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Fatal insomnia

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Fatal insomnia

Fatal insomnia is a neurodegenerative prion disease that results in trouble sleeping as its hallmark symptom. The majority of cases are familial (fatal familial insomnia [FFI]), stemming from a mutation in the PRNP gene, with the remainder of cases occurring sporadically (sporadic fatal insomnia [sFI]). The problems with sleeping typically start out gradually and worsen over time. Eventually, the patient will succumb to total insomnia (agrypnia excitata), most often leading to other symptoms such as speech problems, coordination problems, and dementia. It results in death within a few months to a few years, and there is no known disease-modifying treatment.

The disease has four stages:

Clinically, Fatal Insomnia manifests with a disordered sleep-wake cycle, dysautonomia, motor disturbances, and neuropsychiatric disorders.

Other symptoms include profuse sweating, miosis (pinpoint pupils), sudden entrance into menopause or impotence, neck stiffness, and elevation of blood pressure and heart rate. The sporadic form of the disease often presents with double vision. Prolonged constipation is common as well. As the disease progresses, the person becomes stuck in a state of pre-sleep limbo, or hypnagogia, which is the state just before sleep in healthy individuals. During these stages, people commonly and repeatedly move their limbs as if they were dreaming.

The age of onset is variable, ranging from 13 to 60 years, with an average of 50. The disease can be detected prior to onset by genetic testing. Death usually occurs between 6–36 months from onset. The presentation of the disease varies considerably from person to person, even among people within the same family; in the sporadic form, for example, sleep problems are not commonly reported, and early symptoms are ataxia, cognitive impairment, and double vision.

Fatal familial insomnia is a rare hereditary prion disease that is associated with a mutation in PRNP. The gene, which provides instructions for making the prion protein PrPC, is located on the short arm of chromosome 20 at position p13. Individuals with FFI or familial Creutzfeldt–Jakob disease (fCJD) both carry a mutation at codon 178 of the prion protein gene. FFI is also invariably linked to the presence of the methionine codon at position 129 of the mutant allele, whereas fCJD is linked to the presence of the valine codon at that position. The disease occurs when there is a change of amino acid at position 178 in which asparagine is found instead of the normal aspartic acid. This has to be accompanied with a methionine at position 129.

FFI is an autosomal dominant disease caused by a missense GAC-to-AAC mutation at codon 178 of the PRNP prion protein gene located on chromosome 20, along with the presence of the methionine polymorphism at position 129 of the mutant allele. Pathologically, FFI is characterized predominantly by thalamic degeneration—especially in the medio-dorsal and anteroventral nuclei. Phenotypic variability is a perplexing feature of FFI.

Prion diseases are caused by the accumulation of misfolded prion proteins in the brain. Generally, prion disorders are characterized by long incubation periods and short clinical duration, which means the abnormal prions may accumulate for many years without causing symptoms (long incubation period), but once symptoms begin the disorder rapidly worsens.

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