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REVIEW
Sudden infant death syndrome: a critical review of
approaches to research
P N Goldwater
...............................................................................................................................
Arch Dis Child 2003;88:1095–1100
This review explores the various research approaches
taken attempting to solve the problem of SIDS. It would
appear that major clues provided by pathological findings
have been largely overlooked and as a consequence much
effort, time, and money has been wasted on projects that
satisfy only sub-specialty and political needs. Close
examination of the pathological clues would provide better
insights into the mechanisms underlying this enigmatic and
heartbreaking problem.
...........................................................................
.......................
Correspondence to:
Dr P N Goldwater,
Microbiology & Infectious
Diseases Department, The
Women’s & Children’s
Hospital, North Adelaide,
South Australia 5006;
goldwaterp@
mail.wch.sa.gov.au
Accepted 15 March 2003
.......................
T
he enigma of sudden infant death syndrome
(SIDS) has frustrated researchers for too
long. Part of the failure to determine its
aetiology can be attributed to the approach. With
few exceptions, this could be described as having
been ‘‘flawed’’ since ‘‘scientific’’ inquiry began—
around the time when the condition (‘‘cot
death’’) was first defined in 1969 as ‘‘the sudden
death of any infant or young child, which is
unexpected by history, and which a thorough
post mortem examination fails to show an
adequate cause of death’’.
1
In retrospect, it is
clear that omissions of importance occurred at
the time of the first and second international
conferences on the causes of sudden death in
infants. These omissions included appropriate
consideration of the salient pathological features
observed in the babies who fell under the
accepted definition(s). Many articles which set
out to describe the pathology of SIDS failed to do
so (being incomplete) and drifted off into
unjustified and fanciful supposition as to the
reason for a particular finding.
2–4
Why the
pathological evidence was largely overlooked is
hard to understand. This review will explore in
detail the arguments that abounded at the time
and discover why the thinking about SIDS lacked
the logical and considered approach it deserved.
Much of the debate has come from the two main
schools of thought: (1) that SIDS has a single
cause; and (2) that SIDS is an amalgam of
predisposing host and epidemiological risk fac-
tors (see table 1) and is therefore multifactorial.
The ‘‘single cause’’ school, in the main, has
concentrated on single areas of interest (allergy,
nutrition, metabolism, cardiological, pulmonolo-
gical, neurological, endocrinological, toxicologi-
cal, and infection), and with few exceptions,
without much attention given to pathological
clues. These approaches have been driven largely
by sub-specialty and political interest rather than
evidence. Likewise, the multifactorial/multiple
causes school’s attention to pathological infor-
mation has been similarly blinkered. It is too
simplistic to divide the research into these
schools, for the researchers in the ‘‘single cause’’
school who invoke a bacterial toxin (as a likely
single cause) have given due acknowledgment to
the many risk factors that could play a role in
SIDS.
13–15
In effect, as will be revealed, a single
bacterial toxin cause acting in concert with the
known risk factors could be labelled as ‘‘multi-
factorial’’. Linking prone sleep position (a major
risk factor) to the many other epidemiological
factors has been difficult. Its relation to SIDS
varies considerably in terms of relative risk. If an
asphyxial mechanism is proposed to underlie an
association with prone (and lateral) sleeping, the
same mechanism almost certainly cannot be
applied to supine sleeping, a position in which
SIDS also occurs. Regrettably, there has been
insufficient research and discussion in regard to
supine SIDS deaths.
THE PATHOLOGY OF SIDS
Infants classified as dying from SIDS are most
often normally nourished and hydrated. The
nappies are usually wet and contain stool, and
the bladder and rectum are typically empty.
417
The salient features at post-mortem examination
are the following:
Liquid blood
An early discussion on aspects of pathology that
might have cleared the way to a rational
approach to researching the cause SIDS took
place at the Cambridge Symposium on SIDS in
1970. Liquid, unclotted blood within the cham-
bers of the heart is a common, if not constant
finding in SIDS.
6
In this regard, Professor Francis
Camps, doyen of forensic pathology, questioned
in passing whether asphyxia could cause lique-
faction of blood. He observed that asphyxiated
animals have normally clotted blood and that an
asphyxial mechanism could not be invoked in
SIDS.
18
According to Di Maio and Di Maio,
unclotted blood in the context of adult death
does not infer a particular cause of death.
