News on the diagnosis of myotonic dystrophy

Myotonic dystrophy (DM; OMIM 160900) is the most common genetically transmitted neuromuscular disorder in adults. It is an autosomal dominant multisystemic disease characterized by myotonia and progressive muscle weakness. The mutation is an expansion of an unstable cytosine-thymine-guanine (CTG) trinucleotide repeat in the 3' untranslated region of the DMPK gene in chromosome 19q13.3. In recent years, some autosomal dominant multisystemic disorders similar to DM without CTC repeat expansion at the DM locus (PROMM, PDM, DM2) have been described. In conclusion, recent genetic findings and clinical observations have highlighted a genetic and phenotypic heterogeneity in myotonic myopathies which has led to the updated nomenclature of multisystemic disorders presented in this paper.