ETV4 and renal hypoplasia: Because the renal defects of Etv4−/− kidneys are exacerbated by Etv5 mutations (Etv4−/− mice have a very low frequency of renal hypoplasia or agenesis, while Etv4−/− mice also carrying one or two mutant Etv5 alleles have a much higher frequency of these defects) [25], some embryos also carried 1 or 2 copies of a hypomorphic Etv5 allele (Etv5tm1Kmm, abbreviated Etv5M) [25,45].