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 answer these questions , we have established a yeast system for the coexpression of epitope - tagged alleles of human GALT and investigated both the extent of specific GALT subunit interactions and the activity of defined heterodimer pools .
### Output Text:
To answer these questions , we have established a yeast system for the coexpression of epitope - tagged alleles of human GALT and investigated both the extent of specific GALT subunit interactions and the activity of defined heterodimer pools . 