In the sentence extracted from biomedical literature, identify all the disease entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="disease"> to denote a disease.

### Input Text: Myotonic dystrophy ( DM ) is associated with a ( CTG ) n trinucleotide repeat expansion in the 3 - untranslated region of a protein kinase - encoding gene , DMPK , which maps to chromosome 19q13 .
### Output Text:
<span class="disease">Myotonic dystrophy</span> ( <span class="disease">DM</span> ) is associated with a ( CTG ) n trinucleotide repeat expansion in the 3 - untranslated region of a protein kinase - encoding gene , DMPK , which maps to chromosome 19q13 . 