If familial mediterranean fever is left untreated can it cause death?

He also has a secondry infection of vasculitis.
How long is life expectency if you don't have treatment for both?
What method of treatment is there? Can it make you feel nauseous?
I'm wondering cause my friend's kid was just diagnosed with it and he's only a couple years old.

I know someone who has it. It is fatal if you don't have treatment. As for vasculitis as far as I know that can be fatel to. It's blood vessels so it can evently lead to death.
I don't know how long life expectency is. It's not like 10 days or something like that. It's not short but not 10 years. It's somewhere in between.
Talk the family into getting treatment. It's a tiney pill the kid has to make, smaller than M and M's. It's not worth dying over. It would effect the kid in any other major way. He can still have a normal life. With treatment life expetency as the same for him as it is for the healthiest person alive.

Yes, FMF can be fatal if untreated. Usually death in untreated patients is due to kidney disease, and the morbidity with this disease, when not fatal, is high.

Tough to give life expectancy, as it depends largely on the secondary diseases which are common in people with FMF, and there is not enough data on many groups before therapy (especially Arab populations). Also, different ethnic populations seem to have different complications of/with FMF. Whether this is the result of genetic factors or lack of comprehensive data/study bias, I don't know.

As for therapy, it's colchicine, an ant-inflammatory agent mainly used for gout. Yes it can cause nausea and a host of other side effects, and tends to be dose-related. Having said that, colchicine is very effective at controlling (not curing) FMF, and there are medicines to deal with many of the side effects, including nausea.

Hope this helps, and good luck to your friend's family.