CAST and cystic kidney disease: To evaluate a subset of dominant renal cystic disease-promoting effects associated with CAST-derived Mpkd1-2 loci, we generated Cys1cpk/cpk mice heterozygous for the CAST-derived Mpkd1-2 loci and compared their renal cystic disease severity with Cys1cpk/cpk mice homozygous for B6-derived Mpkd1-2 loci.