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: Twelve aniridia patients , five with a family history and seven presumed to be sporadic , were exhaustively screened in order to test what proportion of people with aniridia , uncomplicated by associated anomalies , carry mutations in the human PAX6 gene .
### Output Text:
Twelve <span class="disease">aniridia</span> patients , five with a family history and seven presumed to be sporadic , were exhaustively screened in order to test what proportion of people with <span class="disease">aniridia</span> , uncomplicated by associated anomalies , carry mutations in the human PAX6 gene . 