The writing and circulation of the amicus brief was coordinated by Jerrold Nadler (D-NY) and was endorsed by 132 Democratic members of the U.. House of Representatives. This is significant because the primary group defending DOMA is the 5-member "Bipartisan Legal Advisory Group" (more commonly known as BLAG) of the House, which thanks to the Republican majority in the House is stacked with notorious homophobes and heterosexual supremacists (like House Speaker John Boehner, Majority Leader Eric Cantor and Majority Whip Kevin McCarthy). Both of the two Democratic members of BLAG, former House Speaker Nancy Pelosi and former Majority Leader Steny Hoyer signed on to the brief opposing BLAG's defense of DOMA and reiterating their position that DOMA is unconstitutional. Since BLAG claims to represent the interests of the U.S. House of Representatives in federal legislation that was passed way back in 1996, it is important to note that a significant fraction of the House does not support BLAG's actions.
However, even though 132 Democrats signed on to the brief, nearly half as many did not. 59 Democratic members, generally from "red" or conservative districts refused to sign on to the brief. The list of these Democrats is above.
Hat/tip to Joe.My.God.