title: TPM3 deletions cause a hypercontractile congenital muscle stiffness phenotype.
abstract: OBJECTIVE
  Mutations in TPM3, encoding Tpm3.12, cause a clinically and histopathologically diverse group of myopathies characterized by muscle weakness. We report two patients with novel de novo Tpm3.12 single glutamic acid deletions at positions ΔE218 and ΔE224, resulting in a significant hypercontractile phenotype with congenital muscle stiffness, rather than weakness, and respiratory failure in one patient.
  
  
  METHODS
  The effect of the Tpm3.12 deletions on the contractile properties in dissected patient myofibers was measured. We used quantitative in vitro motility assay to measure Ca(2+) sensitivity of thin filaments reconstituted with recombinant Tpm3.12 ΔE218 and ΔE224.
  
  
  RESULTS
  Contractility studies on permeabilized myofibers demonstrated reduced maximal active tension from both patients with increased Ca(2+) sensitivity and altered cross-bridge cycling kinetics in ΔE224 fibers. In vitro motility studies showed a two-fold increase in Ca(2+) sensitivity of the fraction of filaments motile and the filament sliding velocity concentrations for both mutations.
  
  
  CONCLUSIONS
  These data indicate that Tpm3.12 deletions ΔE218 and ΔE224 result in increased Ca(2+) sensitivity of the troponin-tropomyosin complex, resulting in abnormally active interaction of the actin and myosin complex. Both mutations are located in the charged motifs of the actin-binding residues of tropomyosin 3, thus disrupting the electrostatic interactions that facilitate accurate tropomyosin binding with actin necessary to prevent the on-state. The mutations destabilize the off-state and result in excessively sensitized excitation-contraction coupling of the contractile apparatus. This work expands the phenotypic spectrum of TPM3-related disease and provides insights into the pathophysiological mechanisms of the actin-tropomyosin complex.
authors.affiliation: National Institutes of Health, Neuromuscular and Neurogenetic Disorders of Childhood Section, Bethesda, MD, USA.
authors.forename: S
authors.initials: S
authors.lastname: Donkervoort
authors.affiliation: National Heart and Lung Institute, Imperial College London, London, UK.
authors.forename: M
authors.initials: M
authors.lastname: Papadaki
authors.affiliation: Department of Physiology, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: J M
authors.initials: JM
authors.lastname: de Winter
authors.affiliation: National Institutes of Health, Neuromuscular and Neurogenetic Disorders of Childhood Section, Bethesda, MD, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Neu
authors.affiliation: Department of Neuropediatrics and Muscle Disorders, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Kirschner
authors.affiliation: National Institutes of Health, Neuromuscular and Neurogenetic Disorders of Childhood Section, Bethesda, MD, USA.
authors.forename: V
authors.initials: V
authors.lastname: Bolduc
authors.affiliation: University of Colorado School of Medicine, Department of Pediatrics and Neurology, Section of Child Neurology, Aurora, CO, USA.
authors.forename: M L
authors.initials: ML
authors.lastname: Yang
authors.affiliation: University of Colorado Denver School of Medicine, Aurora, CO, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Gibbons
authors.affiliation: National Institutes of Health, Neuromuscular and Neurogenetic Disorders of Childhood Section, Bethesda, MD, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Hu
authors.affiliation: National Institutes of Health, Neuromuscular and Neurogenetic Disorders of Childhood Section, Bethesda, MD, USA.
authors.forename: J
authors.initials: J
authors.lastname: Dastgir
authors.affiliation: National Institutes of Health, Neuromuscular and Neurogenetic Disorders of Childhood Section, Bethesda, MD, USA.|Children's National Health System, Washington DC, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Leach
authors.affiliation: Kaiser SCPMG, Cure CMD, P.O. Box 701, Olathe, KS 66051, USA.
authors.forename: A
authors.initials: A
authors.lastname: Rutkowski
authors.affiliation: National Institutes of Health, Neuromuscular and Neurogenetic Disorders of Childhood Section, Bethesda, MD, USA.
authors.forename: A R
authors.initials: AR
authors.lastname: Foley
authors.affiliation: Department of General Pediatrics, Adolescent Medicine and Neonatology, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Krüger
authors.affiliation: Department of Pathology, Children's Hospital Colorado, Aurora, Colorado, USA.
authors.forename: E P
authors.initials: EP
authors.lastname: Wartchow
authors.affiliation: Neuromuscular Diseases Laboratory, Centre for Medical Research, Faculty of Medicine, Dentistry and Health Sciences, The University of Western Australia Crawley, WA, Australia.
authors.forename: E
authors.initials: E
authors.lastname: McNamara
authors.affiliation: Neuromuscular Diseases Laboratory, Centre for Medical Research, Faculty of Medicine, Dentistry and Health Sciences, The University of Western Australia Crawley, WA, Australia.
authors.forename: R
authors.initials: R
authors.lastname: Ong
authors.affiliation: National Institutes of Health, Neuromuscular and Neurogenetic Disorders of Childhood Section, Bethesda, MD, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Nowak
authors.affiliation: Centre for Medical Research, University of Western Australia, Harry Perkins Institute of Medical Research, QEII Medical Centre, Perth, Western Australia, Australia.
authors.forename: N G
authors.initials: NG
authors.lastname: Laing
authors.affiliation: Institute for Neuroscience and Muscle Research, The Children's Hospital at Westmead, University of Sydney, Sydney, Australia.
authors.forename: N F
authors.initials: NF
authors.lastname: Clarke
authors.affiliation: Department of Physiology, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Cac
authors.initials: C
authors.lastname: Ottenheijm
authors.affiliation: National Heart and Lung Institute, Imperial College London, London, UK.
authors.forename: S B
authors.initials: SB
authors.lastname: Marston
authors.affiliation: National Institutes of Health, Neuromuscular and Neurogenetic Disorders of Childhood Section, Bethesda, MD, USA.
authors.forename: C G
authors.initials: CG
authors.lastname: Bönnemann
mesh_terms: D002675:Child, Preschool; D059472:Exome; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D009135:Muscular Diseases / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology; D009154:Mutation; D010641:Phenotype; D012131:Respiratory Insufficiency; D017384:Sequence Deletion; D014335:Tropomyosin / Q000235:genetics*
chemical_list: C498783:TPM3 protein, human; D014335:Tropomyosin