title: Transcriptional complexity in autosomal recessive polycystic kidney disease.
abstract: OBJECTIVE
  Autosomal recessive polycystic kidney disease (ARPKD) is caused by mutations in the PKHD1 gene. The longest open reading frame comprises 66 exons encoding polyductin or fibrocystin, a type I transmembrane protein with 4074 amino acids. Functional investigations are considerably hampered by its large size and lack of expression in tissues that are usually available for analysis such as lymphocytes or fibroblasts.
  
  
  METHODS
  Allegedly strong and clear-cut genotype-phenotype correlations for the type of PKHD1 mutation could be established. Thus far, practically all patients with two truncating mutations showed perinatal or neonatal demise and at least one hypomorphic missense mutation is thought to be indispensable for survival. Mutation analysis of >500 ARPKD families was performed by conventional and next-generation sequencing techniques.
  
  
  RESULTS
  This study presents four unrelated patients with ARPKD with a nonlethal, moderate clinical course despite the burden of two PKHD1 mutations expected to lead to premature termination of translation. In line with parental consanguinity, all mutations occurred in the homozygous state and segregated with the disorder in these families. To try to unravel the mechanisms that underlie this obvious contradiction, these patients were further analyzed in detail by utilizing different methods. In all cases, complex transcriptional alterations were detected. Alternative splicing patterns might disrupt a critical stoichiometric and temporal balance between different protein products and may play a crucial role in defining the phenotype of these patients.
  
  
  CONCLUSIONS
  Although these findings represent rare events, they are of importance for genetic counseling and illustrate that some caution is warranted in the interpretation of mutations and their clinical significance. The authors hypothesize that expression of a minimal amount of functional protein is needed for survival of the neonatal period in ARPKD.
authors.affiliation: Center for Human Genetics, Bioscientia, Ingelheim, Germany;
authors.forename: Valeska
authors.initials: V
authors.lastname: Frank
authors.affiliation: Department of Human Genetics, RWTH Aachen University, Aachen, Germany; and.
authors.forename: Klaus
authors.initials: K
authors.lastname: Zerres
authors.affiliation: Center for Human Genetics, Bioscientia, Ingelheim, Germany; Department of Human Genetics, RWTH Aachen University, Aachen, Germany; and Renal Division, Department of Medicine, University Freiburg Medical Center, Freiburg, Germany carsten.bergmann@bioscientia.de carsten.bergmann@uniklinik-freiburg.de.
authors.forename: Carsten
authors.initials: C
authors.lastname: Bergmann
mesh_terms: D000818:Animals; D019556:COS Cells; D002648:Child; D002675:Child, Preschool; D002522:Chlorocebus aethiops; D019295:Computational Biology; D003241:Consanguinity; D004252:DNA Mutational Analysis; D018450:Disease Progression; D005091:Exons; D005260:Female; D005786:Gene Expression Regulation; D056726:Genetic Association Studies; D020022:Genetic Predisposition to Disease; D006720:Homozygote; D006801:Humans; D008297:Male; D009154:Mutation; D010375:Pedigree; D010641:Phenotype; D017044:Polycystic Kidney, Autosomal Recessive / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism / Q000628:therapy; D011379:Prognosis; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: C451750:PKHD1 protein, human; D011956:Receptors, Cell Surface
keywords: ADPKD; clinical nephrology; cystic kidney; kidney disease; pediatric nephrology; polycystic
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