Men who have daughters after the age of 50 are 'twice as likely to have a grandchild with autism'
Sons of older fathers are also more likely to have children with the conditionOlder parents might be responsible for the growing number of autistic children, say researchers
Genetic risks caused by age can skip generations
Jenny Hope Medical Correspondent
20:07 GMT, 20 March 2013
20:07 GMT, 20 March 2013
Men who have daughters when they are over 50 have almost double the risk of a grandchild being diagnosed with autism.
The risk to grandchildren from older fathers of sons is also higher than for younger dads, warn psychiatrists.
Mounting research suggests the older age of parents might be partly responsible for growing numbers of children with autism, but for the first time the risk of autism in the grandchild has been linked to the age of the grandfather at the time of his child's birth.
Findings from a new study suggest that genetic risk factors for the condition accumulate over generations.
Men who have daughters when they are aged over 50 have almost double the risk of a grandchild being diagnosed with autism
Researchers from Britain, Sweden and Australia analysed the family and psychiatric records of almost 6,000 individuals with autism born in Sweden from 1932.
The data was compared with that from 31,000 unaffected members of the population.
The age when grandfathers on both sides had children was analysed and details of any psychiatric diagnosis considered.
The study found that autism risk in a grandchild increased the older the grandfather was when his son or daughter was born.
Men who had a daughter at the age of 50 or older were 1.79 times more likely to have a grandchild with autism than those aged 20 to 24.
Having a son at 50 or older increased a man's chance of having an autistic grandchild 1.67 times.
The findings were published in the journal JAMA Psychiatry.
In the UK, around one in 100 adults is thought to be affected by autism, mostly men, although the true rate is far higher according to some researchers.
Autism is an umbrella term for a range of developmental disorders that have a lifelong effect on someone's ability to interact socially and communicate.
The risk to grandchildren from older fathers of sons is also higher than for younger dads
Study co-author Dr Avi Reichenberg, from King's College London's Institute of Psychiatry, said: 'We tend to think in terms of the here and now when we talk about the effect of the environment on our genome.
'We tend to think in terms of the here and now when we talk about the effect of the environment on our genome. For the first time in psychiatry, we show that your father's and grandfather's lifestyle choices can affect you.
'This doesn't mean that you shouldn't have children if your father was old when he had you, because whilst the risk is increased, it is still small. However, the findings are important in understanding the complex way in which autism develops.'
Lead researcher Emma Frans, from the Karolinska Institute in Stockholm, said: 'We know from previous studies that older paternal age is a risk factor for autism
'This study goes beyond that and suggests that older grandpaternal age is also a risk factor for autism, suggesting that risk factors for autism can build up through generations.'
Autism is known to be caused by a combination of genetic and environmental factors.
Previous studies have shown that fathers aged 50 and older are more than twice as likely to have a child diagnosed with autism than younger fathers, while some research suggests older mothers may also be more at risk.
Experts think the link with paternal age could be explained by genetic errors creeping into sperm production as men get older.
The new research suggests that 'silent' mutations that leave a son or daughter unaffected may increase the risk of autism in later generations.
A combination of mounting mutations and interactions with other risk factors including persistent environmental chemicals in the body could finally cause the disorder to emerge.