- and age-specific vulnerabilities related to dural bleeding and how sensitization of the dural innervation by bleeding may influence these reflexes, potentially leading to collapse or even death after otherwise trivial insults.

Parent-child bed-sharing: The good, the bad, and the burden of evidence

The practice of parent and child sharing a sleeping surface, or 'bed-sharing', is one of the most controversial topics in parenting research. The lay literature has popularized and polarized this debate, offering on one hand claims of dangers, and on the other, of benefits - both physical and psychological - associated with bed-sharing. To address the scientific evidence behind such claims, we systematically reviewed 659 published papers (peer-reviewed, editorial pieces, and commentaries) on the topic of parent-child bed-sharing. Our review offers a narrative walkthrough of the many subdomains of bed-sharing research, including its many correlates (e.g., socioeconomic and cultural factors) and purported risks or outcomes (e.g., sudden infant death syndrome, sleep problems). We found general design limitations and a lack of convincing evidence in the literature, which preclude making strong generalizations. A heat-map based on 98 eligible studies aids the reader to visualize world-wide prevalence in bed-sharing and highlights the need for further research in societies where bed-sharing is the norm. We urge for multiple subfields - anthropology, psychology/psychiatry, and pediatrics - to come together with the aim of understanding infant sleep and how nightly proximity to the parents influences children's social, emotional, and physical development.

Bed-sharing in the absence of hazardous circumstances: is there a risk of sudden infant death syndrome? An analysis from two case-control studies conducted in the UK

Objective

The risk of sudden infant death syndrome (SIDS) among infants who co-sleep in the absence of hazardous circumstances is unclear and needs to be quantified.

Design

Combined individual-analysis of two population-based case-control studies of SIDS infants and controls comparable for age and time of last sleep.

Setting

Parents of 400 SIDS infants and 1386 controls provided information from five English health regions between 1993–6 (population: 17.7 million) and one of these regions between 2003–6 (population:4.9 million).

Results

Over a third of SIDS infants (36%) were found co-sleeping with an adult at the time of death compared to 15% of control infants after the reference sleep (multivariate OR = 3.9 [95% CI: 2.7–5.6]). The multivariable risk associated with co-sleeping on a sofa (OR = 18.3 [95% CI: 7.1–47.4]) or next to a parent who drank more than two units of alcohol (OR = 18.3 [95% CI: 7.7–43.5]) was very high and significant for infants of all ages. The risk associated with co-sleeping next to someone who smoked was significant for infants under 3 months old (OR = 8.9 [95% CI: 5.3–15.1]) but not for older infants (OR = 1.4 [95% CI: 0.7–2.8]). The multivariable risk associated with bed-sharing in the absence of these hazards was not significant overall (OR = 1.1 [95% CI: 0.6–2.0]), for infants less than 3 months old (OR = 1.6 [95% CI: 0.96–2.7]), and was in the direction of protection for older infants (OR = 0.1 [95% CI: 0.01–0.5]). Dummy use was associated with a lower risk of SIDS only among co-sleepers and prone sleeping was a higher risk only among infants sleeping alone.

Conclusion

These findings support a public health strategy that underlines specific hazardous co-sleeping environments parents should avoid. Sofa-sharing is not a safe alternative to bed-sharing and bed-sharing should be avoided if parents consume alcohol, smoke or take drugs or if the infant is pre-term.