Indeed, mouse models with null mutations in Ret or Gfrα1 demonstrated that signaling through GDNF-RET-GFRα1 is critical for kidney development, as these mice also present renal agenesis or severe renal hypoplasia (Schuchardt et al., 1994; Cacalano et al., 1998). Here, GFRA1 is linked to renal hypoplasia.