title: Nonsense-mediated mRNA decay caused by a frameshift mutation in a large kindred of type 2 long QT syndrome.
abstract: BACKGROUND
  Nonsense and frameshift mutations are common in congenital long QT syndrome type 2 (LQT2). We previously demonstrated that hERG nonsense mutations cause degradation of mutant mRNA by nonsense-mediated mRNA decay (NMD) and are associated with mild clinical phenotypes. The impact of NMD on the expression of hERG frameshift mutations and their phenotypic severity is not clear.
  
  
  OBJECTIVE
  The purpose of this study was to examine the role of NMD in the pathogenesis of a hERG frameshift mutation, P926AfsX14, identified in a large LQT2 kindred and characterize genotype-phenotype correlations.
  
  
  METHODS
  Genetic screening was performed among family members. Phenotyping was performed by assessment of ECGs and LQTS-related cardiac events. The functional effect of P926AfsX14 was studied using hERG cDNA and minigene constructs expressed in HEK293 cells.
  
  
  RESULTS
  Significant cardiac events occurred in carriers of the P926AfsX14 mutation. When expressed from cDNA, the P926AfsX14 mutant channel was only mildly defective. However, when expressed from a minigene, the P926AfsX14 mutation caused a significant reduction in mutant mRNA, protein, and hERG current. Inhibition of NMD by RNA interference knockdown of up-frameshift protein 1 partially restored expression of mutant mRNA and protein and led to a significant increase in hERG current in the mutant cells. These results suggest that NMD is involved in the pathogenic mechanism of the P926AfsX14 mutation.
  
  
  CONCLUSIONS
  Our findings suggest that the hERG frameshift mutation P926AfsX14 primarily results in degradation of mutant mRNA by the NMD pathway rather than production of truncated proteins. When combined with environmental triggers and genetic modifiers, LQT2 frameshift mutations associated with NMD can manifest with a severe clinical phenotype.
authors.affiliation: Division of Cardiovascular Medicine, Department of Medicine, Oregon Health & Science University, Portland, Oregon, USA.
authors.forename: Ignatius Gerardo
authors.initials: IG
authors.lastname: Zarraga
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Stump
authors.forename: Qiuming
authors.initials: Q
authors.lastname: Gong
authors.forename: G Michael
authors.initials: GM
authors.lastname: Vincent
authors.forename: Zhengfeng
authors.initials: Z
authors.lastname: Zhou
mesh_terms: D018076:DNA, Complementary / Q000235:genetics; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics; D005260:Female; D016368:Frameshift Mutation; D056726:Genetic Association Studies; D057809:HEK293 Cells; D006801:Humans; D015151:Immunoblotting; D008133:Long QT Syndrome / Q000235:genetics*; D008297:Male; D059365:Nonsense Mediated mRNA Decay / Q000235:genetics*; D018408:Patch-Clamp Techniques; D010375:Pedigree; D017853:Phosphotransferases (Alcohol Group Acceptor)
chemical_list: D018076:DNA, Complementary; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D017853:Phosphotransferases (Alcohol Group Acceptor); C063242:hygromycin-B kinase