Evidence for a genetic component in sudden infant death syndrome

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.

Sleep physiology and sleep disorders in childhood

Sleep has long been considered as a passive phenomenon, but it is now clear that it is a period of intense brain activity involving higher cortical functions. Overall, sleep affects every aspect of a child's development, particularly higher cognitive functions. Sleep concerns are ranked as the fifth leading concern of parents. Close to one third of all children suffer from sleep disorders, the prevalence of which is increased in certain pediatric populations, such as children with special needs, children with psychiatric or medical diagnoses and children with autism or pervasive developmental disorders. The paper reviews sleep physiology and the impact, classification, and management of sleep disorders in the pediatric age group.

Is shock a key element in the pathology of sudden infant death syndrome (SIDS)?

In developed countries, sudden infant death syndrome (SIDS) is the most common cause of death for infants between 1 month and 1 year of age. The etiology of SIDS is likely to be multifactorial, and current paradigms often describe three overlapping elements of risk. Those elements are a critical developmental period, a vulnerable infant, and one or more exogenous stressors. In the triple-risk model, SIDS infants are described as having an underlying vulnerability in cardiorespiratory control in the central nervous system during a critical period when autonomic control is developing. This vulnerability might affect the response to exogenous stressors, including prone sleeping position, hypoxia, and increased carbon dioxide. In the common bacterial hypothesis and fatal triangle, the focus is on the stressors. In the first, a combination of common respiratory infections can cause SIDS in an infant during a developmentally vulnerable period. This theory also includes 3 factors of vulnerability: a genetic predisposition, a vulnerable developmental age, and infectious stressors. In the fatal triangle theory, infection, inflammation, and genetics each play a role in triggering a SIDS fatality. From our work in an animal model, we have found that rat pups die from a combination of infectious insults during a critical time of development. This is exacerbated by perinatal nicotine exposure, a condition shown to alter the autonomic response in exposed offspring. We are proposing that shock and cardiovascular collapse is a key element that links these theories.

Possible pathomechanisms of sudden infant death syndrome: key role of chronic hypoxia, infection/inflammation states, cytokine irregularities, and metabolic trauma in genetically predisposed infants

Chronic hypoxia, viral infections/bacterial toxins, inflammation states, biochemical disorders, and genetic abnormalities are the most likely trigger of sudden infant death syndrome (SIDS). Autopsy studies have shown increased pulmonary density of macrophages and markedly more eosinophils in the lungs accompanied by increased T and B lymphocytes. The elevated levels of immunoglobulins, about 20% more muscle in the pulmonary arteries, increased airway smooth muscle cells, and increased fetal hemoglobin and erythropoietin are evidence of chronic hypoxia before death. Other abnormal findings included mucosal immune stimulation of the tracheal wall, duodenal mucosa, and palatine tonsils, and circulating interferon. Low normal or higher blood levels of cortisol often with petechiae on intrathoracic organs, depleted maternal IgG antibodies to endotoxin core (EndoCAb) and early IgM EndoCAb triggered, partial deletions of the C4 gene, and frequent IL-10-592*A polymorphism in SIDS victims as well as possible hypoxia-induced decreased production of antiinflammatory, antiimmune, and antifibrotic cytokine IL-10, may be responsible for the excessive reactions to otherwise harmless infections. In SIDS infants, during chronic hypoxia and times of infection/inflammation, several proinflammatory cytokines are released in large quantities, sometimes also representing a potential source of tissue damage if their production is not sufficiently well controlled, eg, by pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP). These proinflammatory cytokines down-regulate gene expression of major cytochrome P-450 and/or other enzymes with the specific effects on mRNA levels, protein expression, and enzyme activity, thus affecting metabolism of several endogenous lipophilic substances, such as steroids, lipid-soluble vitamins, prostaglandins, leukotrienes, thromboxanes, and exogenous substances. In SIDS victims, chronic hypoxia, TNF-alpha and other inflammatory cytokines, and arachidonic acid (AA) as well as n-3 polyunsaturated fatty acids (FA), stimulated and/or augmented superoxide generation by polymorphonuclear leukocytes, which contributed to tissue damage. Chronic hypoxia, increased amounts of nonheme iron in the liver and adrenals of these infants, enhanced activity of CYP2C9 regarded as the functional source of reactive oxygen species (ROS) in some endothelial cells, and nicotine accumulation in tissues also intensified production of ROS. These increased quantities of proinflammatory cytokines, ROS, AA, and nitric oxide (NO) also resulted in suppression of many CYP450 and other enzymes, eg, phosphoenolpyruvate carboxykinase (PEPCK), an enzyme important in the metabolism of FA during gluconeogenesis and glyceroneogenesis. PEPCK deficit found in SIDS infants (caused also by vitamin A deficiency) and eventually enhanced by PACAP lipolysis of adipocyte triglycerides resulted in an increased FA level in blood because of their impaired reesterification to triacylglycerol in adipocytes. In turn, the overproduction and release of FA into the blood of SIDS victims could lead to the metabolic syndrome and an early phase of type 2 diabetes. This is probably the reason for the secondary overexpression of the hepatic CYP2C8/9 content and activity reported in SIDS infants, which intensified AA metabolism. Pulmonary edema and petechial hemorrhages often present in SIDS victims may be the result of the vascular leak syndrome caused by IL-2 and IFN-alpha. Chronic hypoxia with the release of proinflammatory mediators IL-1alpha, IL-1beta and IL-6, and overloading of the cardiovascular and respiratory systems due to the narrowing airways and small pulmonary arteries of these children could also contribute to the development of these abnormalities. Moreover, chronic hypoxia of SIDS infants induced also production of hypoxia-inducible factor 1alpha (HIF-1alpha), which stimulated synthesis and release of different growth factors by vascular endothelial cells and intensified subclinical inflammatory reactions in the central nervous system, perhaps potentiated also by PACAP and VIP gene mutations. These processes could lead to the development of brainstem gliosis and disorders in the release of neuromediators important for physiologic sleep regulation. All these changes as well as eventual PACAP abnormalities could result in disturbed homeostatic control of the cardiovascular and respiratory responses of SIDS victims, which, combined with the nicotine effects and metabolic trauma, finally lead to death in these often genetically predisposed children.

