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: By performing in vitro expression of LCAT minigenes and reverse transcriptase PCR on mRNA isolated from leukocytes of the patient , this gene defect was shown to cause a null allele as the result of complete intron retention .
### Output Text:
By performing in vitro expression of LCAT minigenes and reverse transcriptase PCR on mRNA isolated from leukocytes of the patient , this gene defect was shown to cause a null allele as the result of complete intron retention . 