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: It differs from this and both the classical and connatal forms of PMD in that it is relatively mild in form , onset is delayed beyond age 2 years , nystagmus is absent , tremors are prominent , mental retardation is not severe , some patients show dementia or personality disorders , the disease is progressive rather than static in some , and several females show signs of disease .
### Output Text:
It differs from this and both the classical and connatal forms of <span class="disease">PMD</span> in that it is relatively mild in form , onset is delayed beyond age 2 years , <span class="disease">nystagmus</span> is absent , <span class="disease">tremors</span> are prominent , <span class="disease">mental retardation</span> is not severe , some patients show <span class="disease">dementia</span> or <span class="disease">personality disorders</span> , the disease is progressive rather than static in some , and several females show signs of disease . 