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 incidence of PAX6 mutation in patients with simple aniridia : an evaluation of mutation detection in 12 cases .
### Output Text:
The incidence of PAX6 mutation in patients with simple <span class="disease">aniridia</span> : an evaluation of mutation detection in 12 cases . 