Researchers at Johns Hopkins have discovered the first
genetic evidence that secondhand
smoke can worsen lung disease. The report in the Jan. 30
issue of the Journal of the American
Medical Association describes one gene variation that
can weaken lung function as well as shorten the
lifespan of those who are affected by cystic fibrosis and
are also exposed to secondhand smoke.
"We're really surprised that such a small genetic
change can double the negative effects of
secondhand smoke on lung function in these patients," said
Garry Cutting, a professor of pediatrics
and medicine and a member of the
McKusick-Nathans Institute of Genetic Medicine at Johns
"It's always been suspected that secondhand smoke is
detrimental to lung disease patients, and now we
have a handle on one specific gene that clearly makes it
worse for those with CF."
Of the 812 participants in the study, 188 were exposed
to secondhand smoke at home. The
participants were recruited between 2000 and 2006 as part
of the U.S. Cystic Fibrosis Twin and
Sibling Study and the Cystic Fibrosis Foundation Data
The research team found that secondhand smoke exposure
was associated with decreased lung
function in CF patients, measured by how much air a person
could breathe out in the first second of
expiration. According to Cutting, any secondhand smoke
exposure reduced lung function by 10 percent.
"We know by observation that some patients tend to do
worse than others, so we wondered if
genes played a clear role in how CF patients react to
secondhand smoke," Cutting said.
The research team went on to compare patient lung
function with their particular genetic
variant of CF as well as the genetic variant of another
gene, TGFbeta1, which has been shown to
affect the severity of CF and asthma.
CF patients who also carried particular TGFbeta1
mutations fared twice as badly in lung
function when exposed to secondhand smoke compared with
those who were not exposed.
According to Cutting, secondhand smoke exposure is
roughly equivalent to seven years of lung
function decline. "This means that a 17-year-old CF patient
with a TGFbeta1 mutation and exposed to
secondhand smoke would have lung function similar to that
of a 24-year-old who wasn't exposed to
secondhand smoke," Cutting said. "This gene-environment
interaction drastically accelerates reduced
The research was funded by the National Heart, Lung
and Blood Institute, the Cystic Fibrosis
Foundation and the Flight Attendant Medical Research
Authors on the paper are J. Michael Collaco, Lori
Vanscoy, Lindsay Bremer, Kathryn McDougal,
Scott Blackman, Amanda Bowers, Kathleen Naughton, Jacky
Jennings, Jonathan Ellen and Cutting, all
of Johns Hopkins.