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: Furthermore , DNA marker studies were conducted using known polymorphisms of the C6 , C7 , and C9 genes , confirming the linkage of the observed C9 mutations with defined haplotypes . .
### Output Text:
Furthermore , DNA marker studies were conducted using known polymorphisms of the C6 , C7 , and C9 genes , confirming the linkage of the observed C9 mutations with defined haplotypes . . 