Diabetologia (2007) 50:1161–1169
DOI 10.1007/s00125-007-0648-6
ARTICLE
Relationship between increased relative birthweight
and infections during pregnancy in children with a high-risk
diabetes HLA genotype
H. E. Larsson & K. Lynch & B. Lernmark &
G. Hansson & Å. Lernmark & S.-A. Ivarsson &
DiPiS Study group
Received: 26 November 2006 / Accepted: 7 February 2007 / Published online: 4 April 2007
# Springer-Verlag 2007
Abstract
Aims/hypothesis Children with high-risk type 1 diabetes
HLA genotype have increased risk of high relative birthweight (HrBW), while cord blood islet autoantibodies
decrease the risk. As gestational infections may affect
offspring type 1 diabetes risk, the aims were to test
whether: (1) children of mothers reporting gestational
infections have increased HrBW; (2) gestational infections
explain islet autoantibody reduction of HrBW; and (3)
gestational infections affect the association between HLA
and HrBW.
Subjects and methods HLA genotypes and autoantibodies
to glutamic acid decarboxylase, insulinoma-associated
protein 2 and insulin were determined in cord blood of
children born to non-diabetic mothers in the Diabetes
Prediction in Skåne (DiPiS) study. Mothers reported
gestational infections when the child was 2 months old.
Results Fever or gastroenteritis during pregnancy was
reported by 2,848/19,756 mothers (14%); 339 in more than
Electronic supplementary material The online version of this article
(doi:10.1007/s00125-007-0648-6) contains supplementary material,
which is available to authorised users.
Members of the DiPiS Study Group are listed in the
Acknowledgements
H. E. Larsson : K. Lynch : B. Lernmark : G. Hansson :
Å. Lernmark : S.-A. Ivarsson
Department of Clinical Sciences, University Hospital MAS,
Lund University,
Malmö, Sweden
H. E. Larsson (*)
Department of Clinical Sciences in Malmö-Pediatrics,
University Hospital MAS,
205 02 Malmö, Sweden
e-mail: helena.larsson@med.lu.se
one trimester. Children whose mothers reported infections
had increased risk of HrBW (p=0.0003), particularly in the
absence of cord blood islet autoantibodies (interaction
between HrBW, islet autoantibodies and infections, p=
0.0005). The effect on HrBW by high-risk HLA-DQ2/8 was
aggravated by infections in more than one trimester (odds
ratio [OR]=5.24; p=0.003) (interaction; p=0.022). When
infections were reported, cord blood islet autoantibodies
decreased HrBW (OR=0.34; p=0.0002).
Conclusions/interpretation This study revealed that: (1)
gestational fever, gastroenteritis, or both, increased the risk
of HrBW; (2) cord blood islet autoantibodies decreased the
risk of HrBW only in combination with infections; and (3) infections aggravated the association between HLA-DQ2/8
and HrBW. These data suggest an interaction between
HLA, gestational infections, islet autoantibodies and fetal
growth.
Keywords Birthweight . Fever . GAD65 autoantibodies .
Gastroenteritis . Gestational infections . HLA
IA-2 autoantibodies . Infections . Insulin autoantibodies .
Islet autoantibodies . Type 1 diabetes
Abbreviations
BW
birthweight
DBS
dried blood spot
DiPiS
Diabetes Prediction in Skåne
GAD65Ab autoantibodies to glutamic acid
decarboxylase
HrBW
high relative birthweight
IAA
insulin autoantibodies
IA-2Ab
autoantibodies to insulinoma-associated
protein 2
LrBW
low relative birthweight
1162
OR
rBW
Diabetologia (2007) 50:1161–1169
odds ratio
relative birthweight
Introduction
Type 1 diabetes is a chronic autoimmune disease associated
with destruction of the pancreatic islet beta cells, resulting
in loss of insulin production. The incidence of type 1
diabetes before 18 years of age is increasing [1, 2], and
children tend to be diagnosed at an early age [2–5]. HLA
genes are strong susceptibility factors for type 1 diabetes
[6] but twin studies suggest that environmental factors are
also of importance [7, 8]. The low frequency of first-degree
relatives (10–15%) with diabetes among children newly
diagnosed with type 1 diabetes further supports the
importance of environmental factors. High birthweight
(BW) has been reported as a risk factor for type 1 diabetes
[9–11], in contrast to low BW for gestational age (small for
gestational age), which is a risk factor for type 2 diabetes
[12, 13]. Among environmental factors, viral infections
have frequently been proposed as triggers of the autoimmune reaction resulting in type 1 diabetes. In several
studies, it was shown that children who developed type 1
diabetes were more often born to mothers with Coxsackie
or echovirus infections compared with control children [14–
16], although this could not be confirmed in another study
[17]. Children with congenital rubella have been reported to
have a high frequency of diabetes later in life [18, 19].
