Fatal familial insomnia

**Definition:** A disease of the brain, caused by inheritance of mutation(s) of normal prion protein genes. This disease is characterised by severe insomnia and autonomic system dysfunction, and is fatal. Confirmation is by pathological examination of the brain and genetic testing.

**Long definition:** Fatal familial insomnia (FFI) is a genetic prion disease caused by D178N-129M mutation (aspartate to asparagine at codon 178 on the allele with methionine at the codon 129 polymorphic site). FFI presents with insomnia, ataxia, dementia and akinetic mutism with neuropathology identical to that seen in thalamic sCJD.