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: However , one individual is heterozygous for markers at adjacent C6 loci , showing that there has been an intergenic recombination and suggesting that the deficiency mutation is of appreciable antiquity . .
### Output Text:
However , one individual is heterozygous for markers at adjacent C6 loci , showing that there has been an intergenic recombination and suggesting that the deficiency mutation is of appreciable antiquity . . 