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: No mutation was observed in exons 25 - 27 , although this region contains two CGA codons .
### Output Text:
No mutation was observed in exons 25 - 27 , although this region contains two CGA codons . 