A recent study, published in Scientific Reports, concludes that if a girl's maternal grandmother smoked tobacco during her pregnancy, she is significantly more likely to develop autistic traits.
Autism, characterized by repetitive behaviors and difficulty interacting socially, appears to be on the rise.
Much of this increase is thought to be due to better detection rates and greater awareness. However, many scientists believe that environmental or lifestyle factors might also play a role.
A recent study, carried out by researchers from the University of Bristol in the United Kingdom, looked into three generations of data from the Avon Longitudinal Study of Parents and Children (ALSPAC), a long-term data collection project carried out by the University that began in the early 1990s.
The researchers recruited expectant mothers and took in-depth information about their lifestyle, habits, and health - including whether or not they smoked. They have been followed up regularly since the project first began.
Grandmother's smoking habits
Thanks to the unique ALSPAC cohort, the researchers for the current study could delve even deeper. They wanted to understand whether there are any measurable effects of smoking while pregnant on a person's eventual grandchildren.
In all, 14,500 participants were involved in the study. Once the data had been thoroughly perused and myriad factors controlled for, the results were surprising.
They found that if a girl's maternal grandmother smoked during pregnancy, the girl would be 67 percent more likely to display certain autism-linked traits, as assessed by Social Communication and Repetitive Behavior measures.
Furthermore, it was shown that if the maternal grandmother smoked, the risk of her grandchildren having an autism spectrum disorder (ASD) diagnosis increased by 53 percent.
It is worth noting that for ASD diagnosis, the sex of the grandchildren could not be analyzed separately; the analysis of autistic traits was based on more than 7,000 participants, but there were only 177 ASD diagnoses.
Oddly, the measured effects were more clear cut if the grandmother smoked during pregnancy but the mother had not. There was no association between autism or autism-like traits, and paternal grandparent smoking.
How might this cross-generational effect occur?
It might be that the developing eggs within a fetus are sensitive to the chemicals involved in smoking tobacco and that, later in life, the damage is still present and may eventually affect offspring.
"In terms of mechanisms, there are two broad possibilities. 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."
Prof. Marcus Pembrey, co-author
It could be that this damage is carried down in mitochondria, the so-called powerhouses of the cell. Mitochondria are only passed down to the next generation via the mother's egg. Prof. Pembrey believes that it is possible that small changes in a woman's mitochondria might not affect her, but their influence could be amplified in the following generation.
As for why granddaughters rather than grandsons are affected, the jury is out. Prof. Pembrey says that: "We have no explanation for the sex difference, although we have previously found that grandmaternal smoking is associated with different growth patterns in grandsons and granddaughters."
More research will need to be done to confirm these results and answer new questions that have arisen from the data. The researchers plan to extend their findings, and Prof. Jean Golding, another of the authors, explains that: "We have started studying the next generation of participants, so eventually we will be able to see if the effect carries down from the great-grandparents to their great-grandchildren too."
The upshot of this study is the repetition of some sound advice - do not smoke during pregnancy. As Prof. Golding says: "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."