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: Subsequent direct sequencing of the target exons identified homozygous mutations in exon 16 of case 1 and in exon 15 of case 2 .
### Output Text:
Subsequent direct sequencing of the target exons identified homozygous mutations in exon 16 of case 1 and in exon 15 of case 2 . 