Medical DevicesC-Section Births Cause Genetic Changes That May Increase Odds For Developing Diseases In Later Life
Swedish researchers have discovered that babies born by Caesarean section
experience changes to the DNA pool in their white blood cells, which could be
connected to altered stress levels during this method of delivery, according to the
July issue of Acta Paediatrica.
It is thought that these genetic changes, which differ from normal vaginal deliveries,
could explain why people delivered by C-section are more susceptible to
immunological diseases such as diabetes and asthma in later life, when those
genetic changes combine with environmental triggers.
Blood was sampled from the umbilical cords of 37 newborn infants just after delivery
and then three to five days after the birth. It was analysed to see the degree of DNAmethylation
in the white blood cells - a vital part of the immune system.
This showed that the 16 babies born by C-section exhibited higher DNA-methylation
rates immediately after delivery than the 21 born by vaginal delivery. Three to five
days after birth, DNA-methylation levels had dropped in infants delivered by Csection
so that there were no longer significant differences between the two groups.
"Delivery by C-section has been associated with increased allergy, diabetes and
leukaemia risks" says Professor Mikael Norman, who specialises in paediatrics at
the Karolinska Institutet in Stockholm, Sweden. "Although the underlying cause is
unknown, our theory is that altered birth conditions could cause a genetic imprint in
the immune cells that could play a role later in life.
"That is why we were keen to look at DNA-methylation, which is an important
biological mechanism in which the DNA is chemically modified to activate or shut
down genes in response to changes in the external environment. As the diseases
that tend to be more common in people delivered by C-section are connected with
the immune system, we decided to focus our research on early DNA changes to the
white blood cells."
The authors point out that the reason why DNA-methylation is higher after C-section
deliveries is still unclear and further research is needed.
"Animal studies have shown that negative stress around birth affects methylation of
the genes and therefore it is reasonable to believe that the differences in DNAmethylation
that we found in human infants are linked to differences in birth stress.
"We know that the stress of being born is fundamentally different after planned Csection
compared to normal vaginal delivery. When babies are delivered by Csection,
they are unprepared for the birth and can become more stressed after
delivery than before. This is different to a normal vaginal delivery, where the stress
gradually builds up before the actual birth, helping the baby to start breathing and
quickly adapt to the new environment outside the womb."
The authors point out that the surgical procedure itself may play a role in DNAmethylation
and that factors other than the delivery method need to be explored in
more detail.
"In our study, neonatal DNA-methylation did not correlate to the age of the mother,
length of labour, birth weight and neonatal CPR levels - proteins that provide a key
marker for inflammation" says Professor Norman. "However, although there was no
relation between DNA-methylation and these factors, larger studies are needed to
clarify these issues."
Professor Norman states that the Karolinska study clearly shows that geneenvironment
interaction through DNA-methylation is more dynamic around birth than
previously known.
"The full significance of higher DNA-methylation levels after C-section is not yet
understood, but it may have important clinical implications" he says.
"C-section delivery is rapidly increasing worldwide and is currently the most common
surgical procedure among women of child-bearing age. Until recently, the long-term
consequences of this mode of delivery had not been studied. However, reports that
link C-section deliveries with increased risk for different diseases in later life are now
emerging. Our results provide the first pieces of evidence that early "epigenetic"
programming of the immune system may have a role to play."
The authors feel that their discovery could make a significant contribution to the
ongoing debate about the health issues around C-section deliveries.
"Although we do not know yet how specific gene expression is affected after Csection
deliveries, or to what extent these genetic differences related to the mode of
delivery are long-lasting, we believe that our findings open up a new area of
important clinical research" concludes lead author Titus Schlinzig, a research fellow
at the Karolinska Institutet.
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