Megalencephaly in sudden infant death syndrome

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.

The Science (or Nonscience) of Research Into Sudden Infant Death Syndrome (SIDS)

This Viewpoint paper presents a timely and constructive critique of mainstream SIDS research. It is concerning that twenty-first century medical science has not provided an answer to the tragic enigma of SIDS. The paper helps explain why this is so and illustrates possible shortcomings in the investigation of Sudden Infant Death Syndrome/Sudden Unexplained Infant Death (SIDS/SUID) by mainstream researchers. Mainstream findings are often based on questionable and dogmatic assumptions that return to founding notions such as the Triple Risk Hypothesis and the contention that the mechanisms underlying SIDS/SUID are heterogeneous in nature. The paper illustrates how the pathological findings in SIDS have been under-investigated (or ignored) and that key epidemiological risk factors have slipped from memory. This apparent amnesia has resulted in failure to use these established SIDS facts to substantiate the significance of various neuropathological, neurochemical, or other research findings. These unsupported findings and their derivative hypotheses are therefore ill-founded and lack scientific rigor.

CONCLUSION

The deficits of SIDS "science" revealed in this paper explain why the SIDS enigma has not yet been solved. To make progress in understanding SIDS, it is important that researchers, as scientists, uphold standards of research. Encouragement for new directions of research is offered.

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.

Increased thymus weight in sudden infant death syndrome compared to controls: The role of sub-clinical infections

OBJECTIVE

The goal of the present investigation is to analyze thymus, brain, heart, liver, and kidney weights in SIDS victims compared to controls.

BACKGROUND

Epidemiologic risk factors for SIDS (eg, male gender, genetic, obstetric, environmental, smoke exposure, nonbreastfeeding, etc.) are consistent with an infectious process underlying many of these deaths.

METHODS

Data from autopsy reports on 585 SIDS victims and comparison deaths (n = 294 control, n = 291 SIDS) were analyzed. Cases were obtained from Australia (n = 184 controls, n = 98 SIDS) and Russia (n = 122 controls, n = 181 SIDS). Log₁₀ transform of thymus and other organ weights was computed because variables were skewed. Multivariate analysis of variance (MANOVA) of standardized log values were age-adjusted by multivariate analysis of covariance (MANCOVA). The standardized log₁₀ thymus residual adjusted for age, brain and liver weights was computed for the final analysis.

RESULTS

After controlling for age by MANCOVA, thymus, body, brain and liver weights were significantly higher among SIDS compared to non-SIDS victims. The largest difference as between covariate-adjusted log₁₀ non-SIDS thymus weight differed (mean = 1.423, 95% CI: 1.393-1.452) and log₁₀ non-SIDS thymus weight (mean = 1.269, 95% CI: 1.243-1.294) were significantly different (P < .0001). Heart weight was significantly lower in SIDS victims.

DISCUSSION

When adjusted for confounders (age, body, and organ weights), SIDS victims have a significantly heavier thymus and brain compared to non-SIDS controls who died of trauma. This finding supports previously published studies that link infection to SIDS deaths.

Brain weight in sudden unexpected death in infancy: experience from a large single-centre cohort

AIMS

Published reports of brain weight in sudden infant death syndrome (SIDS) are contradictory, although several have concluded that brain weight is increased in SIDS compared with controls or reference data. This is important as, if brain weight is significantly different, it may be of diagnostic use or provide insights into the aetiology of SIDS. The aim of this study was to use a large series of well-characterized sudden unexpected infant deaths from a single centre to provide definitive data regarding this issue.

METHODS

A retrospective review identified 1100 infants who had died suddenly and undergone a comprehensive autopsy at Great Ormond Street Hospital between 1996 and 2011. They were split into two groups: those in whom death could be explained and those whose deaths remained unexplained despite full investigation (SIDS/unexplained sudden unexpected death in infancy).

RESULTS

There were 1100 cases of whom 573 (52%) were unexplained and 527 (48%) explained. Multiple regression analysis, which adjusted for sex, age and post-mortem interval, showed no difference in the ratio of brain weight : body weight between those infants dying of explained causes and those in whom no cause could be found. This finding remained true when restricting analysis to those with macroscopically normal brains.

