(Reuters) -Sarepta Therapeutics' shares plunged nearly 30% on Tuesday as the failure of two of its approved drugs in a key trial and weak forecast for its top selling gene therapy raised concerns about the strength of the company's portfolio. The trial setback compounds Sarepta's woes as it is already facing scrutiny and restrictions related to its top-selling gene therapy, Elevidys, following deaths of two patients earlier this year. Sarepta was testing its therapies, Amondys 45 and Vyondys 53, in a tri ...