There are two major types of Myotonic Dystrophy (DM) and two types more have been discovered during last few years.
Myotonic Dystrophy Type 1 (DM1) & Myotonic Dystrophy Type 2 (DM2)
They are both caused by a genetic defect, on different genes, even though many symptoms are similar. Both Myotonic Dystrophy Type 1 (DM1) and Myotonic Dystrophy Type 2 (DM2) are characterized by skeletal and smooth muscle weakness and myotonia, heart abnormalities, cataracts and insulin resistance.
DM1 – Myotonic Dystrophy Type 1 is without any doubt the most common type and results from an abnormal DNA expansion in the DMPK gene on chromosome 19.
DM2 – That arises from an abnormal expansion of DNA in the ZNF9 gene on chromosome 3.