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: Vectors derived from a recombinant retrovirus or a DNA / protein complex can efficiently transduce the PAH cDNA into PAH - deficient hepatocytes in vitro , but the application of these vector systems is presently limited by their low transduction efficiency in vivo .
### Output Text:
Vectors derived from a recombinant retrovirus or a DNA / protein complex can efficiently transduce the PAH cDNA into <span class="disease">PAH - deficient</span> hepatocytes in vitro , but the application of these vector systems is presently limited by their low transduction efficiency in vivo . 