19
Despite this, these authors claim fluidity of the
blood is one of the ‘‘classical signs’’ of asphyxia
but go on to say these signs are non-specific and
can occur in deaths from other causes. The
contradiction is obvious. However, in the context
of sudden unexpected death in infancy (SUDI)
without apparent cause, with almost every case
exhibiting this finding, it would suggest a very
limited number of potential causes, especially
when normally clotted blood is the usual
postmortem finding in infants dying suddenly
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from traumatic injury and non-infective causes. Beckwith
20
compared rates of completely fluid blood and partly clotted
blood in SIDS and controls and showed that 92% and 7%
respectively, of SIDS babies and 73% and 16%, respectively of
controls had the above mentioned blood states. Despite well
documented information on the high frequency of unclotted
blood in SIDS, some major articles on the pathology of SIDS
ignore the state of the blood.
2
Confounding these considera-
tions is the observation that many cases of unquestionable
asphyxia have unclotted blood. However, because there are
other conditions in which liquid blood occurs, its finding
does not necessarily infer asphyxia was the basis of the
finding. Nevertheless, the very high frequency of demon-
strable unclotted/liquid blood in SIDS should merit further
investigation.
On consideration of this clue, the logical approach to
investigation would be to: (1) determine whether or not
perturbation of the clotting cascade underlies this phenom-
enon; and (2) if so, examine the origin of the perturbation,
for example, endothelial cell mediated or other precipitating
factor. A study that investigated disseminated intravascular
coagulation (DIC) in neonatal deaths with the use of
immunohistochemistry to look for fibrin related antigens
(FRA) in tissues in which SIDS babies were used as a
comparison group, showed minimal FRA staining, indicating
DIC is an unlikely underlying mechanism in SIDS.
21
Since the
pathogenesis of DIC became understood in the 1960s,
paediatric pathologists have been unanimous in excluding
the condition on histopathological grounds. Although DIC is
not part of SIDS, another mechanism must be sought to
explain the phenomenon of liquid blood. Can fibrin
degradation products be formed as a result of a mechanism
other than DIC? It is clear that consistently higher cross
linked fibrin degradation products are found frequently in
SIDS sera compared with other deaths.
22
This would indicate
that in SIDS, a clotting perturbation has indeed occurred.
Beckwith referred non-specifically to unreferenced experi-
mental findings that ‘‘fibrinolysins are released when the
heart perfuses anoxic tissues, and that they are not released
when the heart stops suddenly’’.
20
Little, if any, progress has
been made on the pathogenesis of unclotted blood for more
than three decades. Clues may be found in the mechanisms
involved in the development of ‘‘shock lung’’ (acute
respiratory distress syndrome)
23
(vide infra) in which
activation of both intrapulmonary and circulating cells
occurs.
24
Notably, SIDS infants have increased numbers of
mast cells in lung tissue and increased levels of mast cell
tryptase,
25
especially in those dying prone.
26
An anaphylactic
reaction (involving degranulation of mast cells), could be
triggered by viral infection (common in SIDS) via interferon
and up-regulation of mast cell MHC II antigens—known
receptors for pyrogenic toxins.
27
Intrathoracic petechial haemorrhages; size, number,
distribution
Much discussion has been devoted to the almost universal
finding in SIDS babies of petechial haemorrhages in their
intra-thoracic organs including the thymus, lungs, visceral
pleura, and epicardium. Indeed, the presence of intrathoracic
petechial haemorrhages is regarded by some pathologists as a
prerequisite for making the diagnosis of SIDS.
28
Regrettably,
most studies have not attempted to delineate differences
between SIDS petechiae and those found in asphyxial deaths.
The few papers that have examined this have shown
differences that would indicate possibly different pathoge-
netic mechanisms. Petechial haemorrhages were encountered
in 87% of SIDS cases, but in non-SIDS cases ‘‘were mostly
absent or less developed in quantitative terms’’.
29
Others have
commented along similar lines.
30 31
Krouse and Jordan
30
compared the distribution of petechiae in SIDS and various
other causes of death and with few exceptions, showed
limitation to within the chest cavity in SIDS but extension (to
below the diaphragm) in cases whose terminal course was
complicated by either hypoxaemia, hypercarbia, metabolic
acidosis, coagulopathy, or infection. Table 2 summarises the
incidence of intrathoracic petechial haemorrhages in SIDS
and non-SIDS reported by several investigators and shows
impressive differences between the two groups. Beckwith
31
has commented on the incidence, distribution and density of
intrathoracic petechiae wherein these differences are appar-
ent. While Prof. Camps had experience with the findings of
experimental asphyxia, he was clearly unaware of the
experimental findings of Handforth,
32
who killed rats by
tracheal occlusion and observed intrathoracic petechiae at
necropsy. The observation by Beckwith that the petechiae
found on the posterior side of the thymus were more
numerous below than above the innominate vein in SIDS
cases led to the hypothesis that the petechial distribution
could be explained by the dampening effect of the vein on
changes in intrathoracic pressure occurring during breathing
against an occluded upper airway.
