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: RT - PCR analysis shows that this gene , which we have called DM locus - associated homeodomain protein ( DMAHP ) , is expressed in a number of human tissues , including skeletal muscle , heart and brain .
### Output Text:
RT - PCR analysis shows that this gene , which we have called <span class="disease">DM</span> locus - associated homeodomain protein ( DMAHP ) , is expressed in a number of human tissues , including skeletal muscle , heart and brain . 