For instance, hypertension has been proposed to be at least partially explained by insufficient nephron number (Brenner et al., 1988), whereas renal agenesis is a relatively frequent congenital defect in humans, mirroring the GDNF knockout in mice, that results in the formation of tiny rudimentary ductal trees in the kidney (Pichel et al., 1996). This evidence concerns the gene GDNF and hypertensive disorder.