Infections with Coxsackie B virus were reported to occur at
an increased frequency in children with newly diagnosed
type 1 diabetes compared with control children [20–22], but
convincing evidence for or against an association between
Coxsackie B virus infection and type 1 diabetes has not
been provided [23].
The autoimmune process destroying the beta cells is
marked by autoantibodies to glutamic acid decarboxylase
(GAD65Ab) [24], insulinoma-associated protein 2 (IA2Ab) [25, 26] or insulin (IAA) [27]. Up to 90% of children
with newly diagnosed type 1 diabetes have at least one of
these antibodies. In children born to non-diabetic mothers,
autoantibodies in cord blood have retrospectively been
found in some children who later developed type 1 diabetes
[28]. In contrast, a recent study of children born to mothers
with type 1 diabetes reported that GAD65Ab and IA-2Ab
in cord blood reduced the risk of developing multiple
autoantibodies, diabetes, or both, later in childhood [29].
Recently we reported that children with HLA conferring
a risk of type 1 diabetes had an increased frequency of a
high relative BW (rBW: BW corrected for gestational age)
[30], suggesting that this high relative BW (HrBW) as a
possible risk factor for type 1 diabetes may be affected by
HLA. In our study, children born to mothers with diabetes
were excluded [30]. It is of interest therefore that an
association between HLA and BW was also reported in
children born to mothers or fathers with type 1 diabetes
[31]. We speculated that this effect by HLA on intrauterine
growth might also be influenced or mediated by other
reported risk factors for type 1 diabetes. For example, we
also reported that rBW was reduced in children born to
non-diabetic mothers with GAD65Ab [30]. Since both islet
autoantibodies [28] and gestational infections [15, 16] have
been proposed as risk factors for type 1 diabetes, the aim of
the present study was to test the following hypotheses: (1)
children born to mothers reporting gestational infections
have an increased risk of HrBW; (2) gestational infections
explain that islet autoantibodies are reducing the risk of
HrBW; and finally (3) that gestational infections affect the
association between HLA and HrBW. The hypotheses were
tested in an extended cohort (19,756 children) of the
previously described Diabetes Prediction in Skåne (DiPiS)
study [30, 32].
Subjects and methods
Population The children in this study participated in DiPiS,
a prospective population-based study in Skåne, the most
southern province of Sweden with 1.2 million inhabitants
[30, 32, 33]. The aim of DiPiS is to determine the positive
predictive value for type 1 diabetes of genetic risk combined
with islet cell autoantibody markers and to identify factors
during and after pregnancy that may trigger type 1 diabetes.
Cord blood was genotyped for HLA and analysed for
GAD65Ab, IA-2Ab and IAA. The parents filled out the
consent form and a questionnaire (partly described in
Electronic supplementary material [ESM]) when the child
was 2 months of age. Apart from family history of diabetes,
BW and gestational age, the questionnaire allowed the
mothers to report infections during pregnancy. There were
two questions on infections including infectious diarrhoea,
vomiting and febrile illness (above 38°C), frequency of
illness and during which trimester (see ESM). The Lund
University Ethics Committee approved the DiPiS study.
