Defective HNF-1β target genes caused by HNF1B mutation, including polycystin (Pkd2), polyductin (Pkhd1), and uromodulin (Umod), lead to the loss of orientation of the mitotic spindles in the renal epithelial cells during tubular elongation, resulting in the formation of renal cysts (polycystic kidney disease) [31]. Here, PKD2 is linked to polycystic kidney disease.