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: Consistent with cellular defects of AT patients , the ATM - / - cells are hypersensitive to gamma - irradiation and defective in cell - cycle arrest following radiation , correlating with a defective up - regulation of p53 .
### Output Text:
Consistent with cellular defects of <span class="disease">AT</span> patients , the ATM - / - cells are hypersensitive to gamma - irradiation and defective in cell - cycle arrest following radiation , correlating with a defective up - regulation of p53 . 