Aberrant splicing in the PKD2 gene as a cause of polycystic kidney disease

It is estimated that approximately 15% of families with autosomal dominant polycystic kidney disease (ADPKD) have mutations in PKD2, Identification of these mutations is central to identifying functionally important regions o f gene and to understanding the mechanisms underlying the pathogenesis of t he disorder. The current study describes mutations in six type 2 ADPKD fami lies. Two single base substitution mutations discovered in the ORF in exon 14 constitute the most COOH-terminal pathogenic variants described to date. One of these mutations is a nonsense change and the other encodes an appar ent missense variant. Reverse transcription-PCR from patient. lymphoblast R NA showed that, in addition, both mutations resulted in out-of-frame splice variants by activating cryptic splice sites via different mechanisms. The apparent missense variant produced such a strong splicing signal that the p rocessed transcript from the mutant chromosome did not contain any of the n ormally spliced, missense product. A third mutation, a nonconservative miss ense change effecting a negatively charged residue in the third transmembra ne span, is likely pathogenic and defines a highly conserved residue consis tent with a potential channel subunit function for polycystin-2. The remain ing three mutations included two frame shifts resulting from deletion of on e or two bases in exons 6 and 10, respectively, and a nonsense mutation due to a single base substitution in exon 4. The study also defined a novel-in tragenic polymorphism in exon 1 that will be useful in analyzing "second hi ts" in PKD2. Finally, the study demonstrates that there are reduced levels of normal polycystin-2 protein in lymphoblast lines from PKD2-affected indi viduals and that truncated mutant polycystin-2, cannot be detected in patie nt lymphoblasts, suggesting that the latter may be unstable in at least som e tissues. The mutations described will serve as critical reagents for futu re functional studies in PKD2.