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: However , these findings suggest that PKU can be completely corrected by somatic gene therapy , and provide some direction for the future development of adenoviral vectors . .
### Output Text:
However , these findings suggest that <span class="disease">PKU</span> can be completely corrected by somatic gene therapy , and provide some direction for the future development of adenoviral vectors . . 