Question: What is (are) Fatal familial insomnia ?
Answer: Fatal familial insomnia (FFI) is an inherited prion disease that affects the brain and other parts of the nervous system. Prion diseases, also known as transmissible spongiform encephalopathies (TSE), are a group of rare neurodegenerative conditions that occur when abnormal proteins clump together and accumulate in the brain, leading to tissue damage. The first symptoms of FFI usually begin in mid-life and may include insomnia that worsens over time and vivid dreams when sleep is achieved. These symptoms may be followed by high blood pressure; episodes of hyperventilation; excessive tearing; and/or sexual and urinary tract dysfunction. As the disease progresses, most affected people develop ataxia. FFI usually leads to death within a few months to a few years. Genetic prion diseases are inherited in an autosomal dominant manner and may be caused by mutations in the PRNP gene. Treatment aims at alleviating symptoms when possible.
Source: GARD

Question: What causes Fatal familial insomnia ?
Answer: What causes fatal familial insomnia? Fatal familial insomnia (FFI) is caused by a specific change (mutation) in the PRNP gene. PRNP encodes the prion protein. Although the exact function of this protein is unknown, scientists suspect that it plays an important role in the brain. Mutations in the PRNP gene result in an abnormal form of the protein that clumps together and accumulates in the brain. This leads to the destruction of neurons (brain cells) and creates tiny holes in the brain, which give the brain a "sponge-like" appearance when viewed under a microscope. The progressive loss of neurons leads to the many signs and symptoms of FFI.
Source: GARD