On a cellular level, these include: the developmental timing of PKD1 inactivation (45, 46); reduction in functional PC1 dosage (38, 47, 48); differences in sensitivity to PC1 dosage (48); and the proximity effect, where a cystic cell or nephron creates a “snowball effect” triggering cyst development in neighboring cells or nephrons (49). This evidence concerns the gene PKD1 and cyst.