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: Allele - specific amino acid substitutions ( Ser189 - - > Phe ; Gly444 - - > Arg ) cause impaired C2 secretion .
### Output Text:
Allele - specific amino acid substitutions ( Ser189 - - > Phe ; Gly444 - - > Arg ) cause impaired C2 secretion . 