First-borns more susceptible to asthma: study

May 21st, 2008 - 4:15 pm ICT by admin  

Toronto, May 21 (IANS) First-borns have a higher risk for developing asthma and other allergies than younger siblings, and researchers have traced the reason to their umbilical cords. A new study of 1,200 children in Britain found first-borns had higher levels of IgE antibody - an immune-response substance responsible for allergic reactions - in their umbilical cord blood than later children.

The study, whose findings were presented Tuesday at the American Thoracic Society’s annual international conference here, also showed that the higher risk persisted in the first-born throughout childhood.

Even at ages four and 10, those with a higher amount of the antibody in their cord blood had about double the risk of having a positive skin-prick test for allergies and asthma compared with a younger sister or brother, the study found.

The study shows the IgE antibodies in first-born “are already higher compared to second-born”, said lead author Wilfried Karmaus, noting that this was a pointer to the fact that it is “prenatal programming” that is responsible.

Karmaus said the amount of IgE is linked to a specific gene. In a first pregnancy, this gene appears to be more active, leading to a greater output of the antibody.

He said it was “unclear” what the driving force behind it was, or what the potential of risk for increased cord-serum IgE was. He noted, however, that women giving birth to their first child also had a higher blood level of the antibody than they did with the second child.

Karmaus said the contact between mother and child could lead to a more “immunological arousal” in the first pregnancy, creating a higher risk of the child’s immune system reacting to allergens.

He estimated that 20 to 30 percent of all cases of asthma and allergy could be prevented if pregnancy conditions for first-born children could be altered somehow, although how that could be done is unknown.

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