Replacement of the myotonic dystrophy type 1 CTG repeat with “non-CTG repeat” insertions in specific tissues

One of the most mutation-prone sequences is the variable number of repeating DNAs at the myotonic dystrophy (DM1) gene, causing muscular dystrophy.  In DM1 individuals the mutant gene has an expansion of a repeated DNA sequence CTG CTG CTG to hundreds or thousands of repeats.  We report a new kind of mutation at the DM1 region.  We found a DM1 individual who, in addition to an expanded repeat, also had the repeat tract completely replaced with a non-repeat DNA sequence from another chromosome.  Replacement mutations occurred only skeletal muscle and cerebellar cortex.  This non-CTG configuration expands our understanding of the sequence variations that can arise at this hypermutable site. (By Christopher E. Pearson, Ph.D., )

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