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 all D - 2 alleles N314D occurred in cis with two intronic sequence changes , on the D - 1 alleles in cis with a neutral mutation in exon 7 .
### Output Text:
On all D - 2 alleles N314D occurred in cis with two intronic sequence changes , on the D - 1 alleles in cis with a neutral mutation in exon 7 . 