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: In case 2 , a homozygous 2 - bp deletion ( 2137delTG / 2138delGT / 2139delTG ) caused a frameshift , generating a premature termination codon 4 to 6 nucleotides downstream .
### Output Text:
In case 2 , a homozygous 2 - bp deletion ( 2137delTG / 2138delGT / 2139delTG ) caused a frameshift , generating a premature termination codon 4 to 6 nucleotides downstream . 