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: On genomic products exons 1 to 13 ( including 740 bp of the 3 untranslated sequence and all intron / exon boundaries ) were screened , as was a neuroretina specific enhancer in intron 4 .
### Output Text:
On genomic products exons 1 to 13 ( including 740 bp of the 3 untranslated sequence and all intron / exon boundaries ) were screened , as was a neuroretina specific enhancer in intron 4 . 