Study group Children included in the DiPiS study
between September 2000 and August 2004 were
analysed. During this period, 48,058 children were born
in the province of Skåne (Fig. 1) and 35,683 cord blood
samples were obtained at the five maternity clinics in
Malmö, Lund, Helsingborg, Kristianstad and Ystad. After
excluding twins, triplets, preterm children (born before
37 weeks of gestation) and children born to mothers with
diabetes, 31,446 children remained. BW, gestational age
and HLA were available from 19,756 children. A limited
Diabetologia (2007) 50:1161–1169
1163
48,058
Newborn children
12,375
Missing cord blood
35,683
Newborn children
2,000
Mothers with diabetes or
gestational diabetes or
missing diabetes status
33,683
Children born to mothers
without diabetes
2,237
Twins, triplets or
preterm children
31,446
Term, singleton
newborn children
854
Missing HLA-DQB1
10,305
Not returned questionnaire
531
Missing relative birthweight
19,756
Newborn children
Fig. 1 Children born in Skåne between September 2000 and August
2004, and their participation in DiPiS. Children born preterm, to mothers
with diabetes or gestational diabetes, and twins or triplets were excluded
number of mothers had more than one delivery within the
inclusion period of the study. The study design precluded
an identification of these siblings. We compared participating with non-participating children, to reveal that
participation was higher with increasing age of the mother
and with increasing gestational age of the child (ESM
Table 1). The participation was also slightly higher when
the child had high-risk diabetes HLA genotype, but there
was no difference if the child had islet autoantibodies in
the cord blood or not (ESM Table 1).
HLA genotyping HLA haplotypes were determined as
previously described [30, 34, 35]. Briefly, cord blood was
dropped onto Whatman filters to generate dried blood spots
(DBS). The DBS was used to obtain 3-mm punches, which
were used directly for PCR amplification of DQA1 and
DQB1 alleles as described [30]. Single-stranded DNA was
hybridised with two sets of probes, the first containing EuDQB1*0602/3, Sm-DQB1*0603/4 and Tb-Control and the
second containing Eu-DQB1*0302, Sm-DQB1*0301 and
Tb-DQB1*02. Samples positive for DQB1*02 were further
analysed for DQA1*0201 and 05 alleles to separate subjects
with DR3 from DR7. HLA-DQA1 typing was performed
with the same technique as for DQB1 typing with some
modifications as described [30] with use of Sm-DQA1*05
and Tb-DQA1*0201 probes.
The HLA genotypes were divided into seven risk groups
for type 1 diabetes: (1) very high risk, having DQB1*0201A1*0501 and DQB1*0302-A1*0301 (DQ2/8) (n=746); (2)
high risk, having DQB1*0302-A1*0301 (DQ8) but not
DQB1*0201-A1*0501 (DQ2) (n=1,860); (3) moderate risk,
having DQB1*0201-DQA1*0501 (DQ2) but not
DQB1*0302-A1*0301 (DQ8) (n=1,682); (4) neutral HLA
(n=5,188); (5) low-risk HLA (n=2,373); (6) very-low-risk
(n=3,087); and (7) no-risk HLA (n=4,820), as described
previously [30].
Autoantibodies to GAD65, IA-2 and insulin Autoantibodies
to GAD65 and IA-2 were determined in DBSs as
previously described [30, 36]. In brief, DBS eluates were
incubated with labelled antigen and immune complexes
precipitated using Protein A-Sepharose. The radioactivity in
the precipitate was measured and positive samples (combined GAD65Ab and IA-2Ab analysis >95th percentile)
were re-analysed for GAD65Ab and IA-2Ab in separate
assays [37, 38]. IAA were analysed with a recently
described microassay, which was adapted for a microtitre
plate format [39].
Statistical methods and dataset All questionnaires and
forms from the DiPiS-study were scanned into a database,
BC/OS system, Biocomputing OS 2000 (Biocomputing
Platforms Ltd Oy, Espoo, Finland). In term newborns, rBW
was calculated as previously described [30]. Briefly, z
scores for each gestational week and sex was calculated by
the following formula: z score = (BW−mean [BW])/SD
[BW] and termed as rBW.
