London - Scientists have come up with a possible explanation for why autism appears to run in families - suggesting it can be triggered by changes in the chemicals attached to DNA.
A study of sperm from 44 fathers of babies who showed early signs of autistic symptoms found that “epigenetic” changes to the men's DNA could transmit the condition to the next generation.
Epigenetic changes involve modifications in chemicals attached to the DNA molecule - rather than mutations to the DNA sequence itself.
The changes detected in this study have been linked with abnormal development of nerve cells in the brain.
It is well established that autism tends to run in families but this is one of the first studies to indicate that epigenetic changes may be involved in increasing the risk of having a child who develops autism.
“This study shows the importance of epigenetics as an area of research for autism, not only in the child but for the parents at the time of conception and childbirth,” said Professor Daniele Fallin of the Johns Hopkins University School of Medicine in Baltimore, Maryland.
The study, published in the International Journal of Epidemiology, analysed the level of changes to the “methylation patterns” present on the DNA of the men's sperm. It compared these epigenetic changes with the degree of autistic-like symptoms shown by the men's babies.
“The higher the methylation in the genes we looked at, the higher the score for observational risk for the autistic symptoms in the children,” Professor Fallin said.
The researchers believe the study revealed a possible clue that could help to explain why parents who have one autistic child have a higher risk than the general population of having a second child with autism.
“This is a pilot study on a small number of special patients so we're not making any generalised statements on the causes of autism,” said Professor Andrew Feinberg of Johns Hopkins University, a specialist in epigenetics.
The researchers looked for epigenetic changes or “tags” at 450 000 positions on the DNA molecule throughout the genome. They found 193 sites where the presence or absence of a tag could be linked statistically with autistic symptoms, and these were close to genes involved in early development, especially of nerve cells in the brain.
The Independent