Smoking while pregnant is dangerous, but new research suggests that the dangers don’t stop once mom snubs out her last cigarette. According to an animal study from Yale University, in utero nicotine exposure may trigger widespread genetic changes that affect the formation of connections between brain cells long throughout an animal's life — a change that could be linked to attention and behavioral problems later in children of smoking mothers.

For the study, now published in the online journal Nature Neuroscience, researchers from Yale University exposed pregnant mice to tobacco smoke in an effort to see what long-lasting effect prenatal nicotine exposure had on the developing fetuses. Once the mice were born, the team noted that those exposed to nicotine early on went on to develop behavioral problems that mimicked symptoms of attention deficit hyperactivity disorder (ADHD) in humans.

In order to understand exactly how and why nicotine might be causing this effect in mice, the researchers dug a bit deeper. They did extensive genomic screenings of the mice exposed to nicotine and found higher levels of activity in a key area of the brain that regulates histone methylation. Histone methylation controls gene expression by changing the way that DNA wraps around chromosomes, mostly in genes responsible for creating brain synapses.

According to lead researcher Dr. Marina Picciotto in a recent statement, “When this regulator is induced in mice “they pay attention to a stimulus they should ignore,” much like humans with ADHD do. The team also found that when the same regulator was triggered in mice that had never been exposed to nicotine, the attention deficit effects ensued, suggesting that this was indeed the cause for the behavioral problems.

"It is exciting to find a signal that could explain the long-lasting effects of nicotine on brain cell structure and behavior," Picciotto said. "It was even more intriguing to find a regulator of gene expression that responds to a stimulus like nicotine and may change synapse and brain activity during development."

What was most alarming was the fact that these genetic changes were maintained well into adulthood for the mice. However, there is some hope. The team noted that when they medically inhibited the master regulator of histone methylation, the mice became calmer and no longer reacted to the irrelevant stimulus. This would suggest that attention problems may be treatable.

This is not the first time that smoking in mothers has been linked to DNA changes in their children. For example, a study released earlier this year found that mothers who smoked daily throughout their pregnancies gave birth to children who had their DNA chemically modified in 6,073 places. These changes were tied to specific genes related to the development of the lungs and nervous system, smoking-related cancers, and birth defects such as having a cleft palate.

Although breathing in secondhand smoke has been linked to health problems in children, theses genetic changes are caused not by inhaling smoke but by exposure to the nicotine through the bloodstream.

"This is a blood-borne exposure to smoking — the fetus isn't breathing it, but many of the same things are going to be passing through the placenta," Stephanie London, co-senior author of the study, previously told Medical Daily.

Source: Picciotto MR, Jung Y, Hsieh LS, et al. An epigenetic mechanism mediates developmental nicotine effects on neuronal structure and behavior. Nature Neuroscience. 2016