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: Furthermore , the broad range of phenotypic severity observed in these patients raises the possibility that allelic combination , not just allelic constitution , may play some role in determining outcome .
### Output Text:
Furthermore , the broad range of phenotypic severity observed in these patients raises the possibility that allelic combination , not just allelic constitution , may play some role in determining outcome . 