Population means (SD) of BW were estimated internally
using the study group and relative BW was divided into
quartiles. Children in the lower quartile were defined as
having a low rBW (LrBW) and children in the upper
quartile had HrBW. Differences in proportions were tested
using chi-square tests. The linear association of HrBW with
number of infections within HLA risk groups was tested
using a χ2 test for trend. Interactions between cord blood
autoantibodies and infections on the risk of HrBW were
tested using logistic regression models. Logistic regression
models also were used to examine whether HLA and cord
blood autoantibodies were independently associated with
HrBW after adjusting for other confounding factors such as
sex, gestational age, jaundice, presence of siblings, health
of the newborn, presence of jaundice, smoking during
pregnancy, maternal age, education of the mother, mother
working during pregnancy, lengthy or serious disease in the
1164
mother over the previous 5 years and maternal weight gain.
p values less than 0.05 were considered significant.
Diabetologia (2007) 50:1161–1169
Table 1 Characteristics of newborns and mothers
Factor
Results
Are infections during pregnancy related to BW? Of the
19,756 mothers answering the questionnaire, 14.4% reported
fever, gastroenteritis or both (diarrhoea, vomiting or both)
during pregnancy (ESM Table 2). Fever was more frequently reported (10.7%) than gastroenteritis (7.7%), while 3.0%
of the mothers reported both in the same trimester. In total,
1.7% of the 19,756 mothers reported fever, gastroenteritis,
or both, in more than one trimester (ESM Table 2). The
mothers tended to report more infections if they were older
(>30 years), better educated, had a previous child or
reported a serious or lengthy disease in the last 5 years
(Table 1). There was also a weak association between
smoking and fewer reported infections, but this was entirely
explained by lower education in smoking mothers. Cord
blood autoantibodies were not associated with the number
of infections reported. However, infections were associated
with increased risk of HrBW (p=0.0003) (Table 1). There
was no difference in odds ratio (OR) between the effect of
fever (OR=1.17 [95% CI 1.06–1.30], p=0.002) or gastroenteritis (OR =1.13 [95% CI 0.99–1.28], p= 0.07) on
HrBW, but the frequency of infections was of importance
(Table 1). When examining the results separately by each
trimester, HrBW was associated with infections in the first
trimester (OR=1.22 [95% CI 1.06–1.40], p=0.005) and
second trimester (OR=1.21 [95% CI 1.06–1.38], p=0.006)
but not with infections during the third trimester (OR=1.11
[95% CI 0.97–1.28], p=0.14).
Are autoantibodies and infections related to rBW? Among
all newborns, cord blood GAD65Ab was associated with
decreased risk of HrBW (OR=0.82 [95% CI 0.67–0.99], p=
0.045) as previously described [30], while there was no
effect of IA-2Ab or IAA. However, when infections during
pregnancy were reported, both GAD65Ab (OR=0.35 [95%
CI 0.19–0.68], p=0.002) and IAA (OR=0.21 [95% CI
0.06–0.80], p=0.02) were significantly associated with
decreased risk of HrBW, as well as several autoantibodies
(GAD65Ab, IA-2Ab and IAA) (OR=0.34 [95% CI 0.19–
0.59], p=0.0002) (Table 2). There was no association
between islet autoantibodies and HrBW in children of
mothers without reported infections.
