Molecular genetics of myotonic dystrophy

Antonio Pizzuti, Giuseppe Novelli, Bruno Dallapiccola

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The myotonic dystrophy (DM) gene was mapped on the long arm of chromosome 19. It codes for a senne/threonine protein kinase whose function is still disputed. The DM gene contains an AGC triplet repeat in the 3' transcribed but untranslated region (UTR). The repeat is polymorphic ia the general population with allele length from 5 to about 50 AGC units. In DM the mutated allele demonstrates an increased repeat length, up to several thousands. The expression variability observed in DM depends on the length of the mutated alleles. In general, the longer the repeat the worse the clinical outcome. Mutated repeats appear very unstable and tend to change their length through generations of the same family. This progressive repeat lengthening corresponds to the clinical phenomenon of anticipation. In most DM families the disease increases its clinical features along with the lengthening of the triplet repeat. Somatic mosaicism is evident in DM patients. The repeat varies its length in different tissues of the same individual, some tissues expanding more than others. Interestingly, sperm cells cannot bear expansions longer than 1000 AGCs, usually associated to congenital DM, explaining the exclusive maternal transmission of this DM form. Direct molecular diagnosis of DM is possible by triplet counting m probands, by either Southern blotting of genomic DNA, or PCR through the repeated region itself.

Original languageEnglish
JournalNuova Rivista di Neurologia
Issue number3
Publication statusPublished - May 1996


  • Myotonic dystrophy
  • Myotonin
  • Triplet repeat

ASJC Scopus subject areas

  • Clinical Neurology

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