Mutations in the genes encoding for angiotensinogen (AGT), renin, ACE, or angiotensin II receptor type 1 (AGTR1) in mice result in severe medullary hypoplasia and hydronephrosis [68], a phenotype not observed in humans with AGT, renin, ACE, or AGTR1 mutations [29]. This evidence concerns the gene REN and hydronephrosis.