Fannie Mae says it expects “a slight increase” in the share of its single-family business that has higher debt-to-income ratios as a result of a tweak to the company’s Desktop Underwriter system. The government-sponsored enterprise generally limits DTI ratios to 45 percent. Under the previous version of DU, applications with debt ratios up to 50 percent could be approved if there were compensating factors, such as a loan-to-value ratio below 80 percent or at least 12 months of ...