The biggest mutual funds in the nation have lost more than an estimated $4 billion in the past week alone on their investments in Fannie Mae and Freddie Mac and related mortgage stocks, Reuters reports, based on analysts’ assessment of fund companies’ latest reports. In the past week, Fannie and Freddie declined 45.4% and 46.5%, respectively.

Among those believed to be hardest hit are the Legg Mason funds that Bill Miller oversees, along with American Funds’ Growth Fund of America and a slew of funds at AllianceBernstein and Fidelity.

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