FRANKFURT, Aug 26 (Reuters) - Shares in DWS fell 5.3% in early Frankfurt trade on Thursday following a news report that U.S. authorities are investigating the fund manager after a former head of sustainability said it overstated how much it used sustainable investing criteria to manage assets. A spokesperson for DWS declined to comment on the report by The Wall Street Journal. (Reporting by Tom Sims Editing by Riham Alkousaa) Our Standards: The Thomson Reuters Trust Principles.