Fannie Mae and Freddie Mac issued $57.72 billion of single-family mortgage-backed securities in January, a 7.8 percent decline from the previous month, according to a new Inside The GSEs ranking and analysis.Freddie actually increased its monthly volume by 7.3 percent from December levels, but Fannie production fell 15.6 percent. It’s not unusual for GSE monthly trends to fluctuate; Fannie’s MBS issuance was up sharply in December. Freddie’s production was buoyed slightly by some $199.3 million of modified mortgages that were securitized last month. And it’s not surprising that the flow of purchase mortgages into GSE securities fell 14.4 percent in January, as the housing market hit a seasonal cooling.However, refinance activity was also [includes exclusive charts] ...