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: The second A - T allele has a different mutation in each patient .
### Output Text:
The second <span class="disease">A - T</span> allele has a different mutation in each patient . 