While cystogenesis does occur in some cases in utero, a second somatic PKD1/Pkd1 mutation appears to be required in a cell for a cyst to form from clonal expansion of this cell [14], [15], [28], [29], and as at least some humans with ADPKD develop cysts in adulthood [30], [31], it is likely that the mutation continues to have a clinically significant effect beyond the fetal stage. Here, PKD1 is linked to cyst.