CONCLUSIONS

In this large series of infants dying of both explained and unexplained causes, brain weight, once corrected for body weight, did not vary consistently with the cause of death. Brain weight cannot be used as a diagnostic indicator of the cause of death or to inform hypothetical models of the pathogenesis of SIDS.

Brain weight-body weight ratio in sudden infant death syndrome revisited

AIMS

To determine whether the brain-body weight ratio is increased in sudden infant death syndrome (SIDS).

METHODS

Review of autopsy files from Forensic Science SA, South Australia was undertaken over an eight-year period from 1999 to 2006, with classification of cases according to the San Diego definition. Sudden and/or unexpected deaths in previously healthy infants due to asphyxia or infection were selected as controls.

RESULTS

There were 42 SIDS cases and 25 controls. The SIDS cases were aged from 1 to 42 weeks (mean: 16.26 ± 1.5 weeks) with a male to female ratio of 26:16. The control infants were aged from 3 to 48 weeks (mean: 19.24 ± 2.9 weeks) (P > 0.05) (M:F = 16:9) and included 13 cases of asphyxia and 12 cases of sepsis. Comparison of the brain-body weight ratios failed to demonstrate a significant difference: SIDS mean = 0.121 ± 0.003; control mean = 0.115 ± 0.003 (P > 0.05).

CONCLUSION

Although, there was a trend towards higher brain-body weight ratios in SIDS infants, this did not reach significance. The role of brain weight in the aetiology of SIDS remains controversial.

Beta-amyloid precursor protein staining in nonhomicidal pediatric medicolegal autopsies

Immunohistochemical staining for beta-amyloid precursor protein (betaAPP) has been validated as a marker for axonal injury in adults surviving > or = 2 hours after white matter damage. The significance of betaAPP staining in pediatric brains and spinal cords is not as well established. We evaluated the white matter immunoreactivity for betaAPP from a variety of pediatric medicolegal autopsies: natural disease (non-Sudden Infant Death Syndrome [SIDS]), SIDS, motor vehicle accidents, drowning, near-drowning, overlay, carbon monoxide toxicity, miscellaneous trauma, and mechanical asphyxia. The cases of carbon monoxide toxicity, motor vehicle accidents (death at scene), drowning (with resuscitation), and a natural (non-SIDS) death had no significant white matter staining. The traumatic deaths with a significant survival interval, a variety of natural deaths, the near-drowning case, and surprisingly, all SIDS had detectable betaAPP white matter immunostaining. These results demonstrate that features other than traumatic axonal injury, such as metabolic insults and hypoxic-ischemic injury secondary to vascular compromise, must contribute to betaAPP immunostaining. In addition, we describe a variety of betaAPP-immunoreactive structures not previously reported in the pediatric population. This study illustrates that betaAPP immunostaining enhances detection of a variety of white matter changes, and provides a basis for interpretation of these results.

In utero brain lesions in SIDS

Serial examination of the cerebral hemispheres of 20 sudden infant death syndrome victims revealed high incidence of leukomalacia (40%), leptomeningeal glioneuronal heterotopias (70%) at the base of the cerebrum, and astrogliosis (65%) in the white matter and medulla reticular formation compared with 20 age-matched controls. These results suggest that an antepartum insult may become an important predisposing risk factor in some patients for sudden infant death syndrome.

