19 March 2012
ByAppeared in BioNews 649
A child's body size may be influenced by genetic modifications that occur in the womb, a new study claims. Scientists found a weak link between specific DNA modifications - called epigenetic marks - present at birth and the child's height at age nine. Several news sources, however, incorrectly reported a link with childhood obesity.
Epigenetic modifications are the additions of chemical groups - in this case methyl groups - to the DNA strand at specific locations. These additions modify the level of gene expression without changing the actual DNA sequence. The exact pattern of epigenetic marks - here, the pattern of methylation - can vary from individual to individual and be influenced by certain environmental factors.
In the first phase of this study - conducted jointly by the Universities of Newcastle and Bristol - scientists identified a number of genes whose expression levels appeared to influence body composition in childhood. They took 24 children aged between 11 and 13 and compared gene expression levels in those with a high body mass index (BMI), with those with a low BMI.
Following this, 29 of the genes identified in phase one were examined in blood samples taken from the umbilical cord of 178 newborns. The level of methylation of each gene at birth was matched with height, weight and body mass measurements taken at age nine. Nine genes were shown to have DNA methylation levels that correlated with certain aspects of body composition, including BMI, fat mass and height.
However, more stringent testing (to remove any false positive results achieved purely by chance) revealed that increased methylation of only one gene was significantly linked to one aspect of body size - height. It remains to be seen whether the DNA methylation actually caused a change in height, or if the two are simply coincidental.
Several news reports incorrectly reported an association with childhood obesity. The study did not specifically investigate a link between DNA methylation and obesity, but rather with BMI and fat mass. None of the initial correlations with these aspects of body composition proved significant. Reports also suggested that a mother's lifestyle during pregnancy may be responsible for their child becoming obese. No such claims would be supported by the research as the reasons why the changes in DNA methylation occurred were not investigated.
The study is published in the journal PLoS ONE.