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 positioning of the polymerase chain reaction ( PCR ) primers was such that the resulting PCR products were of different sizes , which enabled us to analyze two different exons simultaneously and still distinguish between the banding profiles for both ( biplex analysis ) .
### Output Text:
The positioning of the polymerase chain reaction ( PCR ) primers was such that the resulting PCR products were of different sizes , which enabled us to analyze two different exons simultaneously and still distinguish between the banding profiles for both ( biplex analysis ) . 