Phrenic nerves and diaphragms in sudden infant death syndrome

Disturbances of the respiratory system may be an important factor in the cascade of events leading to sudden infant death syndrome (SIDS). Even though the diaphragm is the major respiratory muscle in infants, little is known about alterations of this muscle and of the phrenic nerve in SIDS. In the present study, diaphragms and phrenic nerves of 24 SIDS infants and seven controls were analyzed. Morphometric analysis revealed only slightly larger cross sectional areas of phrenic nerve axons but no increase in myelin sheath thickness in SIDS cases. However, in one SIDS case, myelinated nerve fibre density was severely reduced. Using electron microscopy, several nerve fibres of SIDS infants showed focal accumulations of neurofilaments. Muscle fibre diameters in SIDS diaphragms were significantly larger compared to controls (P < 0.0001). However, in almost all SIDS and control cases, axons and myelin sheaths were artificially swollen, and acute segmental muscle fibre ruptures and contracture bands were found. These prominent nonspecific ultrastructural alterations should advise caution in the interpretation of morphometric data. Thus, in some cases exemplified by one case of the present series, decreased density of phrenic nerve myelinated axons might contribute to SIDS. Still, the present results indicate that development of phrenic nerves and diaphragms is not delayed in most SIDS infants.

Oxidative stress in sudden infant death syndrome

We investigated the hippocampus and parahippocampal cortex of victims of sudden infant death syndrome and of age-matched infants dying acutely of known causes (non-sudden infant death syndrome controls). Tissue sections were investigated for the presence of neurons expressing signs of elevated levels of free radical using immunohistochemical markers for superoxide dismutase and glutathione peroxidase. Brain tissues displayed immunopositive neurons in every infant. In control infants, an age-related decline in the number of superoxide dismutase- and glutathione peroxidase-immunoreactive neurons was apparent in the hippocampus and parahippocampal cortex. Significantly increased numbers of immunoreactive neurons were found in victims of sudden infant death syndrome under 6 months of age compared to age-matched controls. This suggests that infants who later become victims of sudden infant death syndrome may experience antemortem periods of oxidative stress, elevated levels of free radicals, and compensatory up-regulation of the free radical scavenger enzymes superoxide dismutase and glutathione peroxidase.

Brain weight and sudden infant death syndrome

Increased brain weights have been reported in the literature to occur among infants who have died from sudden infant death syndrome, suggesting that cerebral edema might play a role in the cause of death among these children. We have compared brain weights from children between the ages of 1 week and 1 year, autopsied between 1980 and 1992. One group consisted of 125 victims of sudden infant death syndrome and the other of 38 children who had died with a diagnosis other than the sudden infant death syndrome. Brain weights from both groups exceeded the 50th percentile in previously published reference material. We were unable to show any significant differences between the groups in either the ratio between observed and expected brain weights or the ratio between brain weight and body weight. We conclude that there is no evidence for the notion that victims of sudden infant death syndrome have an increased brain weight. Other authors (in previous studies) may have overlooked the low overall weight at gestational age of prematurely born children while collecting data for reference levels. A revision of the figures seems to be necessary.

Organ weights in sudden infant death syndrome

This comprehensive study of organ weights in sudden infant death syndrome (SIDS) should be of use to those studying postmortem data in SIDS and may have application to issues of growth and development. Analysis of data from 500 autopsies, performed over 15 years by one individual, revealed mean body weights generally below the 50th percentile for living infants. The weights of the thymus, lungs, liver, and brain were significantly greater than published norms. Thymic weights in SIDS probably represent the normal state more closely than those reported in several other series; elevated lung weights are presumably due to the intense pulmonary congestion and edema commonly encountered in SIDS; the liver edge routinely extends below the costal margins at SIDS autopsies, but the reason for increased weight is unknown, although a hemodynamic alteration seems likely; elevated brain weight has been described previously in SIDS. Other organs showed trends differing from "normal"--heart weights showed a marginally significant increase above published norms; for the adrenal glands, a uniform decrease was apparent, but slopes of linear regressions were low, hampering statistical analysis. Organ weights correlated more closely with body weight than with age. When victims were classified as "possible SIDS," "probable SIDS," or "classic SIDS," differences in organ weights were rarely significant. Analysis of organ weights using Z scores and their standard deviations (sigma-Z, or "pattern variability index") revealed increased variability in SIDS victims. Explanations for these findings include the possibility that some weights previously published as normal are low due to confounding variables. Changes could also be genuine, resulting from disturbances in growth or physiology, or artifactual, possibly the result of agonal or postmortem changes. A database on carefully selected, previously healthy infants who died suddenly and unexpectedly of known causes (i.e., trauma) is much needed.