The triple risk hypotheses in sudden infant death syndrome

Infant Mortality in Gynaecological and Unemployment Aspects in Opole Province, Poland

In the study the results of the relation between infant (neonatal + post-neonatal) mortality and the gynaecological and unemployment factors are presented. The findings are based on Bayesian modelling and indicate the possible influence of the unemployment situation on mortality, whereas no correlation was found as regards access to the availability of gynaecological health care. The main conclusion is that elevated unemployment which could be referred to a poor socioeconomic situation (amongst other factors) may force pregnant women to pay more attention to improving their life conditions, than to sufficient medical controlling.

Inappropriate mediastinal baroreceptor reflex as a possible cause of sudden infant death syndrome – Is thorough burping before sleep protective?

Despite extensive research, a link between the assumed mechanisms of death and known risk factors for sudden infant death syndrome (SIDS) has not yet been established. Modifiable risk factors such as prone sleeping position, nicotine exposure and thermal stress and non-avoidable risk factors like male gender and some risky socio-economic conditions could be detected, but the etiology of SIDS remains unknown. In many SIDS cases histopathological findings suggest an involvement of vital autonomic control functions and unidentified trigger factors seem to play a role. From a hypothetical point of view, a developmental sympatheticovagal imbalance of the cardiovascular reflex control could cause a predisposition for SIDS. An assumed gastroesophageal trigger impulse is possibly developed during the first weeks of life and could lead to the infant's vagal reflex death. Air swallowed during feeding escapes through the esophagus while the infant is sleeping. The temporarily bloated esophagus exerts pressure on neighboring mediastinal baroreceptors, which is potentially misinterpreted as a rise in arterial pressure. The following cardiodepressoric baroreceptor reflex could lead to arterial hypotension, bradycardia and cardiac arrest. Sleeping in prone position may create an increased thoracic pressure on mediastinal baroreceptors, causing a more pronounced vagal reflex and an increased likelihood of SIDS. Prone position in connection with soft objects in the infant's sleeping environment potentially generates an increased oculobulbar pressure, resulting in an additional cardiodepressoric condition (Aschner-Dagnini phenomenon). From the sixth month of life onwards the sympatheticovagal balance seems to have matured sufficiently to compensate the life-threatening challenges in most infants. Insufficient postprandial burping could either create another independent modifiable risk factor or present the missing link to a common trigger mechanism for SIDS. Further investigations may possibly lead to the explicit recommendation to burp all infants sufficiently and repeatedly before sleep.

Lung-function tests in neonates and infants with chronic lung disease: tidal breathing and respiratory control

This paper is the fourth in a series of reviews that will summarize available data and critically discuss the potential role of lung-function testing in infants with acute neonatal respiratory disorders and chronic lung disease of infancy. The current paper addresses information derived from tidal breathing measurements within the framework outlined in the introductory paper of this series, with particular reference to how these measurements inform on control of breathing. Infants with acute and chronic respiratory illness demonstrate differences in tidal breathing and its control that are of clinical consequence and can be measured objectively. The increased incidence of significant apnea in preterm infants and infants with chronic lung disease, together with the reportedly increased risk of sudden unexplained death within the latter group, suggests that control of breathing is affected by both maturation and disease. Clinical observations are supported by formal comparison of tidal breathing parameters and control of breathing indices in the research setting.

Near-miss apparent SIDS from adrenal crisis

OBJECTIVE

Adrenal crisis from salt-losing congenital adrenal hyperplasia (CAH) typically occurs in the first 2 weeks of life. We evaluated 3 infants with adrenal crisis who presented at 6 to 8 months of age with near-miss sudden infant death syndrome (SIDS).

SUBJECTS

Three 46,XY phenotypic female infants presented near death at 6 to 8 months of age with adrenal crisis and unmeasurable steroid hormones consistent with congenital lipoid adrenal hyperplasia (lipoid CAH).

METHODS

We sequenced genes potentially causing this phenotype: steroidogenic acute regulatory protein (StAR), the cholesterol side-chain cleavage enzyme, adrenodoxin reductase, adrenodoxin, and steroidogenic factor 1 (SF1). Site-directed mutagenesis and functional assays were performed for the missense mutation.

RESULTS

Hormonal values showed complete absence of adrenal and gonadal steroids. Patient 1 was a compound heterozygote for missense mutation R140P and an mRNA splice donor site mutation in the StAR gene. The R140P mutation was wholly inactive in vitro. Patient 2 was homozygous for a 7 base pair StAR deletion causing a frameshift. No mutations were found in Patient 3, suggesting a novel disease.

CONCLUSIONS

Although genetic disorders of steroidogenesis typically present in the first month of life, some defects, especially those in StAR, can present in mid-infancy, when adrenal hyperplasias are rarely considered. Adrenal insufficiency is a subtle disorder that may cause cardiovascular collapse, causing unexplained infant death that resembles SIDS.

