Dysregulation of platelet serotonin, 14-3-3, and GPIX in sudden infant death syndrome.

Sudden infant death syndrome (SIDS) is the leading cause of post-neonatal infant mortality, but the underlying cause(s) are unclear. A subset of SIDS infants has abnormalities in the neurotransmitter, serotonin (5-hydroxytryptamine [5-HT]) and the adaptor molecule, 14-3-3 pathways in regions of the brain involved in gasping, response to hypoxia, and arousal. To evaluate our hypothesis that SIDS is, at least in part, a multi-organ dysregulation of 5-HT, we examined whether blood platelets, which have 5-HT and 14-3-3 signaling pathways similar to brain neurons, are abnormal in SIDS. We also studied platelet surface glycoprotein IX (GPIX), a cell adhesion receptor which is physically linked to 14-3-3. In infants dying of SIDS compared to infants dying of known causes, we found significantly higher intra-platelet 5-HT and 14-3-3 and lower platelet surface GPIX. Serum and plasma 5-HT were also elevated in SIDS compared to controls. The presence in SIDS of both platelet and brainstem 5-HT and 14-3-3 abnormalities suggests a global dysregulation of these pathways and the potential for platelets to be used as a model system to study 5-HT and 14-3-3 interactions in SIDS. Platelet and serum biomarkers may aid in the forensic determination of SIDS and have the potential to be predictive of SIDS risk in living infants.

Abnormalities of the rib growth plate and the periphysis of previously healthy infants and toddlers dying suddenly and unexpectedly.

AIMS: Histological examination of the rib is of critical value in perinatal pathology and points to the health of the child preceding death. The rib is considered ideal because it is the most rapidly growing long bone in infants and demonstrates growth arrest at onset of the insult. We aimed to identify: (1) changes in the perichondrial ring (PR) in the rib of infants and children up to 16 months of age dying suddenly at our institution and (2) any association with presence of histological changes of vitamin D deficiency (VDD)/metabolic bone disease (MBD) in the growth plate. METHODS: Retrospective review of the PR histology and comparison with the presence or absence of histological features of VDD in the growth plate of 167 cases. The cases were anonymised and divided in six age/gender categories. RESULTS: Periphyseal abnormalities were only seen in 38% of the cases; of whom 33% had established and 67% had mild changes. Only 14.5% of cases with established histological appearance of VDD at the growth plate had significant PR abnormality; of whom majority (83%) were ≤3 months of age and none ≥9 months old, reflecting a temporal relation with birth and beyond the perinatal period. CONCLUSION: The histological changes in the PR are significantly associated with histological changes of VDD/MBD at the rib growth plate with an OR of 3.04.

Post mortem tryptase: A review of literature on its use, sampling and interpretation in the investigation of fatal anaphylaxis.

Post mortem tryptase is a commonly-used ancillary test in the investigation of possible anaphylactic deaths. Ante mortem tryptase interpretation differs from post mortem interpretation due to differing priorities, biochemical behaviours and capacity for follow-up. Additionally, post mortem tryptase sampling site, method and even cut-off levels are not standardised between facilities. This review of the literature investigates the existing research and recommendations on the use of post mortem tryptase in suspected anaphylactic deaths. Currently, autopsy recommendations suggest early sampling, standardised sampling technique with clamping of and aspiration from the femoral vein, and for the results to be interpreted within the wider autopsy and clinical context. Areas in need of further research include the effects of cytolysis on tryptase levels and studies to stratify differing tryptase levels based on type of death and anaphylactic trigger.

High serum serotonin in sudden infant death syndrome.

