title: A novel gain-of-function KCNJ2 mutation associated with short-QT syndrome impairs inward rectification of Kir2.1 currents.
abstract: OBJECTIVE
  Short-QT syndrome (SQTS) is a recently recognized disorder associated with atrial fibrillation (AF) and sudden death due to ventricular arrhythmias. Mutations in several ion channel genes have been linked to SQTS; however, the mechanism remains unclear. This study describes a novel heterozygous gain-of-function mutation in the inward rectifier potassium channel gene, KCNJ2, identified in SQTS.
  
  
  RESULTS
  We studied an 8-year-old girl with a markedly short-QT interval (QT = 172 ms, QTc = 194 ms) who suffered from paroxysmal AF. Mutational analysis identified a novel heterozygous KCNJ2 mutation, M301K. Functional assays displayed no Kir2.1 currents when M301K channels were expressed alone. However, co-expression of wild-type (WT) with M301K resulted in larger outward currents than the WT at more than -30 mV. These results suggest a gain-of-function type modulation due to decreased inward rectification. Furthermore, we analysed the functional significance of the amino acid charge at M301 (neutral) by changing the residue. As with M301K, in M301R (positive), the homozygous channels were non-functional, whereas the heterozygous channels demonstrated decreased inward rectification. Meanwhile, the currents recorded in M301A (neutral) showed normal inward rectification under both homo- and heterozygous conditions. Heterozygous overexpression of WT and M301K in neonatal rat ventricular myocytes exhibited markedly shorter action potential durations than the WT alone.
  
  
  CONCLUSIONS
  In this study, we identified a novel KCNJ2 gain-of-function mutation, M301K, associated with SQTS. Functional assays revealed no functional currents in the homozygous channels, whereas impaired inward rectification demonstrated under the heterozygous condition resulted in larger outward currents, which is a novel mechanism predisposing SQTS.
authors.affiliation: Department of Cardiovascular Medicine,  Kyoto University Graduate School of Medicine, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507,  Japan.
authors.forename: Tetsuhisa
authors.initials: T
authors.lastname: Hattori
authors.forename: Takeru
authors.initials: T
authors.lastname: Makiyama
authors.forename: Masaharu
authors.initials: M
authors.lastname: Akao
authors.forename: Eiji
authors.initials: E
authors.lastname: Ehara
authors.forename: Seiko
authors.initials: S
authors.lastname: Ohno
authors.forename: Moritake
authors.initials: M
authors.lastname: Iguchi
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Nishio
authors.forename: Kenichi
authors.initials: K
authors.lastname: Sasaki
authors.forename: Hideki
authors.initials: H
authors.lastname: Itoh
authors.forename: Masayuki
authors.initials: M
authors.lastname: Yokode
authors.forename: Toru
authors.initials: T
authors.lastname: Kita
authors.forename: Minoru
authors.initials: M
authors.lastname: Horie
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kimura
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002478:Cells, Cultured; D002648:Child; D004562:Electrocardiography; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D057809:HEK293 Cells; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D008151:Lown-Ganong-Levine Syndrome / Q000235:genetics* / Q000503:physiopathology*; D023421:Models, Animal; D009154:Mutation / Q000235:genetics*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000502:physiology; D018408:Patch-Clamp Techniques; D010375:Pedigree; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics* / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D014162:Transfection
chemical_list: C489457:KCNJ2 protein, human; C489461:Kir2.1 channel; D024661:Potassium Channels, Inwardly Rectifying