Roughly a quarter of the single-family business that passed through Fannie Mae and Freddie Mac during the first half of 2016 resulted from special treatment bestowed on the GSEs following the housing market collapse. The biggest factor is the so-called GSE patch, which exempts Fannie and Freddie from underwriting restrictions on “qualified mortgages” that are part of the ability-to-repay rule promulgated by the Consumer Financial Protection Bureau. For mortgages to get QM status, the debt-to-income ratio has to be 43 percent or less. However, the CFPB rule waives that requirement for Fannie and Freddie as long as they remain in conservatorship, up to a point.