20
The pathological findings
derived by Valde´s-Dapena and colleagues
33
from the NICHHD
study found petechiae in the pleura less often than most
other studies. Despite this, the finding on gross pathology
(54%) was significantly greater than that in explained (non-
SIDS) deaths (35%). Gross and microscopic results combined
revealed 63% of SIDS cases had pleural petechiae with only
38% of explained deaths. On comparison of frequencies of
intrathoracic petechiae in this analysis, SIDS cases signifi-
cantly more often had these petechiae (82%) compared with
explained deaths (60%). There were discrepancies between
observation of petechiae on gross examination compared
with histopathology, with petechiae of pleura, alveoli, and
septa more often noted on microscopy. Thymic petechiae
were noted in 69% of SIDS cases and 38% of explained deaths
when gross and microscopic findings were combined. Had
quantitative measurements of density of petechiae been
undertaken in this study, further valuable comparative data
Table 1 Predisposing host and epidemiological risk
factors associated with SIDS
Prenatal/pregnancy
5–8
Higher parity
Low birth weight, short gestation (intrauterine growth retardation)
Inadequate prenatal care
Maternal smoking
Smoking within the household during pregnancy
Maternal recreational drug use (opiates, cocaine)
Urinary tract infection
9
Demographic/genetic
8
Lower socioeconomic status
Race-ethnicity: African-American, indigenous populations: Aboriginal
Australian, Maori, Native Americans
Age at death (peak at 2–4 months)
Male gender
Cold season
IL-10 low producer
IL-1b high producers
Neonatal/postnatal
5 6 8 10–12
Infections (URTI or gastroenteritis) (recent illness potentiates effectof
prone sleep position and overwrapping)
Passive exposure to cigarette smoke
Lack of breast feeding
Prone sleep position
Bed sharing
Sofa sleeping
Used mattress
Lack of or late immunisation
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would have been obtained. However, petechial haemor-
rhages, when present in SIDS, are much denser (in number
per area) than in non-SIDS deaths.
3
Given that the NICHHD
study
33
purported to be broad and encompassing all things
pathological in SIDS, it is disappointing that quantitative and
qualitative analysis of petechiae was not undertaken and
organ weights (see below) were not analysed.
Byard and Krous
34
relegated petechial haemorrhages to
‘‘minor’’ pathological findings yet they declare these are well
recognised in cases of SIDS and occur in 68–95% of cases and
may be caused by the mechanisms that led to the terminal
event.
35
Furthermore, the authors contrast the findings seen
in cases of hanging and crush asphyxia in which petechiae of
the conjunctiva and face—findings unusual in infants dying
of other causes (that is, SIDS). They quote Dr John Hilton
36
that petechiae ‘‘are never present on the conjunctiva, eyelids
or on or in other soft tissues of the head or neck in SIDS’’.
Byard and Krous
34
support the contention that finding
petechiae on the face, neck, upper chest, or conjunctivae
warrants suspicion and extremely careful investigation. It has
been presumed, but by no means proven, that intrathoracic
petechiae in SIDS are the consequence of breathing against
an occluded upper airway. Just where the alleged obstruction
is thought to occur has never been established. Nor have
other causes of petechial haemorrhage been vigorously
sought. Potential avenues of research that have been largely
overlooked include the clotting cascade, toxic or immunolo-
gical damage to the capillary basement membrane or other
molecular events taking place during toxic or septic shock.
In summary, while intrathoracic petechial haemorrhages
are extremely common in SIDS they are a non-specific
finding; however, the predictive value of finding petechiae
has never been explored (vide infra). Notwithstanding this,
there has been an almost total absence of research into
mechanisms by which petechiae form (other than a
respiratory one).
Fluid-laden, congested organs
The weights of the thymus, lungs, liver, and brain appear to
be significantly greater in SIDS cases than published norms.
42
The study by Siebert and Haas
42
analysed data from 500
postmortem examinations performed over 15 years by one
pathologist. It is understandable that so-called ‘‘normal’’
weights tend to be low as a result of underlying disease in
this comparison group. Nevertheless, it is clear that in SIDS
the above mentioned organs are fluid laden and thus heavy.
