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: The size of the ( CTG ) n repeat , which increases through generations , generally correlates with clinical severity and age of onset .
### Output Text:
The size of the ( CTG ) n repeat , which increases through generations , generally correlates with clinical severity and age of onset . 