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Splicing mutations of the polycystic kidney disease 1 (PKD1) gene induced by intronic deletion
B Peral1, V Gamble, J L San Millán
1MRC Molecular Haematology Unit, John Radcliffe Hospital, Oxford, UK.
Insights
Two novel mutations in the polycystic kidney disease 1 (PKD1) gene cause aberrant splicing in autosomal dominant polycystic kidney disease (ADPKD). These deletions lead to altered gene transcripts, potentially explaining disease development.
Area of Science:
- Genetics
- Molecular Biology
- Nephrology
Background:
- Autosomal dominant polycystic kidney disease (ADPKD) is a prevalent genetic disorder leading to kidney failure.
- The primary gene implicated in ADPKD, polycystic kidney disease 1 (PKD1), has been recently identified.
- Understanding the genetic basis and molecular mechanisms of ADPKD is crucial for developing effective treatments.
Purpose of the Study:
- To investigate mutations within the PKD1 gene to elucidate the etiology of ADPKD.
- To characterize the mechanism and consequences of identified mutations in the PKD1 gene.
- To explore the potential phenotypic implications of aberrant gene splicing in ADPKD patients.
Main Methods:
- Analysis of three specific regions within the 3' portion of the PKD1 gene.
- Identification and characterization of DNA deletions within a 75 bp intron.
- Assessment of splice site integrity and analysis of resulting RNA transcripts using molecular techniques.
Main Results:
- Two distinct mutations, involving deletions of 18 or 20 bp within the same intron, were identified in the PKD1 gene.
- These deletions, despite not affecting canonical splice sites, resulted in aberrant splicing.
- Two different aberrant transcripts were produced: one retaining the deleted intron and another with a 66 bp deletion due to cryptic splice site activation; no normal transcript was generated.
Conclusions:
- The identified deletions likely impair spliceosome assembly at authentic splice sites due to the intron's reduced size, leading to aberrant splicing.
- A 9 bp direct repeat within the intron may have facilitated these deletions through sequence misalignment.
- The production of multiple aberrant PKD1 transcripts may contribute to the phenotypic variability observed in ADPKD.
Abstract:
Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disease which frequently results in renal failure. The major ADPKD gene, polycystic kidney disease 1 (PKD1), has recently been identified. In an attempt to understand better the aetiology of this disorder we have searched for mutations in the PKD1 gene. Analysis of three regions in the 3' part of the gene has revealed two mutations that occur by a novel mechanism. Both mutations are deletions (of 18 or 20 bp) within the same 75 bp intron and although these deletions do not disrupt the splice donor or acceptor sites at the boundary of the intron, they nevertheless result in aberrant splicing. Two different transcripts are produced in each case; one includes the deleted intron while the other has a 66 bp deletion due to activation of a cryptic 5' splice site. No normal product is generated from the deleted gene. Aberrant splicing probably occurs because the deleted intron is too small for spliceosome assembly using the authentic splice sites; this mechanism has previously only been described from in vitro studies of vertebrate genes. A 9 bp direct repeat has been identified within the intron, which probably facilitated deletion by promoting misalignment of sequence. The possible phenotypic implications of producing more than one aberrant PKD1 transcript in these cases are discussed.