'Imprinted' genes may affect a baby's behaviour and could be involved in the development of autism or schizophrenia.
A Danish study has provided support for a controversial theory that says autism spectrum disorders and schizophrenia are opposite ends of a spectrum, with normal brain function somewhere in between.
The 'Imprinted Brain Theory' postulates that these mental disorders are a result of a 'battle of the sexes', with epigenetic effects subtly controlling certain genes, expressed as a baby develops, to favour the survival of either the mother or the father's genes.
Published in the Proceedings of the Royal Society B
, the study has found relationships between a baby's size and its risk of getting schizophrenia or autism, which fit with the theory.
The theory concerns 'imprinted' genes. These genes are very unusual because they are expressed differently depending on whether they come from the mother or the father. This contrasts with the vast majority of genes for which parental origin makes no difference to their activity.
"There are about 70-80 genes that are thought to be genetically imprinted in humans." says Dr Sean Byars, lead author of the Danish study who is now at the University of Melbourne.
It's thought that imprinted genes affect things like the size of the baby. For example, it is in the father's interests for babies to be big, as they are more likely to survive and pass on his genes.
For the mother, though, a baby that is too large may deplete her resources, and could jeopardise her chance of future pregnancies. This will reduce her genes' chances of being passed on through future children, explains Byars.
Many imprinted genes are thought to act in the placenta, with some from the father favouring larger babies while some from the mother favour smaller ones. What the baby actually ends up with is usually a balance between the two parent's needs.