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 movement disorder investigated in these studies has some features in common with human idiopathic dystonia , and information obtained in these studies may be of potential clinical benefit .
### Output Text:
The movement disorder investigated in these studies has some features in common with human idiopathic dystonia , and information obtained in these studies may be of potential clinical benefit . 