Boys may be more apt than girls
to have childhood asthma, but, when compared to girls, they are also more likely
to grow out of it in adolescence and have a decreased incidence of asthma in the
post-pubertal years. This indicates that there may be a buried mechanism in
asthma development, according to a prospective study that analyzed airway
responsiveness (AR) in more than 1,000 children with mild to moderate asthma
over a period of about nine years.
“We wanted to investigate what
was behind the observed sex differences in asthma rates and AR,” says lead
researcher, Kelan G. Tantisira, M.D., M.P.H., of Brigham and Women’s Hospital
Medical School. “This is the first study to
prospectively examine the natural history of sex differences in asthma in this
Their results appeared in the
second issue for August of the American Journal of Respiratory and Critical Care
Medicine, published by the American Thoracic
Dr. Tantisira and colleagues
used data from the ongoing Childhood Asthma Management Program (CAMP) that
enrolled 1041 children from 5 to 12 years of age with mild to moderate
persistent asthma and performed annual spirometric testing with methacholine
challenges to quantify their AR.
After an average of 8.6 years
and each individual had undergone eight to nine annual methacholine challenges,
the researchers were able to identify a clear pattern: when it came to the amount of methacholine it
took to provoke airway constriction, the girls’ reactivity did not change
markedly over the years. In contrast, boys became increasingly tolerant over
time to larger and larger doses of methacholine, suggesting a possible decrease
in disease severity. By the age of 16, it took more than twice as much
methacholine to provoke a 20 percent constriction in the boys’ airway on average
as it did with the girls.
What’s more, by age 18, only 14
percent of the girls did not demonstrate any significant degree of airways
responsiveness, compared to 27 percent of boys.
“While our results were not
unexpected, they do point to intriguing potential mechanisms, to explain the
gender differences in asthma incidence and severity. Especially intriguing is
that the differences in gender begin at the time of transition into early
puberty.” said Dr. Tantisira.
This study into the natural
history and sex differences in asthma marks the beginning of what many hope will
be a long investigation into the subject.
“It will be of great interest to
follow these children over time to see what happens with AR and severity of
asthma in adulthood,” wrote Jorrit Gerritson, M.D., Ph.D., in an accompanying
This is precisely Dr.
Tantisira’s next step: Dr. Tantisira and colleagues now have 12 years of data
for the cohort, and is looking into investigating the characteristics of the
individuals who attained clinically “normal” AR during follow-up. “Most of the
original cohort has now reached adulthood,” said Dr. Tantisira. “We are now able
to perform a secondary analysis with an emphasis on those who have reached
News release from American Thoracic Society on August 15, 2008.