We identified reduced numbers of VVs and shorter VV leaflets in patients with lymphedema caused by mutations in FOXC2 or GJC2. In mice, we characterized the induction and organization of valve-forming ECs (VFCs), which occur at an earlier point than previously identified, and show that they occur within highly spatially and temporally regulated domains of Prox1, Foxc2, Nfatc1, Cx37, Cx43, and Cx47 expression (Bazigou et al., 2011; Munger et al., 2016). The gene discussed is GJC2; the disease is lymphedema.