MMP2 and dystocia: Moreover, measuring the dystocia frequency among females with double mutations in the Mmp2 and Mmp9 genes, such as the mixed genotypes Mmp2+/−Mmp9+/−, Mmp2−/−Mmp9+/−, Mmp2+/−Mmp9−/− or double-full-knockout (Mmp2−/−Mmp9−/−, dKO), revealed varied results, such as 10.3% (4/39), 42.9% (9/21), 0% (0/11) and 40% (6/15), respectively (Figure 1D).