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: One mutation , a C to A exchange , was detected in exon 2 at cDNA position 166 , the other , a C to T exchange , was located in exon 4 ( cDNA position 464 ) .
### Output Text:
One mutation , a C to A exchange , was detected in exon 2 at cDNA position 166 , the other , a C to T exchange , was located in exon 4 ( cDNA position 464 ) . 