U.S. Rep. Sean Casten (D-IL) announced the death of his 17-year-old daughter, Gwen, on Monday on Twitter. First responders said they were called to the block where Casten’s family lives in Downers Grove, Illinois, where they found an unidentified girl, 17, unresponsive. She was later pronounced dead at the scene, according to the police statement. Gwen’s cause of death has not been revealed. Casten’s tweet said that his family “requests privacy, and we will be issuing no further comment during this heartbreaking time.” Gwen had recently been featured in one of her father’s campaign ads, and her Twitter bio states that she was a co-director for the March For Our Lives Downers Grove chapter.