Somatic PKD2 mutations in individual kidney and liver cysts support a "two-hit" model of cystogenesis in type 2 autosomal dominant polycystic kidney disease.
ABSTRACT An intriguing feature of autosomal dominant polycystic kidney disease (ADPKD) is the focal and sporadic formation of renal and extrarenal cysts. Recent documentation of somatic PKD1 mutations in cystic epithelia of patients with germ-line PKD1 mutations suggests a "two-hit" model for cystogenesis in type 1 ADPKD. This study tests whether the same mechanism for cystogenesis might also occur in type 2 ADPKD. Genomic DNA was obtained from 54 kidney and liver cysts from three patients with known germ-line PKD2 mutations, using procedures that minimize contamination of cells from noncystic tissue. Using intragenic and microsatellite markers, these cyst samples were screened for loss of heterozygosity. The same samples were also screened for somatic mutations in five of the 15 exons in PKD2 by single-stranded conformational polymorphism analysis. Loss of heterozygosity was found in five cysts, and unique intragenic mutations were found in seven other cysts. In 11 of these 12 cysts, it was also determined that the somatic mutation occurred nonrandomly in the copy of PKD2 inherited from the unaffected parent. These findings support the "two-hit" model as a unified mechanism for cystogenesis in ADPKD. In this model, the requirement of a somatic mutation as the rate-limiting step for individual cyst formation has potential therapeutic implications.
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ABSTRACT: Autosomal dominant polycystic kidney disease is a common form of inherited kidney disease that is caused by mutations in two genes, PKD1 (polycystin-1) and PKD2 (polycystin-2). Mice with germline deletion of either gene die in midgestation with a vascular phenotype that includes profound edema. Although an endothelial cell defect has been suspected, the basis of this phenotype remains poorly understood. Here, we demonstrate that edema in Pkd1- and Pkd2-null mice is likely to be caused by defects in lymphatic development. Pkd1 and Pkd2 mutant embryos exhibit reduced lymphatic vessel density and vascular branching along with aberrant migration of early lymphatic endothelial cell precursors. We used cell-based assays to confirm that PKD1- and PKD2-depleted endothelial cells have an intrinsic defect in directional migration that is associated with a failure to establish front-rear polarity. Our studies reveal a role for polycystin signaling in lymphatic development.Cell Reports 04/2014; · 7.21 Impact Factor
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ABSTRACT: Polycystic liver disease (PLD) is the result of embryonic ductal plate malformation of the intrahepatic biliary tree. The phenotype consists of numerous cysts spread throughout the liver parenchyma. Cystic bile duct malformations originating from the peripheral biliary tree are called Von Meyenburg complexes (VMC). In these patients embryonic remnants develop into small hepatic cysts and usually remain silent during life. Symptomatic PLD occurs mainly in the context of isolated polycystic liver disease (PCLD) and autosomal dominant polycystic kidney disease (ADPKD). In advanced stages, PCLD and ADPKD patients have massively enlarged livers which cause a spectrum of clinical features and complications. Major complaints include abdominal pain, abdominal distension and atypical symptoms because of voluminous cysts resulting in compression of adjacent tissue or failure of the affected organ. Renal failure due to polycystic kidneys and non-renal extra-hepatic features are common in ADPKD in contrast to VMC and PCLD. In general, liver function remains prolonged preserved in PLD. Ultrasonography is the first instrument to assess liver phenotype. Indeed, PCLD and ADPKD diagnostic criteria rely on detection of hepatorenal cystogenesis, and secondly a positive family history compatible with an autosomal dominant inheritance pattern. Ambiguous imaging or screening may be assisted by genetic counseling and molecular diagnostics. Screening mutations of the genes causing PCLD (PRKCSH and SEC63) or ADPKD (PKD1 and PKD2) confirm the clinical diagnosis. Genetic studies showed that accumulation of somatic hits in cyst epithelium determine the rate-limiting step for cyst formation. Management of adult PLD is based on liver phenotype, severity of clinical features and quality of life. Conservative treatment is recommended for the majority of PLD patients. The primary aim is to halt cyst growth to allow abdominal decompression and ameliorate symptoms. Invasive procedures are required in a selective patient group with advanced PCLD, ADPKD or liver failure. Pharmacological therapy by somatostatin analogues lead to beneficial outcome of PLD in terms of symptom relief and liver volume reduction.Orphanet Journal of Rare Diseases 05/2014; 9(1):69. · 4.32 Impact Factor
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ABSTRACT: Autosomal dominant polycystic kidney disease (ADPKD) is the most common potentially lethal monogenic disorder, with more than 12 million cases worldwide. The two causative genes for ADPKD, PKD1 and PKD2, encode protein products polycystin-1 (PC1) and polycystin-2 (PC2 or TRPP2), respectively. Recent data have shed light on the role of PC1 in regulating the severity of the cystic phenotypes in ADPKD, autosomal recessive polycystic kidney disease (ARPKD), and isolated autosomal dominant polycystic liver disease (ADPLD). These studies showed that the rate for cyst growth was a regulated trait, a process that can be either sped up or slowed down by alterations in functional PC1. These findings redefine the previous understanding that cyst formation occurs as an “on-off” process. Here we review these and other related studies with an emphasis on their translational implications for polycystic diseases.Trends in Molecular Medicine 02/2014; · 9.57 Impact Factor