Two clinically similar types of DM, characterized by multisystem involvement with progressive muscular weakness and atrophy, cardiomyopathy and cardiac conduction defects, as well as insulin resistance have been identified to date: DM type 1 (DM1 or Steinert’s disease) and DM type 2 (DM2), which are caused by CTG trinucleotide expansion in 3′ untranslated region of DMPK (Dystrophia Myotonica Protein Kinase) gene and by CCTG tetranucleotide expansion in intron 1 of the ZNF9/CNBP (Zinc Finger 9/Cellular Nucleic acid Binding Protein) gene, respectively. This evidence concerns the gene DMPK and Muscle weakness.