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 family studies of three first - degree relatives with heterozygous C9 deficiency , we demonstrated that the two mutations are segregating independently .
### Output Text:
In family studies of three first - degree relatives with heterozygous <span class="disease">C9 deficiency</span> , we demonstrated that the two mutations are segregating independently . 