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: In one family , both alleles were normal in the parents and one sister ; thus , the mutation originated de novo in the proposita .
### Output Text:
In one family , both alleles were normal in the parents and one sister ; thus , the mutation originated de novo in the proposita . 