Association of Sudden Infant Death Syndrome With VEGF and IL-6 Gene Polymorphisms

Evidence for an association of interferon gene variants with sudden infant death syndrome

BACKGROUND

There is evidence that inflammation plays a role in the etiology of sudden infant death syndrome (SIDS). Immune system dysregulation seems to be the background of higher infection susceptibility in SIDS infants. This phenotype is possibly determined by genetic factors.

METHODS

Twenty-three single nucleotide polymorphisms (SNPs) in the following 13 candidate genes governing the immune system were successfully genotyped in 251 Caucasian SIDS cases and 336 controls from Germany: ADAR1, CSF2RB, DDX58, IFNA1, IFNA21, IFNA8, IFNAR2, IFNG, IL6, MX2, OAS1, OAS3, and TNFA. Associations between genotypes and SIDS were then statistically evaluated using logistic regression analyses.

RESULTS

Overall analysis revealed statistically significant results for two variants in interferon gamma (IFNG) (rs2069705: OR 1.40 (1.07; 1.83), p = 0.01; and rs2069727: OR 0.75 (0.59; 0.96), p = 0.02) and for one variant in interferon alpha 8 (IFNA8) (rs1330321: OR 1.85 (1.06; 3.21), p = 0.03). Haplotype analyses identified a three-marker risk IFNG haplotype rs2069727-rs2069718-rs2069705 associated with SIDS (OR = 1.62, 95% CI 1.23-2.13; p = 0.0003). Subgroup associations were found for variants in adenosine deaminase acting on RNA1 (ADAR1), 2',5'-oligoadenylate synthetase-1 (OAS1) and colony stimulating factor 2 receptor beta common subunit (CSF2RB).

CONCLUSION

In summary, this large study of 251 SIDS cases for common variants in 13 candidate genes governing the immune system has provided first evidence for a role of IFNG in the etiology of SIDS and should stimulate further research into the clinicopathological relevance of immunomodulatory genes for this fatal syndrome.

Clinical and experimental aspects of breathing modulation by inflammation

Neuroinflammation is produced by local or systemic alterations and mediated mainly by glia, affecting the activity of various neural circuits including those involved in breathing rhythm generation and control. Several pathological conditions, such as sudden infant death syndrome, obstructive sleep apnea and asthma exert an inflammatory influence on breathing-related circuits. Consequently breathing (both resting and ventilatory responses to physiological challenges), is affected; e.g., responses to hypoxia and hypercapnia are compromised. Moreover, inflammation can induce long-lasting changes in breathing and affect adaptive plasticity; e.g., hypoxic acclimatization or long-term facilitation. Mediators of the influences of inflammation on breathing are most likely proinflammatory molecules such as cytokines and prostaglandins. The focus of this review is to summarize the available information concerning the modulation of the breathing function by inflammation and the cellular and molecular aspects of this process. I will consider: 1) some clinical and experimental conditions in which inflammation influences breathing; 2) the variety of experimental approaches used to understand this inflammatory modulation; 3) the likely cellular and molecular mechanisms.

A systematic review exploring the relationship between infection and sudden unexpected death between 2000 and 2016: A forensic perspective

Death due to infectious diseases is a major health concern worldwide. This is of particular concern in developing countries where poor-socio economic status and a lack of healthcare resources contribute to the high burden of disease. In some cases death due to infection can be acute and aggressive, and death may occur without a diagnosis whilst the person is still alive. These deaths may ultimately lead to a medico-legal autopsy being performed. There are various mechanisms by which sudden death due to infection may occur. In addition, there are many risk factors associated with sudden death due to infection, which differ between infants and older individuals. However, it is unclear which pathogens and risk factors are most frequently associated with sudden death due to infection. Therefore a systematic review of articles and case reports published between 1 January 2000 and 30 June 2016 was undertaken in order to (1) explore the relationship between pathogens and their causative role and (2) identify the relationship between predisposing and/or risk factors associated with sudden death due to infection. Major databases were searched and after critical appraisal 143 articles were identified. It was found that respiratory infections and deaths involving bacterial pathogens were most commonly associated with these deaths. In addition the most common risk factors in infants were exposure to tobacco smoke and co-sleeping. In adults the most common risk factors were co-morbid conditions and illnesses. This information aids in a better understanding of these deaths and highlights the need for more research in this field, particularly in developing countries.

