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 commonly associated with CTG repeat expansions within the gene for DM - protein kinase ( DMPK ) .
### Output Text:
<span class="disease">Myotonic dystrophy</span> ( <span class="disease">DM</span> ) is commonly associated with CTG repeat expansions within the gene for DM - protein kinase ( DMPK ) . 