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Monday, December 6, 2021

Allergies possibly linked to birth order

If you’re the oldest in the family, you may be one of the unlucky ones in terms of allergies.

According to a recent study from the University of South Carolina, first-born children are at a higher risk of developing allergies and asthma because they experience different conditions in the uterus from their younger siblings.

“It’ll tell us what causes allergies and the real value of this teaches us how allergies develop, that’s why it will be very valuable,” said Jesse Joad, a professor of pediatric pulmonology at the UC Davis School of Medicine.

The researchers discovered that first-born babies were more likely to have high levels of an antibody called Immunoglobulin E (IgE) in the umbilical cord blood. The antibody plays a key role in allergic responses.

“There’s a whole of ton research on what causes babies to have allergies,” said Constance Caldwell, a physician with Yolo County health department. “Part of it, but not all of it, is explained by genetics.”

Researchers also believe that the variations in a gene called IL13, which controls the production of stress hormone called cytokine, can influence levels of IgE.

“It’s the first time that I’ve heard of this kind of explanation of allergies,” Caldwell said. “Just one gene affecting the baby turned on or not is fascinating.”

In the past, allergies have not been explained, but most assumed that they were passed on genetically.

“We know there’s some genetic component but we’ve never seen the variability in that,” Caldwell said. “Why is it expressed differently for different kids from the same family and environment?”

Some doctors and scientists followed what they called the hygiene hypothesis, which theorizes that siblings who have more exposure to infection will be less likely to develop allergies, Joad said.

“If you have a lot of [exposure to] infections you have a [lesser] tendency to have allergies,” she said. “If you have older brothers or sisters, then the first-born will go to school and get a bunch of infections and bring it home and will [pass] all those infections, and you will get moved over to the ‘not allergy’ side.”

Babies usually develop asthma because of their living environment, Joad said.

“We know that environmental things can affect you when you’re in the womb, and can make a difference after you’re born,” Joad said. “A known cause of asthma is exposure to tobacco smoke. Those things are preventable, but this one looks much more complicated.”

Some students actually notice that their oldest sibling is the only one with allergies.

“I am so glad I am not the first child in my family,” said first-year UC Davis history major Sarah Hollingsworth. “I am the youngest of the three in my family and my oldest sibling is the only one with allergies.”

The discovery may lead to a new breakthrough.

“Clearly, genetics is not the whole story, but part of the story, and this is another attempt to figure out the other half of the story,” Caldwell said. “It’s very hard to say [how legitimate this study is]. We need to evaluate the scientific article. You need a primary source, look at how they did their studies, statistics, look at their reference and how [they] funded the studies. It’s intriguing, but is it valid? I don’t know.”

 

JANET HUNG can be reached at city@californiaaggie.com

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