Together, Fannie Mae and Freddie Mac in August posted a combined increase in the volume of single-family mortgages securitized, according to a new Inside The GSEs analysis. Fannie and Freddie issued $61.1 billion in single-family mortgage-backed securities in August, a 5.5 percent increase from July.However, August's MBS issuance was down 56.7 percent on a year-to-date basis.