Childhood sexual abuse may leave "molecular scars" on a victim's DNA that could one day be used as evidence in court, scientists have said.

A study found similar alterations in the activity of genes among men who had been abused in childhood.

Researchers at Harvard and the University of British Columbia (UBC) believe the discovery of the difference in a process called methylation between those who had been abused and those who had not could pave the way for a genetic test to indicate whether abuse took place.

Methylation acts as a "dimmer switch" on genes, affecting the extent a particular gene is activated or not, say researchers.

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The study, published in the journal Translational Psychiatry, found a distinct methylation difference between victims and non-victims in 12 regions of the men's genomes.

In eight DNA regions, the genes of victims were dimmed by more than 10 per cent compared with non-victims, and in one region the difference was 29 per cent.

Scientists said they still did not know how methylation affects a person's long-term health.

Michael Kobor, professor of medical genetics at UBC, said: "Methylation is starting to be viewed as a potentially useful tool in criminal investigations for example, by providing investigators with an approximate age of a person who left behind a sample of their DNA.

"So it's conceivable that the correlations we found between methylation and child abuse might provide a percentage probability that abuse had occurred."

"If you think of genes as being like lightbulbs, DNA methylation is like a dimmer switch that controls how strong each light is - which in turn can influence how cells function," said Nicole Gladish, a PhD candidate in UBC's Department of Medical Genetics.

The imprints may also shed light on whether or not trauma can be passed on between generations as has long been hypothesised. Lead author Andrea Roberts said the study "brings us at least one step closer" towards working out if trauma can be transmitted across generations.