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: To learn more about the molecular basis of DTDST chondrodysplasias and about genotype - phenotype correlations , we studied fibroblast cultures of three new patients one with AO - 2 , one with DTD , and one with an intermediate phenotype ( AO2 / DTD ) .
### Output Text:
To learn more about the molecular basis of <span class="disease">DTDST chondrodysplasias</span> and about genotype - phenotype correlations , we studied fibroblast cultures of three new patients one with <span class="disease">AO - 2</span> , one with <span class="disease">DTD</span> , and one with an intermediate phenotype ( <span class="disease">AO2</span> / <span class="disease">DTD</span> ) . 