Altered gene expression and possible immunodeficiency in cases of sudden infant death syndrome

BACKGROUND

A large number of studies have tried to uncover a genetic predisposition for sudden infant death syndrome (SIDS), but there is still uncertainty concerning the pathogenesis of these deaths. The purpose of this study was to investigate mRNA gene expression in SIDS cases and controls, in order to uncover genes that are differentially expressed in the two groups.

METHODS

Tissue from brain, heart, and liver from 15 SIDS cases and 15 controls were included in the study, and mRNA expression was determined using the Illumina whole genome gene expression DASL HT assay.

RESULTS

Seventeen genes showed significantly altered expression compared to controls, after correction for multiple testing. Three genes involved in the immune system were of particular interest, including the downregulation of MyD88 in tissue from SIDS brains, as well as the downregulation of the genes encoding CCL3 and UNC13 in the liver.

CONCLUSION

These findings indicate that there is an altered expression of genes involved in the inflammatory process in a proportion of SIDS cases, which further strengthen the hypothesis that impaired immune response play a role in this syndrome.

Virus Infections and Sudden Death in Infancy: The Role of Interferon-γ

Respiratory infections have been implicated in sudden infant death syndrome (SIDS). As interferon-γ (IFN-γ) is a major response to virus infection, we examined (1) the frequency of single nucleotide polymorphism (SNP), IFNG T + 874A, in SIDS infants, their parents, and ethnic groups with different incidences of SIDS; (2) model systems with a monocytic cell line (THP-1) and human peripheral blood monocytes (PBMC) for effects of levels of IFN-γ on inflammatory responses to bacterial antigens identified in SIDS; (3) interactions between genetic and environmental factors on IFN-γ responses. IFNG T + 874A genotypes were determined for SIDS infants from three countries; families who had a SIDS death; populations with high (Indigenous Australian), medium (Caucasian), and low (Bangladeshi) SIDS incidences. The effect of IFN-γ on cytokine responses to endotoxin was examined in model systems with THP-1 cells and human PBMC. The IFN-γ responses to endotoxin and toxic shock syndrome toxin (TSST-1) were assessed in relation to genotype, gender, and reported smoking. There was a marginal association with IFNG T + 874A genotype and SIDS (p = 0.06). Indigenous Australians had significantly higher proportions of the IFNG T + 874A SNP (TT) associated with high responses of IFN-γ. THP-1 cells showed a dose dependent effect of IFN-γ on cytokine responses to endotoxin. For PBMC, IFN-γ enhanced interleukin (IL)-1β, IL-6, and tumor necrosis factor-α responses but reduced IL-8 and IL-10 responses. Active smoking had a suppressive effect on baseline levels of IFN-γ. There was no effect of gender or genotype on IFN-γ responses to bacterial antigens tested; however, significant differences were observed between genotypes in relation to smoking. The results indicate virus infections contribute to dysregulation of cytokine responses to bacterial antigens and studies on physiological effects of genetic factors must include controls for recent or concurrent infection and exposure to cigarette smoke.

