Children born to fathers who are over 50 years of age are most at risk of autism, according to the largest-ever study into the link between parental age and the disease.

The babies of teenage mothers and mothers over 40 years of age also have a higher probability of developing the condition, the research, funded by the advocacy organisation Autism Speaks, found.

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The study examined the national health records of more than 5.7 million children – including more than 30,000 diagnosed with autism – in Denmark, Israel, Norway, Sweden and Western Australia.

Previous research had demonstrated a link between autism and parental age, but this is the first study to break down the data in terms of the effect of maternal and paternal age both independently and jointly.

The causes of autism include parental age. Source: Shutterstock

The incidence of autism was 66 per cent higher in children born to fathers over 50, compared with fathers in their 20s, the results, published in the Journal of Molecular Psychiatry, showed.

Babies born to teenage mothers and mothers over the age of 40 had an increased risk of developing the disease of 18 per cent and 15 per cent respectively, when compared with mothers in their 20s.

Fathers in their 40s showed a 28 per cent higher risk.

A large age gap between parents was found to be another factor.

The highest risk was shown in fathers between 35 and 44 years of age with partners who were at least 10 years younger.

Mothers in their 30s with partners at least a decade their junior were also at risk.