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: To directly study the role of Col3a1 in development and disease , we have inactivated the Col3a1 gene in embryonic stem cells by homologous recombination .
### Output Text:
To directly study the role of Col3a1 in development and disease , we have inactivated the Col3a1 gene in embryonic stem cells by homologous recombination . 