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: Classical galactosemia is caused by one common missense mutation ( Q188R ) and by several rare mutations in the galactose - 1 - phosphate uridyltransferase ( GALT ) gene .
### Output Text:
<span class="disease">Classical galactosemia</span> is caused by one common missense mutation ( Q188R ) and by several rare mutations in the galactose - 1 - phosphate uridyltransferase ( GALT ) gene . 