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: Although the genes regulated by the VHL gene product have not yet been identified , our findings are compatible with the hypothesis that VHL - mediated control of transcriptional elongation may have a role in normal human development . .
### Output Text:
Although the genes regulated by the <span class="disease">VHL</span> gene product have not yet been identified , our findings are compatible with the hypothesis that <span class="disease">VHL</span> - mediated control of transcriptional elongation may have a role in normal human development . . 