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: These findings suggest that the pathogenesis of HD is not mediated through DNA - protein interaction and that presence of the RNA transcript with an expanded CAG repeat is insufficient to cause the disease .
### Output Text:
These findings suggest that the pathogenesis of <span class="disease">HD</span> is not mediated through DNA - protein interaction and that presence of the RNA transcript with an expanded CAG repeat is insufficient to cause the disease . 