Under pathological conditions, the FGF23 production sites include the kidney in rodent models of polycystic kidney disease (PKD) [29] and a Zucker diabetic fatty (ZDF) rat model of human type 2 diabetic nephropathy [30] and 5/6 nephrectomy [26] and the liver in diethyl-nitrosamine (DEN)-treated mice [31], patients on the Liver-Transplant Waiting List [31] at the time of liver failure, and vascular smooth muscle cells cultured in calcifying medium [24]. Here, FGF23 is linked to polycystic kidney disease.