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: Hemizygous mice carrying a replacement mutation in exon 2 of the ND gene developed retrolental structures in the vitreous body and showed an overall disorganization of the retinal ganglion cell layer .
### Output Text:
Hemizygous mice carrying a replacement mutation in exon 2 of the <span class="disease">ND</span> gene developed retrolental structures in the vitreous body and showed an overall disorganization of the retinal ganglion cell layer . 