Are type 1 diabetes-risk HLA genotypes and infections
during pregnancy related to rBW? No difference was
found in the frequencies of infection with different HLA
genotypes. In children born with HLA-DQ2/8 and without
cord blood autoantibodies, there was a linear trend with
Fever or gastroenteritis-related infection
reported by mother during pregnancy
No
(n=16,908)
Yes, in one
trimester
only
(n=2,509)
p valuea
Yes, across
several
trimesters
(n=339)
Characteristics of newborn
Sex
Boy
51.8
51.6
48.1
Girl
48.2
48.4
51.9
Standard BW
LrBW
25.4
22.4
23.6
Q1–Q3
50.0
50.7
44.8
HrBW
24.6
26.9
31.6
Good health after delivery
Yes
95.1
94.2
94.1
No
4.9
5.8
5.9
Cord blood autoantibodies
Yes
4.0
3.7
5.6
No
96.0
96.3
94.4
Jaundice
Yes
1.9
2.0
1.5
No
98.1
98.0
98.5
Siblings
Yes
47.2
62.5
71.9
No
52.8
37.5
28.1
Characteristics of mother
Age of mother (years)
≤30
49.2
44.0
42.2
>30
50.8
56.0
57.8
Smoker
Yes
9.8
8.2
7.4
No
90.2
91.8
92.6
Mother’s education
Primary
5.9
4.7
5.0
Secondary 51.5
41.9
43.5
College
42.6
53.4
51.5
Weight gain during pregnancy (kg)
<5
3.3
3.1
4.2
5–10
17.4
19.1
16.2
11–15
40.4
39.4
40.1
>15
38.9
38.5
39.5
Lengthy or serious disease in the last 5 years
Yes
11.4
14.0
19.2
No
88.6
86.0
80.8
0.40
0.0003
0.12
0.24
0.69
<0.0001
<0.0001
0.02
<0.0001
0.48
<0.0001
Values are percentages
Q1–Q3, interquartile range
a
p value for heterogeneity
increasing frequency of children with HrBW among
mothers reporting more infections (p=0.007) (Table 3).
When adjusting for confounding factors by multiple
regression analysis, the significant association observed
Diabetologia (2007) 50:1161–1169
1165
Table 2 Association between cord blood autoantibodies and HrBW in children whose mothers did or did not report infections with fever or
gastroenteritis during pregnancy
Autoantibodies
Reported infections with fever or gastroenteritis during pregnancy
No
Yes
n (% with HrBW)
GAD65Ab
No
16,407 (24.6)
Yes
499 (23.0)
IA-2Ab
No
16,846 (24.6)
Yes
60 (20.0)
IAA
No
16,595 (24.6)
Yes
168 (27.4)
GAD65Ab, IAA or IA-2Ab
No
16,235 (24.6)
Yes
673 (24.1)
OR (95% CI)
p value
n (% with HrBW)
OR (95% CI)
p value
0.92 (0.74–1.13)
0.40
2,765 (28.0)
83 (12.1)
0.35 (0.19–0.68)
0.002
0.77 (0.41–1.44)
0.41
2,836 (27.5)
12 (16.7)
0.53 (0.12–2.38)
0.40
1.15 (0.82–1.62)
0.41
2,794 (27.6)
27 (7.4)
0.21 (0.06–0.80)
0.02
0.97 (0.81–1.16)
0.73
2,736 (28.1)
112 (11.6)
0.34 (0.19–0.59)
0.0002
OR, odds of having HrBW when autoantibody(s) present compared with odds of having HrBW when autoantibody(s) not present
between HrBW, HLA and infections was confirmed, and the
negative association between HrBW and islet autoantibodies
in the presence of infection remained pronounced (Table 4).
In addition, the association between HLA-DQ2/8 and
HrBW was aggravated when mothers reported infections in
more than one trimester (Table 4) (interaction between
HLA, HrBW and infections; p= 0.022). Nevertheless,
although the association between HLA and HrBW when
infections were reported in more than one trimester was
strongly positive (OR=5.24 [95% CI 1.75–15.7], p=0.003),
there was still a weak but significant association when no
infections were reported (1.22 [95% CI 1.01–1.48], p=
0.04). Thus, infections with fever, gastroenteritis, or both,
during pregnancy influenced, but did not explain all, the
association between HLA-DQ2/8 and HrBW (Table 4). The
non-diabetes risk-related DQB1*0603 was also associated
with HrBW (p=0.02), but only when several infections
were reported (Table 4).