Sudden infant death syndrome (SIDS), the leading cause of postneonatal infant mortality, likely comprises heterogeneous disorders with the common phenotype of sudden death without explanation upon postmortem investigation. Previously, we reported that ∼40% of SIDS deaths are associated with abnormalities in serotonin (5-hydroxytryptamine, 5-HT) in regions of the brainstem critical in homeostatic regulation. Here we tested the hypothesis that SIDS is associated with an alteration in serum 5-HT levels. Serum 5-HT, adjusted for postconceptional age, was significantly elevated (95%) in SIDS infants (n = 61) compared with autopsied controls (n = 15) [SIDS, 177.2 ± 15.1 (mean ± SE) ng/mL versus controls, 91.1 ± 30.6 ng/mL] (P = 0.014), as determined by ELISA. This increase was validated using high-performance liquid chromatography. Thirty-one percent (19/61) of SIDS cases had 5-HT levels greater than 2 SDs above the mean of the controls, thus defining a subset of SIDS cases with elevated 5-HT. There was no association between genotypes of the serotonin transporter promoter region polymorphism and serum 5-HT level. This study demonstrates that SIDS is associated with peripheral abnormalities in the 5-HT pathway. High serum 5-HT may serve as a potential forensic biomarker in autopsied infants with SIDS with serotonergic defects.

Use of Cortisol and Adrenal Weight at Pediatric Postmortem.

We studied the relationship between adrenal weight and postmortem cortisol level in cases of infant death, and examined use of these measurements in adrenal insufficiency. We analyzed procurator-fiscal postmortem reports in the West of Scotland over a three year period. Combined adrenal weight was expressed as percentage of total body weight (%TBW). Of 106 cases, median (5th, 95th) %TBW was 0.056 (0.025, 0.23) and median plasma cortisol was 8.4 ug/dl (1.0, 47.1). There was no correlation between %TBW and plasma cortisol (r = 0.09, p = 0.4). The lowest and highest plasma cortisol quartile had medians of 1.9 ug/dl (1.0, 3.4) and 34.3 ug/dl (17.3, 71.5), respectively. Infection was present in 6 cases (23.1%) in the lowest quartile and in 16 cases (61.5%) in the highest quartile (p = 0.01). Our results highlight the difficulty in interpretation of cortisol at postmortem and suggest that adrenal weight measurement alone may be insufficient for diagnosis of adrenal insufficiency.

Measurement of nucleated red blood cells in the peripheral blood as a marker of hypoxia in sudden unexpected death in infancy.

AIMS: A recently proposed classification of sudden unexpected infant death incorporates consideration of possibly asphyxia. This depends on an adequate postmortem, scene investigation and history. A reliable marker of asphyxia has yet to be identified. Such a marker could assist in classifying these deaths. Our aim was to determine if the level of nucleated red blood cells (nRBCs) in the peripheral blood could help identify those possibly asphyxia-related deaths and if risk factors could influence this level in the peripheral blood. METHODS: Cases of sudden unexpected deaths in infancy and sudden infant death syndrome (SIDS) which occurred over a period of 6 years (2007-2013) and were autopsied at Sheffield Children's Hospital were reviewed and categorised according to a new classification proposed by Randall et al. The cases were then correlated with the blood level of nRBCs determined at the time of post mortem examination. The study was approved by the Clinical Governance Department, number SE331. RESULTS: 139 deaths were classified into Group A (true SIDS, 67 cases), Group B (possible asphyxia related, 24 cases), Group C (non-asphyxia-related, 6 cases), Group D (no crime scene investigation, 0 cases) and Group E (identifiable cause, 42 cases). The levels were significantly increased in ex-premature babies, in infants with an underlying condition (Group C) and in deaths related to illness or trauma (Group E). There was a trend towards higher levels of nRBCs in younger age groups and in babies born to smoking mothers. CONCLUSIONS: SIDS remains a difficult diagnosis to make despite the current medical technological advances where no marker of hypoxia has yet been identified.

Vitamin D deficiency and sudden unexpected death in infancy and childhood: a cohort study.

