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: Surprisingly , investigation revealed that the patients complement was normal for all components except C9 , which was functionally absent .
### Output Text:
Surprisingly , investigation revealed that the patients complement was normal for all components except C9 , which was functionally absent . 