Myotonic Dystrophy

  • Genetics:
    • DM1: CTG trinucleotide expansion repeat in DMPK on chromosome 19
    • DM2: CCTG tetranucleotide expansion repeat in ZNF9 on chromosome 3
    • Both autosomal dominant
  • Clinical features:
    • Face: ‘myopathic facies’, ptosis, balding, dysarthria, wasting of facial muscles
    • Hands: myotonia, wasting, weakness
    • Eyes: cataracts
    • CVS: cardiomyopathy, pacemaker
    • GI: dysphagia
    • Endo: diabetes, testicular atrophy
  • Diagnosis:
    • EMG: divebomber potentials
    • Genetic testing: >50 CTG repeats = disease-causing