In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: RESULTS : in 11 patients , mutations were found in the BCHE gene , the K - variant being the most frequent .
### Output Text:
RESULTS : in 11 patients , mutations were found in the BCHE gene , the K - variant being the most frequent . 