We sought to (1) determine if there is an increased prevalence of vitamin D deficiency (VDD) in cases of sudden death in infancy and childhood; (2) establish whether there is a link between VDD and infection; and (3) assess if the level of vitamin D can be related to abnormalities in the skeletal survey and rib histology in our cohort. The postmortem reports of cases in which vitamin D levels were measured in 2009 and 2010 were retrieved. When parental consent for audit had been granted, rib histology and skeletal surveys were reviewed. Plasma 25-hydroxyvitamin D levels were measured in 41 postmortem cases. Ten (24.5%) had adequate levels, 5 (12%) had suboptimal levels, 16 (39%) had moderate deficiency, and 10 (24.5%) had severe deficiency. We had only 4 cases with VDD and infection. There were 25 cases of unexplained death in our cohort, and 76% of these had inadequate vitamin D levels. The rib histology was abnormal in 69% of cases that had inadequate vitamin D levels, while the radiology was abnormal in 19% of cases. A significant proportion of infants and children who died suddenly and unexpectedly had inadequate levels of vitamin D. We were unable to confirm or exclude an association between VDD and infection due to the small number of cases with confirmed infection. Further multicenter studies are needed to confirm our findings and explore possible associations between VDD and other known risk factors for sudden unexplained death in infancy and childhood.

Metabolic autopsy with postmortem cultured fibroblasts in sudden unexpected death in infancy: diagnosis of mitochondrial respiratory chain disorders.

Mitochondrial respiratory chain disorders are the most common disorders among inherited metabolic disorders. However, there are few published reports regarding the relationship between mitochondrial respiratory chain disorders and sudden unexpected death in infancy. In the present study, we performed metabolic autopsy in 13 Japanese cases of sudden unexpected death in infancy. We performed fat staining of liver and postmortem acylcarnitine analysis. In addition, we analyzed mitochondrial respiratory chain enzyme activity in frozen organs as well as in postmortem cultured fibroblasts. In heart, 11 cases of complex I activity met the major criteria and one case of complex I activity met the minor criteria. In liver, three cases of complex I activity met the major criteria and four cases of complex I activity met the minor criteria. However, these specimens are susceptible to postmortem changes and, therefore, correct enzyme analysis is hard to be performed. In cultured fibroblasts, only one case of complex I activity met the major criteria and one case of complex I activity met the minor criteria. Cultured fibroblasts are not affected by postmortem changes and, therefore, reflect premortem information more accurately. These cases might not have been identified without postmortem cultured fibroblasts. In conclusion, we detected one probable case and one possible case of mitochondrial respiratory chain disorders among 13 Japanese cases of sudden unexpected death in infancy. Mitochondrial respiratory chain disorders are one of the important inherited metabolic disorders causing sudden unexpected death in infancy. We advocate metabolic autopsy with postmortem cultured fibroblasts in sudden unexpected death in infancy cases.

Cytokines and sudden infant death.

BACKGROUND: It has been hypothesised that inflammatory reactions could play an important role in the pathway(s) leading to sudden and unexpected death in infancy. On a molecular level, these reactions are regulated by various cytokines. METHODS: To characterise the role of IL-1ß, IL-6 and TNFα more precisely, the concentrations of these cytokines were determined quantitatively using specific ELISA techniques in serum and cerebrospinal fluid (CSF) in 119 cases of sudden infant death. The infants were grouped into four categories (SIDS, SIDS with infection, natural death due to infection and unnatural death). RESULTS: A good correlation was found between CSF and serum for IL-6 (Spearman correlation coefficients (SCC), 0.73) and also for TNFα (SCC, 0.57), although the CSF concentrations were lower than that from the serum. There were no significant differences between the categories of death for any of the serum or CSF cytokines. Compared with normal values, increased serum concentrations of IL-1ß, IL-6 and TNFα were found in 70%, 69% and 38% of the cases respectively, indicating possible agonal or post-mortem changes of cytokine concentrations. In three cases very high cytokine concentrations were found (mainly for IL-6). This may have contributed to the mechanism of death (cytokine storm) in two of the cases. CONCLUSIONS: In a small group of patients, very high cytokine concentrations are a possible explanation for the cause of death ("cytokine storm").

