A new study from the University of Bristol in England has found evidence to suggest girls whose maternal grandmothers smoked during pregnancy are 67 percent more likely to show signs linked to autism, such as having trouble communicating and reading emotions. The team theorized that smoking may cause genetic changes that aren't expressed until the third generation, or, it may inspire an adaptive response that leaves kids more vulnerable to ASD.

The study, now published online in Scientific Reports, also found that children are 53 percent more likely to be diagnosed with Autism Spectrum Disorder (ASD) if their maternal grandmother smoked. The researchers suggest that this may explain the recent surge of autism diagnoses, as smoking in women gained popularity during the Second World War, The Independent reported. The team have a theory regarding the link between smoking and autism, although they don't understand why girls were at greater risk.

Read: How Smoking Changes Your Genes: Cigarettes Linked To Epigenetic Alterations

“In terms of mechanisms, there are two broad possibilities,” study co-author Marcus Pembrey said in a recent statement. “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.”

For the study, the team looked at 14,500 participants of the Children of the 90’s study, paying special attention to multiple factors over the course of many years that may have affected the children’s health.

The research is still in its preliminary phase, and at the moment only suggests a link, but does not prove causation. In fact, Peter Hajek, director of the tobacco research unit at Queen Mary University of London, told The Independent that past research that has attempted to find a link between smoking in parents has proved inconclusive. However, as suggested by the new research, this may be because scientists have not looked at old enough branches in the family tree.

We already know that smoking can damage the DNA of mitochondria, known as the “powerhouse of the cell.” However, we inherit our mitochondrial DNA only from our mothers. As explained by Pembrey in a press release, it may be that these initial mitochondrial DNA changes caused by smoking have no effect during the first transmission, and only have an effect when passed onto the third generation.

Past research looking at the effects of tobacco on our genes has found that it's not exactly tobacco, but rather the smoking of tobacco, that does the damage to our DNA. The 2013 study found that, while our genes are set in stone when we are born, smoking can produce something known as epigenetic changes. According to What Is Epigenetics, these changes are usually caused in response to environmental or lifestyle factors, and cause different expression of certain genes, or change the way that our cells read our DNA. Epigenetic changes brought about by smoking can influence everything from the genes that control our immune responses to those that control sperm quality.

While we still may not know for sure whether smoking in grandmothers has a trickle-down effect on grandchildren, we do know that smoking during pregnancy can harm a child. This is just another reason to give up the habit, especially during pregnancy, as it may not only benefit your child, but also your future grandchildren.

Source: Golding J, Ellis G, Gregory S, et al. Grand-maternal smoking in pregnancy and grandchild’s autistic traits and diagnosed autism. Scientific Reports . 2017

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