Sudden infant death syndrome and the genetics of inflammation

Several studies report signs of slight infection prior to death in cases of sudden infant death syndrome (SIDS). Based on this, a hypothesis of an altered immunological homeostasis has been postulated. The cytokines are important cellular mediators that are crucial for infant health by regulating cell activity during the inflammatory process. The pro-inflammatory cytokines favor inflammation; the most important of these are IL-1α, IL-1β, IL-6, IL-8, IL-12, IL-18, TNF-α, and IFN-γ. These cytokines are controlled by the anti-inflammatory cytokines. This is accomplished by reducing the pro-inflammatory cytokine production, and thus counteracts their biological effect. The major anti-inflammatory cytokines are interleukin-1 receptor antagonist (IL-1ra), IL-4, IL-10, IL-11, and IL-13. The last decade there has been focused on genetic studies within genes that are important for the immune system, for SIDS with a special interest of the genes encoding the cytokines. This is because the cytokine genes are considered to be the genes most likely to explain the vulnerability to infection, and several studies have investigated these genes in an attempt to uncover associations between SIDS and different genetic variants. So far, the genes encoding IL-1, IL-6, IL-10, and TNF-α are the most investigated within SIDS research, and several studies indicate associations between specific variants of these genes and SIDS. Taken together, this may indicate that in at least a subset of SIDS predisposing genetic variants of the immune genes are involved. However, the immune system and the cytokine network are complex, and more studies are needed in order to better understand the interplay between different genetic variations and how this may contribute to an unfavorable immunological response.

Immunohistochemical expression of inflammatory markers in sudden infant death; ancillary tests for identification of infection

Aims

Sudden unexpected death in infancy (SUDI) investigation requires extensive ancillary investigations, the results of which, such as postmortem microbiology, can be difficult to interpret. Markers of an inflammatory response, including interleukin 6 (IL-6), c-reactive protein (CRP) and cellular adhesion molecules are elevated in infections, yet little attention has been paid to their assessment after death. This study investigates the role of inflammatory markers in SUDI autopsies for determining cause of death.

Methods

Cases of SUDI over a 14 year period were identified from an autopsy database and 100 cases were selected for immunohistochemical staining of heart and liver for IL-6, CRP, P-selectin, VCAM-1 and ICAM-1 (CD54), with staining patterns compared between five groups, including infectious and unexplained SUDI.

Results

There were significant differences between groups. Cases of histological infection demonstrated strongly positive hepatocyte CRP and ICAM-1 expression and increased myocardial staining for CRP. Half of trauma-related deaths demonstrated diffuse hepatic CRP expression but without myocardial CRP staining. Staining of unexplained SUDI cases were predominantly negative, apart from a subgroup in whom Escherichia Coli was identified, who had increased expression of hepatic IL-6.

Conclusions

There were distinct patterns of organ-specific CRP and ICAM-1 expression in SUDI by cause of death. These markers of inflammation were rarely present in unexplained SUDI suggesting either a non-inflammatory cause of death or a failure to mount an effective acute phase response. Immunohistochemical staining offers potential to identify infection-related deaths and provides insight into SUDI mechanisms.

Serotonin gene variants are unlikely to play a significant role in the pathogenesis of the sudden infant death syndrome

Sudden infant death syndrome (SIDS) is defined as the sudden and unexpected death of an infant less than 12 months of age that is related to a sleep period and remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. The cause of SIDS is unknown, but a major subset of SIDS is proposed to result from abnormalities in serotonin (5-HT) and related neurotransmitters in regions of the lower brainstem that result in failure of protective homeostatic responses to life-threatening challenges during sleep. Multiple studies have implicated gene variants that affect different elements of 5-HT neurotransmission in the pathogenesis of these abnormalities in SIDS. In this review I discuss the data from these studies together with some new data correlating genotype with brainstem 5-HT neurochemistry in the same SIDS cases and conclude that these gene variants are unlikely to play a major role in the pathogenesis of the medullary 5-HT abnormalities observed in SIDS.

Cardiac ion channelopathies and the sudden infant death syndrome

The sudden infant death syndrome (SIDS) causes the sudden death of an apparently healthy infant, which remains unexplained despite a thorough investigation, including the performance of a complete autopsy. The triple risk model for the pathogenesis of SIDS points to the coincidence of a vulnerable infant, a critical developmental period, and an exogenous stressor. Primary electrical diseases of the heart, which may cause lethal arrhythmias as a result of dysfunctioning cardiac ion channels (“cardiac ion channelopathies”) and are not detectable during a standard postmortem examination, may create the vulnerable infant and thus contribute to SIDS. Evidence comes from clinical correlations between the long QT syndrome and SIDS as well as genetic analyses in cohorts of SIDS victims (“molecular autopsy”), which have revealed a large number of mutations in ion channel-related genes linked to inheritable arrhythmogenic syndromes, in particular the long QT syndrome, the short QT syndrome, the Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia. Combining data from population-based cohort studies, it can be concluded that at least one out of five SIDS victims carries a mutation in a cardiac ion channel-related gene and that the majority of these mutations are of a known malignant phenotype.

