A study in mice shows the offspring of older fathers have more genetic changes associated with autism and other brain disorders.

John McGrath of the Queensland Brain Institute and colleagues reported their findings Wednesday in the journal Translational Psychiatry.

"There's quite convincing evidence now that the offspring of older dads have an increased risk of a range of brain disorders like autism and schizophrenia and maybe even slightly lower IQ," said McGrath.

"Compared to men in their early 20s, the offspring of men over age 50 have a two-fold risk of getting schizophrenia or autism."

Such findings come from previous epidemiological studies by McGrath and others.

Now, McGrath and colleagues have used a mouse model to look at the genetics lurking behind this phenomenon.

They have been looking for specific mutations called CNVs (copy number variations), in which whole "chapters" of genetic material are either deleted or repeated.

Researchers believe DNA from the sperm cells of older dads are more likely to develop CNVs than that from younger dads.

McGrath and colleagues looked at the DNA of offspring from older and younger male mice, mated with mothers of the same age, and tested for CNVs that only occurred in the offspring.

"We found more of these mutations in the offspring of older dads," said McGrath.

He said these offspring also have a different shaped brain and different behaviour to those from younger fathers.

Link to brain disorders

McGrath said the CNVs discovered have already been linked to brain disorders in humans.

"In fact one of the mutations we found was in a well known autism gene," he said. "That's what you call a 'lucky strike'."

McGrath says the next step is to look for CNVs in humans, but this will require expensive high throughput technology.

"As the studies are done in the next three to five years ... we predict that the offspring of older dads will have more of these CNVs," said McGrath.

He said showing this would give insight into a potentially modifiable risk factor for autism and schizophrenia.

"Just as women are now aware that there are risks involved in delaying motherhood, then there may well be the need in the future for public health messages to men that there are risks involved in delaying parenthood," said McGrath.