Children whose maternal grandmothers smoked during pregnancy are more at risk of exhibiting autistic traits, a new study has shown.
In the UK it is estimated that about one person in 100 is affected by autism spectrum disorder (ASD). In recent years, there have been reports of dramatic increases in its prevalence.
Part of this increase may be due to increased awareness – and changing definitions of what constitutes ASD. However, scientists still think that some of this increase is concrete, and might be driven by a number of environmental factors.
Even if genetic factors are known to influence the development of autistic traits, it is thought that environmental factors have contributed to this variation in prevalence over time.
A number of studies have looked specifically at the effects of maternal smoking in pregnancy, yielding only contradictory findings. But animal studies have suggested that smoking in pregnancy may actually have a greater impact on the generations that come after – grandchildren and great grandchildren.
Looking at grandmothers for answers
In the study published in the journal Scientific Reports, researchers investigated this issue further, looking at whether there is a link between development of autistic traits in children and the fact that their grandmothers smoked while they were pregnant.
"Good animal experiments show that something that might happen to a grandparent can be reflected in different outcomes to the grandchildren and great grandchildren. This raises the question as to whether we are looking in the right place when we are trying to identify environmental factors that might lead to certain disorders", lead author Jean Golding, from the University of Bristol, told IBTimes UK.
"There were also anecdotal reports of women having had autistic children and finding out that their own mothers had been given certain drugs in pregnancy so it made us wonder whether this is important in autism".
The scientists analysed data collected as part of the Avon Longitudinal Study of Parents and Children (ALSPAC) which has followed approximately 14,500 children since birth.
They studied four different autistic traits – social communication, speech coherence, sociability temperament and repetitive behaviour – looking at whether they were found more often in children whose grandmothers had smoked during pregnancy.
The scientists found a robust association for two of these traits. Having a maternal grandmother who had smoked was linked with an increased risk of poor social communication and repetitive behaviour. Granddaughters appeared to be more affected than grandsons. No association was observed for paternal grandmothers smoking in pregnancy.
In a second part to the study, the scientists confirmed this association by looking at 174 children who had received an autism diagnosis.
More research is needed to back up these findings further. This study is limited by the fact that it is based on reports by the study parents regarding their own parents' smoking habit – and so they may not be entirely accurate.
If the scientists are able to secure more funding, their next step will be to investigate the mechanisms behind this association.
"We know that smoking in pregnancy results in a lot of epigenetic changes in offspring and there is some evidence that this is reflected in the epigenetics of the grandchild, so that's a possible mechanism that we want to investigate in future research," Golding said.
What does "epigenetics" mean?
The definition of what we mean by epigenetics remains controversial but the term has evolved to include any process that alters gene activity without changing the DNA sequence. It leads to changes that can be transmitted to offspring. Smoking may be one of such processes.