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: Here we show that apoptotic extracts and apopain itself specifically cleave the HD gene product , huntingtin .
### Output Text:
Here we show that apoptotic extracts and apopain itself specifically cleave the <span class="disease">HD</span> gene product , huntingtin . 