Evidence for pathogenicity of atypical splice mutations in autosomal dominant polycystic kidney disease.
OBJECTIVE
Mutation-based molecular diagnostics of autosomal dominant polycystic kidney disease (ADPKD) is complicated by locus and allelic heterogeneity, large multi-exon gene structure and duplication in PKD1, and a high level of unclassified variants. Comprehensive screening of PKD1 and PKD2 by two recent studies have shown that atypical splice mutations account for 3.5% to 5% of ADPKD. We evaluated the role of bioinformatic prediction of atypical splice mutations and determined the pathogenicity of an atypical PKD2 splice variant from a multiplex ADPKD (TOR101) family.


METHODS
Using PubMed, we identified 17 atypical PKD1 and PKD2 splice mutations. We found that bioinformatics analysis was often useful for evaluating the pathogenicity of these mutations, although RT-PCR is needed to provide the definitive proof.


RESULTS
Sequencing of both PKD1 and PKD2 in an affected subject of TOR101 failed to identify a definite mutation, but revealed several UCVs, including an atypical PKD2 splice variant. Linkage analysis with microsatellite markers indicated that TOR101 was PKD2-linked and IVS8 + 5G-->A was shown to cosegregate only with affected subjects. RT-PCR of leukocyte mRNA from an affected subject using primers from exons 7 and 9 revealed six splice variants that resulted from activation of different combinations of donor and acceptor cryptic splice sites, all terminating with premature stop codons.


CONCLUSIONS
The data provide strong evidence that IVS8 + 5G-->A is a pathogenic mutation for PKD2. This case highlights the importance of functional analysis of UCVs.
Wang
Kiarong
K
Divisions of Nephrology and Genomic Medicine, University Health Network and University of Toronto, Toronto, Ontario Canada.
Zhao
Xiao
X
Chan
Shelly
S
Cil
Onur
O
He
Ning
N
Song
Xuewen
X
Paterson
Andrew D
AD
Pei
York
Y
D000328:Adult; D018389:Codon, Nonsense; D019295:Computational Biology; D004252:DNA Mutational Analysis; D005091:Exons; D005260:Female; D020022:Genetic Predisposition to Disease; D005820:Genetic Testing; D006239:Haplotypes; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging*; D008297:Male; D018895:Microsatellite Repeats; D008875:Middle Aged; D009154:Mutation; D010641:Phenotype; D016891:Polycystic Kidney, Autosomal Dominant / Q000000981:diagnostic imaging / Q000235:genetics*; D022821:RNA Splice Sites; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050396:TRPP Cation Channels / Q000235:genetics*; D014463:Ultrasonography
D018389:Codon, Nonsense; D022821:RNA Splice Sites; D050396:TRPP Cation Channels