title: A missense mutation in the sodium channel β1b subunit reveals SCN1B as a susceptibility gene underlying long QT syndrome.
abstract: BACKGROUND
  Long QT syndrome (LQTS) is associated with sudden cardiac death and the prolongation of the QT interval on the electrocardiogram. A comprehensive screening of all genes previously associated with this disease leaves 30% of the patients without a genetic diagnosis. Pathogenic mutations in the sodium channel β subunits have been associated with cardiac channelopathies, including SCN4B mutations in LQTS.
  
  
  OBJECTIVE
  To evaluate the role of mutations in the sodium channel β subunits in LQTS.
  
  
  METHODS
  We screened for mutations in the genes encoding the 5 sodium β subunits (SCN1B isoforms a and b, SCN2B, SCN3B, and SCN4B) from 30 nonrelated patients who were clinically diagnosed with LQTS without mutations in common LQTS-related genes. We used the patch-clamp technique to study the properties of sodium currents and the action potential duration in human embryonic kidney and HL-1 cells, respectively, in the presence of β1b subunits.
  
  
  RESULTS
  The genetic screening revealed a novel mutation in the SCN1Bb gene (β1bP213T) in an 8-year-old boy. Our electrophysiological analysis revealed that β1bP213T increases late sodium current. In addition, β1bP213T subtly altered Nav1.5 function by shifting the window current, accelerating recovery from inactivation, and decreasing the slow inactivation rate. Moreover, experiments using HL-1 cells revealed that the action potential duration significantly increases when the mutant β1b was overexpressed compared with β1bWT.
  
  
  CONCLUSIONS
  These data revealed SCN1Bb as a susceptibility gene responsible for LQTS, highlighting the importance of continuing the search for new genes and mechanisms to decrease the percentage of patients with LQTS remaining without genetic diagnosis.
authors.affiliation: Centre de Genètica Cardiovascular, Institut d'Investigació Biomèdica de Girona (IdIBGI), Girona, Catalonia, Spain; Departament de Ciències Mèdiques, Universitat de Girona (UdG), Girona, Catalonia, Spain.
authors.forename: Helena
authors.initials: H
authors.lastname: Riuró
authors.affiliation: Centre de Genètica Cardiovascular, Institut d'Investigació Biomèdica de Girona (IdIBGI), Girona, Catalonia, Spain; Departament de Ciències Mèdiques, Universitat de Girona (UdG), Girona, Catalonia, Spain.
authors.forename: Oscar
authors.initials: O
authors.lastname: Campuzano
authors.affiliation: Hospital Clínic de Barcelona, Universitat de Barcelona, Barcelona, Catalonia, Spain.
authors.forename: Elena
authors.initials: E
authors.lastname: Arbelo
authors.affiliation: Centre de Genètica Cardiovascular, Institut d'Investigació Biomèdica de Girona (IdIBGI), Girona, Catalonia, Spain; Departament de Ciències Mèdiques, Universitat de Girona (UdG), Girona, Catalonia, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Iglesias
authors.affiliation: Hospital Clínic de Barcelona, Universitat de Barcelona, Barcelona, Catalonia, Spain.
authors.forename: Montserrat
authors.initials: M
authors.lastname: Batlle
authors.affiliation: Hospital Clínic de Barcelona, Universitat de Barcelona, Barcelona, Catalonia, Spain.
authors.forename: Felix
authors.initials: F
authors.lastname: Pérez-Villa
authors.affiliation: Hospital Clínic de Barcelona, Universitat de Barcelona, Barcelona, Catalonia, Spain.
authors.forename: Josep
authors.initials: J
authors.lastname: Brugada
authors.affiliation: Centre de Genètica Cardiovascular, Institut d'Investigació Biomèdica de Girona (IdIBGI), Girona, Catalonia, Spain; Departament de Ciències Mèdiques, Universitat de Girona (UdG), Girona, Catalonia, Spain.
authors.forename: Guillermo J
authors.initials: GJ
authors.lastname: Pérez
authors.affiliation: Centre de Genètica Cardiovascular, Institut d'Investigació Biomèdica de Girona (IdIBGI), Girona, Catalonia, Spain; Departament de Ciències Mèdiques, Universitat de Girona (UdG), Girona, Catalonia, Spain.
authors.forename: Fabiana S
authors.initials: FS
authors.lastname: Scornik
authors.affiliation: Centre de Genètica Cardiovascular, Institut d'Investigació Biomèdica de Girona (IdIBGI), Girona, Catalonia, Spain; Departament de Ciències Mèdiques, Universitat de Girona (UdG), Girona, Catalonia, Spain. Electronic address: rbrugada@idibgi.org.
authors.forename: Ramon
authors.initials: R
authors.lastname: Brugada
mesh_terms: D000328:Adult; D018929:Cell Culture Techniques; D002648:Child; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D020022:Genetic Predisposition to Disease; D005820:Genetic Testing; D006801:Humans; D008133:Long QT Syndrome / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D020125:Mutation, Missense; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000235:genetics* / Q000502:physiology; D062547:Voltage-Gated Sodium Channel beta-1 Subunit / Q000235:genetics*; D055815:Young Adult
chemical_list: C470379:SCN1B protein, human; D015222:Sodium Channels; D062547:Voltage-Gated Sodium Channel beta-1 Subunit
keywords: Cardiac sodium channel; SCN1B; SCN5A; Sudden cardiac death; long QT syndrome; β subunits