42
The underlying pathophysiological processes have not been
the subject of investigation.
Brain
To quote Kinney and Filiano,
43
‘‘Of all neuropathologic
findings, heavy brain weight is perhaps the best established,
because of the simplicity and reproducibility of the method of
measurement, i.e. weighing the unfixed brain at autopsy.’’
The underlying cause of the increased brain weight would
include the following possibilities: cerebral oedema (second-
ary to hypoxia/anoxia or toxic/metabolic factors), agonal
vascular congestion, or megalencephaly. However, no inves-
tigation into mechanisms by which the phenomenon of
heavy brain weight in SIDS occurs has been adequately
studied. One exception is the identification of staphylococcal
toxins in various tissues (including brain) of SIDS babies,
44
thus suggesting a toxic cause of brain swelling.
To link the pathological finding of heavy brain weight to
prone sleep position and other epidemiological features
requires a special exercise of imagination. One such exercise
has resulted in the ‘‘triple risk’’ model encompassing
vulnerability, a critical development period and exogenous
stressors.
43
This is fine when applied to the epidemiological
findings in SIDS but becomes convoluted, complex, and
implausible when a link with prone sleep position is
attempted. It may not be a coincidence that periventricular
leukomalacia, a characteristic finding in babies who develop
cerebral palsy, is also common in SIDS.
45 46
Many of the
epidemiological features of SIDS are shared with those of
cerebral palsy. Not only is the incidence of cerebral palsy
similar to SIDS (2–2.5 cases per 1000 live births), but many
risk factors for the occurrence of cerebral palsy are shared
with SIDS, including maternal age, maternal infection,
multiple births, shorter gestational age, and low birth
weight.
47–49
The list of neurohistopathological changes
claimed to be associated with SIDS is long, and with the
use of conventional techniques SIDS brains look normal or
have inconsistent minor changes such as mild brain stem
gliosis.
43
The studies are frequently contradictory.
43
Thymus
As mentioned, thymus weights tend to be heavier in SIDS
cases than in ‘‘normal’’ babies. Again the comparison
(normal) group may have had underlying disease that could
have impacted on the health of the thymus and therefore the
organ’s weight. No data exist that correlate the thymus
weights with the density of petechial haemorrhages.
Lungs
Heavy, fluid laden lungs in SIDS is a frequent, if not
invariable finding. Although asphyxia is described as one of
the conditions in which fluid laden lungs occur, other
Table 2 Incidence of intrathoracic petechial haemorrhages in SIDS and comparison
cases
Reference SIDS cases
Frequency of
petechiae (%) Non-SIDS comparisons
Werne and Garrow
37
31 80 Absent or sparse in infant
suffocation, CO asphyxia,
drowning
Handforth
32
12 100 None
Jacobsen and Voight
38
97 95 Rare in infanticide, accidents
Geertinger
39
80 79 6 of 43 (14%)
Cooke and Welsh
40
91 94 10 of 31 (32%) in no case
were they numerous
Marshall
41
162 68 12 of 42 (29%)
Beckwith
31
109 87 16 of 38 (42%)
Krous
3
100 85 None
Valdes-Dapena et al
33
622 82 39 of 65 (60%)
Risse and Weiler
29
63 (thymus) 87 13 of 33 (39%) (thymus)
SIDS research: a critique 1097
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potential explanations have never been adequately
addressed, especially from the point of view of blood vessel
basement membrane integrity. ‘‘Shock lung’’ is a condition in
which perturbation of the inflammatory pathways leads to
damage of capillary basement membranes and leakage of
fluid into the alveolae and interstitium.
23
Non-asphyxial
explanations deserve appropriate investigation. Intra-alveolar
haemorrhage would contribute to lung heaviness. The causes
of intra-alveolar haemorrhage are many and varied and have
been widely debated; however, pathologists are wary of the
possibility of mechanical asphyxia when more than 5% of
alveolar area is occupied by red blood cells, but appropriate
studies have not been conducted to provide definitive data.
50
Others have examined semiquantitative morphological deter-
minants of asphyxia in lung tissue
51
and showed good
correlation with the types of asphyxia (for example, foreign
body, suffocation, drowning and strangulation) but did not
examine lungs from SIDS cases. Potentially valuable findings
could be forthcoming if similar methodology were to be used
in the context of SIDS.
Liver
Fatty change is described in SIDS, but the finding is variable
and therefore cannot adequately explain the increase in
weight of SIDS babies’ livers over comparison babies. Again
the mechanism by which the liver becomes heavy in SIDS
needs addressing.
