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: We found that DNA methylation within RB1 exons 8 , 14 , 25 , and 27 appeared to be restricted to CpGs , including six CGA codons .
### Output Text:
We found that DNA methylation within RB1 exons 8 , 14 , 25 , and 27 appeared to be restricted to CpGs , including six CGA codons . 