Genomic risk factors in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is a major contributor to postneonatal infant death, and is the third leading cause of infant mortality in the USA. While public health efforts have reduced these deaths in recent years, the pathogenesis of SIDS remains unclear. Epidemiological data on SIDS-related deaths have suggested genetic factors, and many studies have attempted to identify SIDS-associated genes. This has resulted in a large body of literature implicating various genes and their encoded proteins and signaling pathways in numerous cohorts of various sizes and ethnicities. This review has undertaken a systematic evaluation of these studies, identifying the pathways that have been implicated in these studies, including central nervous system pathways, cardiac channelopathies, immune dysfunction, metabolism/energy pathways, and nicotine response. This review also explores how new genomic techniques will aid in advancing our knowledge of the genomic risk factors associated with SIDS, including SNPs and copy number variation. Last, this review explores how the current information can be applied to aid in our assessment of the at risk infant population.

Genetics of the sudden infant death syndrome

The sudden infant death syndrome (SIDS) is currently defined as "the sudden unexpected death of an infant less than 1 year of age with onset of the fatal episode apparently occurring during sleep, that remains unexplained after a thorough investigation". SIDS, whose etiology remains rather vague, is still the major cause of death among infants between 1 month and 1 year of age in industrialized countries with varying incidences in different populations. Herein, after touching on definitory approaches and several current hypotheses concerning SIDS etiology, we focus on the triple risk model of SIDS and discuss two large classes of genetic factors potentially contributing to or predisposing for the generation of a vulnerable infant that, when encountering an environmental trigger, may succumb to SIDS. We conclude by acknowledging that for the integration of the vast and complex genetic evidence concerning SIDS, a lot more research will be required and we briefly discuss the potential use of recently presented animal models for functional studies of SIDS pathology.

Gene variants predisposing to SIDS: current knowledge

Genetic risk factors play a role in sudden unexpected infant death; either as a cause of death, such as in cases with medium-chain acyl-coenzyme A dehydrogenase deficiency and cardiac arrest due to long QT syndrome, or as predisposing factors for sudden infant death syndrome (SIDS). Most likely genetic predisposition to SIDS represent a polygenic inheritance pattern leading to sudden death when combined with other risk factors, such as a vulnerable developmental stage of the central nervous system and/or the immune system, in addition to environmental risk factors, such as a common cold or prone sleeping position. Genes involved in the regulation of the immune system, cardiac function, the serotonergic network and brain function and development have so far emerged as the most important with respect to SIDS. The purpose of the present paper is to survey current knowledge on SIDS and possible genetic contributions.

The role of infection and inflammation in sudden infant death syndrome

Sudden Infant Death Syndrome (SIDS) is the most common cause of post-neonatal mortality in the developed world. The exact cause of SIDS is likely to be multifactorial involving a critical developmental period, a vulnerable infant, and one or more triggers. Many SIDS infants have a history of viral illness preceding death. Prone sleep position, one of the leading risk factors, can increase airway temperature, as well as stimulate bacterial colonization and bacterial toxin production. Markers of infection and inflammation are often found on autopsy along with microbial isolates. Although the causal link between infection and SIDS is not conclusive, there is evidence that an infectious insult could be a likely trigger of SIDS in some infants.

Cytokine gene polymorphisms and sudden infant death syndrome

AIM

Several studies indicate that the mucosal immune system is stimulated in cases of sudden infant death syndrome (SIDS), and our hypothesis is that this immune reaction is because of an unfavourable combination of functional polymorphisms in the cytokine genes.

METHODS

Thus, in this study, single nucleotide polymorphisms (SNPs) in the genes encoding IL-6, IL-8, IL-12, IL-13, IL-16, IL-18 and IFNgamma were investigated in 148 SIDS cases, 56 borderline SIDS cases, 41 cases of infectious death and 131 controls.

