More research is needed into the environmental factors causing autism, according to Irish experts on the condition.

At present, however, there is very limited evidence linking a difficult labour to autism in later life, according to Prof Louise Gallagher, chairwoman of child and adolescent psychiatry at Trinity College Dublin.

Children who had been subjected to a brain injury in the context of pregnancy or who were extremely premature could have higher autistic traits, she said. “However, proving causality would require large-scale studies and I’m not aware of any that have looked specifically at that.”

Retired clinical psychiatrist and a pioneer in the study of autism spectrum disorder in Ireland, Prof Michael Fitzgerald, said 90 per cent of autism was explained by heritability or genetic factors.

The alleged link between a protracted birth and autism has never been determined in an Irish or British court, but on Friday the High Court heard that a settlement had been reached in the case of a 13-year-old boy with autism who had sued over the circumstances of his birth.

The case, settled between Finn Phillips from Lusk, Co Dublin and the National Maternity Hospital for €7.25 million, does not set a precedent because it did not go forward to be determined by the court.

The boy’s solicitor, Cian O’Carroll, said that while there may be other cases there would not be many of them, as a number of specific criteria relating to birth events and subsequent development would have to be fulfilled for a case to be successful.

Prof Gallagher told The Irish Times that, while factors such as being exposed to certain drugs in utero, or early brain injury, had been linked to autism, the association with perinatal events was “not as well known”.

Genetics

She pointed out that autism was generally attributed to genetic and environmental factors. “We know a lot more about the genetic factors these days and we know rare genetic changes in the genes involved in brain development can cause autism in a proportion of cases.”

As for environmental effects, “we don’t have strong data. That doesn’t mean environmental effects don’t cause autism, just that we haven’t studied them as well so far.”

Being an older father or mother was also linked to an increased risk of having a child with autism. However, Prof Gallagher said this was more likely to be due to genetic factors rather than environmental ones, as the older a person got, the more likely they were to have genetic mutations.

Studies have indicated one in every 165 Irish schoolchildren has an autism spectrum disorder, and the number of cases is increasing.

“We don’t know why prevalence is increasing, but it’s thought mainly to be due to improved recognition of cases and the broadening of criteria – more things called autism these days than before,” said Prof Gallagher.