A controlled study of the relationship between Bordetella pertussis infections and sudden unexpected deaths among German infants

OBJECTIVE

This was a prospective, controlled, multicenter study to investigate the relationship between Bordetella pertussis infections and sudden unexpected deaths among German infants.

DESIGN

Between 1995 and 1997, all infants who died at 7 to 365 days of age and for whom autopsies were performed in 1 of 8 participating institutes of legal medicine were enrolled. During a standardized autopsy, nasopharyngeal specimens (NPSs) and tracheal specimens were obtained for polymerase chain reaction (PCR) assays to detect B pertussis. The oligonucleotide primers PTp1 and PTp2, which specifically amplify a 191-base pair DNA fragment of the pertussis toxin operon of B pertussis, were used. Two control subjects (matched according to residence, age, gender, and nationality) were enrolled for each case subject, via a network of pediatricians in private practice, and NPSs were obtained from those infants. Parents of case subjects and control subjects were asked to provide specific information on respiratory illnesses of the child, contact with a known case of pertussis, or close contact with a person with a cough illness during the 4 weeks before death or enrollment, as well as the child's pertussis immunization status. The pathologists performing the autopsies were unaware of the PCR results.

RESULTS

Enrolled were 254 infants (66% male) with sudden unexpected deaths and 441 matched control subjects. Autopsies according to protocol were performed for 234 of the case subjects (92%); a diagnosis of sudden infant death syndrome (SIDS) was made for 76%. For the remaining subjects, causes of death were respiratory or other infections (14%), congenital anomalies or organ failures (4%), aspiration (2%), or accidents or traumatic events (4%). PCR results were positive for B pertussis for 12 case subjects (5.1%) (all with SIDS or respiratory infections) and 5.3% of control subjects. Of the 12 case subjects with positive PCR results, 10 (83%) were male. Questionnaires had been returned by the parents of 5 of the 12 infants. Three had experienced a respiratory illness (all with cough), beginning 7, 14, and 19 days before death. None had a known contact with a case of pertussis. Four of 15 control infants (27%) with positive PCR findings for B pertussis had a cough illness, indicating possible pertussis, and 2 of those 4 developed typical symptoms (whooping). Background information was received from 116 parents (46%) of case subjects and from parents of all control subjects. Upper respiratory tract infections within 4 weeks before death were reported for 53% of case subjects and 38% of control subjects. Also, fewer case subjects (33%) than control subjects (68%) had received age-adequate numbers of pertussis vaccine doses.

CONCLUSIONS

The concept of infection as a factor in SIDS is supported by a number of observations, including the seasonal distribution of the occurrence of SIDS; the high incidence of concurrent upper respiratory tract infections among infants dying as a result of SIDS; the peak age at 3 to 4 months; nicotine use in a child's household, which predisposes children to respiratory infections such as otitis media; and the protective role of breastfeeding. A prominent role might be suspected for B pertussis, for several reasons. 1) B pertussis infections in infancy are frequently associated with apneic spells, which are occasionally life-threatening and, if leading to death, might be reported as SIDS. 2) Epidemiologic evidence from the United Kingdom, Sweden, and Norway indicates that SIDS is associated with B pertussis infection. 3) In a previously published study, we detected B pertussis DNA in the nasopharynx of 9 of 51 consecutive infants (18%) with sudden unexpected deaths. This is the first prospective, controlled study to investigate the possible etiologic role of B pertussis in SIDS. Clinically unrecognized B pertussis infections were relatively frequent (5.3%) among control infants during the course of our study. The rate of infection was similar or perhaps greater for control subjects, compared with case subjects (1.7%), when only NPS results were compared. This may seem surprising but is supported by other studies, in which asymptomatic infections or mild respiratory illnesses were observed among infants exposed to B pertussis. Careful autopsies, including histologic evaluations of organ specimens and use of PCR to detect B pertussis in NPSs and tracheal specimens, represented a strength of this study. Our general findings were as expected. The majority of cases were classified as SIDS. The second largest group included infants for whom respiratory infections were found. The findings of various other diagnoses, which in several instances would have been undiscovered otherwise, emphasize the need for autopsies after unexpected infant deaths. What is the significance of the identified B pertussis infections in 12 cases? Several pieces of evidence support the plausibility of a cause-and-effect relationship. Eight of the 12 case subjects died before 6 months of age, the typical age for death attributable to pertussis. In autopsies, 9 of the subjects were found to have signs of respiratory infections; for 2 infants, the autopsies suggested that death was attributable to a respiratory infection. One additional infant (data not shown) had brain edema (which could have been attributable to hypoxemia during pertussis). Lower rates of completed primary series or age-adequate numbers of pertussis vaccine doses among case subjects than among control subjects may indicate that immunization against pertussis protects children from death attributable to unrecognized B pertussis infection. Moreover, a recent study indicated that immunization with diphtheria-tetanus-pertussis vaccine induces antibodies that cross-react with pyrogenic staphylococcal toxins, which have been implicated in several cases of SIDS. Other microorganisms may be involved in the sudden death of infants, as suggested in this study by the higher rate of a history of concurrent upper respiratory tract infections among case subjects, compared with control subjects. Similarly, in a Scandinavian study, 48% of 244 SIDS case subjects, compared with 31% of 869 control subjects, exhibited symptoms of upper airway infection during the last week before death or interview, respectively. Because SIDS is a diagnosis of exclusion, every attempt should be made to identify a cause of death during autopsy. This should include the search for pathogenic microorganisms in the respiratory tract with the use of PCR and other sensitive tests. In conclusion, B pertussis infection was found for 12 of 234 infants (5.1%) with unexpected deaths, and the infections might have contributed to the deaths.

