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 DM region of chromosome 19 is gene rich , and it is possible that the repeat expansion may lead to dysfunction of a number of transcription units in the vicinity , perhaps as a consequence of chromatin disruption .
### Output Text:
The <span class="disease">DM</span> region of chromosome 19 is gene rich , and it is possible that the repeat expansion may lead to dysfunction of a number of transcription units in the vicinity , perhaps as a consequence of chromatin disruption . 