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 test this proposition , we bred HPRT - APRT - deficient mice .
### Output Text:
To test this proposition , we bred <span class="disease">HPRT - APRT - deficient</span> mice . 