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: We describe two sibs with typical PWS presenting deletion of SNRPN detected by fluorescence in situ hybridization ( FISH ) .
### Output Text:
We describe two sibs with typical <span class="disease">PWS</span> presenting deletion of SNRPN detected by fluorescence in situ hybridization ( FISH ) . 