Younger Siblings May Boost Brain Tumor Risk

The link might be infections passed on in adolescence, researchers say.

By Rick Ansorge
HealthDay Reporter
Tuesday, December 12, 2006; 12:00 AM

Copyright © 2006 ScoutNews, LLC. All rights reserved.

TUESDAY, Dec. 12 (HealthDay News) -- Can the number of brothers and sisters you have affect your risk of developing a brain tumor?

Possibly, German researchers report. They found that children with three or more younger siblings face two to four times the risk of developing a brain tumor by age 15 compared to children with no siblings.

This risk was not seen in children with three or more older siblings or in adults who grew up in large families, however.

"The association with number of younger siblings, and not with number of older siblings, suggests that infections or re-infections in late childhood may play an important role in the development of pediatric nervous system tumors," said lead researcher Dr. Andrea Altieri, of the German Cancer Research Center in Heidelberg, Germany. The findings are published in the Dec. 12 issue of Neurology.

The population-based study, which Altieri called the largest of its kind, analyzed more than 13,600 Swedish brain tumor cases.

It found that children with three or more younger siblings had twice the risk of nervous system tumors known as neuroblastomas, more than twice the risk of brain cancers such as medulloblastoma or ependymoma, and nearly a quadruple risk of meningioma (cancer of the brain's lining, the meninges) compared to children with no siblings.

"The association between the number of siblings and other measures of child overcrowding and the risk of infections is well-documented," Altieri said. "The strongest evidence comes from several studies showing that children attending day-care centers have a two- to fourfold increased risk of infection compared to children cared for at home."

But how would the age of siblings influence brain tumor risk? Altieri has a theory.

"When you have many younger siblings, you have a higher risk of infection during early adolescence and a higher risk of being re-infected from your younger siblings," the researcher pointed out.

On the other hand, the presence of many older siblings increases the risk of infection in infancy and early childhood. "As has been reported for other childhood malignancies, very early infection could even be protective against nervous system tumors," Altieri said, which could explain why no increased risk was seen in children with three or more older siblings.