New U.S. stress test needed: higher interest rates

``AAA-rated mortgage-backed securities backed by Uncle Sam are also vulnerable. For example, when 10-year Treasury yields rose 1.3 percentage points over four months beginning in October 2010, it shaved about 9 percent off the value of Fannie Mae mortgage bonds, according to a report from Fitch Ratings earlier this year. By way of comparison, that's nearly double the expected credit losses on prime mortgages originated during the frothy years of 2005 to 2008.''