Grandmothers’ smoking linked to autism traits in granddaughters, study finds

Researchers say findings are 'statistically significant', but call for further research before conclusions can be drawn on causality

While the smoking rate in Japan has declined in recent years, it remains one of the world's largest tobacco markets (Getty)

Girls whose grandmothers smoked are more likely to display behavioural traits linked to autism, a new large-scale study suggests.

Scientists at the University of Bristol analysed detailed information on the health and development of 14,500 children.

They found girls whose maternal grandmother smoked during pregnancy are 67 per cent more likely to show certain traits such as poor social communication skills and repetitive behaviours.

The study, published in Scientific Reports, also found grandchildren of both genders were 53 per cent more likely to be diagnosed with Autism Spectrum Disorder (ASD) if their maternal grandmother smoked.

“We were intrigued about why autism seems to be gathering more prevalence. General smoking, particularly women’s smoking in pregnancy, came to a peak round the Second World War,” said Jean Golding, the study’s co-author.

Professor Golding told The Independent previous research in animals has shown the effects of environmental factors like exposure to cigarette smoke can be passed down family lines.

She said the findings were “statistically significant”, but called for further research before conclusions can be drawn on causality – especially into DNA, as it has been shown smoking can damage mitochondria, small structures inside cells that are passed down the female genetic line.

Peter Hajek, director of the tobacco research unit at Queen Mary University of London, said: “Several large studies examined possible links between maternal smoking during pregnancy and autism and their meta-analysis shows no link, so this finding, if real, would be surprising.”

Professor Hajek said more data was needed to rule out “a chance finding”, as data on children who are actually diagnosed with autism, instead of displaying behavioural traits, was more important but no significant link had been found.

Professor Golding, who holds an OBE for services to medical science, used data from her ‘Children of the 90s’ study, in which she enrolled thousands of pregnant women in 1991 and monitored the health and development of their children.

She and her team hypothesised that if a female foetus is exposed to cigarette smoke in the womb, the chemicals could trigger molecular changes in her own developing egg cells, which could then in turn affect the development of her own children.

Of the 14,000 participants in the study, 7,000 were found to have autistic traits while 177 were diagnosed with ASD – too few to separate grandsons and granddaughters, said the researchers.

“The study applies careful analyses to data from a world-leading birth cohort project. But conclusions are drawn from ‘reported or possible’ autism diagnoses and ‘predictive traits’,” said James Cusack, director of science for the organisation Autistica.

“Also, although confounding factors are taken into account, there may be others not considered in the analyses Further research is needed to understand whether grandmother’s smoking during pregnancy is linked to autism in grandchildren. This study alone does not indicate a causal link.”