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: Most large analyses that defined the limits of the normal and pathological size ranges employed PCR assays , which included the CAG repeats and a CCG repeat tract that was thought to be invariant .
### Output Text:
Most large analyses that defined the limits of the normal and pathological size ranges employed PCR assays , which included the CAG repeats and a CCG repeat tract that was thought to be invariant . 