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 have determined the genomic organization of CHRNA4 , which consists of six exons distributed over approximately 17 kb of genomic DNA .
### Output Text:
We have determined the genomic organization of CHRNA4 , which consists of six exons distributed over approximately 17 kb of genomic DNA . 