Scientists have found patterns of change in gene activity involved in autism
in a study that shed light on how environmental factors can work to turn certain
genes on or off and contribute to the development of the brain disorder.
In the largest study of its kind, researchers analysed data from 50 sets of
twins to try to find out what might have caused some of them to develop autism
while their genetically identical siblings did not.
Chloe Wong, of the Institute of Psychiatry (IoP) at King's College London,
who worked on the study, explained that epigenetic changes affected levels or
activity of genes without changing the underlying DNA sequence.
Scientists think they are one way in which the environment interacts with the
genome. Importantly, she said, epigenetic changes are
also potentially reversible, so finding out more about them may point
researchers towards the development of new medicines or treatments.
People with autism have varying levels of impairment across three common
areas - social interaction and understanding, repetitive behaviour and
interests, and language and communication.
As many as one in 50 school age children in the United States are diagnosed
with autism, although some of these will be milder cases that have been
diagnosed partly because of better recognition of autism symptoms by caregivers
and doctors. In Europe experts say the rate is around one in 100 children.
Genetic code component
Previous studies have shown there is a strong genetic component to autism. In
identical twins, in around 70% of cases where one twin has autism, so does the
other. But in 30% of cases, one twin has autism while the other does not.
Because identical twins share the same genetic code, this suggests
non-genetic, or epigenetic, factors may be important.
Wong's team studied a particular epigenetic mechanism called DNA methylation,
which acts to block access to genetic sequences and can turn gene activity on or
They looked at DNA methylation at over 27 000 sites across the genome using
samples taken from 50 identical twin pairs. Of the 50 pairs, 34 had one twin
with autism and one without, five had both twins with autism, and 11 pairs were
healthy controls with no autism traits or diagnoses.
The researchers found that DNA methylation at some genetic sites was
consistently altered for all the children with autism, while differences at
other sites were specific to certain groups of symptoms or traits of autism.
The number of altered DNA methylation sites across the genome was also linked
to the severity of autism symptoms suggesting a quantitative relationship, said
Wong, whose study was published in the journal Molecular Psychiatry.
"We identified distinctive patterns of DNA methylation associated with both
autism diagnosis and related behaviour traits, and increasing severity of
symptoms," she said.
Jonathan Mill, of the IoP and the University of Exeter, who led the study,
said research into the intersection between genetic and environmental influences
was crucial "because risky environmental conditions can sometimes be avoided or
He said the next step was to conduct larger studies to see whether
researchers can identify key epigenetic changes that are common to the majority
of people with autism and use them to help develop ways of preventing or
treating the disorder.
It was too early in the process to identify which environmental factors may
have had an impact.