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: Classical phenylketonuria ( PKU ) is an autosomal recessive disorder caused by a deficiency of hepatic phenylalanine hydroxylase ( PAH ) .
### Output Text:
Classical <span class="disease">phenylketonuria</span> ( <span class="disease">PKU</span> ) is an <span class="disease">autosomal recessive disorder</span> caused by a <span class="disease">deficiency of hepatic phenylalanine hydroxylase</span> ( PAH ) . 