Discussion
In this study we further analysed our previously reported
associations between HrBW and high-risk diabetes HLA
genotypes, as well as islet autoantibodies, by testing the
Table 3 Percent of newborns with HrBW by different type 1 diabetes HLA risk groups and frequency of reported infections with fever or
gastroenteritis during pregnancy
Diabetes risk
Very high
High
Moderate
Neutral
Lowc
Very lowd
No riske
HLA-DQ
DQ2/8
DQ8/8, 8/X
DQ2/2, 2/X
Other
DQBI*0301
DQBI*0603
DQBI*0602
Fever or gastoenteritis-related infections by the mother (n=18,971)a
No
Yes, in one trimester only
Yes, across several trimesters
582 (27.8)
1,555 (24.4)
1,387 (24.4)
2,431 (24.7)
3,766 (24.0)
2,545 (26.0)
3,969 (24.0)
90 (31.1)
214 (30.8)
191 (27.8)
395 (26.3)
584 (25.7)
364 (28.0)
578 (28.0)
19
25
36
52
55
53
80
(63.2)
(28.0)
(27.8)
(26.9)
(29.1)
(41.5)
(30.0)
Values are n (% with HrBW)
DQ8 = DQB1*0302, DQ2 = DQA1*0501−DQB1*0201, DQX = not DQB1*0201, 0301, 0302, 0602, 0603
a
All children with no cord blood autoantibodies
b
Test of linear trend in per cent of newborns with HrBW
c
Not including DQB1*0602/0301 and 603/0301
d
Including DQB1*0602/0604 due to shared probe DQB1*0602/3/4
e
Not including DQB1*0602/0603
Linear trend p valueb
0.007
0.06
0.30
0.44
0.23
0.03
0.02
1166
Diabetologia (2007) 50:1161–1169
Table 4 Adjusted ORs of type 1 diabetes HLA risk genotypes on HrBW when mothers reported no infection with fever or gastroenteritis,
infection with fever and/or gastroenteritis in one trimester only or infections with fever and/or gastroenteritis in more than one trimester
Fever or gastroenteritis-related infection reported during pregnancy
No
One trimester only
OR (95% CI)
HLA risk group
DQ2/8
DQ8/8, 8/X
DQBI*0603a
DQBI*0602a
Autoantibodies
Yes
1.22
0.97
1.07
0.95
p value
OR (95% CI)
(1.01–1.48)
(0.85–1.11)
(0.97–1.19)
(0.86–1.04)
0.04
0.66
0.13
0.24
1.17
1.23
1.05
1.03
(0.72–1.92)
(0.88–1.72)
(0.80–1.39)
(0.81–1.30)
0.98 (0.81–1.18)
0.80
0.37 (0.19–0.71)
In more than one trimester
p value
OR (95% CI)
0.52
0.22
0.71
0.83
5.24
1.18
2.43
1.20
(1.75–15.7)
(0.42–3.34)
(1.15–5.15)
(0.62–2.30)
0.003
0.11 (0.01–0.80)
p value
0.003
0.75
0.02
0.59
0.03
For actual numbers of children, see Table 3
ORs were calculated using multiple logistic regression adjusted for sex, gestational age, presence of jaundice, whether newborn has a sibling and
health of newborn, as well as working or smoking during pregnancy, age, education, lengthy or serious disease over the previous years and
weight gain of mother
Reference group is all other HLA genotypes. DQ8=DQB1*0302, DQ2=DQA1*0501−DQB1*0201, DQX=not DQB1*0201, 0301, 0302, 0602,
0603
a
See Table 2 for details
hypothesis that infections during pregnancy may affect the
rBW [30]. The major observation in the present investigation is that there was a significant, but complex interaction
between rBW and infections and islet autoantibodies as
well as HLA.
First, reported infections with fever, gastroenteritis, or
both, increased the risk of HrBW. This finding supported
our hypothesis that reported gestational infections in the
general population of non-diabetic mothers might increase
the risk of the child being born with HrBW. This type of
association in humans has not, to the best of our
knowledge, been reported before, although an adipogenic
effect of adenovirus has been described [40].
Second, the significant decreased risk of HrBW in the
presence of cord blood islet autoantibodies [30] was
observed only when the mother reported fever, gastroenteritis, or both, during pregnancy. Thus, our previously
reported reduced risk of HrBW in the presence of
GAD65Ab may be explained by gestational infections.
