In contrast to HNF-1α, the renal-specific inactivation of HNF-1β develops polycystic kidney disease, and renal cyst formation is accompanied with a drastic defect in the transcriptional activation of several polycystic kidney disease (PKD)-related genes, such as Umod, Pkhd1, Pkd2 and Tg737/Polaris[8]. The gene discussed is HNF1B; the disease is cystic kidney disease.