RESULTS

Regarding genotype distribution, no differences between the investigated groups were found. However, in the SIDS group, the genotypes IL-8 -251AA/AT and IL-8 -781CT/TT were significantly more frequent in the SIDS cases found dead in a prone sleeping position, compared with SIDS cases found dead in other sleeping positions. In addition, there was an association between fever prior to death and the genotype IL-13 +4464GG in the cases of infectious death.

CONCLUSION

This study indicates that specific interleukin genotypes are a part of a genetic make up that make infants sleeping prone at risk for SIDS.

IL-1 gene cluster polymorphisms and sudden infant death syndrome

Several studies indicate that interleukin gene polymorphisms are of importance to sudden infant death syndrome (SIDS), and so far it has been reported that associations between SIDS and polymorphism in the genes encoding tumor necrosis factor alpha, IL (interleukin)-6, and IL-10. IL-1 are important for the synthesis of acute phase proteins, and it is a pyrogen cytokine that may cause fever. The purpose of the present study was to investigate two polymorphisms in the IL-1alpha gene; a variable number of tandem repeat (VNTR) in intron 6 and a single nucleotide polymorphism in +4845G/T, as well as the -511C/T polymorphism in the gene encoding IL-1beta, and a VNTR in intron 2 of the competitive antagonist IL-1Ra, in SIDS cases, cases of infectious death, and controls. Furthermore, the genotypes were correlated with known external risk factors for SIDS. When investigating each polymorphism separately, no differences in genotype distribution between the diagnosis groups and controls were found. However, when combining VNTR and single nucleotide polymorphism genotypes, an association between the gene combination IL-1alpha VNTR A1A1/IL-1beta+ +4845TT and SIDS was disclosed (p < 0.01). In the SIDS group it was also found that the genotypes IL-1beta -511CC/CT were significantly more frequent in the SIDS victims found dead in a prone sleeping position, compared with SIDS victims found dead in other sleeping positions (p = 0.004). The findings in the present study indicate that specific interleukin gene variants may be a predisposing factor for sudden unexpected infant death.

VEGF gene polymorphisms and susceptibility to colorectal cancer disease in Italian population

BACKGROUND

The vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen involved in the process of angiogenesis, a crucial phase in tumor growth and metastasis. We carried out a case-control study to evaluate whether polymorphisms of VEGF gene modulate the risk of developing colorectal cancer disease (CCD).

MATERIALS AND METHODS

We evaluated VEGF -2578A/C, -460T/C, and +405C/G genotypes obtained from a series of 302 CCD patients and 115 controls from the Italian population using polymerase chain reaction restriction fragment length polymorphism assay.

RESULTS

Strong linkage disequilibrium (LD) was detected between -2578A/C and -460T/C (D' = 0.97; CI = 0.93-1) and between -2578A/C and +405C/G (D' = 0.97; CI = 0.98-1) in the case group. Complete LD was detected between -2578A/C and +405C/G and between -460T/C and +405C/G (D' = 1; CI = 0.84-1; CI = 0.82-1, respectively) in the control group. A reduced risk for the disease was associated with -2578C/A and -2578C/C (odds ratio (OR) = 0.34, CI = 0.162-0.676 and OR = 0.38, CI = 0.181-0.775, respectively). A direct association was found for carriers of the VEGF -460C/C polymorphism (OR = 3.55; CI = 1.659-8.469). We identified a protective haplotype -2578A, -460T, and +405G (OR = 0.04; CI = 0.009-0.19) and two different high-risk haplotypes -2578A, -460C, and +405G (OR = 1.90; CI = 1.31-2.27) and -2578C, -460C, and +405C (OR = 9.62; CI = 1.3-70.87).

CONCLUSIONS

The present study suggests that the VEGF gene polymorphisms may play a role in the development of colorectal cancer.

