PKD1 and cystic kidney disease: Previous studies have suggested that a decrease in Pkd1 expression levels below a critical threshold can lead to the formation of renal cysts and other clinical signs of ADPKD.[33] Transfer of Pkd1/2 through the germ line to Pkd1 null mice may be effective, for Pkd1/2 conditionally inactivated at weeks 4-6.