GSE Share of Mortgage Market Takes Nose Dive Facing a slumping mortgage origination environment as well as a major shift to adjustable-rate product, the GSEs watched their share of the residential mortgage market tumble to a four-year low in the first half of 2004. According to numbers compiled by Inside The GSEs, the combined business of Fannie Mae, Freddie Mac and the Federal Home Loan Banks amounted to only 47.3 percent of estimated total mortgage