What Disease(s) could Kill an Immortal?

Ignorance is curable, living is forever. _{Robert A. Heinlein¹}

Cutting to the hard data:

Due to some or another reason² the genetic information stored inside cells (aka DNA) of my Immortals does not deteriorate over time. Replacing old cells with new cells does not result in inferior/misaligned copies of the contained genetic code, thus cells can be renewed indefinitely.

The genetic code of any born Immortal can also not be altered by influence of radiation thus during the lifespan of an Immortal their cells will not mutate and thus will not get cancerous.
Now the cells of any unborn Immortal may still produce mutations and thus the species will further evolve more or less unhindered.

Q: Considering the above stated rules, Whatdiseases will still be able to bring death to an Immortal, and Why?

_{¹Well mostly at least
²Call it magic if that helps you}