Identical twins who differ in autism traits can shed light on the epigenetic mechanisms involved in the disorder. Scientists from King’s College London identified patterns of epigenetic changes involved in autism spectrum disorder (ASD) by conducting what they say is the first systematic epigenomic analyses of monozygotic twins discordant for ASD.

Twin studies provide evidence that there is a strong genetic component to ASD: in approximately 70% of cases, when one identical twin has ASD, so does the other. However, in 30% of cases, identical twins differ for ASD. This suggests that genes alone are not always responsible for the disorder; epigenetic factors may be involved. The researchers add that epigenetic changes are potentially reversible and may therefore provide targets for the development of new therapies.

The team studied DNA methylation, which acts to block the genetic sequences that drive gene expression, silencing gene activity. They examined DNA methylation at over 27,000 sites across the genome using samples taken from 50 identical twin pairs from the UK Medical Research Council-funded Twins Early Development Study: 34 pairs who differed for ASD or autism related behavior traits, 5 pairs where both twins have ASD, and 11 healthy twin pairs.

“We’ve identified distinctive patterns of DNA methylation associated with both autism diagnosis and related behavior traits, and increasing severity of symptoms,” says Chloe Wong, Ph.D., first author of the study from King’s College London’s Institute of Psychiatry. “Our findings give us an insight into the biological mechanism mediating the interaction between gene and environment in autism spectrum disorder.”

DNA methylation at some genetic sites was consistently altered for all individuals with ASD, and differences at other sites were specific to certain symptom groups. The number of DNA methylation sites across the genome was also linked to the severity of autism symptoms, suggesting a quantitative relationship between the two, the team reports. Additionally, some of the differences in DNA methylation markers were located in genetic regions that previous research has associated with early brain development and ASD.

“Research into the intersection between genetic and environmental influences is crucial because risky environmental conditions can sometimes be avoided or changed,” adds Jonathan Mill, Ph.D., lead author of the paper from King’s College London’s Institute of Psychiatry and the University of Exeter. “Epigenetic changes are potentially reversible, so our next step is to embark on larger studies to see whether we can identify key epigenetic changes common to the majority of people with autism to help us develop possible therapeutic interventions.”

The study was published today in Molecular Psychiatry, in a paper titled “Methylomic analysis of monozygotic twins discordant for autism spectrum disorder and related behavioural traits”.

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