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: The majority of patients with Canavan disease are from an Ashkenazi Jewish background .
### Output Text:
The majority of patients with <span class="disease">Canavan disease</span> are from an Ashkenazi Jewish background . 