Lymphovenous valve insufficiency is a feature of several lymphedema mouse models with disruptions in genes including Prox1, Foxc2, Cx37, Gata2, Pdpn, or Clec2 (Uhrin et al., 2010; Hess et al., 2013; Geng et al., 2016; Bianchi et al., 2018). Here, PROX1 is linked to lymphedema.