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: The results suggest that , for a given variant , the extent of the enzyme defect in muscle may be determined , using this equation , from the G6PD activity of erythrocytes
### Output Text:
The results suggest that , for a given variant , the extent of the enzyme defect in muscle may be determined , using this equation , from the G6PD activity of erythrocytes 