Remarkably, most of the Six4−/−;Six5+/− fetuses had ventral body closure defects, including the omphalocele phenotype, at E18.5 (Fig. 1F-H′) (enlarged umbilical ring, n=9/16, 56.3%; small omphalocele, n=3/16, 18.8%; large omphalocele, n=2/16, 12.5%; Table S2). This evidence concerns the gene SIX4 and omphalocele.