PREDICTIVE VALUE OF SPECIFIC PATHOLOGICAL
FINDINGS
To my knowledge, no effort has been made to determine the
predictive value of a particular pathological finding in helping
to reach a diagnosis or exclude a diagnosis of SIDS. For
instance, what is the predictive value of thymic petechiae of a
particular density, or pleural or cardiac petechiae at a
particular age? Or, what is the predictive value of an organ
weight at a particular age? Examination of the data from the
NIHCHD study provides some insights. For instance, the
predictive value of finding thymic petechiae (gross and/or
microscopic examination) would be 95.5% predictive of SIDS;
the absence of petechiae would give a predictive value of
14.8%. In the case of intrathoracic petechiae the predictive
value of such a finding is equally high at 94.1% and the
predictive value of their absence would be 16.1%.
Inflammatory infiltrates
Inflammatory changes in the respiratory epithelium is a
common finding in SIDS and probably reflects recent viral
respiratory symptoms noted in up to 44% of cases within the
last two weeks of life.
52
The degree of inflammation in the
trachea and bronchioles observed in SIDS is considered
inadequate to represent a cause of death.
53
Nevertheless, a
contributory role of virus infection in SIDS through viral
potentiation of bacterial toxins remains a possibility (vide
infra).
54
Bacterial toxins, viral infection, smoke
Blackwell and colleagues
13
have given due prominence and
summarised a microbiological perspective of SIDS, but the
focus was mainly on staphylococcal toxins. Independent
studies have shown an increased colonisation rate by
toxigenic bacteria in the gut of babies who have died of
SIDS compared with healthy living babies or babies who died
of other causes.
13–16
Other studies have shown nasopharyngeal colonisation by
Escherichia coli
55 56
and Staphylococcus aureus,
56
with increased
colonisation of the latter in infants who slept prone.
56
Furthermore, if toxins were involved in SIDS causation,
these should be demonstrable in the sera of SIDS cases.
Indeed the lethal toxicity of serum from SIDS babies
compared to controls has been shown by Alexander and
colleagues
57
in infant mice and by Sayers and colleagues
58
in
chick embryos. Notably in both studies the sera from control
infants were non-lethal. In addition, E coli strains isolated
from SIDS babies (but not healthy babies) are lethal to
mice.
59
This work failed to show known E coli toxins (for
example, ST, LT, stx) in most SIDS cases and was thus a
stimulus to seek new toxic bacterial proteins; this led to
the discovery of soluble curlin in all SIDS sera of an
Australia series examined.
60
This finding awaits independent
validation.
Generally not appreciated is the fact that bacterial protein
toxins are potentiated (that is, made more lethal) with co-
existent viral infection
54 61 62
and/or exposure to smoke.
63 64
The latter two factors belong in the list of risk factors for
SIDS. It is noteworthy that bacterial toxins potentiate each
other,
65
indicating a potential role for multiple toxin
(staphylococcal, E coli, clostridial) involvement in SIDS.
PRONESLEEPINGPOSITIONANDTHECHANGING
PREVALENCE OF SIDS
The ‘‘reducing the risk’’ and ‘‘back to sleep’’ campaigns were
based on epidemiological findings from several studies in
relation to prone sleep position.
66
The campaigns perpetuate a
biased approach to this enigmatic and important cause of
post-neonatal death. Although since 1991 the rate of SIDS
seems to have fallen by about 50% in a number of countries,
SIDS remains a major contributor to post-neonatal mortality
and SIDS incidence varies considerably geographically.
67
Notwithstanding the possible influence of inconsistent
autopsy protocols and criteria for SIDS diagnosis, this
apparent fall may only be a reflection of natural variation.
This idea is supported by Swedish figures, showing that the
rate in the late 1990s has returned to the level observed in the
early 1970s. The decline seen in the early 1990s began before
the introduction of the ‘‘back to sleep’’ campaign.
68
Australian data are similar to those of Sweden but do not
go back as far. In support of the phenomenon of natural
variation in rates of SIDS is the observed upswing in
Victorian SIDS numbers in 2002 (Victorian Institute of
Forensic Medicine data). This may herald a return to the
disturbing figures observed in the 1980s and 1990s. If the
current practice of avoiding prone sleep position sustains,
reappraisal of sleep position in relation to a rising SIDS
incidence will be necessary.
