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 demonstration of mutations giving rise to a slightly milder phenotype in A - T raises the interesting question of what range of phenotypes might occur in individuals in whom both mutations are milder .
### Output Text:
The demonstration of mutations giving rise to a slightly milder phenotype in <span class="disease">A - T</span> raises the interesting question of what range of phenotypes might occur in individuals in whom both mutations are milder . 