The development of renal cysts in mice deficient for the Vhl tumor suppressor gene can be repressed by genetic inactivation of the Hif dimerization partner Hif-1β (Arnt) but not Hif-1α; thus suggesting a causal role for Hif-2α in renal cyst development (Rankin et al., 2006). Here, ARNT is linked to cystic kidney disease.