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: A wide variety of A - T mutations , most of which are unique to single families , were identified in various ethnic groups , precluding carrier screening with mutation - specific assays .
### Output Text:
A wide variety of <span class="disease">A - T</span> mutations , most of which are unique to single families , were identified in various ethnic groups , precluding carrier screening with mutation - specific assays . 