We therefore considered the possibility that infections
during pregnancy would induce islet autoantibodies. However, our data did not reveal an increased incidence of
positive cord blood autoantibodies in children born to
mothers who reported gestational infections.
The third major finding was that reported infections
during pregnancy aggravated, but did not explain all of the
previously reported association between HLA and HrBW
[30] (Table 4). The remarkable increase in the risk of
HrBW in HLA-DQ2/8-positive children born to mothers
reporting infections is of considerable interest as more than
30% of children developing type 1 diabetes have this HLA
genotype [41, 42].
Taken together, our major finding was that infections
interact with HLA in modifying intrauterine growth,
resulting in children with HrBW. This finding is supported
by our observation that also the diabetes low-risk allele,
DQB1*0603, had an increased risk of HrBW when fever,
gastroenteritis, or both, was reported in more than one
trimester. Thus, it cannot be excluded that infections during
pregnancy may explain the previously reported increase in
BW with the DQB1*0603-linked DR13 [43].
At present there is no simple explanation of the
interaction between infections, HLA of the child and
HrBW. Our speculation is that certain infectious agents
are taken up by antigen-presenting cells in the mother,
processed by these cells and then presented at the cell
surface by HLA class heterodimeric proteins as part of the
trimolecular complex. The peptides presented by HLA will
be different for different HLA genotypes but may nevertheless induce a vigorous immune response when seen by
the T cell receptors on CD4-positive T lymphocytes. The
ensuing immune response is expected to induce a marked
production in cytokines, resulting in fever and metabolic
changes. It is, for example, possible to speculate that the
well-known insulin resistance during infection may lead to
hyperinsulinaemia, resulting in an increased growth of the
fetus. Alternatively, transient hyperglycaemia associated
with insulin resistance might also affect fetal growth. While
metabolic responses in the mother are likely to influence
the growth of the fetus, other explanations of the interaction
between infections, HLA and HrBW may include a direct
effect of the infectious agent on the fetus.
In the present study, we HLA typed the child, not the
mother, but at least one of the HLA heterodimers of the
Diabetologia (2007) 50:1161–1169
fetus will be shared with the mother. It is therefore possible
that the effect of an infection is aggravated if the mother
and the child share an HLA genotype that is associated with
a vigorous immune response to a certain infectious agent.
Further studies will be needed to dissect these intricate but
potentially important interactions between infections and
fetal growth.
The present study is a unique population-based cohort of
newborn children representing 35,683/48,058 newborns
during 4 years of ascertainment. Although it was not
possible to obtain complete questionnaires from all the
parents to be filled out when the child was 2 months of age,
our previous analyses indicate that there was little bias in
missing data [30, 33]. Since the study design was
population-based in a defined geographical area and since
the mothers answered the questionnaires without any
information about HLA risk of the child or cord blood
autoantibodies, the risk of recall bias was minimised. This
study therefore allowed us to examine differences in rBW,
to reveal relationships between rBW and reported infections, and HLA as well as cord blood autoantibodies. When
excluding children born to diabetic mothers, preterm babies
and twins or triplets, we removed potential confounders
without reducing statistical power.
The questionnaire response rate of 67% might have
given some bias to different subgroups as those displayed
in ESM Table 1. Although our results reveal that infections
affect rBW, it is important to note that HLA genotypes are
influencing intrauterine growth also in the absence of
reported infections. This observation may be a result of
under-reporting of infections due to the fact that mothers do
not recall minor infectious events, especially if they
occurred early in pregnancy. The optimal solution to this
problem would have been blood sampling during pregnancy, but this could not be done in this study. The frequency
of reported gastroenteritis was low in our study (6.7%)
compared with a recent study (30%), where no relationship
was seen between BW and gastroenteritis [44]. However,
the author did report a small increase in preterm labour in
women with gastroenteritis in months 4, 5 and 7 of
pregnancy [44]. The difference in frequencies of gastroenteritis between these two studies may be due to imprecise
reporting of infections. Another possible explanation could
be that our question to the mothers was distinctly focused
on infectious gastroenteritis and fever, and did not include
chronic diarrhoea or nausea during early pregnancy (ESM:
Questionnaire, Question 1). Further studies will be needed
to clarify frequencies and type of infections in relation to
rBW and the HLA of both the mother and the child.
