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: These results strengthen the contention that simple loss - or gain - of - expression of DMPK is not the only crucial requirement for development of the disease . .
### Output Text:
These results strengthen the contention that simple loss - or gain - of - expression of DMPK is not the only crucial requirement for development of the disease . . 