Both Fannie Mae and Freddie Mac retained sizeable shares of mortgage securities with a not insignificant bump during the fourth quarter of 2011, according to a new Inside The GSEs analysis.The GSEs issued a combined $261.6 billion in MBS in the fourth quarter, a 13.0 percent increase from the third quarter.Fannie and Freddie dropped to $852.8 billion in MBS issued for the year, an 11.1 percent decrease in MBS issuance during the January to December period. The GSEs’ issuance represented 72.1 percent of total MBS produced during 2011.Between the two companies, Fannie and Freddie registered an ample 77.1 percent share of new MBS issued during the quarter that ended Dec. 31, 2011, up from the 69.1 percent the two companies held during the third quarter and surpassing the 74.8 percent share both GSEs held during the first quarter.