Evidence for this trans‐heterozygous hypothesis is the identification of somatic mutations in PKD2 in cyst DNA from patients with a PKD1 germline mutation and vice versa.15, 16 Also copy number variations (CNVs) and small pathogenic somatic mutations at various loci in the genome of cyst lining cells have been reported.17, 18 However, the contribution of these mutations to cyst initiation has not been proven. This evidence concerns the gene PKD1 and cyst.