What does Fatal familial insomnia mean in medical term?

Fatal familial insomnia means: FFI: Fatal familial insomnia. A hereditary disorder that causes sleep disruption, motor abnormalities, myoclonus and dysphagia. Also known as FFI. A missense mutation in codon 178, chromosome 20, causes prion protein gene mutation. Also, fatal insomnia can also occur in sporadic cases.
(in Medical Dictionary)