Neuromuscular disorder characterized by PROGRESSIVE muscular atrophy; myotonia, and various multisystem atrophies. Mild intellectual disability may also occur. Abnormal trinucleotide repeat expansion in the 3' untranslated regions of DMPK PROTEIN gene is associated with myotonic dystrophy 1. dna repeat expansion of zinc finger protein-9 gene intron is associated with myotonic dystrophy 2.