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: Two alternatively spliced VHL mRNAs characterized by inclusion ( isoform I ) or exclusion ( isoform II ) of exon 2 are transcribed in adult tissues .
### Output Text:
Two alternatively spliced <span class="disease">VHL</span> mRNAs characterized by inclusion ( isoform I ) or exclusion ( isoform II ) of exon 2 are transcribed in adult tissues . 