I have a seemingly healthy character who knows she will die suddenly in her the twenties due to an illness. I can’t find a suitable culprit, genetic or otherwise. Can anyone help? -She knows she is going to pass away, at an early age, but is able to conceal this from others. -Her illness has no symptoms, or ones she can hide until close to the end. -There is no cure. The best I can come up with is some form of heart defect – but most heart defects can be treated. For her there is no way out. Yes – I have googled, but no luck yet! Thanks…
She could have a weakened arterial wall deep in her brain, that will at some point rupture as a catastrophic cerebral aneurysm. She may not know when it will give out, but perhaps there is a genetic defect causing the wall to gradually break down, so even if she keeps her blood pressure well-controlled, it will give way. Its location may make it inoperable. Maybe it showed up on a CT scan when a smaller vessel gave way.
There are certain protists (tiny microorganisms) that can be contracted and will incubate for a couple of decades before killing its host. Very few symptoms are shown until death.
Aneurysm was what I was thinking too. Those don't always have any warning symptoms and some are impossible or near impossible to operate on. Plus it can happen so fast if your character was alone there would be no way for her to call for help before she passed out.
