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By Neil Bowdler Health reporter, BBC News
New evidence has linked the environment in the womb with increased body weight
in later life.
Scientists found changes around the DNA at birth which may result from a
mother's diet or exposure to pollution or stress.
They then linked these changes to a higher Body Mass Index (BMI) in children
aged about nine years of age.
But the researchers say more work is needed to definitively prove the link
between these changes and obesity.
Details are published in the journal Plos One.
Childhood or adult obesity has many causes, not least childhood or adult diet,
but scientists have previously linked specific genes, such as the FTO gene,
with increased body weight.
Others have looked at not the genes, but associated molecular changes - what
are called epigenetics - which can play a role in how a gene functions in the
body, switching genes on and off.
These changes are thought to be caused in part by exposure to environmental
factors such as diet, stress, smoking or hormones, particularly in the womb and
during early childhood.
While epigenetic changes in the womb have already been associated with later
obesity, there is still little data to prove the link.
Dr Caroline Relton, of Newcastle University, and colleagues took blood samples
from 24 children aged 11 to 13 and looked for differences in the way genes are
"expressed" or encoded into the many proteins which we need to grow and
function.
Prof Tim Spector of King's College London, explains what epigenetics are
They identified epigenetic changes in 29 genes which could be associated with
higher body mass among the children.
They then looked at data from a larger study of 178 individuals, for whom there
were both cord blood samples from birth, and body composition data from aged
about nine.
Among these individuals, epigenetic changes to nine of the 29 genes previously
identified appeared to correspond to increased body weight, although only one
of these associated changes withstood rigorous further analysis, admit the
researchers.
"Other studies have just taken genes at birth and looked at differences
irrespective of whether they are differently expressed with different levels of
obesity," Dr Relton told the BBC.
"The difference between this study and others is that we had a reason to focus
on the genes we looked at because we knew they were differently expressed in
children with a higher BMI."
However, Dr Relton says more research is needed to prove the epigenetic
differences observed at birth and originating in the womb, are actually
contributing to obesity.
"While we have discovered an association between these genes and body size in
childhood we need to carry out further studies to establish whether influencing
the expression of these genes by altering epigenetic patterns is indeed a
trigger to obesity."
Early signals
Commenting on the paper, Prof Gudrun Moore of University College London told
BBC News: "The paper is an interesting study on epigentic variations and their
potential association with body size indices."
Prof Tim Spector of King's College London, said the paper represented "an
exciting piece of research exploring new ways of looking at the causes of
obesity".
"Although it is limited by the small size and the fact that they only looked at
29 genes, the researchers found that a third of the genes they looked at
contained epigenetic marks at birth that were related in some way to measures
of later obesity.
"This means that chemical signals that turn genes on or off at birth can
influence susceptibility to being fat at age 10.
"We know from differences in identical twins that genes and DNA are not the
whole answer. Understanding how we could manipulate these signals in early life
- via better understanding epigenetics - has great potential in battling the
obesity epidemic," he said.