Having younger siblings linked to brain tumor risk

NEW YORK (Reuters Health) - The chances of developing certain types of brain cancer appears to be increased in people who have several younger siblings, according to a new study. By contrast, no elevated risk is seen in individuals with only older siblings.

"Since the size of a family and the number of younger siblings correlate with the incidence of brain tumors, this suggests infectious agents may be causing the disease," lead author Dr. Andrea Altieri, from the German Cancer Research Center in Heidelberg, said in a statement.

"The number of siblings a person has indicates they were exposed at an early age to infections," the researcher explained, "since children come in close contact with each other and thereby share exposures to many infectious agents."

The findings stem from an analysis of data for 13,613 cases of brain cancer entered in the Swedish Family-Cancer Database. Age, birth cohort, socioeconomic status, and family history of cancer were all factored into the analysis.

The likelihood of developing certain brain tumors (hemangioblastoma, childhood neuroblastoma, and ependymoma) was up to two-times higher for people having four or more younger siblings compared to those with no siblings, the team reports in the medical journal Neurology.

Having older siblings was associated with a trend toward decreased risk.

As to why only younger siblings increased the risk of brain tumors, Dr. Altieri said it might be because people are only susceptible to cancer-inducing effects of infection in late, not early, childhood.

The investigators call for further studies to examine the mechanisms underlying the associations seen.

SOURCE: Neurology, December 12, 2006.