Edith O’Brien, the MF Global Holdings Ltd. (MF) assistant treasurer who has become a key figure in the disappearance of as much as $1.6 billion in customer funds, declined to answer questions from U.S. lawmakers. O’Brien, who appeared today under subpoena before a House Financial Services subcommittee, invoked her constitutional right against self-incrimination during a hearing on the New York firm’s Oct. 31 bankruptcy, the eighth largest in U.S. history.