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: Marker haplotype studies of the C6 and C7 gene region and Southern blots show that the Irish family with the splice defect also segregate for the deletion , which is not easily detected in heterozygotes .
### Output Text:
Marker haplotype studies of the C6 and C7 gene region and Southern blots show that the Irish family with the splice defect also segregate for the deletion , which is not easily detected in heterozygotes . 