title: Does cytosine-thymine-guanine (CTG) expansion size predict cardiac events and electrocardiographic progression in myotonic dystrophy?
abstract: OBJECTIVE
  To assess whether the size of the cytosine-thymine-guanine (CTG) expansion mutation in myotonic dystrophy predicts progression of conduction system disease and cardiac events.
  
  
  METHODS
  Longitudinal study involving ECG and clinical follow up over (mean (SD)) 4.8 (1.8) and 6.2 (1.9) years, respectively, of patients stratified by CTG expansion size (E0 to E4).
  
  
  METHODS
  73 adult patients under annual review in a regional myotonic dystrophy clinic. Patients were grouped into E0/E1 (n = 25), E2 (n = 34), and E3/E4 (n = 14).
  
  
  RESULTS
  The proportion of patients with a QRS complex > 100 ms at baseline increased with the size of the CTG expansion (EO/E1, 4%; E2, 12%; E3/E4, 36%; p = 0.02). This trend was more pronounced at follow up (E0/E1, 4%; E2, 21%; E3/E4, 57%; p = 0.0004). The rate of widening of the QRS complex (ms/year) was similarly related to the size of the mutation (EO/E1, 0.4 (1.3); E2, 1.4 (2.5); E3/E4, 1.5 (1.6); p = 0.04). First degree atrioventricular block was present in 23% of patients at baseline and 34% at follow up, with no significant relation to expansion size. Seven patients suffered a cardiac event during follow up (sudden death in two, permanent pacemaker insertion in three, chronic atrial arrhythmia in two), of whom six were in CTG expansion group E2 or greater. Patients who experienced a cardiac event during follow up had more rapid rates of PR interval increase (9.9 (11.1) v 1.6 (2.9) ms/year; p = 0.008) and a trend to greater QRS complex widening (3.6 (4.5) v 0.9 (1.5) ms/year; p = 0.06) than those who did not.
  
  
  CONCLUSIONS
  Larger CTG expansions are associated with a higher rate of conduction disease progression and a trend to increased risk of cardiac events in myotonic dystrophy.
authors.affiliation: Cardiology Department, John Radcliffe Hospital, Oxford Radcliffe NHS Trust, Oxford, UK. nigelra.clarke@btinternet.com
authors.forename: N R
authors.initials: NR
authors.lastname: Clarke
authors.forename: A D
authors.initials: AD
authors.lastname: Kelion
authors.forename: J
authors.initials: J
authors.lastname: Nixon
authors.forename: D
authors.initials: D
authors.lastname: Hilton-Jones
authors.forename: J C
authors.initials: JC
authors.lastname: Forfar
mesh_terms: D000328:Adult; D000368:Aged; D001145:Arrhythmias, Cardiac / Q000235:genetics* / Q000503:physiopathology / Q000628:therapy; D003596:Cytosine; D016757:Death, Sudden, Cardiac / Q000209:etiology; D017147:Defibrillators, Implantable; D018450:Disease Progression; D004452:Echocardiography / Q000379:methods; D004562:Electrocardiography / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D006147:Guanine; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics* / Q000502:physiology; D009223:Myotonic Dystrophy / Q000235:genetics* / Q000503:physiopathology; D010138:Pacemaker, Artificial; D013941:Thymine; D019680:Trinucleotide Repeat Expansion / Q000235:genetics* / Q000502:physiology
chemical_list: D006147:Guanine; D003596:Cytosine; D013941:Thymine