Biochemical, cytological and histopathological examination of sudden unexpected death in infancy.

To evaluate the pathophysiological mechanisms underlying sudden infant death syndrome (SIDS), four sudden unexpected death in infancy (SUDI) and four sudden deaths in children over 1 year of age were examined. In the SUDI cases, increased numbers of scavenger receptor A positive (SRA(+) ) cells (4/4), numerous platelet aggregates (3/4), and tumor necrosis factor (TNF)-α(+) cells (4/4) were observed in the peripheral blood (PB) smear preparations. Macrophage colony stimulating factor, interleukin (IL)-6, IL-8, TNF-α and IL-1ß all exceeded the normal levels. Minute foci of inflammatory lung injury (4/4), numerous platelet emboli in lungs and among cardiac myocytes (3/4) and appreciable contraction band necrosis (1/4) were observed. And neutrophils accumulated in the capillaries of injured organs and endothelial cells were extensively injured. From these findings, cytokine abnormality induced by SRA(+) cells in PB was considered to play an important role in the development of tissue injury, and platelet emboli or contraction band necrosis might have been the leading cause of death in our SUDI cases. Patients with characteristics thought to be similar to our SUDI cases were included in the SIDS group; cytokine abnormality was considered to be one of the underlying mechanisms in SIDS.

Cardiac muscarinic receptor overexpression in sudden infant death syndrome.

BACKGROUND: Sudden infant death syndrome (SIDS) remains the leading cause of death among infants less than 1 year of age. Disturbed expression of some neurotransmitters and their receptors has been shown in the central nervous system of SIDS victims but no biological abnormality of the peripheral vago-cardiac system has been demonstrated to date. The present study aimed to seek vago-cardiac abnormalities in SIDS victims. The cardiac level of expression of muscarinic receptors, as well as acetylcholinesterase enzyme activity were investigated. METHODOLOGY/PRINCIPAL FINDINGS: Left ventricular samples and blood samples were obtained from autopsies of SIDS and children deceased from non cardiac causes. Binding experiments performed with [(3)H]NMS, a selective muscarinic ligand, in cardiac membrane preparations showed that the density of cardiac muscarinic receptors was increased as shown by a more than doubled B(max) value in SIDS (n = 9 SIDS versus 8 controls). On average, the erythrocyte acetylcholinesterase enzyme activity was also significantly increased (n = 9 SIDS versus 11 controls). CONCLUSIONS: In the present study, it has been shown for the first time that cardiac muscarinic receptor overexpression is associated with SIDS. The increase of acetylcholinesterase enzyme activity appears as a possible regulatory mechanism.

Release of erythroblasts to the peripheral blood suggests higher exposure to hypoxia in cases of SIDS with co-sleeping compared to SIDS non-co-sleeping.

Sudden unexpected death in infancy (SUDI) includes sudden infant death syndrome (SIDS). Co-sleeping is regarded as a major risk factor for SIDS. Under normal circumstances, nucleated red blood cells (nRBCs) are absent from the peripheral blood and their release can occur in cases with a probable hypoxic mode of death. The aim of our study was to assess the significance of the release of nRBCs in SIDS occurring during co-sleeping and the association with hemorrhages in the dura and the lungs. 35 cases were retrospectively assigned to one of the following categories: (I) 9 SUDI (of various causes) with no co-sleeping; (II) 16 SIDS while co-sleeping; (III) cause of death in hypoxic circumstances (3 hangings, 2 cardiac malformations, 1 meningitis 1 intoxication with diazepam); (IV) 3 SIDS in the cot. nRBCs were present in 5/9 cases of Category I (mean: 0.5%); 10/16 cases of Category II (mean: 1.87%); 7/7 cases of Category III (mean: 3.8%) and 0/3 cases of Category IV (mean: 0). ANOVA one-way test showed a significance of 0.003 amongst the 4 groups. The presence of diffuse intra-alveolar hemorrhage was associated with a higher release of nRBCs (mean: 3.1%) than focal hemorrhage (mean 0.6%). nRBCs were associated with focal hemorrhages in the falx and tentorium (mean: 2.3 vs. 0.9% when no hemorrhages were seen). The high mean of nRBCs seen in the co-sleeping SIDS cases suggests a higher exposure to hypoxia in the co-sleeping group which may have led to the release of nRBCs. More cases need to be analyzed to confirm this hypothesis.

