The disease manifests as noted above, resulting in visible trembling, which can be taken as a sign of mental illness. Apollo comes from a long line of psychopathic emperors who routinely overthrow each other using the family motto for cover: Only the mentally fit shall rule! Apollo has a half-brother who wants the throne but is not in the direct line of succession, so he's looking for an excuse to move against Apollo.
There are many ways I could represent this, including a disease that's not well understood but is believed to be the result of long-term genetic engineering. With that sentence alone, I'm halfway home. I could stop there, but I'd like to throw in a little genetic depth, on the order of a paragraph.
For example, if the illness is the result of genetic engineering that modified a single gene who's only other known purpose is to, say, improve night vision, then you stop messing with that gene in humans, and the illness goes away. If, however, the gene change(s) provide the only known defense against the "Ebola" of the fifth millenium, then there is no alternative. Again, I could stop there.
However, I'd like to make it so fundamental to genetically-engineered humans that there is no way to change the gene(s) in question without a cascade of deadly effects from other, dependent genes that have also been messed with. Essentially, is it possible to construct a house of cards from which there is no realistic hope of return?
My second question I can probably research on my own, which is how is gene therapy able to alter all copies of a defective gene in a body with trillions of cells that are constantly dividing?
Ideas?
Dirk