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: We hypothesize that the patient is heterozygous for a complete deficiency of C9 and for a gene directing hyposynthesis of a defective C9 .
### Output Text:
We hypothesize that the patient is heterozygous for a <span class="disease">complete deficiency of C9</span> and for a gene directing hyposynthesis of a defective C9 . 