The proliferative capacity—as required for the assay, which leads to structures of 8–20 cells deriving from a single UREC within the 6-day period—was observed in preparations of only a limited number of patients: 6 participants with ARPKD, 2 with NPH (both carrying a homozygous NPHP1 deletion) and 3 displaying a Bardet Biedl syndrome (with variants of BBS4 and BBS7). This evidence concerns the gene BBS4 and autosomal recessive polycystic kidney disease.