Girls whose grandmothers smoked while their mothers were in utero are 67 percent more likely to display certain traits linked to autism, such as poor social communication skills and repetitive behaviors, according to a new study by researchers at the University of Bristol in the U.K.
In addition, boys and girls whose grandmothers smoked while their mothers were in utero are 53 percent more likely to be diagnosed with an autism spectrum disorder (ASD).
The findings overwhelmingly suggest that if a female is exposed to cigarette smoke while she is still in the womb, it could affect her developing eggs, resulting in changes that may eventually affect the development of her own children.
“We already know that protecting a baby from tobacco smoke is one of the best things a woman can do to give her child a healthy start in life. Now we’ve found that not smoking during pregnancy could also give their future grandchildren a better start too,” said the noted British epidemiologist and researcher Professor Jean Golding.
For the study, the researchers combed through the data of 14,500 participants enrolled in the Children of the 90s study, the birth cohort study developed by Golding that produced a detailed data set of children born in the area in 1991 and 1992.
Unlike the analysis of autistic traits, which was based on over 7,000 participants, the 177 diagnosed with ASD were too few to analyze grandsons and granddaughters separately.
By using detailed information collected over many years on multiple factors that may affect children’s health and development, the researchers were able to rule out other potential explanations for their results.
More research is needed to discover what the exact mechanisms are behind these molecular changes and to see whether the same associations are present in other groups of people.
Previous studies of maternal smoking during pregnancy and ASD in children have been inconclusive. Going back a generation has revealed an intergenerational effect, which surprisingly is most clear-cut when the mother herself did not smoke in pregnancy. The reasons for this are not entirely clear.
“In terms of mechanisms, there are two broad possibilities,” said researcher Professor Marcus Pembrey. “There is DNA damage that is transmitted to the grandchildren or there is some adaptive response to the smoking that leaves the grandchild more vulnerable to ASD.
“We have no explanation for the sex difference, although we have previously found that grand-maternal smoking is associated with different growth patterns in grandsons and granddaughters,” he said.
“More specifically, we know smoking can damage the DNA of mitochondria, the numerous ‘power-packs’ contained in every cell, and mitochondria are only transmitted to the next generation via the mother’s egg. The initial mitochondrial DNA mutations often have no overt effect in the mother herself, but the impact can increase when transmitted to her own children.”
The prevalence of ASD has increased in recent years, and while some of this increase is probably due to improved diagnosis, changes in environment or lifestyle are also likely to play a role. The researchers also stress that many different factors, including genetic variation, are believed to affect an individual’s chances of developing ASD.
The findings are published in the journal Scientific Reports.
Source: University of Bristol