Analysis of repetitive regions in myotonic dystrophy type 1 and 2

Myotonic dystrophy is an autosomal dominant disorder characterized by myotonia, progressive muscle wasting, and cataracts. There are two forms identified: myotonic dystrophy type 1 (DM1), caused by an expansion of a CTG repeat in the 3' untranslated region of the myotonin-protein kinase (DMPK) gene on chromosome 19, and myotonic dystrophy type 2 (DM2), caused by an expansion of a CCTG repeat in intron 1 of the cellular nucleic acid-binding protein (CNBP) gene on chromosome 3. There is no single method that can identify all ranges of repeats in both disorders. Protocols in this unit describe the analysis of PCR-amplified CTG repeats from the DMPK gene and CCTG repeats from the CNBP gene, respectively, using a fluorescent-labeled primer followed by capillary electrophoresis. An additional protocol describes the analysis of genomic DNA by Southern blot and hybridization for DM1, while yet another describes a similar technique to analyze the repeat in DM2 using field-inversion gel electrophoresis. Both techniques identify 100% of cases of these two disorders.