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: C9 is a single - chain serum protein that is encoded by a gene located on chromosome 5p .
### Output Text:
C9 is a single - chain serum protein that is encoded by a gene located on chromosome 5p . 