Sleeping position, oxygenation and lung function in prematurely born infants studied post term.

OBJECTIVE: To determine the effect of sleeping position on the lung function of prematurely born infants when post term, whether any effect was similar to that before discharge from the neonatal unit, and if it differed according to bronchopulmonary (BPD) status. DESIGN: Prospective study. SETTING: Tertiary neonatal unit. PATIENTS: Twenty infants, median gestational age 30 weeks (range 25-32); 10 had BPD. INTERVENTIONS: Before neonatal unit discharge (median age 36 weeks postmenstrual age (PMA)) and when post term, infants were studied prone and supine, each position maintained for 3 h. MAIN OUTCOME MEASURES: Oxygen saturation was monitored continuously and, at the end of each 3 h period, functional residual capacity (FRC) and compliance (CRS) and resistance (RRS) of the respiratory system were measured. RESULTS: At a median of 36 weeks PMA and 6 weeks later (post term), respectively, oxygen saturation (98% vs 96%, p = 0.001; 98% vs 97%, p = 0.011), FRC (26 vs 24 ml/kg, p<0.0001; 35 vs 31 ml/kg, p = 0.001) and CRS (3.0 vs 2.4 ml/cm H(2)O, p = 0.034; 3.7 vs 2.5 ml/cm H(2)O, p = 0.015) were higher in the prone than the supine position. In the prone position, both BPD and non-BPD infants had significantly greater FRCs on both occasions and oxygen saturation at 36 weeks PMA, but oxygen saturation was significantly better post term only in non-BPD infants. Twelve infants had superior oxygen saturation and 17 superior FRCs in the prone compared with the supine position at both 36 weeks PMA and post term. CONCLUSIONS: These results suggest that lung function impairment does not explain why prematurely born infants are at increased risk of sudden infant death syndrome in the prone compared with the supine position.

TNF-alpha promoter polymorphisms in sudden infant death.

Several studies indicate that the immune system is stimulated in sudden infant death syndrome (SIDS). Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine that strongly affects the cytokine cascade. A genetic variant associated with high production of TNF-alpha may thus be of significance in the pathogenesis of SIDS. The purpose of the current study was to investigate possible relationships among the promoter polymorphisms -1031T/C, -857C/T, -308G/A, -244G/A, and -238G/A in the TNF-alpha gene and SIDS. The subjects investigated consisted of 148 SIDS cases, 56 borderline SIDS cases, 41 cases of infectious death, and 131 adult controls. When investigating each single nuclear polymorphism (SNP) separately, associations between -238GG and SIDS (p=0.022) and between -308GA and borderline SIDS (p=0.005) were found. There were no associations between any of the other SNPs investigated. Furthermore, a SNP profile was constructed by creating a genotype pattern from the investigated SNPs. Fifteen gene combinations were obtained, and 4 profiles had significantly different frequencies in SIDS cases and controls. The two SNP profiles -1031CT, -238GG, -857CC, -308GG and -1031TT, -238GG, -857CC, -308AA were found more often in SIDS and may thus be unfavorable. The findings add evidence to the theory that an unfavorable genetic profile in the TNF-alpha gene may be involved in SIDS by exposing the infant to both a high level of and prolonged exposure to TNF-alpha.

