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: In the work described herein , we have selected two distinct naturally occurring null mutations of GALT , Q188R and R333W , and asked the questions ( i ) what are the impacts of these mutations on subunit assembly , and ( ii ) if heterodimers do form , are they active ?
### Output Text:
In the work described herein , we have selected two distinct naturally occurring null mutations of GALT , Q188R and R333W , and asked the questions ( i ) what are the impacts of these mutations on subunit assembly , and ( ii ) if heterodimers do form , are they active ? 