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: A novel homeodomain - encoding gene is associated with a large CpG island interrupted by the myotonic dystrophy unstable ( CTG ) n repeat .
### Output Text:
A novel homeodomain - encoding gene is associated with a large CpG island interrupted by the <span class="disease">myotonic dystrophy</span> unstable ( CTG ) n repeat . 