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: Molecular heterogeneity of classical and Duarte galactosemia : mutation analysis by denaturing gradient gel electrophoresis .
### Output Text:
Molecular heterogeneity of <span class="disease">classical and Duarte galactosemia</span> : mutation analysis by denaturing gradient gel electrophoresis . 