Myotonic dystrophy

Myotonic dystrophy is an autosomal dominant trinucleotide repeat disorder which causes muscle weakness and myotonia

It classically presents around the age of 30.

There are 2 main types:
  • Dystrophia myotonica type 1
    • Commonest – greater than 95% of myotonic dystrophy cases
    • On chromosome 19
    • More than 50 CTG repeats
    • Weakness begins distally
  • Dystophia myotonica type 2
    • On chromosome 3, CCTG repeats
    • Weakness begins proximally
    • More benign than dystophia myotonica type 1

Features associated with myotonic dystrophy 1 include
  • Frontal balding
  • ptosis
  • Raised IgG
  • Raised CPK
  • cataracts
  • Daytime hypersomnolence
  • Testicular atrophy
  • Cardiac conduction abnormalities
  • Diabetes mellitus (5%)

There is no cure

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