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 clinical picture resembles somewhat that of X - linked spastic paraplegia ( SPG ) .
### Output Text:
The clinical picture resembles somewhat that of <span class="disease">X - linked spastic paraplegia</span> ( <span class="disease">SPG</span> ) . 