NEW YORK (Reuters Health) - The number of teenagers who have experienced mania -- a hallmark of bipolar disorder -- is close to the number of adults estimated to have the mood disorder, suggesting that for many the condition begins during adolescence, according to a new study.

"The traditional wisdom has been that mania begins in your 20s and 30s," said Kathleen Ries Merikangas, the study's lead author and chief of the genetic epidemiology branch at the National Institute of Mental Health. Learn more: