I'd like to know if there's a blood or vascular disease/disorder that fits, or could conceivably fit, all the following criteria, even if only in theory:
- Present from birth
- Onset of symptoms, or a sudden severe increase of symptoms, in young adulthood (anywhere from age 20 to 40, let's say)
- Relatively high fatality rate
- Incurable (though not necessarily untreatable)
- Not restricted to developing societies; can affect upper-middle class Westerners
I've landed on sickle-cell anemia as a promising candidate, although I don't know whether it can fulfill criterion #2.