Myotonic dystrophy

Disease class: Muscular dystrophies

Disease class: Myotonic disorders

Genetics

• In DM1, there is an expansion of the cytosine-thymine-guanine (CTG) triplet repeat in the DMPK gene.
• Genetic anticipation 
• DM2 is caused by a defect of the CNBP gene on chromosome 3. The specific defect is a repeat of the cytosine-cytosine-thymine-guanosine (CCTG) tetranucleotide in the CNBP gene. As it involves the repeat of four nucleotides, it is not a trinucleotide repeat disorder, but rather a tetranucleotide repeat disorder.