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: The aim of the study was to assess the clinical significance of genetic variants in butyrylcholinesterase gene ( BCHE ) in patients with a suspected prolonged duration of action of succinylcholine after ECT .
### Output Text:
The aim of the study was to assess the clinical significance of genetic variants in butyrylcholinesterase gene ( BCHE ) in patients with a suspected prolonged duration of action of <span class="chemical">succinylcholine</span> after ECT . 