BW in the general Swedish population of newborns is
increasing, especially the incidence of children with a high
BW and those large for gestational age [45]. BW corrected
for gestational age, rBW, is an outcome of intrauterine
1167
growth rate, which is influenced by multiple factors such as
intrauterine infections, cord blood flow, maternal disease,
drugs and maternal weight gain [46, 47] as well as the HLA
type of the child [30]. High BW and increased growth in
infancy have been reported as risk factors for type 1
diabetes [9–11]. This phenomenon is not understood. Prior
studies by others have not examined relationships between
rBW and HLA as well as islet autoantibodies in the
newborn child. Our data suggest that the interaction
between HLA, islet autoantibodies and rBW is complex.
We interpret the data in Table 4 to indicate that islet
autoantibodies in the cord blood of children of mothers
reporting infections reduced the rBW regardless of the HLA
of the child. Although we do not know the HLA type of the
mother we would anticipate that she may carry at least one
allele that is diabetes high-risk, which in turn is associated
with islet autoantibodies also in the healthy population [41].
It is therefore possible that the reduced risk of HrBW is due
to the possibility that islet autoimmunity was already
present in some mothers reporting infections. The immune
response to infections may be affected in islet autoantibodypositive mothers in a way that fetal growth is reduced rather
than accelerated by a gestational infection.
Thus, the previously reported association between high
BW and risk of type 1 diabetes [9], may be explained by the
interaction between infections and diabetes high-risk HLA
affecting intrauterine growth. This is, to the best of our
knowledge, a novel finding and may be important for the
understanding of type 1 diabetes aetiology.
In conclusion, our reported [30] association between
diabetes high-risk HLA and HrBW may be explained by
infections during pregnancy. The aggravating effect on
HrBW by infections also on HLA-DQB1*0603 (DR13) is
underscoring the importance of HLA. While mothers
reporting infections had no increased risk to give birth to
a child with cord blood islet autoantibodies, their islet
autoimmunity was associated with a reduced risk of HrBW.
Gestational islet autoimmunity could therefore possibly
explain the observation that children born with islet
autoantibodies have a reduced risk of developing autoantibodies against GAD65, IA-2 or insulin later in life [29]. As
reported infections affected rBW in association with HLA,
it will be necessary in future studies to determine the nature
of such infections and carefully document the infectious
agents. The children affected by intrauterine infections may
have an altered infant growth rate, which may be important
for type 1 diabetes risk [48–50]. The DiPiS study is
longitudinal and children in this report are followed for
the development of islet autoimmunity and type 1 diabetes
as well as growth. These future analyses may allow us to
establish whether the complex interaction between rBW and
infections, and HLA as well as islet autoantibodies is
increasing the risk of type 1 diabetes.
1168
Acknowledgements Co-authors in the DiPiS study group are: P.
Almgren, B. Buveris-Svendburg, A. Carlsson, E. Cederwall, C. Cilio,
J. Gerardsson, B. Jönsson, K. Kockum, K. Larsson, B. Lindberg, J.
Neiderud, A. Nilsson, M. Pelkonen, H. Rastkhani and S. Sjöblad. We
thank all the participating parents and children in DiPiS. Our research
is supported in part by the Swedish Research Council (Grant 14064),
Juvenile Diabetes Research Foundation, Wallenberg Foundation,
Swedish Childhood Diabetes Foundation, Swedish Diabetes Association, Nordisk Insulin Fund, National Institutes of Health (DK26190),
UMAS funds, Terry & Louise Gregg Diabetes in Pregnancy Award
from the American Diabetes Association, Lion Club International,
District 101-S and the Skåne County Council Foundation for Research
and Development.
Diabetologia (2007) 50:1161–1169
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18.
Duality of interest There is no duality of interest
19.
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