Childhood Asthma, Allergies Traced to Womb

New research suggests birth order, method of delivery all play a part

By Alan Mozes
HealthDay Reporter

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WEDNESDAY, May 21 (HealthDay News) -- At least some of the biological risk for childhood asthma and allergies traces back to the womb, new research suggests.

Both the order of birth and even the way a baby is delivered have a significant impact on the long-term strength of a child's allergic defenses, scientists say.

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The findings were presented Wednesday during the American Thoracic Society's International Conference, in Toronto.

At the meeting, one team of scientists said it had evidence indicating that when a specific genetic marker for allergic and asthmatic development is present among a first-born child, it appears to raise the risk for allergic conditions as far as 10 years down the road. However, when the exact same marker is present in a family's second or third child, the gene seems to have exactly the opposite effect -- actually lowering such risk.

"This is the first time it has been demonstrated that birth order can affect the behavior of genes related to asthma and allergies, and that birth order can therefore affect the risk for developing one or the other," said study author Dr. Wilfried Karmaus, a professor in the department of epidemiology and biostatistics at the University of South Carolina in Columbia.

On a second front, another team of researchers suggested that regulatory cells associated with proper immune function may be impaired in babies delivered by Caesarean section.

"We found a dysfunctional cellular response in the normally protective immune system among C-section babies," observed Dr. Ngoc Ly, an assistant professor of pediatrics at the University of California at San Francisco. "And although more work needs to be done to follow how long this response might endure, we think this disrupted immune pathway may influence the development of asthma later on."

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