Grandmother's Smoking Associated With Grandchildren's Autism Spectrum Disorder

There's no shortage of guidance around the dangers of smoking cigarettes – but this latest finding could prompt further scrutiny of the practice.

A University of Bristol study, published in Scientific Reports, found that if a girl's maternal grandmother smoked
 while pregnant, she gave her granddaughter a 67 percent higher chance of showing signs associated with autism, such as poor social communication and repetitive behaviors. She also gave all her grandchildren a 53 percent higher risk of being diagnosed with autism spectrum disorder. The research is a piece of a larger study on how maternal and paternal grandmother's pregnancy smoking affects their grandchildren.

Scientists examined data from the Avon Longitudinal Study of Parents and Children for the study, also called the Children of the 90s, which kept up with 14,000 children in the United Kingdom by enrolling pregnant women in 1991 and 1992.

The autistic traits analysis involved more than 7,000 participants. Only 177 were diagnosed with autism spectrum disorder, too few to allow analysis by grandsons and granddaughters separately.

But how does a phenomenon like this happen, exactly?

It seems that cigarette smoke could affect a baby girl's developing eggs in the womb, resulting in side effects when it comes to having children of her own.

"In terms of mechanisms, there are two broad possibilities," one of the study authors, professor Marcus Pembrey from the University of Bristol, said in a 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. 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."

Researchers say that now more research must be done to determine what the molecular changes could be in addition to other possible associations. They also say a multitude of factors like genetic variation are thought to impact autism spectrum disorder development.

The study did have its limitations, including that it depended on how correct parents' reports were on their own parents and that the results relate most to white grandparents in Britain. The study wasn't supposed to look at autism in the first place.

In the U.S., 1 in 68 children has autism spectrum disorder, according to the Centers for Disease Control and Prevention.