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: Deletion of small nuclear ribonucleoprotein polypeptide N ( SNRPN ) in Prader - Willi syndrome detected by fluorescence in situ hybridization : two sibs with the typical phenotype without a cytogenetic deletion in chromosome 15q .
### Output Text:
Deletion of small nuclear ribonucleoprotein polypeptide N ( SNRPN ) in <span class="disease">Prader - Willi syndrome</span> detected by fluorescence in situ hybridization : two sibs with the typical phenotype without a cytogenetic deletion in chromosome 15q . 