Arousal and ventilatory responses to mild hypoxia in sleeping preterm infants.

A failure to adequately respond to hypoxia has been implicated in the Sudden Infant Death Syndrome (SIDS). Preterm infants are at increased risk for SIDS, thus we compared ventilatory and arousal responses to mild hypoxia [15% oxygen (O2)] in preterm and term infants. Eight preterm and 15 term infants were serially studied with daytime polysomnography during which nasal airflow was monitored by pneumotachograph at 2-5 weeks, 2-3 and 5-6 months. At each age, in both groups, hypoxia induced a significant decrease in oxygen saturation (SpO2) during both active sleep (AS) and quiet sleep (QS). Infants invariably aroused in AS; and in QS either aroused or failed to arouse. In preterm infants arousal latency in AS was longer than in term infants (P < 0.05) at 2-5 weeks. Compared with term infants, preterm infants reached significantly lower SpO2 levels at 2-5 weeks in both AS and QS non-arousing tests and at 2-3 months in QS. A biphasic hypoxic ventilatory response was observed in QS non-arousing tests in both groups of infants at all three ages. We conclude that the greater desaturation during a hypoxic challenge combined with the longer arousal latency in preterm infants could contribute to greater risk for SIDS.

Hemoglobin F in sudden infant death syndrome: a San Diego SIDS/SUDC Research Project report.

Whether levels of fetal hemoglobin (HbF), a possible marker of antecedent hypoxemia, are increased in sudden infant death syndrome (SIDS) compared to controls is unresolved. Our aims are to: (1) Compare percent fetal hemoglobin (%HbF) levels in SIDS and control cases, and (2) compare our findings with those reported in previous studies. Using Triton-acid-urea gel electrophoresis and quantitative densitometry, %HbF was determined in whole blood specimens obtained at autopsy from SIDS and control cases accessioned into the San Diego SIDS/SUDC Research Project database. The SIDS and control cases were not different with respect to mean age, gender, gestational age, method of delivery, birth weight, or mean autopsy interval; %HbF levels in SIDS and control cases were not significantly different. Given that our results were obtained using optimal methods in well-defined SIDS and control cases, we concur with others that %HbF is not elevated in SIDS.

The relationship between bedding and face-down death in infancy: mathematical analysis of a respiratory simulation system using an infant mannequin to assess gas diffusibility in bedding.

Rebreathing is a model for the relationship between a prone sleeping position and sudden infant death syndrome. This study used a mechanical simulation model to establish the relationship between types of bedding and rebreathing potential for an infant placed prone (face down) at different postnatal ages. The infant mannequin was connected to a respirator set to deliver physiologically appropriate combinations of tidal volume (V(T)) and respiratory rates (RR) across a range of postnatal ages (0-18 months). Before measurements were made, CO(2) flow was regulated to 5+/-0.1% of end-tidal PCO(2) (EtCO(2)). After the model was placed in a prone position, any increase in the fractional concentration of inspired CO(2) (FiCO(2)) was measured. FiCO(2) increased immediately and rapidly, and reached a maximum value within a few minutes. The maximum FiCO(2) ranged from under 2% to over 10%, depending on the bedding. FiCO(2) was also affected by V(T) and RR. This model is not applicable to actual infants because of the large tissue stores of CO(2) in infants; however, it is useful for evaluation of gas diffusibility of bedding and will simplify the investigation of sleeping environments when a baby is found dead with its face covered by soft bedding. In general, the higher the FiCO(2), the greater the rebreathing potential. Theoretically, considering the paucity of body stores of O(2), changes in FiO(2) would be affected not by changes in FiCO(2), but by CO(2) production and gas movement around the infant's face. The rapid decrease of FiO(2) is approximated at the inverse of the FiCO(2) timecourse, suggesting the significance of not only CO(2) accumulation but also O(2) deprivation in the potential space around the baby's face.