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: In contrast , where the C7 genes are both defective ( but still partially functional ) , there may be a profound deficit of circulating C7 because there is ample C6 to produce C56 and consume the already small amount of C7 .
### Output Text:
In contrast , where the C7 genes are both defective ( but still partially functional ) , there may be a profound deficit of circulating C7 because there is ample C6 to produce C56 and consume the already small amount of C7 . 