IL-10 gene polymorphisms in infectious disease and SIDS

Interleukin-10 (IL-10) is a regulatory cytokine, and its principal role in vivo is to limit inflammatory response. IL-10 has been shown to influence both the susceptibility and course of various diseases, and the different polymorphisms in the IL-10 gene promoter have been associated with disease prevalence and severity. The genes involved in the immune system are also assumed to be of importance with regard to sudden infant death syndrome (SIDS), and specific haplotypes in the IL-10 gene promoter have been reported associated both with SIDS and sudden unexpected death due to infection.

IL-10 gene polymorphisms are associated with infectious cause of sudden infant death

Cytokines are involved in regulating the intensity and duration of the immune response, and cytokine production is carefully regulated. With regard to sudden infant death, interleukin-10 (IL-10) is of special interest. This is an immunoregulatory cytokine that plays an important role in the development of infectious disease. The purpose of this study was to elucidate the relationship between polymorphisms in the promoter region of the IL-10 gene and sudden infant death due to either sudden infant death syndrome (SIDS) or infection. The polymorphisms investigated include the SNPs in base pairs (bp) -1082, -819, -592, and the two microsatellites IL-10G and IL-10R. The main finding is an association between the ATA haplotype and the ATA/ATA genotype and infectious death. The group of infectious deaths also had a higher percentage of the genotypes G21/G22 and G21/G23, compared with the SIDS patients. In addition, G21/G22 was found in a higher percentage of the SIDS patients than in the controls. These findings lead us to speculate that, in some situations, an infant with an unfavorable IL-10 genotype may exhibit aberrant IL-10 production, which in turn leads to an imbalance in the immune response and renders the infant unable to cope with the infection.

Sleep apnea in mice: a useful animal model for study of SIDS?

Although the incidence of sudden infant death syndrome (SIDS) has been decreased by education programs to avoid sleeping in prone position, the pathological mechanisms of SIDS have not fully been understood. Basic research on sleep apnea using experimental animals may help further understanding and prevention of SIDS because the syndrome is thought as inability to wake up from respiratory arrest (apnea) during sleep. Although several animal models of sleep apnea have been described previously, mice would be useful experimental animals in that these animals are frequently used in genetic engineering. Those considerations prompted us to establish a method for measuring ventilation of mice concomitantly with electroencephalography and electromyography for assessing sleep-wake states. Normal wild-type mice developed two types of central sleep apneas (CSA), that is, post-sigh and spontaneous apneas, as normal humans do. Moreover, post-sigh apneas in mice were observed exclusively during slow-wave sleep (SWS) while spontaneous apneas were seen in both SWS and rapid eye movement (REM) sleep. These characteristics are very similar to those of sleep apneas in healthy human infants and children. Therefore, mice seem to be a promising experimental animal model for studying the genetic and molecular basis of respiratory regulation and dysregulation during sleep in humans, especially infants and children. However, we should keep in mind limitations in studying mice as an animal model of SIDS, since they are nocturnal rodents and they sleep in the prone position.

Sleep disorders in children

PURPOSE OF REVIEW

Childhood sleep disorders are one of the most prevalent complaints in the pediatrician's office. Infant sleep rhythm complaints from new mothers reach 46%, while childhood obstructive sleep apnea has a prevalence of 2% and adolescent insomnia with daily consequences surpasses that percentage.

RECENT FINDINGS

Each sleep disorder must be considered in context of age, as age influences the presentation and impact on the developing child or adolescent. For example, sleep-disordered breathing resulting in adult sleepiness can contribute to death in infants. The symptoms of narcolepsy are often masked until after adolescence, resulting in psychologically costly misdiagnoses.

SUMMARY

There are no outcome studies that track the long-term consequences of pediatric sleep disorders or their contribution to adult sleep problems, but this is an area of increasing research interest. This review assesses the most recent literature on pediatric sleep disorders from May 1, 2002, until April 30, 2003.