Fannie Mae expanded its multifamily mortgage-backed structured finance product availability Monday. The government-sponsored enterprise introduced “Guaranteed Multifamily Structures,” or Fannie Mae GeMS. GeMS include delegated underwriting and servicing of mortgage-backed securities megas, DUS real estate mortgage investment conduits (REMICs) and syndicated DUS megas. Megas are groups of Fannie mortgages pooled together according to similar characteristics in the underlying collateral. Syndicated mega deals, those involving large banks, will be managed by broker-dealers and offered in issuance sizes similar to DUS REMIC transactions. DUS issuance happens when Fannie Mae purchases individual, newly-originated mortgages from specially-approved lenders. The MBS products will provide stable funding to support the nation's rental housing market, the GSE said. "When many financial institutions pulled out of the multifamily financing market during the financial crisis, we stayed and increased our participation to help keep credit flowing," said Kenneth Bacon, executive vice president, multifamily mortgage business for Fannie Mae. The new GeMS syndicated mega offerings expand on Fannie’s MBS products already offered  in its multifamily DUS program. Fannie revitalized its multifamily MBS program in 2009, increasing issuance and using the company's portfolio to enhance liquidity for multifamily MBS. Fannie Mae issued $16.4 billion of DUS MBS and $4.8 billion of DUS structured securities in 2010. The Fannie Mae GeMS execution is designed to be more nimble to alternate mortgage financing vehicles, such as conduit-style deals, the GSE said. As of Sept. 30, 2010, the DUS market consisted of $44.6 billion in outstanding DUS MBS. DUS MBS production reached $16.4 billion last year. Multifamily mortgage debt outstanding accounted for approximately 7.6% of the $11.9 trillion total mortgage debt outstanding, or $908 billion, according to the Mortgage Banker’s Association’s analysis of the Federal Reserve Board Flow of Funds data for the first quarter of 2009. Write to Kerry Curry. Follow her at @communicatorKLC.