What is fatal familial insomnia? what causes it?

Genetics: This is a very rare, progressive inherited fatal brain disease that presents in adulthood but can be tested for earlier. It kills w/in a few years or less and progresses through 4 stages. Here's info: https://en.wikipedia.org/wiki/Fatal_familial_insomnia It's not considered treatable - but some can find ways to live a bit better and longer. I wish you well.

FFI is a very rare : genetic neurodegenerative disorder caused by a mutant prion protein gene on Chromosome 20p13. Each child of a parent with FFI has a 50% chance of inheriting it. Mis-folded prion protein "spreads" in the thalamus, the brain area that controls sleep-wake cycles, progressively damaging neurons there. www.cureffi.org/2012/12/03/introduction-to-fatal-familial-insomnia/ explains symptoms & prognosis.