"Sibling Effect" Caused in Utero

Research at Michigan State University indicates that first-born children are more likely to suffer from asthma, eczema and various allergies than their later-born siblings - a phenomenon known as the "sibling effect" - because of changes that occur in the mother's womb prior to birth.

Until now the scientific community assumed that the "sibling effect" was caused postnatally by first-born children being less exposed to infections from other siblings, an exposure that would serve to strengthen the child's immune system.

However, the work of Wilfried Karmaus, associate professor of epidemiology, and his colleagues shows that the effect takes place before the infants are even born.

The research, published in the recent edition of the American Journal of Epidemiology, found that first-born babies have higher levels of a key immune protein. This protein, known as cord blood immunoglobulin, or IgE, has been determined to be a risk factor for asthma and various allergies.

There have been a number of other studies indicating that children born with high levels of IgE in their umbilical cord blood have an increased risk of developing allergies.

The scientists examined nearly 1,000 children who were born in the United Kingdom's Isle of Wight between 1989 and 1990. What they found was that the more older siblings a child had, the less likely the child was to have elevated levels of IgE.

Of the first-born children, 16.5 percent had high IgE levels (higher than 0.5 kilounits per liter). These high levels were found in only 12.8 percent of children with one older sibling and in just 8 percent of children with two or more older siblings.

"The challenge is to identify risk factors that are responsible for increased IgE levels in first-borns," said Karmaus. "This may include hormones and endocrine disruptors since, for instance, the levels of endocrine disruptors such as DDE and PCBs are higher in mothers who have their first pregnancy."

Other collaborators in the research are Hasan Arshad of the David Hide Asthma and Allergy Research Centre, St. Mary's Hospital, in England; and Jorg Mattes of the John Curtin School of Medical Research, Australian National University.

Contact: Wilfried Karmaus, Epidemiology(517) 353-8623, Ext. 115, or [email protected]

or Tom Oswald, University Relations(517) 355-2281 or [email protected]