As mentioned above, mechanisms culminating in
asphyxia
69
cannot provide the answer to SIDS because the
findings in asphyxial death fly in the face of pathological
evidence; especially in regard to the number and distribution
of petechiae, not to mention organ weight information. Cases
of SIDS captured on 24 hour computerised memory monitors
(tracing pulse, respiratory rate, and blood pressure) also
show asphyxia was an impossibility.
70 71
Invoking an asphyx-
ial mechanism for prone position must logically exclude the
same mechanism for most deaths in supine and lateral
positions.
The effect of prone sleep position could hypothetically be
explained on the basis of: (1) greater chance of ingestion of
bacteria contaminating the sleeping surface;
72 73
(2) induction
of temperature dependent bacterial toxins;
74
and (3) possible
differences in rates of delivery to the systemic circulation of
gut derived lethal toxin.
75 76
A candidate ‘‘toxin’’ is soluble curlin antigen, CsgA (the
subunit of curli fimbriae—a colonisation/adherence factor
common to most Enterobacteriaceae), accompanied (or not)
by other toxins absorbed through the gut reaching the
circulation via the portal system which takes it to the liver.
Fatty change (for which toxaemia is a cause) is found in the
livers of some SIDS babies.
17 77
A second, possibly more
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important route of curlin/toxin absorption, would be via the
lymphatic system and the thoracic duct. Curlin protein/toxin
would be delivered via the duct to the innominate vein and
thence to the right side of the heart. The first organ exposed
to curlin would be the lungs followed by the heart and the
thymus. These are the organs in which classical pathological
findings in SIDS are seen (petechiae, and wet/heavy lungs).
Bacterial toxins/products can perturb basement membranes
of small blood vessels leading to the small haemorrhages
(petechiae) and fluid laden organs seen in SIDS. Curlin binds
to fibronectin
78
and this could precipitate damage to capillary
basement membranes and perturb the clotting system. The
pattern of distribution of petechiae is distinctive and could be
explained by the fact that these would be the first organs
exposed (as explained above) or that these organs are replete
with toxin receptors.
75 76
This hypothesis explains why more
deaths occur in the prone position in which a lethal amount
of toxin is delivered; and in other positions, by inference, a
usually sublethal dose is delivered to the systemic circulation.
Paracelsus’ notion
79
that ‘‘the dose makes the poison’’
predated our understanding of minimal lethal dose or
LD50. The above mentioned pathological findings in SIDS
include:
N
Liquid (unclotted) blood within the chambers of the
heart,
17 20
and increased cross linked fibrin degradation
products
22
(seen in toxaemia/sepsis); in this context, curlin
protein represents contact phase bacterial components
which can activate the proinflammatory pathway,
80 81
involving reactions with fibrinogen and fibronectin
82
which can lead to depletion of coagulation factors
resulting in a hypocoagulability state.
22
N
The finding of an empty bladder in most SIDS cases
17 77
suggests decreased renal perfusion (toxaemic shock)
during the last sleep. Thus this proposed hypotension
could be explained by curlin protein induction of pro-
inflammatory cytokines with release of bradykinin and/or
NO.
83
The link between infection, inflammation, and the risk
factors for SIDS has been expressed similarly by Blackwell
and colleagues.
84
The role of endotoxin seems in doubt, which
simplifies the search for a more specific toxin candidate. A
number of studies have been unable to ascertain the presence
of endotoxin in amounts different from controls.
85
Disseminated intravascular coagulation (DIC) would be an
expected finding if endotoxin were involved to any great
extent. The absence of DIC in SIDS supports this.
FUTURE RESEARCH
It is time to address the deficiencies in direction and funding
of SIDS research. Many unresolved issues need clarification:
Clues including susceptibility to infection need to be
addressed by examining several aspects of the innate
immune system which would likely play an important role
through induction of adverse reactions to infection in
infancy. Examination of polymorphisms for mannose-bind-
ing lectin, and pro- and anti-inflammatory cytokines might
provide insights into differences in incidence of SIDS among
different ethnic groups. Energy should go into independent
confirmation of the findings in relation to soluble curlin—a
candidate toxin that seems to fulfil the necessary attributes of
a causal agent. Development of models of infection in the
susceptible host must also be attempted to provide a better
understanding of the mechanism(s) involved in SIDS. There
is a need to reassess the suspected ‘‘red herrings’’ of brain
stem astrocytosis, pulmonary haemosiderin, mycotoxins,
organophosphates, and similar ideas with poor correlations
with SIDS. If SIDS research funding organisations are serious
about finding a solution to SIDS it would be helpful if they
could reassess their directions and philosophical approach.
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