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A loss-of-function model for cystogenesis in human autosomal dominant polycystic kidney disease type 2
R Torra1, C Badenas, J L San Millán
1Department of Nephrology, Hospital Clínic, 08036 Barcelona, Spain. rtorra@medicina.ub.es
Abstract:
Autosomal dominant polycystic kidney disease (ADPKD) is genetically heterogeneous, with at least three chromosomal loci (PKD1, PKD2, and PKD3) that account for the disease. Mutations in the PKD2 gene, on the long arm of chromosome 4, are expected to be responsible for approximately 15% of cases of ADPKD. Although ADPKD is a systemic disease, it shows a focal expression, because <1% of nephrons become cystic. A feasible explanation for the focal nature of events in PKD1, proposed on the basis of the two-hit theory, suggests that cystogenesis results from the inactivation of the normal copy of the PKD1 gene by a second somatic mutation. The aim of this study is to demonstrate that somatic mutations are present in renal cysts from a PKD2 kidney. We have studied 30 renal cysts from a patient with PKD2 in which the germline mutation was shown to be a deletion that encompassed most of the disease gene. Loss-of-heterozygosity (LOH) studies showed loss of the wild-type allele in 10% of cysts. Screening of six exons of the gene by SSCP detected eight different somatic mutations, all of them expected to produce truncated proteins. Overall, >/=37% of the cysts studied presented somatic mutations. No LOH for the PKD1 gene or locus D3S1478 were observed in those cysts, which demonstrates that somatic alterations are specific. We have identified second-hit mutations in human PKD2 cysts, which suggests that this mechanism could be a crucial event in the development of cystogenesis in human ADPKD-type 2.
Insights
Somatic mutations, or second-hit mutations, were found in over 37% of renal cysts from Autosomal Dominant Polycystic Kidney Disease (ADPKD) type 2 patients, suggesting a key role in cyst development.
Area of Science:
- Genetics
- Nephrology
- Molecular Biology
Background:
- Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder affecting the kidneys.
- Mutations in the PKD2 gene cause approximately 15% of ADPKD cases.
- ADPKD exhibits focal expression, with less than 1% of nephrons developing cysts.
Purpose of the Study:
- To investigate the presence of somatic mutations in renal cysts from patients with PKD2 gene mutations.
- To determine if a "second-hit" mechanism contributes to cystogenesis in ADPKD type 2.
Main Methods:
- Analysis of 30 renal cysts from a patient with a germline PKD2 deletion.
- Loss-of-heterozygosity (LOH) studies to detect loss of the wild-type allele.
- Screening of PKD2 gene exons using Single-Strand Conformation Polymorphism (SSCP) to identify somatic mutations.
Main Results:
- Loss of the wild-type allele (LOH) was observed in 10% of the analyzed cysts.
- SSCP analysis identified eight distinct somatic mutations in the PKD2 gene across the cysts.
- Over 37% of the studied renal cysts exhibited somatic mutations, many predicted to produce truncated proteins.
- No LOH for the PKD1 gene or locus D3S1478 was detected, indicating specificity of the somatic alterations.
Conclusions:
- Second-hit somatic mutations in the PKD2 gene were identified in human ADPKD type 2 renal cysts.
- These somatic mutations are likely a crucial event in the development of cystogenesis in ADPKD type 2.
- The findings support the two-hit theory for cyst formation in ADPKD.