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 small nuclear ribonucleoprotein polypeptide N ( SNRPN ) gene is regarded as one of the candidates for Prader - Willi syndrome ( PWS ) .
### Output Text:
The small nuclear ribonucleoprotein polypeptide N ( SNRPN ) gene is regarded as one of the candidates for <span class="disease">Prader - Willi syndrome</span> ( <span class="disease">PWS</span> ) . 