Sheila Hedstrom-Pelger, a nurse in Chandler, Ariz., thought she knew the signs of depression. She had sought professional help for her oldest son, Alex, when he admitted feelings of hopelessness, sadness, anxiety and suicidal thoughts while in high school. But when her second son, Tyler, started verbally lashing out at her when he was a teen, Hedstrom-Pelger didn’t consider depression as a possible cause for Tyler’s out-of-character behavior.