These early affected ADPKD patients are sometimes clinically indistinguishable from the recessive form ARPKD with mutations in PKHD1. Although much rarer, several further phenocopies are known and mutations in HNF1B (as a master regulator with a major effect on many cystic kidney disease genes) or genes that typically cause other ciliopathies with extrarenal features such as nephronophthisis (NPH) and Bardet-Biedl syndrome (BBS) can mimic PKD especially in the prenatal setting and early childhood [12]. The gene discussed is HNF1B; the disease is Bardet-Biedl syndrome.