Minocycline suppresses morphine-induced respiratory depression, suppresses morphine-induced reward, and enhances systemic morphine-induced analgesia

Recent data suggest that opioids can activate immune-like cells of the central nervous system (glia). This opioid-induced glial activation is associated with decreased analgesia, owing to the release of proinflammatory mediators. Here, we examine in rats whether the putative microglial inhibitor, minocycline, may affect morphine-induced respiratory depression and/or morphine-induced reward (conditioned place preference). Systemic co-administration of minocycline significantly attenuated morphine-induced reductions in tidal volume, minute volume, inspiratory force, and expiratory force, but did not affect morphine-induced reductions in respiratory rate. Minocycline attenuation of respiratory depression was also paralleled with significant attenuation by minocycline of morphine-induced reductions in blood oxygen saturation. Minocycline also attenuated morphine conditioned place preference. Minocycline did not simply reduce all actions of morphine, as morphine analgesia was significantly potentiated by minocycline co-administration. Lastly, morphine dose-dependently increased cyclooxygenase-1 gene expression in a rat microglial cell line, an effect that was dose-dependently blocked by minocycline. Together, these data support that morphine can directly activate microglia in a minocycline-suppressible manner and suggest a pivotal role for minocycline-sensitive processes in the mechanisms of morphine-induced respiration depression, reward, and pain modulation.

Small for gestational age infants and sudden infant death syndrome: a confluence of complex conditions

Perspective on the paper by Malloy (see page 473)

The IL6 −174G/C polymorphism and sudden infant death syndrome

The interleukin-6 genotype (IL6 -174GG) has been proposed to be associated with sudden infant death syndrome (SIDS). The aim of this study was to investigate the -174G/C polymorphism in 175 Norwegian SIDS cases and 71 controls. There were no differences in genotype distribution between these two groups (p = 1.0). This confirms the findings in a combined SIDS group compared with European Caucasian controls, but not findings in smaller cohorts of SIDS cases from Australia and England. The discrepancy may result from bias introduced when investigating only a few SIDS cases, differences in diagnostic criteria when diagnosing the cause of death as SIDS, and differences in the distribution of the -174G/C polymorphism in different ethnic groups. Findings of an activated immune system in SIDS indicate that genes involved in the immune response are of importance. However, because there are several polymorphisms in the IL6 gene promoter that could potentially regulate the expression of the gene, more than one polymorphism should be investigated to assess the involvement of the IL-6 gene in SIDS.

Identifying infants at risk for sudden infant death syndrome

PURPOSE OF REVIEW

This review examines recent research relevant to the underlying pathophysiology and risk factors for sudden infant death syndrome.

RECENT FINDINGS

Current research focuses on the linkage between known risk factors and vulnerability, genetic contributions, and the role of dysfunctional brainstem neurotransmission in the pathogenesis of this syndrome. While social inequalities, prematurity, maternal smoking, infant sleeping practices and sleep environment, arousal failures and environmental pollutants remain important risk factors, new evidence is emerging that certain genetic polymorphisms may contribute to vulnerability. New neuropathological studies have provided strong support for abnormal brainstem serotonergic function. Since serotonin influences a wide range of physiological systems including breathing, the cardiovascular system, temperature, and sleep-wake cycles, this finding strongly supports the hypothesis that sudden infant death syndrome is the result of dysregulation of the autonomic nervous system and provides biological plausibility for certain risk reduction strategies.

SUMMARY

Despite a putative diagnostic shift, sudden infant death syndrome remains the most common cause of death from 1 month to 1 year of age. Recent studies confirmed established risk factors and have suggested new genetic vulnerabilities. Finally, new evidence supports a key role for abnormalities in brainstem serotonin systems in the pathophysiology of this syndrome.

Modifiable risk factors, sleep environment, developmental physiology and common polymorphisms: understanding and preventing sudden infant deaths

Unexpected death in infancy may be a consequence of recognisable pathophysiological processes, or may remain unexplained after thorough investigation. We review the appropriate investigations that should be performed after unexpected infant deaths, and the recent changes to UK law that will make such investigations mandatory from 2008. Current knowledge of the epidemiology and pathophysiology of unexpected infant deaths, together with knowledge of infant developmental physiology leads to an emphasis on the importance of a range of potential gene-environment interactions occurring in vulnerable infants at vulnerable stages of their development.