Myotonic expansion

Myotonic dystrophy (DM) is the most common form of adult muscular dystrophy. DM Type 1 caused by expansion of a CTG repeat in the 3' untranslated region of the dystrophia myotonica-protein kinase (DMPK) gene. In the August 3 Science, Christina Liquori and colleagues from the University of Minnesota report that DM2 is also caused by microsatellite expansion in non-coding sequences (Science 2001, 293:864-867). While characterizing the DM2 locus on chromosome 13q21, Liquori et al. discovered an expansion ranging from 10 to 48 kilobases in DM2 patients. The expansions consisted of 75-11,000 CCTG repeats. The expansion lies within intron 1 of the zinc finger protein 9 (ZNF9) gene. It will be important to understand how both these microsatellite repeat expansions contribute to the pathology of DM diseases.