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: To identify the genetic basis of C9 deficiency , we developed an approach using exon - specific PCR and direct DNA sequencing .
### Output Text:
To identify the genetic basis of <span class="disease">C9 deficiency</span> , we developed an approach using exon - specific PCR and direct DNA sequencing . 