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: HPRT - deficient mice generated using mouse embryonic stem cells exhibit none of the behavioral symptoms associated with the Lesch - Nyhan syndrome .
### Output Text:
<span class="disease">HPRT - deficient</span> mice generated using mouse embryonic stem cells exhibit none of the behavioral symptoms associated with the <span class="disease">Lesch - Nyhan syndrome</span> . 