PKD1 and cyst: Although all nephron segments can originate cysts including proximal tubules [25], apparently those derived from collecting ducts appear to be larger and in higher numbers than those from other segments [26], 3) Finally, it was recently demonstrated that the origin of cysts may be related with the presence of multiple PKD1 mutations that determine the severity of the disease and that cyst formation in the collecting ducts was associated with disease severity [27, 28].