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 While prenatal smoke exposure has long been linked to an increased
risk of childhood asthma, the current study offers fresh evidence
that it's not just a pregnant mother's smoking that can cause harm.
Researchers followed 756 babies for six years. Almost one in four
were exposed to tobacco by fathers who smoked while the child was
developing in the womb; only three mothers smoked.
Overall, 31% of kids with fathers who smoked during pregnancy
developed asthma by age 6, compared with 23% of kids without fathers
who smoked, the study found.
Asthma was also more common among kids whose fathers were heavier
smokers, senior study author Dr. Kuender Yang of the National
Defense Medical Center in Taipei said by email.
"Children with prenatal paternal tobacco smoke exposure
corresponding to more than 20 cigarettes per day had a significantly
higher risk of developing asthma than those with less than 20
cigarettes per day and those without prenatal paternal tobacco smoke
exposure," Yang said.
About 35% of the kids with fathers who were heavier smokers
developed asthma, compared with 25% of children with fathers who
were lighter smokers and 23% of kids with fathers who didn't smoke
at all during pregnancy.
Smoking by fathers during pregnancy was also associated with changes
in methylation - a chemical code along the DNA strand that
influences gene activity - on portions of genes involved in immune
system function and the development of asthma.
Researchers extracted infants' DNA from cord blood immediately after
birth and examined methylation along the DNA strand. The more
fathers smoked during pregnancy, the more methylation increased on
stretches of three specific genes that play a role in immune
function.
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Children who had the greatest methylation increases at birth,
affecting all three of these genes, had up to almost twice the risk
of having asthma by age 6 as other kids in the study.
While smoking by fathers during pregnancy was linked to childhood
asthma, it didn't appear to impact children's sensitivity to
allergens or total levels of IgE, an antibody associated with
asthma.
This suggests that the risk of asthma from tobacco exposure is
unlike allergic asthma, which is driven by allergies or allergic
sensitization via IgE antibody, said Dr. Avni Joshi, a researcher at
the Mayo Clinic Children's Center in Rochester, Minnesota, who
wasn't involved in the study.
The study wasn't designed to prove whether or how prenatal smoking
exposure might directly cause so-called epigenetic changes, or how
those changes cause asthma in children.
It's not yet clear how the alterations seen along the DNA strand
where methylation increased might cause asthma, the study team notes
in Frontiers in Genetics.
Still, the message to parents should be clear, Joshi said by email.
"Smoking is bad at ANY point in time: before the baby is born and
after the baby is born," Joshi said. "Many parents defer quitting
until the baby is born, but this study stresses that the prenatal
exposure to tobacco creates changes to the unborn child's immune
system, hence it is best to quit as a family decides to have
children, even before the conception happens."
SOURCE: https://bit.ly/2WG9lhM Frontiers in Genetics, online May 31,
2019.
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