Sudden death among infants and adults: companion disorders of maladaptive sympathetic bias

Sudden infant death syndrome is the leading cause of death in infancy, but its pathophysiological mechanism has been elusive. Sudden death in adults is a common phenomenon, but the etiology in many cases remains unknown at autopsy. We hypothesize that maladaptive sympathetic bias is the explanatory mechanism that links many cases of sudden demise among adults and infants as companion syndromes. Normally, sympathetic response occurs as an adaptation to physiologic demands of the body through various autonomic reflex arcs such as chemoreceptors. Sympathetic response can become chronic and maladaptive when the normal sympathetic response fails to correct the precipitating physiologic trigger, leading to chronic activation of autonomic reflex arcs. In conditions such as infant sleep apnea or adult heart failure, a pernicious cycle of sympathetic bias may result. Chronic sympathetic bias increases susceptibility to sudden fatal arrhythmias, QT-related and otherwise, in the setting of an exaggerated adrenergic challenge. Examples of such adrenergic stressors include trauma, hypoxia, hypercapnia, acidosis, sleep arousal, illness, medical procedures, and physical activity, all of which have associations with sudden death. Our hypothesis may not only help explain the survival benefits of drugs such as beta-blockers and devices such as synchronization therapy, but also portend new application of similar therapies for many conditions of sympathetic bias.

Maternal and obstetric risk factors for sudden infant death syndrome in the United States

OBJECTIVE

The objectives of this study were to 1). study the incidence of sudden infant death syndrome (SIDS) among singleton births in the United States and 2). identify maternal and obstetric risk factors for SIDS.

METHODS

A cohort of all live births in the United States from 1995 to 1998, formed the source population (n = 15627404). The data were obtained from the National Centers for Health Statistics Linked Births and Infant Deaths File. A nested case-control study was used to examine risk factors for SIDS. From this birth cohort, all SIDS deaths (n = 12404) were first identified (case group). From the remaining non-SIDS births, a 4-fold larger sample (n = 49616) was randomly selected as a control group.

RESULTS

The overall incidence of SIDS was 81.7 per 100000 live births. More mothers in the case group than in the control group were reported to have placenta previa (odds ratio [OR]: 1.70; 95% confidence interval [CI] 1.24, 2.33), abruptio placentae (OR 1.57; 95% CI 1.24, 1.98), premature rupture of membranes (OR 1.48; 95% CI 1.33, 1.66), or small for gestational age (OR 1.40; 95% CI 1.30, 1.50 for the 10th percentile). SIDS cases were also more likely to be male. Mothers of cases were more likely to be younger, less educated, and nonwhite, and more of them smoked during pregnancy and did not attend prenatal care.

CONCLUSION

This analysis confirms the importance of several well known demographic and lifestyle risk factors for SIDS. In addition, placental abnormalities were risk factors for SIDS.

LEVEL OF EVIDENCE

II-2

Is sudden infant death syndrome (SIDS) an autoimmune disorder of endogenous vasoactive neuropeptides?

