As part of the research, a team of health care experts at the University of Bristol in the U.K. examined 14,500 children born in the 1990s. The research team found that girls whose maternal grandmothers smoked during pregnancy had a 67 percent likelihood of exhibiting autism-related traits such as repetitive behaviors and poor social communication skills. The experts also noted that the risk of being diagnosed with autism increased by 53 percent in girls whose maternal grandmothers smoked.
The findings suggested that girls exposed to cigarette smoke while still in the womb may undergo negative changes in the developing eggs, which in turn can be carried over to her own children. The research team noted that more studies are needed to identify these molecular changes and whether they apply to other groups of people.
"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. 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. 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," said study co-author Professor Marcus Pembrey in ScienceDaily.com.
The findings were published in the journal Scientific Reports.
Previous study links smoking, autism onset
A study published in 2012 demonstrated that smoking during pregnancy may raise the odds of developing high-functioning autism. To carry out the study, a team of researchers at the University of Wisconsin-Milwaukee Zilber School of Public Health examined data on 634,000 U.S. children born in 11 states. The experts then compared these participants against more than 3,000 children diagnosed with autism.
The study revealed that about 13 percent of mothers smoked during pregnancy, while 11 percent of the mothers of children with autism reported smoking during pregnancy. The research team also found that children born to mothers who smoked during pregnancy had a 25 percent increased odds of developing high-functioning autism such as Asperger's syndrome.
"It really supports the idea that there are multiple causes of autism, both genetic and environmental. When we talk about autism being one group or disorder, we really need to ensure we have these groups as well-defined as possible. This is a very heterogeneous disorder. There are many potential biological pathways for which tobacco can harm the developing baby," said Alycia Halladay, Director for Environmental Research for Autism Speaks, in an article on Health.USNews.com.
The findings were published in the journal Environmental Health Perspectives.
Fast facts about autism spectrum disorder
- According to the Centers for Disease Control and Prevention, about one percent of people worldwide suffer from autism.
- More than 3.5 million Americans live with the condition.
- The prevalence of autism in the U.S. is about one in 68 births.
- The prevalence of autism among American children rose by 119.4 percent from 2000 to 2010.
- The prevalence of autism among American children increased from six percent to 15 percent between 2002 and 2010.
- The U.S. spends as much as $262 billion annually on autism-related health costs.
- Autism-related costs incurred by children range between $61 billion and $66 billion.
- A majority of autism-related costs are incurred by adults, at $175 billion to $196 billion.
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