Yields on Fannie Mae and Freddie Mac mortgage securities that guide home-loan rates fell to the lowest in five months as US Treasuries gained on concern that the sovereign debt crisis will stunt economic growth. Fannie Mae’s current-coupon 30-year fixed-rate mortgage- backed securities tumbled 0.08 percentage point to 4.19% as of 12:10 p.m. in New York, the lowest since Dec. 8.