Since the relative intensity of the two RT-PCR bands (499 bp and 452 bp), corresponding to PKHD1 transcripts A and B, is different between control and ARPKD cells (Fig. 2b), we hypothesised that alternate splicing of exon 43 occurs at a basal level, but is promoted by the synonymous change p.(Asn2300=). This evidence concerns the gene PKHD1 and autosomal recessive polycystic kidney disease.