Sudden infant death syndrome (SIDS) remains a perplexing diagnosis with conflicting laboratory investigation and lack of a biologically plausible aetiology. Investigations into the endogenous vasoactive neuropeptides, including pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are revealing the critical role these substances have in homeostasis including thermo- and cardiovascular regulation. For example, studies in PACAP receptor-deficient mice have revealed sudden neonatal death attributed to respiratory control defects, possibly due to mutations in genes encoding components of PACAP signalling pathways. PACAP and VIP belong to the secretin/glucagon superfamily of hormones and function as vasoactive neuropeptides. They act as hormones, neurotransmitters, immune modulators and neurotrophes. They are readily catalysed to small peptide fragments. They and their binding sites are immunogenic and are known to be associated with a range of autoimmune conditions. Vasoactive neuropeptides have a known role in thermoregulation and deficiency states are associated with higher neonatal death rates in rats. PACAP plays a significant role in carbohydrate and lipid metabolism and impairment of functioning has potentially serious consequences. It is postulated PACAP and VIP receptors in brain may become compromised through autoimmune phenomena resulting in cardio-respiratory dysfunction and death. This paper discusses the potential role of certain vasoactive neuropeptides in causing autoimmune responses in susceptible infants predisposing them to SIDS.

Sudden infant death syndrome among extremely preterm infants: United States 1997-1999

BACKGROUND

Preterm infants have been reported to be at higher risk than term infants for sudden infant death syndrome (SIDS). Reasons for this higher risk are not clear.

OBJECTIVE

The objective of this study was to analyze medical and demographic characteristics among infants 24 to 32 weeks gestation to identify characteristics more prevalent among infants dying of SIDS in the postneonatal period than among infants of similar gestation who survived or who died of other causes in the postneonatal period.

DESIGN/METHODS

United States linked birth and death certificate period data for 1997 to 1999 were used for this analysis. The population used was limited to infants 24 to 32 weeks gestation weighing 500 to 2500 g. SIDS deaths were limited to the postneonatal period and compared to survivors and infants dying in the postneonatal period of other causes.

RESULTS

There were 469 postneonatal SIDS deaths with complete data (rate=2.2/1000 live births surviving > or =28 days); 3950 other postneonatal deaths (rate=18.7/1000) and 206,640 survivors. Compared with survivors, infants dying of SIDS were more likely to be born to mothers with <12 years of education (odds ratio=2.5, 95% confidence interval (95% CI=1.8, 3.3); be born to mothers < or =17 years of age (OR=2.0, 95% CI=1.4, 2.8); and be born to mothers with >3 previous pregnancies (OR=2.6, 95% CI=1.9, 3.5). Compared with infants dying in the postneonatal period of other causes, these same demographic factors continued to be significant risk factors for SIDS. There were no medical risk factors such as breech presentation, abruptio placenta, Apgar score <4 at 5 minutes, or mechanical ventilation for >30 minutes after birth, for which infants dying of SIDS were at greater risk than survivors or infants dying of other causes.

CONCLUSIONS

Risk factors for SIDS among infants 24 to 32 weeks gestation appear to be more associated with sociodemographic characteristics than medical characteristics. This suggests that for the immediate future, the risk for SIDS among very preterm infants will be best addressed through further modification of the environment and parent behavior.

Physiology of breathing and related pathological processes in infants

There is little information describing control of breathing in the fetus and infant. The available data have largely been drawn from studies in animals and awake adults. Although the hierarchy of control of breathing is the same in adults and infants, feedback emphasis is different, with behavioral states and the sleep/wake cycle primary in the fetus and infant and integrated chemoreceptor response primary in the older child and adult. Control of breathing during the transition from the fetal state to a breathing child and the process of maturation are very different from that in adults. The article begins with an overview of the changes in the systems responsible for breathing at the developmental stages from fetus to neonate, with differences highlighted. It then discusses the possible pathology related to difficulties in negotiating this transition period, including apnea, sudden infant death syndrome, and chemoreceptor control abnormalities.

Sudden neonatal death in PACAP-deficient mice is associated with reduced respiratory chemoresponse and susceptibility to apnoea

Pituitary adenylate cyclase-activating polypeptide (PACAP)-deficient mice are more prone to sudden death during postnatal weeks 1-3 than wild-type littermates. Given that PACAP is localized in brainstem regions associated with respiratory chemosensitivity, we examined whether PACAP-null neonates have reduced respiratory responses to hypoxia and hypercapnia. Using unrestrained, whole-body, flow-through plethysmography we found that, by postnatal day 4, the PACAP-null neonates had significantly reduced ventilation during baseline breathing, and blunted responses to both hypoxia (10% O2-90% N2) and hypercapnia (8% CO2-92% air). To determine whether the respiratory phenotype of the PACAP-null mice may contribute to their greater neonatal mortality, we used ECG to examine respiration and cardiovascular function of littermates. We demonstrate that, under conditions that exacerbate mortality of knockout but not wild-type animals, PACAP-deficient mice experience prolonged apnoeas that precede atrio-ventricular block. Both apnoeas and atrio-ventricular block were absent in wild-type littermates. These data suggest that PACAP-deficiency results in higher neonatal mortality primarily as a result of respiratory control defects and raise the possibility that mutations in genes encoding components of the PACAP signalling pathways may contribute to neonatal breathing disorders in humans.