title: Spectrum and Prevalence of CALM1-, CALM2-, and CALM3-Encoded Calmodulin Variants in Long QT Syndrome and Functional Characterization of a Novel Long QT Syndrome-Associated Calmodulin Missense Variant, E141G.
abstract: BACKGROUND
  Calmodulin (CaM) is encoded by 3 genes, CALM1, CALM2, and CALM3, all of which harbor pathogenic variants linked to long QT syndrome (LQTS) with early and severe expressivity. These LQTS-causative variants reduce CaM affinity to Ca(2+) and alter the properties of the cardiac L-type calcium channel (CaV1.2). CaM also modulates NaV1.5 and the ryanodine receptor, RyR2. All these interactions may play a role in disease pathogenesis. Here, we determine the spectrum and prevalence of pathogenic CaM variants in a cohort of genetically elusive LQTS, and functionally characterize the novel variants.
  
  
  RESULTS
  Thirty-eight genetically elusive LQTS cases underwent whole-exome sequencing to identify CaM variants. Nonsynonymous CaM variants were over-represented significantly in this heretofore LQTS cohort (13.2%) compared with exome aggregation consortium (0.04%; P<0.0001). When the clinical sequelae of these 5 CaM-positive cases were compared with the 33 CaM-negative cases, CaM-positive cases had a more severe phenotype with an average age of onset of 10 months, an average corrected QT interval of 676 ms, and a high prevalence of cardiac arrest. Functional characterization of 1 novel variant, E141G-CaM, revealed an 11-fold reduction in Ca(2+)-binding affinity and a functionally dominant loss of inactivation in CaV1.2, mild accentuation in NaV1.5 late current, but no effect on intracellular RyR2-mediated calcium release.
  
  
  CONCLUSIONS
  Overall, 13% of our genetically elusive LQTS cohort harbored nonsynonymous variants in CaM. Genetic testing of CALM1-3 should be pursued for individuals with LQTS, especially those with early childhood cardiac arrest, extreme QT prolongation, and a negative family history.
authors.affiliation: Department Molecular Pharmacology & Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN.
authors.forename: Nicole J
authors.initials: NJ
authors.lastname: Boczek
authors.affiliation: Department of Medicine, Vanderbilt University, Nashville, TN.
authors.forename: Nieves
authors.initials: N
authors.lastname: Gomez-Hurtado
authors.affiliation: Department Molecular Pharmacology & Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN.
authors.forename: Dan
authors.initials: D
authors.lastname: Ye
authors.affiliation: Department Molecular Pharmacology & Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN.
authors.forename: Melissa L
authors.initials: ML
authors.lastname: Calvert
authors.affiliation: Department Molecular Pharmacology & Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN.
authors.forename: David J
authors.initials: DJ
authors.lastname: Tester
authors.affiliation: Department of Medicine, Vanderbilt University, Nashville, TN.
authors.forename: Dmytro
authors.initials: D
authors.lastname: Kryshtal
authors.affiliation: Department of Medicine, Vanderbilt University, Nashville, TN.
authors.forename: Hyun Seok
authors.initials: HS
authors.lastname: Hwang
authors.affiliation: Departments of Biochemistry & Chemistry and Center for Structural Biology, Vanderbilt University, Nashville, TN.
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Johnson
authors.affiliation: Departments of Biochemistry & Chemistry and Center for Structural Biology, Vanderbilt University, Nashville, TN.
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Chazin
authors.affiliation: Department Molecular Pharmacology & Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN.|Mayo Medical School, Mayo Clinic, Rochester, MN.
authors.forename: Christina G
authors.initials: CG
authors.lastname: Loporcaro
authors.affiliation: Children's Hospital of Philadelphia, Philadelphia, PA.
authors.forename: Maully
authors.initials: M
authors.lastname: Shah
authors.affiliation: Department of Pediatric Cardiology, Phoenix Children's Hospital, Phoenix, AZ.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Papez
authors.affiliation: Department of Pediatrics, Division of Pediatric Cardiology, University of Alabama at Birmingham, Birmingham, AL.
authors.forename: Yung R
authors.initials: YR
authors.lastname: Lau
authors.affiliation: Division of Cardiology, Nicklaus Children's Hospital, Miami, FL.
authors.forename: Ronald
authors.initials: R
authors.lastname: Kanter
authors.affiliation: Department of Medicine, Vanderbilt University, Nashville, TN.
authors.forename: Bjorn C
authors.initials: BC
authors.lastname: Knollmann
authors.affiliation: Department Molecular Pharmacology & Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN.|Department of Medicine, Division of Cardiovascular Diseases, Mayo Clinic, Rochester, MN.|Department of Pediatrics, Division of Pediatric Cardiology, Mayo Clinic, Rochester, MN.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ackerman
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002147:Calmodulin / Q000737:chemistry / Q000235:genetics*; D003710:Demography; D005260:Female; D006801:Humans; D008133:Long QT Syndrome / Q000235:genetics*; D008297:Male; D008810:Mice, Inbred C57BL; D020125:Mutation, Missense / Q000235:genetics*; D015995:Prevalence; D055815:Young Adult
chemical_list: D002147:Calmodulin
keywords: L-type calcium channels; calmodulin; long QT syndrome; ryanodine receptor; sodium channels