title: Genetic, cell biological, and clinical interrogation of the CFTR mutation c.3700 A>G (p.Ile1234Val) informs strategies for future medical intervention.
abstract: OBJECTIVE
  The purpose of this study was to determine the molecular consequences of the variant c.3700 A>G in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, a variant that has been predicted to cause a missense mutation in the CFTR protein (p.Ile1234Val).
  
  
  METHODS
  Clinical assays of CFTR function were performed, and genomic DNA from patients homozygous for c.3700 A>G and their family members was sequenced. Total RNA was extracted from epithelial cells of the patients, transcribed into complementary DNA, and sequenced. CFTR complementary DNA clones containing the missense mutation p.Ile1234Val or a truncated exon 19 (p.Ile1234_Arg1239del) were constructed and heterologously expressed to test CFTR protein synthesis and processing.
  
  
  RESULTS
  In vivo functional measurements revealed that the individuals homozygous for the variant c.3700 A>G exhibited defective CFTR function. We show that this mutation in exon 19 activates a cryptic donor splice site 18 bp upstream of the original donor splice site, resulting in deletion of six amino acids (r.3700_3717del; p.Ile1234_Arg1239del). This deletion, similar to p.Phe508del, causes a primary defect in folding and processing. Importantly, Lumacaftor (VX-809), currently in clinical trial for cystic fibrosis patients with the major cystic fibrosis-causing mutation, p.Phe508del, partially ameliorated the processing defect caused by p.Ile1234_Arg1239del.
  
  
  CONCLUSIONS
  These studies highlight the need to verify molecular and clinical consequences of CFTR variants to define possible therapeutic strategies.
authors.affiliation: 1] Programme in Molecular Structure and Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada [2] Department of Biochemistry, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Steven V
authors.initials: SV
authors.lastname: Molinski
authors.affiliation: 1] Programme in Physiology and Experimental Medicine, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada [2] Department of Pediatrics, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Tanja
authors.initials: T
authors.lastname: Gonska
authors.affiliation: Programme in Molecular Structure and Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Ling Jun
authors.initials: LJ
authors.lastname: Huan
authors.affiliation: Department of Immunology, Genetics and Pathology, The Rudbeck Laboratory, Uppsala University, Uppsala, Sweden.
authors.forename: Berivan
authors.initials: B
authors.lastname: Baskin
authors.affiliation: Section of Pediatric Pulmonology, Department of Pediatrics, Hamad Medical Corporation, Doha, Qatar.
authors.forename: Ibrahim A
authors.initials: IA
authors.lastname: Janahi
authors.affiliation: 1] Programme in Genetics and Genomic Biology, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada [2] Department of Molecular Genetics, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Peter N
authors.initials: PN
authors.lastname: Ray
authors.affiliation: 1] Programme in Molecular Structure and Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada [2] Department of Biochemistry, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada [3] Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Christine E
authors.initials: CE
authors.lastname: Bear
mesh_terms: D000293:Adolescent; D000328:Adult; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D052117:Benzodioxoles / Q000494:pharmacology; D002460:Cell Line; D006224:Cricetinae; D003550:Cystic Fibrosis / Q000188:drug therapy / Q000235:genetics*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics* / Q000378:metabolism*; D005091:Exons; D057809:HEK293 Cells; D006720:Homozygote; D006801:Humans; D007532:Isoleucine / Q000378:metabolism*; D008297:Male; D020125:Mutation, Missense; D011780:Qatar; D012326:RNA Splicing; D014633:Valine / Q000378:metabolism*
chemical_list: D000631:Aminopyridines; D052117:Benzodioxoles; C505032:CFTR protein, human; D007532:Isoleucine; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; C569105:lumacaftor; D014633:Valine